Sixth H^Aii^Icmal Symposium on Gas Flow & Chemical Lasers

INIS-mf--10917

Sixth h^aii^icmal Symposium on Gas Flow & Chemical Lasers Jerusalem, 8 "XI September 1986, TftfflT 5MIS DOCUMENT

GCL Sixth International Symposium on Gas Flow& Chemical Lasers Jerusalem, 8-12 September 1986,

ORGANIZED BY: Ben-Gurion University of the Negev UN3ER THE AUSPICES OF: The Israel Academy of Sciences and Humanities Israel Laser & Electro-Optics Society

SYMPOSIUM ORGANIZERS International Ltd. P.O.Box 29313 61292 Tel-Aviv, Israel Telephone: (03) 654541 Telex: 33-554, Cables: Intertours CONTENTS

Page Timetable 3 Commi ttees 5 Acknowledgements , 6 General Information •• ...7 Social Program 8 Program for Registered Accompanying Persons..... , 9 Program: Sunday, 7 September 10 Monday, 8 September ,10 Tuesday, 9 September 11 Wednesday, 10 September =,...15 Thursday, 11 September...... 17 Friday, 12 September. 20

Abstracts 21 Author Index 135 TIMETABLE

SUNDAY, 7 SEPTEMBER 1986

from 16:00 Registration and distribution of material 20:00 Get-together reception and lecture on Jerusalem

MONDAY, 8 SEPTEMBER 1986

08:00 - 09:00 Registration (cont.) 09:00 - 10:30 Opening Session: Marquet, Webb 10:30 - 11:00 Coffee break 11:00 - 12:20 Chemical Oxygen Iodine Lasers: Bacis, Georges, Pigache 12:20 - 13:30 Lunch break 13:30 - Tour of Jerusalem (for overseas participants)

TUESDAY, 9 SEPTEMBER 1986

08:30 - 10:30 Optics: Bigio, Feldman, Mclver, Wildermuth 10:30 - 11:00 Coffee break 11:00 - 12:20 Optics (cont.): Jueptner Fluid Dynamics: Brunet, Bauer, Bonn 12:20 - 14:00 Lunch break 14:00 - 15:20 Novel Applications: Bobin, Yogev 15:20 - 17:30 Poster Session 1: Lilenfeld, Badzlak, Brunet, Brunne, Cenian, Iyoda, Kallsky, Mayerhofer, Rosenberg, Saito, Sentis, Biblarz, Nachshon, Sato, Schall, Berger, Bigio, Campargue, Margalith, Rabczuk, Konefal, Kramer, Walter, Autric, Kanazawa, Joeckle, Fishman, Koren 20:00 Visit to the Israel Museum

WEDNESDAY, 10 SEPTEMBER 1986

08:00 - 10:00 Short Wavelength Lasers: Sauerbrey, Cefalas, Feltham, Fontaine, Walter 10:00 - 10:30 Coffee break 10:30 - 11:50 New Developments in CO2 Lasers: Hugel, Yuasa, Brunne 11:50 - 12:50 High Power CO Lasers: Saito, Terunuma 12:50 - 14:00 Lunch break 14:00 Professional tour to Laser & Electro-Optics Industries (for overseas participants) THURSDAY, 11 SEPTHvBER 1986

08:30 - 10:30 Laser Propagation and Interaction: Dufresne, Schuocker, Cassady, Hugenschmidt 10:30 - 11:00 Coffee break 11:00 - 12:40 Applications: Basting, Hashimoto, Baumert 12:40 - 13:40 Lunch break 13:40 - 15:20 Laser Design and Diagnostics: Sugawara, Agmon, Spalding & Steen 15:20 - 18:00 Poster Session 2: Dorko, Wolf, David,B. Walter, Brunne, Cenian, Temkin, Yackerson, Spencer, R.F. Walter, Zeitoun, Flusberg, Golub, Gastaud, Sliwinski, Chuchem, Cruciani, Jueptner, Carbucicchio, Viol.Schmid

20:00 Farewell Dinner and Folklore Performance

FRIDAY, 12 SEPTEMBER 1986

08:30 - 10:30 New Laser Media: Davis, Torchin, Rossi, Voignier, Meinzer 10:30 - 11:00 Coffee break 11:00 - 12:30 Panel Discussion: Prospects for Short Wavelength Chemical Lasers: Levine, Brunet, Davis, Jones, Kompa, Rosenwaks, Rossi, Spencer

12:30 CLOSING OF THE STiWOSIlM INTBRNATIONAL SCIENTIFIC ADVISORY COMMITTEE H.G. Ah I strom, USA H. Oguchi, Japan J.R. Airey, USA M. Onorato, Italy V.Y. Baranov, USSR A.N. Oraevsky, USSR N.G. Basov, USSR F. Pandarese, Italy W.L. Bohn, W. Germany P.E. Philippe, France G. Born, W. Germany D. Pigache, France H. Brunet, France A.N- Pirri, USA M.P. Brunne, Poland N.L. Rapagnani, USA J.P. Caressa, France J.P. Reilly, USA C. Creput, France P. Rigny, France J. Daugherty, USA J. Rom, Israel C. Fenstermacher, USA S. Rosenwaks, Israel M. Fiebig, W. Germany H.N. Rutt, UK M.H. Flaum, Sweden D. Schuocker, Austria B. Forestier, France D.C. Smith, USA T. Fujioka, Japan S. Sollmeno, Italy A. Hertzberg, USA R.I. Soloukhin, USSR H.E. Hugel, W.Germany !.J. Spalding, UK G. Inglesakis, France Y.M. Timnat, Israel R. Ja!in, France C. Verdier, France A.S. Kaye, UK W.R. Warren, USA K. Kasuya, Japan W.S. Watt, USA P.G. Kryukov, USSR J.F. Wendt, Belgium E.M. Kudriavtsev, USSR L.E. Wilson, USA A.V. La Rocca, Italy W.J. Witteman, Holland B.A. Leporcq, France J.D.L.H. Wood, UK M.M. Mann, USA Yan Hai-Xing, China R.A. Meinzer, USA Zhang Cunhao, China

LOCAL SCIENTIFIC ADVISORY COMMITTEE

S. Rosenwaks*, Beer-Sheva - Symposium Chairman O. Amlchai, Tel-Aviv M. Or on, Yavne D. Chuchem*, Beer-Sheva M. Rokni, Jerusalem A. Gedanken, Ramat-Gan J. Rom, Haifa J. Jortner, Tel-Aviv A. Shachrai, Tel-Aviv L.A. Levin*, Beer-Sheva M. Shapiro, Rehovot R.D. Levine, Jerusalem Y.M. Timnat, Haifa E. Margalith*, Beer-Sheva S. Yatsiv, Jerusalem Y. Nachshon, Haifa A. Yogev, Rehovot U.P.. Oppenheim, Haifa •Member of the Organizing Committee ACKNOWLEDGEMENTS

The Organizing Committee gratefully acknowledges the assistance rendered by:

Bar-Ilan University Ben-Gurion University of the Negev Coherent Inc. El-Al Israel Airlines El-Op, Israel Electro-Optical Industry Ltd. Elbit Computers Ltd. Israel Atomic Energy Commission Lambda Physik M.L.I. Metalworking Lasers International (IL) Ltd. Ministry of Defense - Directorate of Research and Development Ministry of Foreign Affairs Ministry of Industry and Trade Ministry of Science and Development Ministry of Tourism Municipality of Jerusalem Office of Naval Research, London (sponsoring the session on New Laser Media) Ophir Optics Jerusalem Ltd. Optical Society of America Optrotech Ltd. RAFAEL - Armament Development Authority SPIE - The International Society of Optical Engineering Spectra-Physics Inc. Technion - Israel Institute of Technology The Fritz Haber Research Center for Molecular Dynamics - The Hebrew University, Jerusalem The Israel Academy of Sciences and Humanities The Weizmann Institute of Science US Army Research, Development and Standardization Group - UK USAF European Office of Aerospace Research and Development GENERAL INFORMATION

SYKffSDSILM SITE The Israel Academy of Sciences and Humanities, 43, Jabotinsky St., Jerusalem, Tel: (02) 636211 Lectures will be held at The Van Leer Jerusalem Foundation Audi torium

OFFICES AND DESKS Registration/Information Travel - International Ltd.

BADGES The personal envelope which you receive upon registration contains, among other items, your name badge. Please wear the badge to the scientific sessions and social functions.

VEALS In order to adhere strictly to the timetable, we have arranged for lunch to be served at the Symposium site. Please purchase lunch vouchers at the Registration Desk.

FLIGHT REGONFIRM\TION Please note that I.A.T.A. regulations require that outgoing flights be reconfirmed at least 72 hours prior to departure. You are kindly requested to complete your flight reconfirmation form and return it to the Travel Desk as soon as possible.

INSTRUCTIONS TO SPEAKERS AND CHAIRPERSONS Speakers and Chairpersons are requested to meet with each other 15 minutes prior to the commencement of their session, in the session hall, in order to coordinate introduction of speakers. Presenters at poster sessions are requested to mount their posters before the morning session of the day of presentation, and remove them at the lunch break on the following day.

PROJECTION Speakers are kindly requested to check their slides and hand them over to the projectionist prior to the relevant session. Slides should be collected from the projectionist immediately after presentation. Special requirements must be coordinated at the beginning of the Symposium.

PROCEEDINGS The proceedings of the Symposium wi11 be published by Springer-Verlag and will be referenced as: S. Rosenwaks (ed.): Gas Flow and Chemical Lasers VI, Springer Proc. Phys., (Springer, Berlin, Heidelberg 1987). All lecturers are required to hand over the^r original manuscript and one copy to the Registration Desk at the Symposium. SOCIAL PROGRAM

GET-TOGETHER RECEPTION Sunday, 7 September, 20:00 hrs. A welcoming reception will be held on the lawn at the Symposium site. The reception will be followed by a guest lecture and a slide presentation entitled: "Jerusalem Throughout the Ages", by I. Goldrath

TOUR OF JERUSALEM (for overseas participants) Monday, 8 September, 13:30 hrs. The tour begins with a visit to the Mount of Olives for a magnificent panaromic view of Jerusalem. From there proceed to the Western Wall, Jewish Quarter and the Cardo, the recently reconstructed Roman shopping arcade. The tour also includes visits to the Christian Quarter with the Church of the Holy Selpulchre and the Armenian Quarter. After visiting the Old City, the tour will proceed to modern Jerusalem for a view of the Presidential residence, the Jerusalem Theater and the Knesset (Israeli Parliament). Return to hotels. Assemble for departure at the Symposium site.

VISIT TO THE ISRAEL MUSEUM Tuesday, 9 September, 20:00 hrs. (departure at 19:45) By courtesy of the Municipality of Jerusalem, participants are invited for a guided tour, to view the archeologica1 treasures of the-museum. Light refreshments will be served*. Buses will depart from the Moriah.Larrome,Kings and Menorah hotels at 19:45 hrs., and return from the parking lot at the entrance to the Museum at 22:15 hrs.

PROFESSIONAL TOUR (for overseas participants) Wednesday, 10 September, .14:00 hrs. Visit to El-Op, Israel Electro-Optical Industry Ltd. in Rehovot and to M.L.I. Metalworking Lasers International (IL) Ltd. in Tel-Aviv. Please confirm participation in the tour on the "Tour confirmation form" in your personal envelope, and return it to the registration desk by Monday afternoon. Assemble for departure at the Symposium site.

FAREWELL DINNER AND FOLKLORE PERFORMANCE Thursday, 11 September, 20:00 hrs. (departure at 19:45) Dinner and entertainment featuring Israeli folklore will take place at Beit Maiersdorf on Mt. Scopus, overlooking the Old City of Jerusalem (please present invitation at entrance). Buses will depart at 19:45 hrs. from the Mori ah, Larrome, Kings and Menorah hotels. PROGRAM FOR REGISTERED ACCOMPANYING PERSONS

All social events as listed in the Social Program

- TOUR OF JERUSALEM Monday, 8 September, 13:30 hrs. See details in Social Program Assemble for departure at the Symposium site. - TOUR OF JERUSALEM AMD BETHLEHEM (full day) Wednesday, 10 September, 08:30 hrs. Starting in the Old City, participants will visit the Via Dolorosa, the Stations of the Cross and the Arab Bazaar. From there, we will proceed to the Garden Tomb, the Garden of Gethsemane and Mary's Tomb. Proceed to the model of ancient Herodian Jerusalem, Yad Va'shem (the Holocaust Memorial), and Mount Herzl. In the afternoon, drive to Bethlehem and visit the Church of the Nativity. Return to hotels. Lunch Break en route (to be paid by participants).

Assemble for departure at the Symposium site.

Additional tours may be purchased at the Symposium Travel Desk PROGRAM

SUNDAY, 7 SEPTEMBER 1986

from 16:00 Registration and distribution of material

20:00 Get-together reception (at the Symposium site), followed by guest-lecture and slide presentation: "JERUSALEM THROUGHOUT THE AGES", by I. Goldrath

MONDAY, 8 SEPTEMBER 1986

08:00 Registration (cont.)

09:00 - 09:10 Greetings: S. Rosenwaks, Symposium Chairman J. Jortner, Vice-President, The Israel Academy of Sciences and Humanities 09:10 - 10:30 OPENING SESSION Chairman: H. Rutt, UK 09:10 L.C. Marquet - invited - SDIO, USA SCIENTIFIC AND TECHNICAL ASPECTS AND PROSPECTS OF HIGH POWER LASERS FOR THE SDI

09:50 C.E. Webb - invited - Oxford U., UK METAL VAPOUR LASERS: RECENT ADVANCES & APPLICATIONS 10:30 Coffee break

11:00 - 12:20 CHEMICAL OXYGEN IODINE LASERS Chairman: K.L. Kompa, FRG

11:00 R. Bacis - invited - Lyon U., France CHEMICAL OXYGEN IODINE LASER MECHANISMS AND HIGH RESOLUTION SPECTROSCOPY STUDIES

11:40 E. Georges et al., ONERA, France THEOREflCAL AND EXPERIMENTAL STUDIES ON O2(1A) GENERATION AND TRANSFER

12:00 D. Pigache et al., ONERA, France THEORETICAL MDDELLING AND EXPERIMENTAL ANALYSIS OF CHEMICAL OXYGEN-IODINE LASERS

12:20 Lunch break

13:30 Tour of Jerusalem - for overseas particip'ants (departure from the Symposium site)

10 TUESDAY, 9 SEPTEMBER 1986 08:30 - 10:30 OPTICS Chairman: A. Flusberg, USA 08:30 I.J. Bigio - invited - LANL, USA NEW DEVELOPMENTS IN OPTICAL PHASE CONJUGATION

09:10 B.J. Feldman et al., NRL, USA STIMULATED BRILLOU1N SCATTERING WITH HF CHEMICAL LASERS 09:30 A.H. Guenther and J-K. Mclver - invited - AFWL and New Mexico U. ,USA CONSIDERATIONS RELATING TO THE CHOICE OF OPTICAL MATERIALS FOR HIGH PERFORMANCE LASERS 10:10 E. Wildermuth et al., DFVLR, FRG EXPERIMENTAL INVESTIGATIONS OF A FREE-VORTEX AERODYNAMIC WINDOW 10:30 Coffee break 11:00 - 12:20 OPTICS (cont.) and FLUID DYNAMICS Chairman: J. Rom, Israel 11:00 W. Jueptner et al.,Bias, FRG MIRROR OPTICS FOR HIGH POWER LASERS 11:20 H. Brunet et al.,CRCGE, France CHARACTERISTICS OF TURBULENT FLOW STABILIZED DC-DISCHARGES FOR CO2 LASERS 11:40 S.H. Bauer et al., Cornell U., USA KINETICS OF CONDENSATION IN SUPERSONIC EXPANSION (Ar) 12:00 W.L. Bohn et al.,DFVLR, FRG EFFECT OF BEAM QUALITY ON THE SCALING OF HIGH ENERGY FLOW LASERS 12:20 Lunch break 14:00 - 15:20 NOVEL APPLICATIONS Chairman: W.L. Bohn, FRG 14:00 J.L, Bob in - invited - P. et M. Curie U., France PARTICLE ACCELERATION IN LASER PLASMA INTERACTION 14:40 M. Shapiro and A. Yogev - invited - Weizmann Inst., Israel IBr PHOTODISSCCIATION LASERS AS A SIMULATION FOR A SOLAR PUMPED SYSTEM

11 TUESDAY, 9 SEPTEMBER 1986 (cont.)

15:20 - 17:30 POSTER SESSION""!

Panel 1 H.V. Lilenfeld et al., McDonnell Douglas, USA KINETICS OF PRODUCTION OF ELECTRONICALLY EXCITED IF 2 J. Badziak et al., Inst. of Plasma Phys. and Laser Microfusion, Poland LASER PULSE DEFORMATIONS IN KrF AMPLIFIER

3 H. Brunet et al., CRCGE, France FORMATION OF I.(2P 1/2)ATOMS IN THE F+I2 and H+12 REACTIONS

4 M.Brunne, Acad. of-Sci., Poland RATE EQUATION DESCRIPTION OF TINC-DEPENDENT PROCESSES IN GAS-DYNAMIC LASER ACTIVE CAVITY

5 A. Cenian, Acad. of Sci., Poland INVESTIGATIONS OF THE POPULATION INVERSION AND GAIN IN THE CW GDL-CM AS A FUNCTION OF THE RELATIVE CONCENTRATION OF CO2 M3LECULES

6 M. Iyoda et al., Chiba Inst. of Tech., Japan PARAMETRIC ANALYSIS OF A CW CO EDL BY CCWUTER SIMULATION

7 Y. Kali sky et al., NRCN, Israel EXPERIMENTAL STUDIES AND KINETIC MODELLING OF AN HF CHEMICAL LASER AT LOW TEMPERATURES

8 W. Mayerhofer et al., DFVLR, FRG OPTIMIZATION OF DISCHARGE STABILITY OF AN E-BEAM SUSTAINED SUPERSONIC CO-LASER BY OPTICAL DIAGNOSTIC MEASUREMENTS

9 Z. Rosenberg et al., Hebrew U., Israel DIRECT MEASUREMENT OF THE ELECTRON DENSITY IN THE ACTIVE MEDIUM OF E-BEAM PLMPED ARGON FLUORIDE LASER

10 H. Saito et al., IHI, Japan KINETIC MODELING OF A SUPERSONIC FLOW CO CHEMICAL LASER 11 M. Sent is et al., IMFM, France HIGH PULSE REPETITION RATE LIMITATIONS IN A HIGH AVERAGE POWER XeCl LASER

12 O. Biblarz et al., Naval Postgraduate Sen., USA FLUID-DYNAMIC EFFECTS, INCLUDING TURBULENCE, ON A HIGH-PRESSURE DISCHARGE

12 TUESDAY, 9 SEPTEMBER 1986 (cont.) Panel 13 Y. Nachshon et al., MOD, Israel AERODYNAMIC CURTAIN DESIGN FOR GAS FLOW LASER CAVITIES 14 S. Sato et al., Tokyo U., Japan GAIN OF A GASDYNAMIC LASER UTILIZING PRODUCTS OF LIQUID C6H6 AND GASEOUS 02 COMBUSTION 15 W.O. Schall et a I., DFVLR, FRG FLOW INVESTIGATIONS OF PULSED ARC DISCHARGE RECOMBINATION LASERS 16 M. Berger et a I., Oriel, FRG DEFORMATION MEASUREMENTS ON CO2-LASER OUTPUT COUPLERS IN OPERATING HIGH POWER LASER SYSTEMS 17 I.J. Bigio et al., LANL, USA SCALABLE SATURABLE ABSORBER FOR KrF LASERS 18 R. Campargue et al., CEN de Sac lay, France QUANTITATIVE INVESTIGATION OF THIRD HARMONIC GENERATION IN THE XUV RANGE USING A CO FREE-JET ZONE OF SILENCE 19 E. Margalith ,HLX Lasers, USA HIGH EFFICIENCY RAMAN CONVERSION OF UV TO BLUE-GREEN LIGHT 20 G. Rabczuk, Acad. of Sci., Poland A NUMERICAL STUDY INTO CHARACTERISTICS OF A CDL WITH UNSTABLE MULTIPASS CAVITY 21 J. Konefal, Acad. of Sci., Poland COMPARATIVE INVESTIGATIONS OF THE ELECTRIC DISCHARGE IN THE HIGH-POWER FAST-FLOW CO2 LASER 22 R. Kramer et a)., Fraunhofer-Inst. fur Lasertech., FRG A DIAGNOSTIC SYSTEM FOR MEASUREMENT OF THE FOCUSED BEAM DIAMETER OF HIGH POWER C02-LASERS 23 B. Walter et al., Wien TU, Austria MEASUREMENT OF CURRENT FLUCTUATIONS IN A 1 KW GAS TRANSPORT LASER 24 M. Autric et al*, IMFM, France INCREASE IN THE CO2 LASER ENERGY TRANSMISSION THROUGH THE ATMOSPHERE USING A PRECURSOR PULSE

13 TUESDAY, 9 SEPTEVBER 1986 (cont.) Panel 25 H. Kanazawa et al., Tokyo Inst. of Tech., Japan INITIATION PROCESSES AND DEVELOPNENT OF LASER INDUCED LOW PRESSURE SPARK CHANNELS 26 R. Joeckle et al., ISL, France THE DEEP PENETRATION OF HF LASER LIGHT INTO GLASS AND ITS POSSIBLE INDUSTRIAL USE 27 D. Fishman et al., M,I, Israel LASER CLADDING OF HEAT TREATED STEELS 28 M. Koren et al., Robomatix, Israel ROBOLASER IN THE CAR INDUSTRY

20:00 Visit to the Israel Museum (departure at 19:45 from Mori ah, Laronme, Kings and Menorah hotels)

14 WEDNESDAY, 10 SEPTEMBER 1986 08:00 - 10:00 SHORT WAVELENGTH LASERS Chairman: 3. Forestier, France 08:00 R.A. Sauerbrey - invited - Rice U., USA NEW VUV AND XUV LASER SYSTEMS BASED ON INNER-SHELL EXCITATION AND I0NI2ATI0N OF ATOMS AND MOLECULES 08:40 A.C. Cefalas et al., Theor. Phys. Chem. Inst., Greece AN OPTICALLY PUMPED SUPERSONIC HgBr(B-X) MOLECULAR BEAM LASER 09:00 A.M. Felt ham et a I., Hull U., UK PUMPING MECHANISM DEPENDENCE OF EMISSION SPECTRA IN HgBr LASERS 09:20 B.L. Fontaine et al., IMFM, France MODELING OF THE X RAY PREIONIZED, SELF SUSTAINED DISCHARGE XeCl LASER 09:40 R.F. Walter et al., Schafer, USA NUMERICAL [NVESTIGATfON OF FORMATION PROCESSES IN ELECTRON-BEAM PUMPED XeCl LASERS 10:00 Coffee break 10:30 - 11:50 NEW DEVELOPMENTS IN 002 LASERS Chairman: J. Daugherty, USA 10:30 H.E. Huge I and S. Yatsiv - invited - DFVLR/Stuttgart U., FRG and Hebrew U./Alumor, Israel 002 LASERS WITH RF EXCITATION AND CONDUCTIVE COOLING 11:10 M. Yuasa et al., IHI, Japan DEVELOPMENT OF A COMBUSTION-DRIVEN AFTER-MIXING GASDYNAMIC LASER UTILIZING A LIQUID FUEL AND LIQUID OXIDIZER 11:30 M. Brunne et al., Acad. of Sci., Poland NUMERICAL MODEL FOR CALCULATION OF POPULATION INVERSION AND GAIN IN CHANNELS OF CW-GDL(S) OPERATING AT TRANSITIONS PERTAINING TO VI AND V2 MODES OF 002

15 WEDNESDAY, 10 SEPTEMBER 1986 (CONT.) 11:50 - 12:50 HIGH POWER CO LASERS Chairman: R.A. Meinzer, USA 11:50 H. Saito et al. - invjted - IHI, Japan DEVELOPMENT OF MULTIKILCWATT CLOSED CYCLE CO LASER 12:30 K. Terunuma et al., Kelo U., Japan EFFECTS OF RF PREION1ZATION IN A TRANSVERSE-DISCHARGE-EXCITED CW CO LASER 12:50 Lunch break 14:00 Professional tour to Laser and Electro-Optics Industries - for overseas participants (departure from the Symposium site)

16 THURSDAY, 11 SEPTEMBER 1986 08:30 - 10:30 LASER PROPAGATION AM? INTERACTION Chairman: T. Fujioka, Japan 08:30 D. Dufresne - invited - IMFM, France INTERACTION OF HIGH ENERGY PULSED 002 LASER WITH MATERIAL 09:10 D. Schuocker and A.V. La Rocca - invited - Wien TU, Austria and FIAT, Italy LASER MATERIAL PROCESSING AND ITS PHENOMENOLOGY 09:50 P.F.. Cassadv et al., Boeing, USA AERO-OPTICAL ANALYSIS OF A COMPRESSIBLE SHEAR LAYER 10:10 M. Hugenschmidt. ISL, France INPROVED ENERGY TRANSFER IN LASER TARGET INTERACTION PROCESSES BY USING REPETITIVELY PULSED LASERS 10:30 Coffee break 11:00 - 12:40 APPLICATIONS Chairman: J. Shwartz, Israel 11:00 D. Basting - invited - Lambda Physik, FRG INDUSTRIAL APPLICATIONS OF EXCINER LASER 11:40 K. Hashimoto - invited - Tohoku U., Japan VITRIFICATION AND MDDIFICATION OF ftiETAL SURFACES BY LASER FOR CHEMICAL APPLICATIONS 12:20 R. Baumert. Spectra Physics, FRG INDUSTRIAL APPLICATIONS OF HIGH POWER CO2 LASERS, POWER RANGE 1-5 KW 12:40 Lunch break 13:40 - 15:20 LASER DESIGN AND DIAGNOSTICS Chairman: P. Savorelli, Italy 13:40 H. Sugawara et al. - invited -Hitachi, Japan 20-KW FAST-AXIAL-FLOW CO2 LASER WITH HIGH-FREQUENCY TURBO-BLOWERS 14:20 P. Agmon et aI.,MI, Israel MULTIKILOWATT INDUSTRIAL CO2 LASER 14:40 I.J. Spalding and W.M. Steen - invited - Culham and Imperial College, UK HIGH POWER LASER BEAM DIAGNOSTICS

17 THURSDAY 11 SEPTEMBER 1986 (conti) 15:20 - 18:00 POSTER SESSION~2~ Panel 1 E. Dorko et al., AF Inst. of Tech., USA EXPERIMENTAL STUDY OF THE LEVEL-TO-LEVE?, ROTATIONALLY INELASTIC TRANSITION RATES OF IODINE M0NOFLUORIDE DURING COLLISIONS WITH NOBLE GASES 2 P.J. Wolf et al., AFWL, USA INTERHALOGEN COLLISIONAL DYNAMICS: THE B3n(0+) STATE OF IF & BrCl 3 D. David et al., ONERA, France HIGH VIBRATIONAL LEVELS OF IODINE AS INTERMEDIATE STATE IN THE IODINE DISSOCIATION BY O2{1 A ) 4 B. Walter et al., Wien TU.Austria NEW CORONA PREIONISATION TECHNIQUE FOR MEDIUM REPETITION RATE TEA LASERS 5 M. Brunne, Acad. of Sci,, Poland APPROXIMATE THEORY OF CASCADE PHENOMENA IN THE ACTIVE CAVITY OF CW GASDYNAMIC LASER 6 A. Cenian, Acad. of Sci., Poland THEORETICAL MODEL OF THE GDL-CM (CO2>. DEVELOPMENT OF THE SSH-THEORY FOR THE QUASIRESONANT PROCESSES OF W AND VT TYPES 7 A.Ya. Temkin. Tel-Aviv U., Israel TRANSLATIONALLY STRONGLY NON-EQUILIBRIUM HOT ATOM ASSEMBLIES AND CHEMICAL LASER PUMPING 8 N. Yackerson et al., Ben-Gurion U., Israel NON-OPTOGALVANIC SIGNAL CHARACTERISTIC TIMES IN PREBREAKDCWN DISCHARGES D.J. Spencer et al., Aerospace, USA CHEMICAL LASLASEI R F2 FLOW DISTRIBUTION STUDIES 10 R.F. Walter. Schafer, USA VIBRATIONAL KINETICS MODELS FOR COMBUST I ON-DRIVEN CO2 GASDYNAMIC LASERS 11 P. Zeitoun et al., Provence U., France EFFECT OF INLET PRESSURE ON CHEMICAL LASER FLOWF1ELD 12 A. Flusberg et al., AVCO, USA THEORY OF WAVEFRONT REPLICATION IN THE DIRAC BRACKET OPERATOR FORMALtSM

18 THURSDAY, 11 SEPTEMBER 1986 (cone) 13 I. Golub et al., LROL, Laval U., Canada LASER CONTROLLED REFLECTION WITH A DISTRIBUTED FEEDBACK DYE LASER 14 M. Gastaud et al., CROGE, France DESIGN AND PERFORMANCE OF A FAST AXIAL FLOW HIGH POWER CO2 LASER 15 G. Sltwinski et al., Acad. of Sci., Poland SOVE CHARACTERISTICS OF A HIGH-POWER TRANSVERSE-FLOW CO2 LASER 16 D. Chuchem et al., AVCO, USA HIGH FREQUENCY TURBULENCE DIAGNOSTIC 17 D. Cruel an 1 et al., Torino Politec, Italy PLASM* CONTROL DURING WELDING PROCESS AT HIGH POWER AND LOW TARGET VELOCITY 18 W. Jueptner. et al., Bias,FRG DIAGNOSTICS OF HIGH POWER LASER BEAMS 19 M. Carbucicchlo et al., Parma U., Italy INFLUENCE OF PROCESSING CONDITIONS ON SURFACE MELTING OF STEELS 20 W. Viol et al., Dusseldorf U,, FRG GENERATION AND APPLICATION OF A PULSED 002-LASER OF HIGH AVERAGE POWER 21 W.E. Sctimid et al., MM, FRG HIGH POWER CW-DISCHARGE MULTI-kHz-REPETITION RATE Q-SWITCHED 002 LASERS 20:00 Farewell Dinner and Folklore Performance at Beit Maiersdorf on Mt. Scopus (departure at 19:45 from the Mori ah, Laromme, Kings and Menorah hotels)

19 FRIDAY, 12 SEPTEMBER 1986 08:30 - 10:30 NEW LASER MEDIA (sponsored by the Office of Naval Research,London) Chairman: C.R. Jones, USA 08:30 S.J. Davis - invited - PS I, USA SHORT WAVELENGTH CHEMICAL LASERS 09:10 L. Torchin et al., CRCGE, France THE C + N2O * CN(A,X) + NO REACTION: A POSSIBLE CANDIDATE FOR A NEAR INFRARED ELECTRONIC TRANSITION CHEMICAL LASER? 09:30 M.J. Rossi et al., SRI, USA LLMINESCENCE STUDIES OF SOLID AND GAS-PHASE TETRAMETHYLDIOXETANE: POTENTIAL FOR A VISIBLE CHEMICAL LASER 09:50 F. Voignier, CRCGE, France COMBUSTION-DRIVEN CW HBr CHEMICAL LASER 10:10 R.A. Meinzer et al., United Tech., USA HBr CW CCMBUSTION-DRIVEN LASER 10:30 Coffee break 11:00 - 12:30 Panel Discussion PROSPECTS FOR SHORT WAVELENGTH CHEMICAL LASERS Moderator: R.D. Levine, Hebrew U., Israel Panelists: H. Brunet, France S.J. Davis, USA C.R. Jones, USA K.L. Kompa, FRG S. Rosenwaks, Israel M.J. Rossi, USA D.J. Spencer, USA

12:30 CLOSING OF THE SYMPOSIUM

20 ABSTRACTS

21 ABSTRACTS OF PAPERS presented at the Sixth International Symposium on Gas Flow & Chemical Lasers have been prepared by photographic reproduction of texts submitted by the respective authors. Underlined names identify the authors presenting the papers. The abstracts appear in the order of presentation . Each abstract is identified in the upper left corner by a code: the first 3 letters indicate the day of presentation, while the last specifies the mode of presentation: INV = invited, O = oral, P + number = poster and panel number.

22 CONTENTS

Page MONDAY, 8 SEPTEMBER 1986

Opening Session 27

Chemical Oxygen Iodine Lasers 29

TUESDAY, 9 SEPTEMBER 1986

Optics 35

Fluid Dynamics 40

Novel Appl icat ions. 43

Poster Session 1 45

WEDNESDAY, 10 SEPTEMBER 1986

Short Wavelength Lasers 77

New Developments in CO2 Lasers ...... 82

High Power CO Lasers 86

THURSDAY, 11 SEPTEMBER 1986

Laser Propagation and Interaction 91

Applications 95

Laser Design and Diagnostics. 98

Poster Session 2 102

FRIDAY, 12 SEPTEMBER 1986

New Laser Media 125

Post-dead 1 ine papers ...... 133

23 [••1

25 MON-INV

SCIENTIFIC AND TECHNICAL ASPECTS AND PROSPECTS OF HIGH POWER LASERS FOR THE SDI.

Dr. Louis Marquet Strategic Defense Initiative Organization Washington, DC (USA)

Significant scientific and technical advances have been made in high-power lasers in support of the US Strategic Defense Initiative (SDI) effort. Since its inception in 1983, the SDI has served as focal point for research of a variety of technologies aimed to achieving a multi-tiered defense against ballistic missiles. At present, laser candidates for SDI missions include infrared chemical, excimer, free electron, and short wavelength chemical lasers. Particularly important has been the recent completion of the Mid Infrared Advanced Chemical Laser (MIRACL) at White Sands Missile Range, New Mexico. This deuterium fluoride chemical laser is the first high-power,high-brightness "weapons class" laser in the free world. Its completion demonstrates that the basic physics and engineering principles for entry level linear chemical lasers are in hand. The ALPHA hydrogen fluoride chemical laser is currently under construction and will represent the first large- scale cylindrical laser designed to operate in a simulated space environment. Results in excimer lasers include the single- pulse operation of near diffraction limited performance at the kilojoule level for xenon fluoride. In addition,the Raman process has been laboratory demonstrated and offers the potential of major reductions in the complexity required to achieve high quality output from large lasers. Several years of intense effort to demonstrate feasibility and scalability of free electron lasers using induction linacs and radio frequency linacs have led to significant technical advancements in these concepts. Research is continuing with short wavelength chemical lasers which may offer an optimum solution. Included in this work are efforts in Israel to exploit a new chemical laser concept for generating short wavelength pulses based on detonation of a solid fuel.

27 MON-INV METAL VAPOUR LASERS: RECENT ADVANCES & APPLICATIONS

C.E. Webb The Clarendon Laboratory, Parks Rd, Oxford, OX1 3PU, England. Copper Vapour Lasers have established themselves as efficient, practical, and reliable sources of high power visible radiation. State-of-the-art commercial systems provide 40W of average power on the 511 and 578 nm transitions of neutral copper, in the form of a continuous train of pulses of 300 kW peak power 25 ns duration and 5 kHz repetition frequency. Air-cooled systems which provide more than 10 W output but can be run from a domestic single phase outlet are also marketed. Development of CVL devices with output power in excess of 200 W from a single module has been accomplished at LLNL in the USA. Important milestones in the development of the present generation of CVL devices will be reviewed, together with a discussion of the physical and technological factors which affect their efficiency, repetition rate and output power capabilities. Among the recent advances to be described will be the use of injection locked unstable resonator cavities to improve beam quality, and a new technique for limiting the pulse duration to 12 ns FWHM. This development has considerable significance for the generation of-picosecond pulse trains, application of CVL technology which is rapidly growing. The application of CVLS and the closely related gold vapour systems to medicine will be discussed, with particular emphasis on a new form of cancer treatment - photoradiation therapy. Finally, the application of metal vapour lasers to high brightness display systems and the problems still outstanding before full-colour pulsed laser projection TV is a reality will be outlined.

28 MON-IMV

CHEMICAL OXYGEN IODINE LASER MECHANISMS AND HIGH RESOLUTION SPECTROSCOPY STUDIES.

R. BACI$ - Laboratoire de Speetrometrie Ionique et Moleculaire - Universite LYON I (France)

In the C.O.I.L. the initiating process (dissociation of I. 1 l by 0 ( A )) remains unexplained. Various attemps have been made to interpret this dissociation mechanism and to determine its influence on the power of the laser. Firstly we carried out a comprehensive study of the chemiluminescence of the- reaction in the infrared (Alu-XO system) and the visible (BO -X0 ) with a high resolution Fourier Transform Spectrometer. Recording the spectra over a long time interval (up to 32 hours) and using a non linear least-squares fit inversion procedures enabled rotational temperatures and vibrational populations of excited states to be determined. Their origin in the dissociation reaction will be discussed. Also collisional broadening of the hyperfine lines of the iodine atom were precisely measured-. Secondly we used the Baehar-Rosenwaks1 laboratory laser to check directly the influence of the dissociation mechanism on the laser power. The measured consumption of 0_( A ) in the dissociation is higher than that given from the currently available approximate dissociation models. From measurements of particular parameters describing the working-conditions of the laser (width or the line^ power density, ...) the full power can be calculated from a model using the known rate constants.

29 MON-0

THEORETICAL AND EXPERIMENTAL STUDIES ON 02(1 A) GENERATION AND TRANSFER

E. GEORGES, B. LEPORCQ, C. VERDIER Office National d'Etudes et de Recherches Aerospatiales BP 72, 92322 CHATILLON CEDEX, FRANCE

Abstract

The development of a chemical oxygen-iodine laser is based on 02(l

30 MON-0 THEORETICAL MODELLING AND EXPERIMENTAL ANALYSIS OF CHEMICAL OXYGEN-IODINE LASERS

D. David. E. Georges. B. Leporcq, P. Pigache, and C. Verdier 0. N. E. R. A. BP 72, 92322 Chatillon Cedex, FRANCE.

A one-dimensional flow model of the chemical oxygen-iodine laser is proposed. It includes the

main chemical reactions of the 02A - I2 system with temperature-dependent rates and the effect of channel cross-section variations, heat release and heat transfer to the walls. Heidner's model [1] is used for the dissociation process of the iodine molecules. A classical cavity model with a uniformly distributed loss is used for the calculation of the laser power, but the effect of finite translational and hyperfine relaxation rates of the iodine atoms [21 is included. Subsonic and supersonic flow conditions are both considered. Experiments have been performed on two low pressure subsonic flow lasers described in 131. The laser power and the concentrations of all important species are measured. The highest laser power obtained so far is 150 H. Very good agreement is achieved between model and experiments. The main conclusions are the following: Heidner's model for iodine dissociation does apply under low pressure laser conditions; gas temperature and translational relaxation effects should- be considered; supersonic flow conditions are attractive at high flow rates. (11 - R. F. Heidner et al. , J. Phys. Chem. , 1983, 87, 2348. [21 - M. V. Zagidullin, Sov. J. Quant. Elect., 1984, 1,4, 9 30. ( 31 - J. Bonnet et al. , 5th G. C. L. , Oxford, 1984.

31 TUESDAY, 9 SEPTEMBER 1986 TUE-INV

NEW DEVELOPMENTS IN OPTICAL PHASE CONJUGATION

Irving J. Bigio Los Alamos National Laboratory Los Alamos, New Mexico 87545

Optical phase conjugation may become a highly useful tool in laser systems, especially in very ]:irge laser systems where corrections of optical distortions and beam combining of multiple elements may be required for such systems to work. Following a brief introduction to the subject, we will review some of the recent developments, focusing on work done at the Los Alamos National Laboratory. Topics to be covered will include the discovery of dynamical effects in photore- fractive materials, the study of seeding and beam overlap in stimulated Brillouin scattering (SBS), and the measurement of transverse spatial coherence as a function of SBS threshold.

35 TUE-0 STIMULATED BRILLG'.IIN SCATTERING WITH HF CHEMICAL LASERS

W.T. Whitney, Michael T. Duignan*, and B.J. Feldman Naval Research Laboratory, Washington, DC USA *Potomac Photonics, Inc., College Park, MD USA We have used a fiashiamp-initiated HF pulsed chemical laser to demonstrate stimulated Brillouin scattering (SBS) in high pressure xenon gas. This is the first reported demonstration of SBS in the 3 micron spectral region, and is more than a factor of two deeper into the infrared than has previously been reported in gaseous media. The HF laser was grating tuned to a single wavelength (2.91 ym) producing a 1-2 ysec pulse of approximately 3 joules. The laser beam was focused into a high pressure cell containing 30 to 60 atmospheres of xenon gas, producing backscatter reflectivities approaching 50%. Threshold for the SBS signal was 0.6 joules. The onset nf the reflected pulse was delayed by - 1 ysec with respect to the input pulse indicating the transient nature o£ the SBS response. We will report results of measurements nf SBS thresholds and reflectivities for a varfety of experimental conditions including multiple wavelengths. Results of experiments to measure phase conjugate fidelity of the SBS will also be reported.

36 TUE-INV CONSIDERATIONS RELATING TO THE CHOICE OF OPTICAL MATERIALS FOR HIGH PERFORMANCE LASERS

ARTHUR H. GUENTHER, AIR FORCE WEAPONS LABORATORY, KIRTLAND AIR' FORCE' BASE, NEW MEXICO AND PR JOHN K. MCIVER, UNIVERSITY OF NEW.MEXICO, ALBUQUERQUE, NEW MEXICO

The laser induced damage threshold of optical components is still one of the critical design considerations in high power of high energy lasers and optical beam trains. . In this presentation we discuss our current understanding of the processes leading to laser induced damage. In particular, some of the models currently thought to describe these are Introduced and important material properties defined. Particular emphasis is placed on optical thin films, generally the weakest class of materials both from' the laser induced as well as environmentally induced degradation of performance. Trends in the damage thresholds predicted by the models as a function of material properties and experimentaIs variable are compared with experimental data. Unexplained observed parametric variations not adequately explained by current models are also discussed.

37 TUE-0 EXPERIMENTAL INVESTIGATIONS OF A FREE-VORTEX AERODYNAMIC WINDOW

E. V7ildermuth, A. Giesen, H. Hiigel (DFVLR, Institut fur Technische Physik, Stuttgart, FR Germany)

One cf the critical components of high power lasers is the output coupling element. If output power ex- ceeds a certain limit, it can become necessary to replace the solid window by another conception. There are many proposals employing mechanical or aerodynamic windows. An aerodynamic window has been chosen that uses a curved supersonic jet to seal the low pressure region of a simulated laser-cavity (100 mbar) against the ambient environment. A short introduction will be given of the principle, design and numerical calculations. Pressure measurements prove the fluidmechanical feasibility of the device. Its optical quality will be discussed along a series of shadowgraphs and interferograms.

38 TUE-0 MIRROR OPTICS FOR HIGH POWER LASERS W. Jueptner, R.Rothe, G. Sepold Bias, Bremen, FR6 Modern CO2 "laser for material processing exceed an output power of 10kw- Additionally the beam quality e.g. given by the focusing criterion, increase. The achieved high intensity requests mirror optics. The conditions for their use were examined and will be reported. Additionally future aspects such as correctable telescopes or Intelli- gient optics discussed.

39 TUE-0

CHARACTERISTICS OF TURBULENT FLOW STABILIZED DC-DISCHARGES

FOR C02 LASERS

H. BRUNET, M. MABRU and M. GASTAUD LABORATOIRES DE MARCOUSSIS, C.R.C.G.E. Route de NJozay 91460 MARCOUSSIS - FRANCE

Studies of nitrogen dc-discharges stabilized by an aerodynamic technique were carried out in our laboratory for more than years. The high pressure-high power nitrogen discharges were used to develop very high power CO2 lasers operating in an open-gas cycle mode. Recently, the original aerodynamic technique was successfully modified for achieving uniform axial dc-discharges in gas mixtures containing CO2 along with the capability of operating in a closed-gas cycle mode. Basic investigations of the discharge characteristics were conducted in open gas cycle through-measurements of both the thermodynamic and electric properties of the gas flow and of the small-signal gain coefficient at 10.6 /um. A numerical model was also developped for predicting the gain coefficient and the laser output power as a function of the discharge properties. Experiments were performed in discharge tubes having 80 cm in length with diameter varying from 3 to 10 cm at total pressure between 40-60 mbar. Results are presented of 5 and 10-cm-diameter discharges operating at a pressure of 55 mbar. Uniform and stable axial dc-discharges were typically achieved in C02~N2-He = 0.04-0.48-0.48 gas mixture up to a specific power close to 600 kW/kg/s. The volumetric power density was 5 and 2.6 W/cm^ for the 5 and 10 cm diameter discharge tube, respectively. The small-signal gain coefficient was found to be 0.60 and 0.45 % per cm for the 5 and 10-cm tube, respectively. By using two 8-cm diameter tubes aerody- namically connecteu in parallel and optically in series, we obtained a laser output power of 5 kW with an electrical efficiency of 24 ?o.

40 TUE-0

KINETICS OF CONDENSATION IN SUPERSONIC EXPANSION (Ar)

S. H. Bauer, N-S. Chiu and C. F. Wilcox, Jr. Department of Chemistry, Cornell University, Ithaca, New York 14853 USA

The temperature and density in an overexpanded jet (Ar) were mapped by the method of characteristics. The kinetics of condensation in the supersaturated gas along the central streamline was analyzed on the basis of four models, but constrained by thermodynamic relations which must apply during the homogeneous condensation of any supersaturated vapor. Cluster growth is due to successive associations: + An-1 A2 + An, each stabilized by a single collision or by a sequence of two energy removing collisions, for which kinetic parameters based on U potentials were estimated. Coupled differential rate equations (up to 192) were solved, both for cas-es when the heat of condensation was neglected, and when it was partially or fully distributed throughout the flow fluid. The distribution of cluster sizes declines exponentially, according to: N(n)=A exp(-an)+B exp(-bn), in agreement with generally observed distributions for monatomic species. Downstream, past a distance somewhat less than twice the aperture diameter, condensation becomes kinetically controlled. After (3-4) aperture lengths "freezingin" takes place. A fraction of the nascent clusters retain some of the heat of condensation and. remain at temperatures higher than the ambient gas.

41 TUE-0

EFFECT OF BEAM QUALITY ON THE SCALING OF HIGH ENERGY FLOW LASERS

W.L. Bohn, Th. Hall DFVLR-lnstitut fuer Technische Physik D-7OO0 Stuttgart 80, F.R. Germany

The maximum far field intensity obtained from high energy flow lasers depends on the specific power or power density that can be achieved in the laser medium and on the outcoupling efficiency of the laser resonator. Whereas the power loading of the laser gas medium has been extensively discussed elsewhere, this paper is devoted to a theoretical investigation on the limiting of gas flow inhomoge- neities on the maximum obtainable far field intensity. For a number of characteristic density profiles near and far field laser intensity distributions have been obtained using a KIRCHHOFF-FRESNEL code. A simplified far field intensity scaling has been derived and will be presented and discussed for typical electrical and chemical high energy laser candidates.

42 TUE-INV

PARTICLE ACCELERATION IN LASER PLASMA INTERACTION

J.L BOBIN University Pierre et Marie Curie, Paris, France

Future progress of elementary particle physics are depending on new generations of accelerators in the multi T.e.V. range. It is generally agreed that leptons ( electrons ) should be the right projectiles in linear colliders. On the other hand, it is known that longitudinal plasma waves are efficient in accelerating electrons over short distances: gradients over 1 6.e.V./m can be foreseen. High power lasers are well suited to create such waves through non linear interaction processes. Raman forward scatterig and beat waves, either between two lasers or between a laser and a wiggler in presence of an electron beam, have been considered as possible mechanisms in that perpective. Preliminary results from theory, numerical simulation and experiment, are encouraging. In order to be a good candidate, a laser should deliver very intense short ( picosecond ) pulses with a high degree of coherence for one or two lines. An efficiency greater than \O% and a repetition rate over I kHz are mandatory. Present state of the art lasers will be dicussed with repect to these requirements.

43 TUE-INV IBr PHOTCDISSOCIATION LASERS AS A SIMULATION FOP A SOLAP PUMPED SYSTEM

* * M. Shapiro and A. Yogev, Department of Physical Chemistry and Department of Isotope Research, Veizmann Institute of Science, P.ehovot 76100, Israel Laboratory simulations of solar pumped IBr laser were carried out, in order to clarify the following issues:the prospects for operating the IBr laser using the solar concentrator, now being built at W.I.S. The dependence of excited Br atom formation, on the spectral excitation range. Methods for enhancing the recombination process by adding inert gases to the laser gain mediun, in order to improve laser performance. Lasing with three different experimental set ups, under various conditions has been investigated, leading to the following conclusions: (1) laser output energy and peak power is considerably improved by using suitable dye solutions as folters. This fact provides indirect evidance for the formation of ground state Br atoms, by UV radiation, and prove the strong Br formation dependence on the spectral excitation range. (2) Addition of inert gas has been found to increase laser power and decrease threshold and onset tines. Neon whose role is to aid in the recombination of Iodine and ground state Bromine atoms, is most efficient in this respect. (3) Laser pulse width can be made considerably longer by usinp long excitation pulses. Short excitation pulses (1.5-3 microaec) lead to very short laser pulses (200 nsec), whereas longer (170 microsec) excitation pulses, lead to 15 microsec pulses. (4) Threshold input energies for lasing is estimated to lie between 3000-6000 solar constants. This is similar to the results achieved by Zapata et al. and various calculations which were done on this subject. This concentration factor is lower than that attained in the solar furnace (theoretically limited to about 20,000 solar constants). In light of the above conclusions, the prospects of operating the Br*- laser system on the CW mode with solar energy, seem promising.

44 TUE-P-1

KlMETICS OF PRODUCTION OF ELECTROIICALLY EXCITED IF*

H. V. Lilenfeld and G. R. Bradburn, McDonnell Douglas Research Laboratories, St. Louis, MO 63166, USA

Recent experiments have shown that IF can be excited to its B state by making IF in the presence of electronically or vibrationally excited species. The mechanism for production of electronically excited IF, however, is not well un- derstood. Our experiments described below are aimed at obtaining an understanding of the mechanisms of excitation of IF. The following mechanism has been used to describe the experimental results:

F2 + I2 •*• I2F + F (1)

I2F + F * IF* + IF (2)

I2 + F •* IF + I (3)

I + F2 -> IF + F (4)

IF* •> IF + hv (5) We have investigated the mechanism above in a fast-flow reactor. We have determined the room-temperature rate constant for reaction (H) to be 1.3 x 10~1^ cm3 molecule"^ s~1. In addition, the formation of I, IF, IF3, and I2F produced when I2 and F2 are reacted was monitored. Injection of F downstream of the point where F2 was added to the I2 flow caused an increase in the IF(B) emission rate. Based upon the emission intensity of IF(B), an estimate of k2 was also obtained.

* This research was performed under the McDonnell Douglas Research and Development Program.

45 TUE-P-2 LASER PULSE DEFORMATIONS IN KrF AMPLIFIER

J.Badziak, A.Dubicki Institute of Plasma Physics and Laser Microfusion Warsaw,Poland The problem of the pulse deformation in the KrF laser amplifier was considered as well as the possibilities of its compression in the amplifier -saturable absorber system. In the case of quasistationary interaction between the pulse and the amplifying medium there were obtained analytical expressions describing the change in the pulse duration as a function of its peak intensity and the shape parameter and of the amplifier parameters. It was shown that in thfe case of transversal distribution of radiation different from the rectan- gular one, in result of non - linear interaction with the amplifying medium, the temporal-spatial structure of the pulse can -^andergo considerable deformations. Detailed numerical analysis of the pulse propagation in the amplifier was based on the complete set of equations describing the kinetics of e-beam pumped KrF laser. The case of quasistationary and non-stationary interaction in a wide range of amplifier parameters and of input pulse was considered. The possibility of the pulse compression in the multipass amplifier - saturable absorber system was discussed and the system was optimized in order to obtain maximum power of the pulse.

46 TUE-P-3 2 AT0MS IN THE FORMATION OF I( P1/2) F + I2 AND H + I2 REACTIONS

H. BRUNET, M. MABRU, Ph. CHAUVET and L. TORCHIN LABORATOIRES DE MARCOUSSIS, C.R.C.G.E. Route de Nozay 91460 MARCOUSSIS - FRANCE

In a search for a new way of producing I( P1/2) atoms, different from the well-known 0.2(1 A )-I energy transfer, we investigated the F + I2 and H + I2 reactions. The presence of excited iodine atoms as a product of the F + I2 reaction has been a subject of controversy. In 1983, Trickl and Wanner suggested, from the results of their cross-beam experiment, that the reaction pathway leading to excited I(2Pj_/2) atoms was much probable (by a factor of 8.3) than that leading to unexcited 1(^3/2) atoms. However two different experiments have recently shown that the pathway leading to I(2pjy2) atoms was very unlikely. In 1979, Lorentz, Wagner and Zellner studied the H + I2 reaction in a discharge flow system and, using UV resonance fluorescence, detected I(2pjy2) atoms. We studied the reaction of F and H atoms with I2 molecules in a fast-flow tube reactor. The F atoms were produced by using either electric dissociation of SFg (or NF3 or CF4 or F2) diluted in He or thermal dissociation of F2 in a combustor. The H atoms were produced by electric dissociation of H2 diluted with He. Iodine molecules were delivered into the main gas flow through a heated stainless steel injector. The pressure in the reaction zone was 1.2 Torr and the mean flow velocity was about 40 m/s. I(2p^/2) atoms were searched by de- tecting the 1.315 /um fluorescence. Strong I(2P]y2) emission was observed from the F+I2 reaction but we did not see any emission from the H+I2 reaction. The branching ratio I*/I was determined by comparing the 1.315/tm emission intensity to that of HF emission lines observed either from the F + H2 or H+ F2 reaction by replacing I2 by H2 or F£. A preliminary lower limit of 0.03 was found for the microscopic branching ratio of the F + I2 reaction. For the H + I2 reaction, I* emission, if any, was below the detection limit and therefore an upper value of 0.005 can only be set up for the branching ratio.

47 TUE-P-4

RATE EQUATION DESCRIPTION OP TIME-DEPENDENT PROCESSES IN GAS-DYNAMIC LASER ACTIVE CAVITY

M. Brunne Institute of Fluid-Plow Machinery, Polish Academy of Sciences, Gdansk, Poland

The rate equation formalism is used to describe the time-dependent processed induced in CW gas-dynamic laser active cavity by the sudden changes of the gain at the cavity entrance and/or its optical quality. The CO2 and N?0 classical gasdynamic lasers are kept in mind as a practical analogue of the laser under consideration. The paper aim consists in determining the time needed for the photon number density distribution over the mirrors surfaces to reach the new CW regime of the laser pperation.

48 TUE-P-5 INVESTIGATIONS OF THE POPULATION INVERSION AND GAIN IN THE CW GDL-CM AS A FUNCTION OF THE RELATIVE CONCENTRATION OF COg MOLECULES Adam Cenian Institute of Fluid-Flow Machinery Polish Academy of Sciences, Gdansk, Poland

Research carried out by means of a shock tube had indicated that the population inversion should depend on the relative concentration of CO2 molecules in the CW GDL-CM. Investigations of this dependence gave rise to development of a new version of the mod&l of GDL-CM which takes the coupling of gasdynamic and kinetic processes into account. The results showed the existence of a maximum of the population inversion as a function of relative concentration of CO2. The available experimental results are in qualitative agreement with presented here.

49 TUE-P-6

PARAMETRIC ANALYSIS OF A CW CO EDL BY COMPUTER SIMULATION.

M. IYODA, Chiba Inst. of Tech., Narashino, JAPAN, K.TERUNUMA, Keio Univ. , Yokohama, JAPAN, and S. SATO and T.FUJIOKA, Industrial Res. Inst. , Tokyo, JAPAN.

The output performance of a subsonic flow transversely excited cw CO electric discharge laser (EDL) has been parametrically analyzed by using computer simulation. The simulation which is the revised version of the authors' work presented in the last GCL consists of a discrete vibration level model, a semi 1- dimensional flow model, and a plane-parallel cavity model. In the discrete model 50 vibration levels are taken into account both for CO and N~. Direct excitation from the ground levels to l-8th levels are calculated by Boltzmann's equations. 300 V-R/T processes of CO and N9 and 7500 V-V processes of CO-CO, CO-Ng, and N2~N2 are computed based on the most reliable collision theory. The 1-dimensional differential equations are solved downstream the axis which is set along the flow. The laser power is calculated by a constant gain method. As a function of the parameters , e. g. gas mixture ratio, pressure, temperature, flow velocity, and discharge current, the characteristics of the laser are examined in terms of laser power, gain, conversion efficiency, number density in each vibration level, and gas temperature. By the comparison of the simulation and the experiment, the support and prediction of the output performance of the CO EDL are realized.

50 TUE-P-7

EXPERIMENTAL STUDIES AND KINETIC MODELLING OF AN HF CHEMICAL LASER AT LOW TEMPERATURES

K. Waichman, D. Chuchem and Y^ Kali sky Nuclear Research Centre-Negev, P.O.Box 9OO1, Beer—Sheva, 84190 Israel

The delay time between the initiating pulse and the development of the laser emission for various vibrational transitions in HF chemical laser have been measured. The measurements have been performed for various low temperatures by varying the Mach number and stagnation pressure in a supersonic-flow premixed, electric-di«charge laser. The direct measurement of the time development of the lacing P-branch transitions as a function of the temperature *rm compared to a theoretical model which yields information on the F + H=> reaction rates. The relative temperature—dependent peak power in the P-branch lines for the pulsed HF laser at 115K and 158K were also measured and analyzed.

51 TUE-P-0

OPTIMIZATION OF DISCHARGE STABILITY OF AN E-BEAM SUSTAINED SUPERSONIC CO-LASER BY OPTICAL DIAGNOSTIC MEASUREMENTS W. Mayerhofer, W. Hennig, R. Nowack, H. Hugel DFVLR, Institut fur Technische Physik, Pfaffenwald- ring 38-40, D-7000 Stuttgart 80, F.R. Germany

Gasdynamic CO-lasers are very attractive candidates for high power lasers with respect to their efficiency, provided a homogeneous deposition of high energy into the gas is possible. Experimen- tally values of energy loading of 0,3 eV/CO molecule were achieved in a supersonic Ar/C0-9/l-mixture at 200 mb, extracting 1,8 Joule laser pulse energy with an efficiency of 15 %. At higher loading a discharge streamer instability is setting in which leads to arcing at about 0,45 eV/CO. Utilizing optical diagnostic measurement the electrode phenomena of the discharges in both flowing and still gases were studied. Removing the sustai- ner electrode from the supersonic boundary layer in a new type deep cavity (alcove)-electrode im- provement of power loading by a factor of two was achieved. In addition, experiments were performed to investigate aspects of the maximum pulse repetition frequency and the volumetric up-sealing.

52 TUE-P-9 DIRECT MEASUREMENT OF THE ELECTRON DENSITY IN THE ACTIVE MEDIUM OF E-BEAM PUMPED ARGON FLUORIDE LASER

Z. Rozenberg, M. Lando and M. Rokni The Racah Institute of Physics The Hebrew University of Jerusalem, Jerusalem 9]904, Israel

The secondary electron density in electron-beam irradiated Ar/F gas mixtures has been measured by time resolved interferometry, using a 9.6p Mach-Zender interferometer. This method of measurement is direct in the sense that the measured refractive index increment depends only on the electron density. Measurements were performed for gas mixtures with various F2 concentrations between 0.0025% and 1% and total pressures between 0,5 Atm and 2 Atm. The electron-beam pulse was 350 ns long at an energy of 150 KeV and current density ranging from 0,025A/cm2 to 6,3A/'cm2, From the dependence of the measured electron density on the fluorine density the rate constant for electron attachment to F2, with no external electric field, has been determined experimentally for the first time, For a given electron-beam current density, the attachment rate constant is found to be a decreasing function 9 3 1 of the F2 concentration, with a value of 3.5xlO- cm~ sec" for 9 3 1 low concentration and O,7xlO"" cm sec" for high F2 concentration. On the other hand, for a given fluorine concentration the attachment rate constant is found to be an increasing function of the e-beam current density. We attribute this behayiour to an increase in the electron mean energy with increasing F2 concentration at low F2 concentrations, and a decrease in the electron mean energy with increasing e-beam current density, A simplified model describing this effect will be discussed.

S3 TUE-P-10 KINETIC MODELING OF A SUPERSONIC FLOW CO CHEMICAL LASER

W. MASUDA*, N. OGAWAHARA* and H. SAITO** * Technol. Univ. Nagaoka, Nagaoka, Japan ** IHI Co. Ltd., Yokohama, Japan A computer model is developed for the coupled gasdynamics and kinetics in a CO chemical laser, which utilizes the supersonic mixing of the dissociated products of CS2 and O2 diluted in Ar (or He). The gases, which are in thermo-chemical equilibrium at the plenum, are exhausted through the nozzles that freeze the recombination kinetics, thereby preserving the high 0 and CS concentrations and generate low temperature supersonic flows. Downstream of the nozzle exits, the chemically and vibrationally nonequilibrium flows mix, react and produce vibrationally excited CO molecules. In the present study, it is assumed that the flows are quasi-one-dimensional and the mixing takes place instantaneously at the nozzle exits. A chemical and vibrational model encompassing twenty four reactions and twenty eight vibrational transitions is used to approximate the reacting and relaxing mixture contained within the combustor. The present simulation is used to study the effects of various parameters on the species concentrations, CO vibrational population distributions and the small signal gain coefficients of a supersonic flow GO chemical laser and the proper gasdynamic conditions to give good performance is discussed.

54 TUE-P-11

HIGH PULSE REPETITION RATE LIMITATIONS IN A HIGH AVRAGE POWER XeCl LASER*

M. SENTIS, B. FORESTIER, B. FONTAINE, P. ISSARTIER I.M.F.M. AIX-MARSEILLE UNIVERSITY AND D. PIGACHE O.N.E.R.A. 93320 CHATILLON FRANCE Potential applications of high average power ultraviolet lasers stimulate studies of this class of lasers. A testbed "LUX" has been developed at I.M.F.M. to study with a scale factor equal to 1 the physic of main limitations. Due to the laser transition caracteristics the emission has a short duration and so average power means repetitive pulses. The goal of this paper is to study the problems related with high repetition rate (PRF). The device mainly consist of a subsonic stainless steel loop in which an Ne/Xe/HCl mixture is excited by an X-Ray stabilised discharge. As soon as high PRF are considered, problems of active medium homogeneities are encountered due to the strong acoustic waves, induced by the active medium excitation. These problems are for a large part related to the mechanic of fluids. This paper will give the up to date results achieved with the LUX device. A power of 150 Watts has been achieved with a PRF of 1000 Hz and an efficiency of 2 % in an active medium volume of 60 cm^ preionised by a new X-Ray gun. This gun of wire ion plasma type has been specially design for LUX device at O.N.E.R.A. It will now be possible to work continuously. Results corresponding to long burst mode experiment at high PRF and high power loading will be given as well as results concerning long time experiment at moderate PRF and loading. Effects of high PRF on homogeneity, laser pulse shape, discharge stability will be described. The influence of preionisation level on discharge stability at low and high PRF will be too underlined.

Work supported by French D.R.E.T. and C.E.A.

55 TUE-P-12

FLUID-DYNAMIC EFFECTS, INCLUDING TURBULENCE, ON A HIGH-PRESSURE DISCHARGE

Oscar Biblarz and Jon L. Barto* Naval Postgraduate School Monterey, CA 93943, USA

High pressure discharges involving molecular gases are generally stabilized by flows of varying degrees of turbulence. This paper reviews our present understanding of the role of turbulence in stabilization as well as the various mechanisms for introducing turbulence in regions of the discharge where it will be most beneficial. We report on a non-uniform discharge in an electron attaching gas mixture (air). The glow is produced between a highly stressed anode and a plate cathode. We study various electrode-to-flow orientations including the common cross flow configuration. Because the positive ion mobility is low enough, convection and drift due to the electric field are of comparable magnitude within the anode region. An "anode extension" is thereby forme

*Present address: Hanscom AFB, MA 01731, USA

56 TUE-P-13 AERODYNAMIC CURTAINS DESIGN FOR GAS FLOW LASER CAVITIES

S. Kaizerman, Y. Nachshon, and F.. Wacholder Ministry of Defence, Scientific Department P.O.Box 2250, Haifa 31021, ISRAEL

A significantly improved flow-field can be achieved by designing supersonic aerodynamic jet curtain devices in the laser cavity. In the analysis of these devices special attention has been devoted to reduce the disturbances in the cavity flow-field and to preserve the optical beam quality. A judiciously "tailored" version of the general- ized-mesh Eulerian APACHE code has been used for this purpose. This version includes all the important physical models for accurate prediction of the system transients, but it possesses also greater problem geometry flexibility and is simpler to use and reasonably economic for extensive parametric and sensitivity studies. Computations of the combined laser cavity/curtain flow-field of various geomettical configurations have been successfully applied to the study of aerodynamic curtains for several kinds of gas flow lasers. Typical examples of computed results for an HF chemical laser are presented and discussed. General conclusions of practical importance are drawn.

57 TUE-P-1'i

GAIN OF A GASDYNAMIC LASER UTILIZING PRODUCTS OF LIQUID Cells AND GASEOUS O2 COMBUSTION

Shigery SATO, Tadaharu WATANUKI, Masayoshi MATSUZAKA, Makoto YAMAGUCHI and Hirotoshi KUBOTA University of Tokyo, Bunkyo, Tokyo, 113 , Japan

ABSTRACT This paper presents characteristics of a combustion- driven CO2GDL operating with liquid fuel Celfe and gaseous oxidizer O2. The purpose of this study is to develope a radiative heating simulator for re-entry problems, which brings high power density and continuous power output. The most suitable system for these two requirements is a combustion-driven CO2GDL. Since the most important problem in a combustion-driven GDL is that plenum temperature depends on working gas fractions, it is difficult to optimize laser performance. A process of gain optimization of a combustion- driven GDL is discussed from experimental view points. This combustion system was designed on the basis of rocket engine systems. Liquid fuel atmizing mechanism is an impinging type injector of "like on like". The ignition sequence is driven automatically by a preset program. The combustion pressure and temperature achieved were approximately 30 atm, 1600 K at the most, respectively. The flame was found very bright blue, and soot problem hardly occurred. This GDL system is such a kind of a high-temperature supersonic wind tunnel of open cycle. Supersonic nozzle is a two-dimensional single nozzle : h* = 0.5 mm, A/A* = 70. The Mach number achieved is 4-5. Laser cavity has three windows along the gas flow. The active medium was probed with a diagnostic laser of wave length 10.6 micron at each distance of 15,105 and 195 mm from the nozzle exit. Gain path is 138 mm wide. An achieved gain is about 0.4 nr1 at plenum pressure 20 atm, temperature 1100 K, working gas fraction C02:N2:H20 = 8:87:4 * (by volume). The rest 1 % includes other gases. A GDL utilizing Ceffe-Oa products can not make very high temperature existence of dilutant N2 so that it seems to be not of great advemtage to laser efficiency. But the results of our experiments show that products of C6H6-O2 are also active media for wcCOzGDLs.

58 TUE-P-15 FLOW INVESTIGATIONS OF PULSED ARC DISCHARGE RECOMBINATION LASERS

W. 0. Schall, W. Mayerhofer, G. Spindler DFVLR- Institut. fiir Technische Physik D-7000 Stuttgart 80, F.R. Germany

SPER type metal vapor recombination lasers make use of arc discharge pulses across a series of narrow gaps. Electrode material is ionized and expands into a background gas. During the expansion the plasma recombines and population inver- sions are established. A laser has been operated in neutral Cd at 1.4 p,m wavelength. The process of arc ignition, the expansion of Cd I and Cd II, and the expansion of a leading shock wave has been observed using streak photography in combination with line filters and a Schlieren optical arrange- ment. In order to describe the initial plasma parameters and the development of the state variab- les in space and time, measured speeds of the shock and plasma front are compared with the results of a computer code for a spherical expansion into a background gas. The calculation includes recombination of singly ionized cadmium and heat conduction across the contact front with the background gas. The best correlation to measured shock speeds is found for an initial plasma temperature between 10.000 and 12.000 K.

59 TUE-P-16

DEFORMATION MEASUREMENTS ON CO2-LASER OUTPUT CO UPLERS IN OPERATING HIGH POWER LASER SYSTEMS

BERGER, KOTTLER, ORIEL GMBH, DARMSTADT,FRG

The dynamic behaviour of output couplers in high power CO2 -lasers with power levels in excess of 1 kW has been invest! gated by means of interferometry. The deformation of the fro nt- and back-surface of a ZnSe-partial reflector could be con firmed. When examining the transmitted wavefront the bulk m aterial clearly shows a power-correlated behaviour. The impa ct of these measurements on laser optics will be discussed.

60 TUE-P-17

SCALABLE SATURABLE ABSORBER FOR KrF LASERS

Irving J. Bigio and Scott J. Thomas Los Alamos National Laboratory Los Alamos, New Mexico 87545 505/667-6448

We report the first demonstration of an effective and scalable saturable absorber for KrF lasers operating at 248 ran. Four centimeters of ozone at 0.4-torr transmits only 2% for fluences under 50 mj/cm2, but the transmission saturates to >90% for fluences above 1 J/cm2. The addition of a buffer gas can allow operation at atmospheric pressure, simplifying the scaling to very large apertures.

61 TUE-P-18 QUANTITATIVE INVESTIGATION OF THIRD HARMONIC GENERATION IN THE XUV RANGE USING A CO FREEST ZONE OF SILENCE F. Aguillon, A. Lebdhot, J. Rousseau, and R. Camparque Laboratoire des Jets Mole'culaires Departement de Physico-Chimie CEN de Saclay, 91191 Gif-nur-Yvette Cedex, France The third harmonic of a pujsed. UV laser radiation (X = 280 to 300 nm) is generated thrcugb. a supersonic flow of CO in,a CW free-jet zone of silence ' , instead of a pulsed jet . Also, a cell of CO is used, for comparison, as a gaseous nonlinear medium. This four wave mixing is investigated by taking the greatest care cf the laser geometry stability which is found to be very important for the conversion efficiency. It is shown thai the non-resonant third harmonic generation (THG) is entirely governed by the phase matching factor. An enhancement of several oxxiers of magnitude is obtained at the two-photon resonance and especially in the free jet where the cooling increases significantly the relative number densities tf the resonant ststes. The THG spectra thus obtained ars well correlated- to.the two-rphoton laser induced fluorescence spectra recorded simultaneously. In these spectra, the assignment of the resnnant states is very easy and the line intensities reflect the internal state populations in the CW CO fr&e jet. Finally, it is possible,to calculate the .y filiations of Jthe nonlinear-susceptibility x versus the quantum rotational numbers-of the resonant levels of CO. Thus, rotational temperatures in the jet are obtained in agreement with those given by other methods.

1. R.Campargue. 3. Phys. Cham. 88, 4*66-4474 (1984) 2. F.Aguillon, A.Lebihot, O.Rousseau, and R.Campargue, 10th International Symposium an Molecular -beams, Cannes, France (June 3-7, 1985), Book of ..Abstracts, VII-I,1-3 ; also, 1985 Conference on the dynamics of Molecular ..Collisions, Snowbird, Utah, USA (July 14-19, 1985). 3. A.H.Kung, Opt. Lett. 8, 24 (1983) J.Bokor, R.Bucksbaum, R.freeman, Opt. Lett* .8-, 237 (1983) C.T.Rettner, E.E.Marinerq, R.N.Zare and A.H,Kung, 3. Phys. Chem. 88, 4459-4465 (1984).

62 TUE-P-19

HIGH EFFIC IENCY RAMAN CONVERS ION OF UV TO BLUE-GREEN LIGHT

El i Marqa1 ith, HLX Laser 1 nc. , 5^52 Ober1i n Dr i ve San Diego, Ca. 92121, U.S.A.

Two methods to achieve high efficiency Raman conversion of 308 nm to ^SSnm via lead vapor are compared and discussed: (1) a single-pass focused pump beam technique and (2) a seed-amplifier configuration. In the first configuration, a focused pump beam is converted to Stokes photons in a single oass through the Raman cell. In the other, a small fraction of the pump beam is used to Droduce a blue seed beam. The seed is recombined with the rest of the pump beam and amplified in a second ppss through the Raman cell. The tradeoffs in usinq the two conversion techniques are di scussed.

63 TUE-P-20 A NUMERICAL STUDY INTO CHARACTERISTICS OP A GDL WITH UNSTABLE .MULTIPASS CAVITY

(j.Rabczuk, Institute of Fluid Plow Machines, Po- lish Academy of Science, Gdansk, Poland

It follows from approximate optimizing calculations of the GDL that an optical cavity of large Presnel number ought to be chosen so that the GDL working region be fully covered by the radiation field. Mo- reover, the optical cavity should be placed near the nozzle throat in the region of highest small signal gain. There the GDL channel and thus the cavity mirrors have an increasing height. There are technological problems associated with the manufacturing of oblong cylindrical mirrors appropriate for a large Fresnel nuniber cavity. A multipass cavity composed of circular mirrors placed on the si- de walls of the GDL working region seems to be more practicable. A numerical code for an analysis of the GDL with an unstable multipass circular mirror cavity has been developed. The results concerning the steady-state field patterns, gain and inversion population distributions along the channel as well as values of the output power for configurations considered are discussed in the paper.

64 TUE-P-21

COMPARATIVE INVESTIGATIONS OF THE ELECTRIC DISCHARGE IN THE HIGH-POWER FAST-FLOW CO LASER

J. Konefal Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Gdansk, Poland This paper aims at presentation of a convective-cooled CO2 laser excitation system [1]. The modified excitation system is compared with the one presented in [1], con- sidering both physical parameter's and the technical point of view. The working medium is excited by a self-sustained DC discharge. In [1] it occurs between the common planer anode and tungsten wire cathodes of 1.5 mm dia and packing density 0.9 pin per cm . The distance between the anode and the pins amounts to 63 mm.816 such elements were used for excitation of a volume of 5 dm^. The elastic power deposited in the working mixture has reached 6QkU, with the average current density equal to about 22 mA/ent^ and the specific power unit volume equal to about 12 W/cm3. For a stable work of the laser each pin cathode must be cooled and connected to an individual ballast resistor. This system in technically guite complicated. The modification of the excitation system is based on a change of the .cathode configuration and the ballast resistors system. The cathodes are of 10 mm dia and the working surface is rounded, ther packing density being 5 to 8 times lower than in the previous system. First experiments seem to be promising. It was found that the mean current from one segment cathode amounts to more than 150 mA, and the power dissipated in the gas-to about 500 W. Ballast resistors (power rating of 50 W) previously cooled by the flowing air stream, have been replaced by the resistors which have the power rating of 25 W and are submerged in a transformer oil. It should be mentioned that the resistor load increased more than 7 times. [1] Stanco J., et al, Second Int.Conf."Trends in Quantum E- leetronics",Bucharest, Sept. 1935, Conf. Abstracts, p. 69

65 TUE-P-22 A DIAGNOSTIC SYSTEM FOR MEASUREMENT OF THE FOCUSED BEAM DIAMETER OF HIGH POWER CO2-LASERS

Kramer R., Beyer E., Herziger G., Loosen P. Fraunhofer-Institut fur Lesertechnik, Drosselweg 37, 5100 Aachen, Fed. Rep. Germany

A novel diagnostic system is presented in ord'r to measure the two dimensional intensity distribution cf C02-laser beams. Beam diameter, divergence annlo ^.nd maximum intensity are calculated from contour lines of constant intensities. The evaluation of beam parameters by the contour lines yielding 90 % of the total laser power in suitable for any laser beam, including asymetric dirtributions and intensity distribution of stable an

66 TUE-P-23 MEASUREMENT OF CURRENT FLUCTUATIONS IN A 1 KW GAS TRANSPORT LASER

Bruno Walter, Dieter Schuocker TU Wien, Inst. f .Nachr.lchtent .u.Hochf requenztechn. Gusshausstrasse 25, A-1O4O Vienna, Austria

The ability of material processing of a high power CO2 laser depends on the qua]ity of the laser beam in terms of the output power stability and the mode fluctuations. The transient mode fluctuations may occur due to local current density variations in the glow discharge- For this reason a computer controlled system has been developed to measure the current fluctuations in a fast transverse flow gas transport laser. This lasex- uses a dc-glow- discharge between a cathode rod and 7 3 anode pins ballasted by series resistors. To estimate the current distribution over the entire length of the laser the currents of 12 anode pins are measured and monitored on a display. Furthermore the amplified signal of the laser power meter is stored and displayed with the current fluctuations on a monitor. It is shown that the output power fluctuations depend mainly on the variations of the total discharge current, whereas the fluctuations of the beam pattern rely on the variations of the internal current distribution.

67 TUE-P-24

INCREASE IN THE CO LASER ENERGY TRANSMISSION THROUGH THE ATMOSPHERE USING A PRECURSOR PULSE

M. AUTRIC, P. VIGLIANO, D. DUFRESNE, Ph. BOURNOT Laser-Matter Interaction Group Institute of Fluid Mechanics, 1, rue Honnorac, 13003 - MARSEILLE FRANCE

Propagation of pulsed high power laser beams through the atmosphere is limited by different linear or nonlinear phenomena such as aerosol and molecular absorption and scattering, atmospheric turbulence, thermal blooming and optical breakdown. The aerosol-induced breakdown plays a preponderant role for relatively short and high power pulse. An experimental investigation has been conducted to study the possibility of increasing the transmission of CO2 laser energy using a precursor pulse (fluence 6-56 J/cm2 ; interpulse time 0,1 to 10-3 ms) . A clearing effect is characterized by an increase in the air breakdown threshold values(strongly connected with variations of meteorological conditions and distribution of aerosols particles) and in the transmitted energy through the cleaned zone (factor of three) as a function of the precursor fluence, interpulse time, size distribution of airborne particles and meteorological conditions.

68 TUE-P-25

INITIATION PROCESSES AND DEVELOPMENT OF LASER INDUCED LOW PRESSURE SPARK CHANNELS v. Worioka, H. Tamura, H. Kanazawa* and K. Kasuya Department of Energy Sciences, The Graduate School at Nagatsuta, Tokyo Institute of Technology, ^259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 227, Japan "I HI Co., LTD., Shin Nakahara-cho 1, Isogo-ku, Yokohama, Kanagawa 235, Japan The initiation processes and the development of discharge channels triggered by laser lights have been investigated experimentally, in a parameter range of discharge current I=1O3-IO5A and gas density /j=10~ -10Kgm"3. A simple theoretical estimation was also performed. Electrical discharges of long gaps (up to 700mm) were initiated by laser lights in alkaline metal vapors. Sodium or Cesium vapor was resonantly excited by a dye laser light. For example, a high power laser light tuned to the resonance line of Cesium atom (^55.5nm) induced the sufficient photoionization of the atom in Ar buffer gas and initiated a discharge channel of 60 cm in length.- The minimum voltage allowing the laser initiation and the time lag from the"laser injection to the breakdown were measured. The time lags depended on the Cs and Ar number density and the applied voltage. Their value were between ^00 nsec and 2/nsec. A good agreement was obtained between these values and theoretical ones. By a fast streak camera, it was observed that the intitial diameter of the discharge channels was decided by the beam diameter of laser lights. Such electrical discharge channels are usually accompanied by high speed flows, because the discharge energy induces an outward motion to the ambient gas. The behavior of discharge channels was also observed by the camera, and the gross behavior of them has been investigated theoretically by a simple model. It is clarified that the current core is ex- pansive within a parameter range investigated in this study. At higher current levels, the expansion of the discharge radius is suppressed due to the magnetic force produced by the current itself. It is shown that the effect on the radius of discharge channel can be characterized by a physical parameter, which is a function of I^/j> ^ .

69 TUE-P-26

THE DEEP PENETRATION OF HF LASER LIGHT INTO GLASS AND ITS POSSIBLE INDUSTRIAL USE

Rene JOECKLE and Andre SONTAG French-German Research Institute of Saint-Louis B.P. 301 - (68301) SAINT-LOUIS, France

Working of glass requires heating over the melting temperature of a certain depth of material. Conventional heat sources release heat at the surface of the glass, whereas HF laser light is absorbed in a depth of several millimeters. The purpose of this study is to investigate the ability of HF laser radiation for precision heating of glass. A C.W. HF laser of 180 w power has been used. The fluorine atoms are generated by a thermal dissociation of SF6 in a electric arc burner, expanded and cooled through a nozzle array producing a supersonic stream, in which the hydrogen is mixed. The absorption coefficients of the different laser lines have been measured. They range from 0.8 cm for the short wavelength line Pi(4) to ID cm for the P2(4) line. The knowledge of these values and of the power repartition in the lines allows for the calculation of the heat input obtained with a given beam power and beam geometry. Welding of two 3.2 mm thick Pyrex plates has been obtained with a small apparent distortion of the geometrical form of the plates. Cutting of 2 mm thick glass plates by focussing the laser beam oh the plate and blowing away the liquid glass has been (tried. A cutting speed of 15 cm/inn has been achieved. However, cracks propagate along the welding or the cutted edge. These cracks result from the fast cooling of the melted glass, occuring by conduction into the bulk of the heat released in the melted zone. High tensile stresses are generated in this non- stabilized glass slab.

70 TUE-P-27

LASER QAEDING (F HEftT TKEftCED SIBEIS

D. Fishman A. Shachrai >fTAIMMING LASERS INTERNATIONAL (IL) LTD. TEL-AVIV ISRAEL

Some high strength tools require special characteristics to withstand certain adverse conditions such as wear and corrosion. Che such method of achieving these qualities is to coat metal with a.special alloy. The bulk material chosen for this work was SAE 4340 hardened and tempered, and the cladding material was STELLITE SF6 (cobalt base powder with carbides). The stellite powder was flame sprayed onto the metal. Laser beam scanning was used for melting and adhesion of powder to the metal surface. The laser advantages for this job are several, e.g. (a) local heating and melting of the coated powder and the bulk surface is performed without causing damage to the whole material and thus preserving its characteristics. (b) cladding powder is completely melted and porosity almost totally eliminated, (c) cladding treatment on heat treatable materials is considerably easier, (d) coated powder penetration to the bulk is controlled, (e) distortion of the coated products is minimized. The samples were scanned by a 4KW laser with a scanning speed of 0.25 - 2m/min and a laser beam diameter of 7mn. As the speed increased, the penetration of the coated powder to the bulk decreased. The heat affected zone was minimized and the hardness of the cladding increased with a cladding hardness of 400-550 HV achieved. A low rate of porosity was found on the cladding after the scanning as opposed to very high porosity prior to scanning. Complete sticking of the cladding to the bulk was achieved with minimum distortion. The process is adequate to coat heat treatable materials without spoiling the bulk characteristics, and getting the desired results on the surface.

71 TUE-P-28

"ROBOLASER IN THE CAR INDUSTRY'

Zand Abernan Moshe Koren ROBOMATIX Ltd. Pitach Tikva, Israel An existing requirement of the car industry is, to deliver to the end user differnt variations and combinations of features on the car, such as left or right-hand drive, exhausts, antenna etc. For economic reasons, the required corrbinations should be incorporated in the car-body as late in the production line as possible. This obligate the manufacturer, to prepare the car-body to suit the maximum number of selected possibilities, whilst allowing rraximum flexibility in the final definition of each car-body. The Robot-Laser which has been developed, presents a flexible tool, enabling the opening of the required vents in the car- body in the final stages of body manufacture, and goes into action with the designation of the vehicle. The system provides a saving in the number of superfluous openings which have to be cut for all car types, and which must later be closed up at high cost, if conventional manufacturing techniques are applied. The main requirements of the Laser Robot are .- Finding the precise location of the required cut; The Laser beam cut must be totally drossless, to avoid problems of corrosion and non-adherence of paint.

72 WEDNESDAY. 10 SEPTEMBER 1986 WED-INV

NEW VUV AND XUV LASER SYSTEMS BASED ON INNER-SHELL EXCITATION AND IONIZATION OF ATOMS AND MOLECULES R. Sauerbrey Department of Electrical and Computer Engineering Rice University Houston, Texas 77251-1892 U.S.A.

This talk will discuss new families of laser media in the vacuum ultraviolet (VUV) and extreme ultraviolet (XUV). One proposed laser scheme relies on the production of ionic molecules which are iso electric to the rare-gas halide, halogen, and interhalogen molecules. A doubly-ionized alkali ion A2+ has in its ground state the same electron configuration (np5 2P) as a rare gas ion Rg+. It may form ionically-bound compounds with the negatively-charged halogen ion X~ abbreviated by A2+X~. These states may then decay by the emission of photons to a weakly-bound potential curve correlating to the singly^charged alkali ion A+ and the neutral halogen atom X". Recently, the fluorescence from Cs2+F~ was observed around 185nm, lying well within the wavelength range predicted by calculations. The cross section for stimulated emission for the alkali halide ions A2+X~ are of the order of lxlO~16cm2. This is comparable to the values known for the rare gas halides. Therefore, the ionic excimer molecules appear suitable candidates for VUV and XUV lasers. Anti- Stokes Raman lasers in alkali atoms have been proposed as possible sources for coherent XUV radiation. Population mechanisms fo the quasi- metastable quartet states of potassium and rubidium by collisions with meta stable helium and neon atoms are described. Optical gain of up to 1 cm~ is predicted around 60nm in potassium and 80nm in rubidium. Finally, new molecular anti-Stokes Raman laser schemes yielding radiation in the VUV and XUV will be presented.

77 WED-0

AN OPTICALLY PUMPED SUPERSONIC HgBr(B-X) MOLECULAR BEAM LASER

A.C.Cefalas, C.Skordoulis,S.Spyrou, and C.A.Nicola 4 des,N.H.R.F.,The or.Phys.Chem.In s t. 48,Vas.Constar ,,'nou Ave.,1i6/35»Ath ens, Greece Stimuli. ~d emission from the B-X transition of HgBr in a supersonic molecular beam has been obtained in the blue-green region of the spectrum from the photodissociation of HgBr? with a tunable ArF excimer laser at 193nm. The excimer pump beam crosses the molecular beam at right angles and the laser action is observed in the same direction. The cooling of the internal degrees of free- dom and the reduced Doppler width of the molecular transition ensures good population inversion between the B and X states and a high gain of the B-X transition enough to exhibit laser action despite the very small active region of the laser medium. Laser pulses having a FWHM of 15ns have been observed with this method. The optical cavity was 50cm long and laser action took place at moderate temperatures above 4-00 K. A number of noble gases (He, Ar, Ne) have been used to provide the required pressure for the supersonic expansion of the HgBrp molecules through a specially constructed pulsed molecular beam apparatus at moderate temperatures.

78 WED-0

PUMPING MECHANISM DEPENDENCE OF EMISSION SPECTRA IN HGBR LASERS

H J Baker and A M Feltham Applied Physics Department University of Hull HULL HU6 7RX UK

The gain spectrum of the B-X emission band of the HgBr molecule has been studied in a UV preionised, discharge excited mercury bromide laser and correlated with computer simulations of the expected spectrum. The results are- interpreted as showing that the excitation processes which lead to dissociation into the HgBr (B) state are vibrationally selective. At a two atmosphere working pressure, the vibrational state selectivity is not masked by vibrational relaxation, showing that relaxation times are long compared to the spontaneous lifetime of the B state. Modelling of the spectrum shows that power extraction from the v' = 0 level is poor at the usual 502 nm laser wavelength, and at very high pressure operation may favour blue wavelengths.

79 •JED-0 MODELING OF THE X RAYS PREIONISED, SELF SUSTAINED DISCHARGE XeCl LASER*

A. GEVAUDAN, B.L. FONTAINE, B.M. FORESTIER and M.L. SENTIS Institute of Fluid Mechanics of Marseille (IMFM),UM 34 CNRS AIX-MARSEILLE II UNIVERSITY, 1, rue Honnorat 13003 MARSEILLE FRANCE A complete model of a long pulse X rays preionised self sustainde discharge XeCl laser has been established for C-L-C and P.F.N. types of electrical circuits and Ne/Xe/HCl active medium. The model with C-L-C circuit simulates the IMFM high average power 1UX laser system testbed. The model includes a) rate equations for species with the most recent values of rate constants including Xe2Cl and HCl(v) forma- tions b) rate equation for laser emission at A = 308 ran including absorption c) circuit equations with time dependant plasma impedence. Comparison between numerical modeling and experimental results from LUX laser system have given very good quantitative agreement (20-30 % departure for large variations of excitation conditions) for electrical parameters behavior as well as for XeCl* laser power and energy. A parametric study of XeCl laser ETehavior by use of the IMFM numerical code has shown the strong effects of electron quenching and Xe2Cl trimer formation on laser upper level population and laser output. In particular the IMFM model shows the dominant effect of Xe2Cl* on both XeCl population lowering and absorption at laser wavelength {oL =l,2%cm~ ) with a strong effect on laser output and efficiency.The model shows also that Xe2Cl absorption is strongly satured for conditions of high intracavity photon density(ot jf 0,2%cfn Results are in good quantitative agreement with those published very recently and are compared with results from other models and with experimental results and discussed with the aim of efficiency and specific energy per pulse enhancement of XeCl laser system for development of future high average power high repetition rate XeCl lasers (P\¥ 1 KW ; P.R.F. ^ 500 Hz - 1000 Hz).

* Work supported by French D.R.E.T. and C.E.A.

80 WED-0

NUMERICAL INVESTIGATION OF FORMATION PROCESSES IN ELECTRON-BEAM PUMPED XeC1 LASERS

L. J. Palumbo, G. A, Hart and R. F. Walter W. J. Schafer Associates, Inc. Wakefield, MA 01880 USA and Albuquerque, NM 87106 USA

ABSTRACT

The e-beam pumped XeCl laser system was modeled using a symbolic laser analysis code which computes the time evolution of approximately forty chemical species and photons. This comprehensive computer model calculates the time-varying energy distribution of secondary electrons for use in obtaining" Tate coefficients from electron-impact reactive cross sections. The role of the neutral channel was examined in numerical experiments in which selected neutral channel pumping and* relaxation rates were varied. Our results indicated that there are conditions under whch the neutral channel can deminate the formation of the XeCl (B) state, in contrast to ~a1 common assumption in many previous kinetics simulations. The sensitivity of the gain/loss ratio to the *de-gree of vibrational enhancement of dissociative electron attachment to HCl was investigated as well as its dependence on the e-beam power applied.

81 WED-INV

C02LASERS WITH RF EXCITATION (Hugel's part)

H.E. HtlGEL, DFVLR/University Stuttgart, F.R. Ger- many ,

Industrial applications of high-power C02-lasers require a high beam quality and its control in accordance with the production process in que- stion. The most important prerequisite to achieve this is the possibility of producing a temporal and spatial uniform laser active medium. In this as well as in other respects the rf-discharge offers many advantages as compared to other electrical excitation techniques. The most important feature of the rf-discharge in view of attaining high values of power density at enhanced uniformity and stability is its demand of but low electrical field strength to establish a self-sustained discharge. The possible iTse of dielectric elec- •trodes which permits a most simple current-stabilization without ohmic losses and the easy modu- lation of the discharge make this technique most promising for a new class of high-power C02-lasers. A review will be given of various technical concepts utilizing auxiliary and main rf-discharges.

82 WED-INV

CONDUCTIVELY COOLED R.F. EXCITED COMPACT C02 LASER FOR HIGH POWERS.

Shaul Yatsiv, The Hebrew University and Alumor Lasers Ltd. ~~~ Jerusalem, Israel

In general, the active gas flows rapidly through the optical cavity in high power C0_ lasers. This is done to maintain the low temperature needed for optimum operation. We have demonstrated an alternative technique in which excess heat is dissipated by conduction through a thin gas layer confined by adjacent metal electrodes of extended lateral dimensions. A power output of 135 watt was demonstrated in a laser of a strip line geometry which is 85 cm long. The gas at pressure of 75 to 150 millitors is excited by a RF discharge at 30 MHZ. The discharge is similar to that in RF excited wave guide lasers and exhibits comparable stratified structure due-to space charge formation in the gas. The gas is either stagnant or flows slowly to reduce effects of chemical decomposition of molecules in the discharge..Technical and physical processes common to wave-guide and strip-line laser geometries will.be reviewed. The role of gas composition, degree of molecular dissociation, electrode material and.impedance matching-between the laser head and the.RF generator will also be.reviewed. Finally, technical .-) imi tat ions associated with the size of the RF generators will be discussed

We estimate that the present technology offers a viable method for medium and high power CO- lasers.

83 WED-0 DEVELOPMENT OF A COMBUSTION-DRIVEN AFTER-MIXING GASDYNAMIC LASER UTILIZING A LIQUID FUEL AND LIQ- UID OXIDIZER

SHIGERU Yamaguchi , RYOICHI Satani, HIDEAKI Saito, HIROTAKA Kanazawa, TAKASHI Maruyama, TAKESHI Yokozawa and MASAMI Yuasa (Ishikawajima-Harima Heavy Industries, Yokohama, Japan) A combustion-driven after-mixing Gasdynamic laser incorporating a screen nozzle has been designed and demonstrated utilizing liquid CgH,- and liquid N^O as a fuel and oxidizer,respectively. Since employing a high temperature decomposed gas of liquid N-H. as an igniter,the supplying system of a fuel, an oxidizer and an igniter prior to the combustor was for all liquid phase and this realized a compact device. A reliable firing of liquid CAl& and liquid N~0 combustion has been demonstrated with this novel igniter. Simultaneously, a stable combustion both at a high pressure (~100atm) and at a high temperature(~2000K) has been achieved bv sup- pressing pressure oscillations due to the acoustic vibration inside the combustor. Before the iaser oscillation was tested,each component such as an after-mixing screen nozzle consisting of a number of small conical nozzles,a lasing chamber,a passive diffuser and a subsonic diffuser was assembled so that characteristics of gas dynamics had to be ex- mined. Non-heated C02 gas was injected through nozzles supersonically into the lasing chamber, which was characterized as downstream mixing type GDL. Consequently, at a combustion pressure of excess llOatm, starting and sustaining supersonic flow, which gives the static pressure of around 50Torr, has been obtained in the downstream of the screen nozzle by passive diffuser against the ambient pressure. Then, applying a suitable resonator to this system, laser oscillation has been attained through thus produced supersonic flow.

84 WED-0

NUMERICAL MODEL TOR CALCULATION OF POPULATION IN- VERSION AMD GAIN IN CHANNELS OF CW--GDL(S) OPERATING AT TRANSITIONS PERTAINING TO V, AND vl, MODES OF1 CO 2 A. Cenia.n and M. Brunne Institute of Fluid-Flow Machinery Polish Academy of Sciences. Gdansk. Poland A. Makowski, Institute of Physics. Nicholas Coper- nicus University, Toruri. Poland A theoretical model of population inversion ana gain formulation by means of rapid expansion of previously heated mixture of CO2 and diluent is described. Various admissible transitions between CO2 levels comparised in coupled and modes are con sidered without imposed assumption regarding the form of the pertinent vibrational energy distribution function. The vibrational energy exchange and relaxation processes and thus induced changes in population of thirty CO2 levels are described ba- sing on SSH theory used to determin the pertinent rate constants. An example concerning the expansion of C02/Ar mixture is given indicating that quide a large number of new COp GDLs can be thermally excited and pumped by a frasdynamic technique. The partial optimization of these lasers is performed.

85 WED-INV

DEVELOPMENT OF MULTIKILOWATT CLOSED CYCLE CO LASER

HIDEAKI SAITO, HIROTAKA KANAZAWA, KENJI WATANABE, TATSUJI TAIRA, ASIIUN-ICH SATO, & *TOMOO FUJIOKA IHI RES.TNST., *IRI LASER LAB., YOKOHAMA ,JAPAN.

Scaling-up of a closed-cycle self-sustained discharge- excited CO laser was carried out to produce multikilowatt output power. The developed apparatus is characterized by the fact that laser gas can be controlled from room temper^ ature to about 100 K with the heat exchanger using Freon R502 and liquid Nitrogen as coolants. The mixed gas with mol. fractions of CO/N2/O2/He=4/16/0.2/balance % was used, and when the charged gas pressure at room temp, was 70 Torr and the gas temp, was 170 K, the max. output power of 3.1 kW was obtained at the cenversion efficiency of 14 %. When the charged gas pressure was 30 Torr and the gas temp, was 110 K, the highest conversion efficiencyof 21.7% was obtained^ the output power of 1.6 kW. Performances of this high-power closed cycle CO laser will be presented.

86 UED-0

EFFECTS OF RF PREIONIZATION IN A TRANSVERSE- DISCHARGE- EXCITED CW CO LASER Kazuaki Terunuma and Akira Noguchi Department of Electrical Engineering, Keio University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama-shi 223, Japan Shun-ichi Sato, Ilideaki Saito, and Tomoo Fujioka Industrial Research Institute, 1201, Takada, Kashiwa-shi 277, Japan Abstract: Effects of rf preionization in a transverse- discharge-excited cw CO laser and an optimization of an rf discharge frequency are discussed. In a CO laser, the rf preionization significantly improves the laser output and the conversion efficiency, because the mean discharge electron energy can be tailored for more efficient excitation. In addition, the discharge is stabilized by the preionization so^that an input power density can be increased, and an operating temperature can be reduced. It was made clear in our previous work that the operating temperature region and input power density were limited by the discharge instability in case of the self-sustained dc discharge excited cw CO laser. To confirm the effects of the rf preionization experimentally, we designed a test laser facility where the spacing between rf electrodes is 2 cm. Under the typical conditions an optimum rf frequency is estimated to about 800 kHz. Comparing with the self-sustained discharge excitation, much improved performance should be obtained.

87 THURSDAY, 11 SEPTEMBER 1986 THU-INV

INTERACTION OF HIGH ENERGY PULSED CO LASER WITH MATERIAL

P. DUFRESNE Institut de Mecanique des Fluides de Marseille 1, rue Honnorat - 13003 - MARSEILLE - FRANCE

The interaction of a high power laser on material induces various phenomena which depend mainly on the nature of the material, the intensity of the laser, and the pressure of the surrounding atmosphere. In particular, when solid and liquid targets are irradiated by a CO2 laser, or when the ]aser beam propagates through the atmosphere, thermo- mechanical effects are observed by measuring the mechanical coupling and by characterizing the plasma created above the surface of the target. The influence of the aerosol particles on the propagation of a laser beam through the atmosphere is also presented. All these effects are experimentally studied.

91 THU-INV LASER MATERIAL PROCESSING AND ITS PHENOMENOLOGY; Part II Theoretical modelling cf laser material processirg

Dieter Schujcker, Lhiversity cf Technology, lOW-Viana, Austria and fi.V. La Rocca. Fiat, Italy

Future progress of laser material processing in terms of performance, elficience and quality demands for a clear understanding of the physica] mechanism and the resulting technical limits of laser machining. Therefore, theoretical modelling is of large importance. Modelling of laser cutting has yet reached the highest degree of maturity anu thus a review of cutting models; is given here. One of these elaborated recently is treated in detail and compared with other work. That model considers heating by absorbed lastr radiation and by exotherimc reaction and material removal by eavaporation and due to the friction between molten material and the reactive gas -flow. A steady state analysis yields the dependance of the cutting speed on the thickness of the workpiece as all other cutting model also d«j. Due to the use of six balance equations, the model yields much more information as less sophisticated models, as for instance on the temperature of the molten material and the relative contributions of evapoation and ejection of liqid to total material removal. A dynamic treatment of the model described above demonstrates that the periodic striations of the cut may be caused by temporal fluctuations of the laser power or other parameters, that excite fluctuations, of the liquid region of the workpiece. A similar result has been obtained also with other models. These dynamic models show ways to improve cut quality. The dynamic model mentioned above has also been used to analyse cutting with pulsed radiation and yields important hints for an optimum choice of the parameters of that new process.

92 THU-0

AERO-OPTICAL ANALYSIS OF A COMPRESSIBLE SHEAR LAYER

dy» Stanley F, Birch and P, John Terry Boeing Aerospace Company, Seattle, Washington, USA

The degradation of optical beams passing through turbulent media has been studied for many optical imaging applications including astronomy through the atmosphere and laser propagation through gaseous media, Analyses of these phenomena involve two coupled models: a fluid dynamic description of the turbulent medium, and an analysis of optical propagation through the described distribution of gaseous properties, Recent advances in computer capabilities allow a more realistic description of turbulent mixing layers. A time dependent, two-dimensional Navier Stokes computer code has been used to model the flowfield associated with a compressible shear layer in Sir, Optical ray tracing and image formation codes using fast Fourier transforms have been developed to generate time histories of focal plane optical image intensities, Predictions of image steering and image jitter agree with those generated by a less detailed analytic model and wind tunnel measurements. Image blur is shown to depend on the details of coherent structures in the shear layer that are presently very difficult to theoretically predict.

93 THU-0 IMPROVED ENERGY TRANSFER IN LASER TARGET INTERACTION PROCESSES BY USING REPETITIVELY PULSED LASERS

Manf ro-1 IinCFMSCKMIDT Franco-German-Research Institute Saint-Louis P.O.Box 301 F-68301 SAINT-LOUIS CEDEX (France)

During the last years, less emphasis was in developing reliable high ''average-power" pulsed C02-lasers, than in improving the performance characteristics of continuous wave C02~lasers up to the multi-kW-range. The experiments to be reported in the present paper, however, have clearly shown that the efficiency of energy transfer to any given material is substantially improved by using repetitively pulsed laser radiation as compared to continuous wave radiation. The closed cycle gas transport laser used in our experiments was capable of delivering pulses with energies of 20 J at any repetition rate up to 100 pps. Mean powers up to 2 kW were thus available for pulse trains of arbitrary length up to several hundreds of pulses. Experimental results obtained so far show, that the improvements observed are both due to the enhanced thermal coupling mechanisms during the initial phase of the heat- Ing processes which are valid up to maximum frequency of 100 Hz that could be investigated and by the strongly coupled thermo-mechanical processes that are of great importance during the later phases of the interaction. Experimental results concerning investigations of the heating and ablation phase both for dielectric and metallic materials will be given and will be discussed.

94 THU-INV

INDUSTRIAL APPLICATIONS OF EXCIMER LASER

DR. D. BASTING LAMBDA PHYSIK GMBH 3400 GOETTINGEN - GERMANY.

Excimer Lasers providing megawatts of pulsed UV-power show basically different type of interaction compared to CO2 or Yag-Lasers when used in material processing. High spatial resolution in pattern generation and heat free photochemical etching have stimulated new applications in semiconductor processing and medicine.

95 THU-INV VITRIFICATION AND MODIFICATION OF METAL SURFACES BY LASER FOR CHEMICAL APPLICATIONS

Ko.ii HASHIMOTO, The Research Institute for Iron steel and Other Metals, Tohoku University, Sendai, 980, Japan

The laser is able to melt instantaneously a restricted volume of a metal surface, and hence overlapped laser irradiation melting of metal surfaces and subsequent self quenching are one of effective methods for rapid solidification of the surfaces. Rapidly solidification leads to formation of new materials with various unknown characteristics. In particular, rapid quenching from the liquid state of alloys with proper compositions forms amorphous alloys having very attractive and unique properties. For instance some of them have extre- mely high corrosion resistance even in hot concentrated hy- drochloric acids. Others have very high electrocatalytic activities and selectivities of specific reactions as they are suitable for anodes for electrolysis of sodium chloride solutions. Nevertheless, rapid solidification of a melt through heat absorption from the meft restricts the volume of the melt, and hence the amorphous alloys prepared by conventional methods are generally of several tens of micrometer thickness except those prepared by sputtering or plating. It is quite inconvenient to utilize the ribbon-shaped thin amorphous alloys as the corrosion-resistant materials and particularly as the anode materials because the electric resistance along the longitudinal directions of the ribbon-shaped alloys is very high when they are used as the electrode. On the other hand, the laser processing gives rise to formation of amorphous surface alloys on bulk metals if the surface compositions are suitable for vitrification by rapid quenching from the liquid state. In order to utilize supe- rior characteristics of rapidly solidified alloys, attempts have been made to prepare amorphous and crystalline surface alloys by laser processing. There are various problems encountered in preparing amorphous surface alloys on conventional bulk metals, but have been solved by suitable combinations of surface alloys and substrate metals in addition to decision of a proper processing conditions.

96 THU-0

INDUSTRIAL APPLICATIONS OF HIGH POWER CO, LASERS, POWER RANGE 1-5 KW

Dr. Reinhard Baumert, Spectra-Physics GmbH, Siemensstr. 20, 6100 Darmstadt, West Germany

The laser as a cutting tool for sheet metal cutting has been well accepted in industry for many years. Several hundreds of units are used for contour cutting of small and medium-sized series on plane metal sheets up to 6 mm thick. Within the last three years, cutting systems have been expanded in three ways: thicker material up to 12 mm can now be cut by using higher powered lasers (1500 W); with the introduction of flying optic systems which cover sheet dimensions up to 4 m x 3 m, the cutting of larger sized metal sheets is possible. In addition, the use of five or six axis systems allows cutting of three- dimensional plastic and metal material. Besides laser cutting, the acceptance of systems'for laser welding applications is increasing. Several systems have been running in production for a couple of years and laser welding will probably become the fastest growing «narket in laser material processing within the next five years. The laser technology is regarded as a beneficial tool for welding, whenever low heat input and, consequently, low heat distortion is requested. To day's main welding application areas are: components of car engines and transmissions, window spacer and stainless steel tube welding, and also car body welding with laser robots or five axis gantry type systems. The output power of CO--lasers for welding applications is between 1 and 5 kw in most cases.

97 THU-IMV

20-kW FAST-AXIAL-FLOW CO^ LASER WITH HIGH-FLEQUENCY TURBO-BLOWERS

H.Sugawara, K.Kuwabara, S.Takeaori, A.Wada, and K.Sasaki Hitachi Research Laboratory, Hitachi, Ltd. Hitachi, 319—12 Japan

A Fast-axial-flow CO2 laser has been considered to be less suited for scaling to a few tens of kilowatt of laser power, Mainly because it has been equipped with a large displaceaent blower for the gas flow systea. In tens of industrial applications, however, the axial-flow-type has soae advantages over the cross-flow-type.These include a stable output, a good bean quality and a high discharge efficiency. The authrs developed fast-axial-flow COZ lasers with an output power ranging 2-5 kW, by using high-frequency turbo- blowers developed especially for laser operation. Based on design techniques developed in the 2-5 kW CO, lasers, a 20-kW fast-axial-flow CO, laser has been realised. The equipment is 4.8 • long, 1.8 • wide, and 2.1 • high. A total length of the folded cavity is 13.6 •. Each of the two high- frequency turbo-blowers utilized in the equipment has a revolution of 8,800 rpa, a gas flow rate of 8.4 •"/s, and an adiabatic head of 4,000 kgf'a/kg. The equipment has six discharge-tubes connected optically in series, and each is 134 aa in diaaeter, and 1,000 aa in length. Stable glow discharge is established in the large-voluae region without any preionization. The laser output power of 20 kW is extracted floa an unstable resonator with an equivalent Fresnel nuaber of 3.5, and a beaa aagnification of 2.0. The output beai through a zinc-selenide window has a diaaeter of 90 aa. Laser output characteristics and aetal processing capabilities will be presented in the session.

98 THU-0

MULTIKILOWATT INDUSTRIAL CO2 LASER

Agmon P., Hoch E., Katz D., Shachrai A., Zinman Y. Metalworking Lasers International (IL) Ltd., Tel-Aviv ISRAEL

A multikilowatt Industrial CCL Laser was developed. An output power of 10KW was measured. The laser is AC excited and ballasted by capacitors. A unique optical system improves beam uniformity, mode pattern and power and pointing stability. Long run and application tests will be reported.

99 THU-INV HIGH POWER LASER BEAM DIAGNOSTICS

IJ Spalding, UKAEA Culham Laboratory, Abingdon, Oxon 0X14 3DB, UK

The output power, temporal or spatial mode, and even the polarization-state, of an industrial (machining) laser can each fluctuate in ways which may affect process- reproducibility. Such fluctuations typically havt frequencies in the range 10"3-106Hz: in extreme situations amplitude fluctuations of 50-100% have been reported. This paper will briefly review some of the causes of such laser (sourse) fluctuations and their practical significance over a range of representative thermo-mechanical applications (i.e. cutting, welding and heat- treatments). To monitor all these fluctuations on-line, in real-time, may be scientifically feasible, but for commercial applications the diagnostics must be relatively cheap and ideally should lend themselves to adaptive (servo) control. Work at Culham on 5 and lOkW C02 lasers over the past 4 or 5 years has paid particular attention to techniques which sample the laser beam without distorting its optical quality; some comparisons will be drawn with results published elsewhere.

100 THU-INV

HIGH POWER LASER BEAM DIAGNOSTICS

W.M. Steen Imperial College, London, U.K.

It is necessary to know the operating parameters for laser processing if the process is to be repeatable or automated. A number of devices have been developed to measure; in- process, the main operating parameters of beam power, beam diameter, beam mode structure, traverse speed, and focal position. These are briely summarised. The Laser Beam Analyser (LBA) is described. It is capable of in-process measurement of beam power, diameter and mode structure as well as obtaining a signal on back reflection. This device is based on a reflecting rod. Acoustic methods of in-process sensing are also described. These include a new sensor capable of signalling thermal expansion of the laser, and mirror warping as well as power density and back reflected power. Another acoustic experiment is discussed in which the extent of martensitic transformation is measured by its acoustic emission signal.

101 THU-P-1 EXPERIMENTAL STUDY OF THE LEVEL-TO-LEVEL ROTATIONALLY INELASTIC TRANSITION RATES OF IODINE MONOFLUORIDE DURING COLLISIONS WITH NOBLE GASES

ty E« A. Dorko, Air Force Institute of Technology, Wright Patterson AF Base, OH 45433, U. S. A. and P. J. Wolf and L. Hanko, Air Force Weapons Laboratory, kirtland AF Base, NM 87117, U. S. A. Iodine monofluoride (IF) was prepared in a flow tube reactor. A narrow width beam (2-10mhz) from a ring dye laser operating in the CW mode was used to excite a single rotational level of a particular vibrational state of IF(B). Known pressures of bath gas (M) were added to the flow tube such that single collisions could occur between IF and M. Wavelength resolved fluorescence from the initially prepared rotational level (Jj) and from the levels populated after IF-M collisions (Jf) was observed. Under the steady state conditions of the experiment, relative peak heights (Pjf/Pj-j) are proportional to the relative number densities in each rotational level populated during an IF-M collision, (i.e., Pjf/Pjj = Njf/Nji). For steady state 1 1 conditions, NJf/Nji = kifM/(Kt M + A) = kjfM where M = kt M + A, kt = sum of vibrational and quenching rate constants and A = Einstein coefficient for radiative decay. A plot of Njf/Njj vs M1 produces a straight line whose slope is the Level-to-Level rotationally inelastic transition rate constant (kjf). Rate constants are being determined for transfer from three different initial rotational levels of IF during collisions with He, Ar, and Kr. Initial results obtained for IF(Jj = 39)-Kr collisions produced k^f values of 3 X 10~l2 to 7 X 10~12 cc/molecule sec. A plot of the log k-jf vs log AJ pro- c'jced a nearly straight line. This result is as preliminary analysis indicates that the rates are a function of the energy gap transcended during transition.

102 THU-P-2 INTERHALOGEN COLLISIONAL DYNAMICS: THE B3&(0+) STATE OF IF AND BrCl

P. J. Wo1f» G. P. Perram, and S. J. Davis Advanced Chemical Laser Branch, Air Force Weapons Laboratory, Kirtland AFB New Mexico 87117-6008, USA

Electronic quenching, vibrational, and rotational transfer rate constants were measured in the B3TT(0+) state of BrCl using both cw and pulsed LIF techniques. The collision partners included He, Ne, Ar, Kr, Xe, N2, O2, and a BrCl/Cl2 mixture. Electronic quenching was generally slow with rate constants ranging from 7.8 x lO'*4 to 6.5 x 10~12 cm^ molecule~ls~l for Ne to O2, respectively. The BrCl(B) removal rates with Cl2/BrCl showed a strong dependence on vibrational quantum number. The results are interpreted as a population loss via vibrational ladder climbing to predissociated states and a resonant exchange of energy with CI2. The B state vibrational manifold thermalizes relatively rapidly through both single and multiple quantum transitions. However, the process is relatively inefficient when compared to the gas kinetic 3 values. The efficiency (a(l,0)/og) ranged from 8.5 x 10" to 1.8 x 10~2 for the He to Xe, respectively. The cross- sections showed a linear dependence on v', while the rate constants for Cl2/BrCl - BrCl(B) collisions approximately scaled as v625. Tne relatively small vibrational spa- cings (we - 200 cm~l) accounted for the high probability for multiquantum transfer and upward vibrational ladder climbing. Rotational transfer is the most efficient kinetic process. The estimated efficiency is about a factor of 100 greater than that for vibrational transfer. The cross- sections display a smooth dependence on collision reduced mass. The qualitative results of this study are interpreted in relation to traditional energy transfer theories. The quantitative and qualitative results are also compared to those obtained in IF(B), and conclusions are drawn concerning the potential of IF and BrCl as potential candidates for visible chemical lasers.

103 THU-P-3 HIGH VIBRATIONAL LEVELS OF IODINE AS INTERMEDIATE STATE IN THE IODINE DISSOCIATION BY 02

D. Dav id, V. Joly and A. Fausse Office National d'Etudes et de Recherches Aerospatiales, BP 72, 92322 Chatillon Cedex, France

A model of the iodine dissociation in the presence of 0£ *Ag is proposed. This model assumes the excitation of molecular iodine by excited iodine atoms into high vibrational levels, followed by the dissociation of iodine in these levels, occurring after a collision with O2 Ag. The iodine atoms are quickly excited by 02 Ag, allowing the mechanism of dissociation to take pface as soon as some iodine atoms are produced. The dependence of some reaction rates with the vibrational quantum number is reported: a comparison with different experimental results and with other models is given.

104 THU-P-4 NEW CORONA PREIONISATION TECHNIQUE FOR MEDIUM REPETITION RATE TEA LASERS

Bruno Walter, Dieter Schuocker TU Wien, Inst.f.Nachrichtent.u.Hochfrequenztechn. Gusshausstrasse 25, A-1040 Vienna, Austria

A modified corona preionisation technique has been developed. This new preioniser uses a copper clad epoxy board with a slit aperture in the middle of it. The slit width is equal to the main electrode gap so that a rapid transverse gas flow can cir- culate through corona preioniser and main electrodes sequentially. The corona-electrode is made from aluminium and directly connected with the anode of the main discharge. The copper opposite- electrode is enclosed with an insylating resin to prevent arcing from the edge of the corona-electrode. When a voltage pulse is applied a corona surface discharge develops even over the aperture and illuminates the laser gas. A TEA C02 laser utilizing this new preioniser generates output pulses with 480 mJ energy and 10,7% over all efficiency. With a fast transverse gas flow repetition rates up to 100 Hz could be achieved limited only by the maximum frequency of the triggered spark gap.

105 THU-P-5 APPROXIMATE THEORY OF CASCADE PHENOMENA IN THE ACTIVE CAVITY OP CW GASDYNAMIC LASER

M, Brunne, Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Gdansk, Poland

Based upon the rate equation formalism the problem of the cascade phenomena in the active cavity of CW gasdynamic laser is considered. The flat parallel mirror cavity supplied with a fast transverse flow of the optically active medium is analyzed. The analytical' formulae for the total output and laser efficiency are given. The I4*t m - l8/4m transition in .C02 are kept in mind as a practical analogue for the optically activated medium under consideration.

106 THU-P-6 THEORETICAL MODEL OP THE GDL-CM (CO?). DEVELOPMENT OF THE SSH-THEORY FOR THE QUASIRESONANT PROCESSES OF W AND VT TYPES.

Adam Cenian Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Gdansk, Poland

The expression we get according to SSH-theory for the rate coefficients of the quasiresonant energy exchange processes of W and VT types does not include the Boltzmann factor of type exp[- ££^i J . Because oF this, it does not describe correctly the vibrational energy relaxation in the GDL-CM. In the paper it is shown that: 1° The lack of the Boltz- mann factor in the SSH-theory rate coefficients expression is due only to applied approximation and not to the basic assumption of that theory. 2° For exact resonance our result is equal to within a constant to that obtained by 'standard SSH calculations one.

107 THU-P-7

TRANSLATIONALLY STRONGLY NON-EQUILIBRIUM HOT ATOM ASSEMBLIES AND CHEMICAL LASER PUMPING

A. Ya. Temkin, Dept. of Interdisciplinary Studies, Faculty of Engineering, Tel-Aviv University, Ramat-Aviv, 69978, Tel-Aviv, Israel. The kinetics of the pump—ing of such chemical lasers is considered where the excited molecules are produced by hot atom reactions with bulk molecules. These hot atoms appear at the photo- (particle beam, electric discharge, etc.) dissociation of other bulk molecules. The translationally strongly non-equilibrium hot atom assemblies are described by use of the multi-group approximation well known in the neutron transport theory. The choice of the energy groups depends on physical properties of the considered system. Pulse chemical lasers are considered. The number densities of active molecules in different states and the inverse population are found by use of the solution of the multi-group equations. The dependence of the inverse population on the moder- ating power of the medium with respect to hot atoms is obtained and studied. For the two-level model of the active molecule it was found that t&e inverse population is proportional to the total pressure, If to add to the system a large concentration of a rart gas as the inert modulator, the inverse population would be independent from the total pressure and proportional to'the second degree of the devia- tion from 1002 of the rare gas concentration. Group constants can be determined by use of convenient kinetic experimental data. This problem and the choice of sucn experiments are discussed,- Tfre used method can be applied also to cw chemical lasers, but in this case the pumping cannot be separated in time from the lasing and so it must be considered together with, the lasing, relaxation and spontaneous emission. The multi-group approximation is'applied also to the strongly hot atom kiii*tlcs in the laser chemistry.

108 THU-P-8

NON-OPTOGALVANIC SIGNAL CHARACTERISTIC TIMES IN PREBREAKDOWN DISCHARGES

N. Yackerson and N. S. Kopeika Department of Electrical and Computer Engineering Ben-Gurion University of the Negev Beer Sheva, Israel

The prebreakdown regime is characterized by low field intensities. In our experiment, d.c. biased gas cells were illumina- ted with laser pulses. Both the incident laser field and d.c. field were smaller, sometimes much smaller, than those required for gas breakdown. Under these conditions, clear-cut electrical signals are observed as a response to laser pulse irradiation at wavelengths non-resonant to any gas atomic transitions. We called these non-breakdown responses "prebreakdown or precursor signals". These responses involve four different stages of varying time durations and signal polarities, as opposed to essentially only three when the light is resonant to an atomic transition of the gas. The major difference derives from inertial properties of the gas involving collisional de-excitation of metastables dependent upon photoionization-assisted electron heating which exists primarily for non-optogalvanic wavelengths because of the energy difference between absorbed photon energy and that required for photoionization. The temporal features of these signals characterize radiation detection sensitivity to weak incident illumination for different gas energy states. The signal characteristic time values are significant for practical device utilization. However, to explain gas internal physical processes, a better criterion seems to be the rates of signal growth and decay speeds. These new criteria are defined and appear to introduce order and consistency into measurements here and in the literature.

109 TflU-P-9

CHEMICAL LASER F FLOW DISTRIBUTION STUDIES

Donald J. Spencer & Donald A. Durran The Aerospace Corporation, Los Angeles, CA, U.S.A.

A sensitive F2 absorption diagnostic, employing a HeCd laser operating on the 325 nm line, suitable for slit nozzle scanning was developed and applied to the measurement of an F2 boundary layer in an arc heated CW HF chemical laser flow. The probe beam provided a 0.006-in. (0.15-mm) diameter spatial resolution over a l^-in. (3.81cm) slit nozzle path length. Intensity difference sensitivities of Al/Io=3xl0~^ were obtained with this system. This detection sensitivity cor- responds to a lower limit measurability of ~ 15 milli Torr F2 at T *. 300°K over the 1%-in. (3.81cm) path length. The F2 boundary layer profile was determine to be of exponential decay form with peak at the nozzle wall and of width ~ 1/3 the viscous boundary layer as inferred from pitot pressure measurements. The F2 concentration profile was displaced in- wardly and slightly compressed by the H2 slit injection at the nozzle exit plane, which penetration profile followed the relation 6=0.1/x". Measurements made near, and also lJj-in. (3.81cm) downstream of the nozzle exit plane, tranverse to both flow and slit axis directions, indicated only ~ 15 p.er- cent reduction in F2 flow concentration. The F2 profile apparently remains fairly intact in passing through the lasing zones. Application of this diagnostic method to an NF-j combustor laser flow operating in the stagnation temperature range (1000-1600 °K) exhibited no measurable F2 concentration Spectral analysis determined that a strong concentration of NF radicals were present in the nozzle flow. NF radical recombination with F(F2) to form NF£ or NF3, totally dominates over F2 formation from F atom recombination in the nozzle flow environment. Thus the strong presence of NF radicals in a flow can account for both the otherwise thoroughly anomalous absence of F2 molecules determined in this study and the reduced laser efficiency observed with NF_ combustor driven chemical lasers typically operating at combustor tem- eratures T < 1600K.

110 THU-P-10

VIBRATIONAL KINETICS MODELS FOR

COMBUSTION-DRIVENiCO2 GASDYNAMIC LASERS

R. E. Walter W. J. Schafec Associates, Inc. Albuquerque, NM 87106 USA

ABSTRACT

The performance of combustion-driven C0£ gasdynamic lasers (GDL's) was -modeled using a steady-state nozzle kinetics code. The kinetics model was expanded to include the effects of a number of->species which are byproducts of combustion of-complex hydrocarbon molecules with an oxidizer such as N2O. In addition Do N2, CO2, and H2O, this model includes processes involving CO, NO, O2, H2, N, 0, and H. Calculated revolts 'from this model were compared with those obtained from an earlier model which did not include the effects of the ^combustion byproduct species. Results from both mode-Is were compared with small signal gain data obtained -from a @DL which used the combustion products of several hydrocarbon fuels. The new model was found to give more accurate1 predictons over a broad range of operating conditions. A rate sensitivity study was conducted to determine the- kinetic processes for which the measured rate data presented the greatest uncertainty for combustion-driven GDL calculations.

Ill THU-P-11

EFFECT OF INLET PRESSURE ON CHEMICAL LASER FLOWFIELD

D. ZEITOUN", M. IMBERT", L. TORCHING and R. BRUN- ;{ Universite de Provence (UA 1168) MARSEILLE - FRANCE t C.G.E. MARCOUSSIS - FRANCE

In the CW chemical laser cavity, the mixing of reactive supersonic jets, emerging from small size adjacent nozzles, depends strongly on reservoir conditions. Moreover the structure of the flowfield has an effect on the shape of the diffusion zone and consequently on the distribution of the small-signal gain coefficients across and along the cavity. The aim of this work is to study of the influence of the reservoir conditions - more particularly of the pressure - on the behaviour of the mixing zone and of the small-signal gain coefficients. Thus, the unsteady complete Navier-Stokes equations have been solved numerically in the nozzles and in the laser cavity. The used gases are a mixture of He and D~ in the secondary nozzle and a mixture of F, F~, HF and He in the primary nozzle. In the mixing zone, ten vibrational levels of DF have been taken into account, and as each level is considered as a particular species, the system is composed of a set of nineteen equations for fifteen species. These equations have been solved by a numerical method based on an explicit finite-difference predictor- corrector scheme, with time splitting and local integration step time in flow direction. The explicit method has the advantage to be easily vectorizable on a CRAY-ONE computer. Depending on reservoir conditions, the results show, first the different structures of the flowfield, second the effect of this flow on the shape of the diffusion zone in the cavity and finally the small-signal gain coefficients for different rotational-vibrational levels.

112 THU-P-12 THEORY OF WAVEFRONT REPLICATION IN THE DIRAC BRACKET OPERATOR FORMALISM

A. Flusberg and D. Avco Research Laboratory, Textron Everett, MA 02149 U.S.A. We present the theory of wavefront replication by stimulated scattering in a new formalism which utilizes the Dirac bracket notation commonly used in quantum mechanics „ We represent the laser- wave entering the scattering medium in the momentum representation, i.e., as a vector "ket" in a Hilbert space, witli basis vectors corresponding to plane-wave momentum states. Using the bracket notation, we show explicitly the well-known result that for a sufficiently (spatially) incoherent laser, a Stokes wave which is spatially correlated with the laser experiences twice the small-signal gain of any other type of Stokes wave ; in our notation the ket representing the spatially correlated Stokes wave lies parallel to the laser ket in the Hilbert space. The bracket formalism, which applies to both backward scattering (e.g., stimulated Brillouin scattering) and forward scattering (e.g., stimulated Raman scattering) clarifies the mechanism by which replication occurs and simplifies the mathematics describing the effect.

Present address: Northeast Research Associates, Woburn, MA 01801

113 TIIU-P-13 LASER CONTROLLED REFLECTION WITH A DISTRIBUTED FEEDBACK DYE LASER

I. Golub*t, R. Shuker and G. Erez* *Physics Dept., Ben-Gurion University, Beer-Sheva, Israel +LROL, Dept. de Physique, University Laval, Quebec, Canada G1K7P4 Spatially modulated gain of a distributed feedback dye laser (DFDL) is used to obtain 1:;: c^- cent rolled reflection. A beam of a grating tuned Haasch type dye laser is directed at an angle of 5*10 mrad into the DFDL dye cell. When the frequency of the incident beam is tuned in the vicinity of the DFDL frequency, the Bragg scattering off the gain grating results in a reflected beam. The spectral selectivity and bandwidth of the reflected beam are governed by the properties of the DFDL. The reflectivity has a bandwidth of =* 4 cm"*, and exhibits saturation with increasing incident intensity. The reflected signal time behaviour follows the time characteristics of the DFDL, i.e. it consists of a train of subnanosecond pulses. The demonstrated device may find applications in laser controlled real-time optics and narrow bandpass filtering. The experimental scheme may be used to generate phase conjugated signals with a distributed feedback structure, where the two DFDL counterpropagating waves play the role of pumping beams.

114 DtSIGN AND PERFORMANCES OF A FAST AXIAL FLOW HIGH POWER CO2 LASER

M. GASTAUD, A. PONS. P. BOUSSELET. G. HUTIN Division Optronique - LABORATOIRES DE MARCOUSSIS. C.R.C.G.E.. Route d© Nozay 91460 MARCOUSSIS - FRANCE

A high power industrial CO2 laser based on a fast axial flow design has been developped. Progress in our understanding of the stabilisation mechanism provided by aerodynamic turbulen- ces in large volume DC electrical discharge makes it feasable to reach high efficiency in fast axial flow design at input power densities as high as 4 kW/l. Basic design principles are currently under test with a four discharges prototype. Each of the four identical gain sections is made up of a 75 mm diameter and 800 mm long discharge tube. The laser gas mixture of CO2. N£. He (3. 47, 50) is injected by means of twenty four nozzles evenly distributed around a circular section of the upstream portion of the discharge tube. The injectors are used both as electrical anode and expansion nozzles for the turbulent flow. In the discharge, axial gas velocity is 120 m/s at a pressure of 45 Torr. The expansion ratio at the nozzle is four. The laser output power is extracted from a folded unstable resonator with an annular scrapper and a ZnSe window. The output beam has a diameter of 70 mm and two different magnifications are under test with M = 2 and M = 1.6. A laser output power of 7 kW was achieved with a stable resonator. With the prototype under test, we plan to demonstrate that the axial flow design remains an attractive option for industrial laser products in the range from 5 to 25 kW of output power.

115 THU-P-15

SOME CHAEACTERISTICS OF A HIGH-POT<7ER TRANSVERSE-FLOW CO2 LASER

J. Starico, G. Sliwinski, J. Konefal, P. Kukiello, G. Rabczuk, Z. Rozkwitalski, R. Zaremba Institute of Fluid-Flow Machines, Polish Academy of Sciences, Gdansk, Poland A high-power transverse-flow, transverse-discharge CO2 laser has been built as a laboratory facility for materials processing. The gas, a mixture of CO2, N2, and He, is excited in a self-sustained normal glow discharge between a multipin cathode an a planar anode. The discharge region of constant heighthas the cross-section of 0.7 x 1.25 m2. The gas is circulated in the laser by a controllable-speed centri- fugal compressor. Typical values of the gas pressure and velocity at the discharge region inlet are 80 hPa and 80 m/s, respectively. The electric power deposited in the working mixture has reached 60 kW, with the average current density e- qual to about 22 mA/cm2, the specific power per unit volume • equal to about 12 W/cm3,and the specific power per unit mass flow of about 220 kj/kg. Measurements of the small-signal gain distribution have shown it to vary considerably in the direction of flow, with a maximum of about 1 m~1. Single- and two-pass unstable optical resonators have been utilized. For a two-pass resonator with a single amplifying pass the power extracted from the cavity has been k,k kW. From preliminary attempts at optimizing the lasing mixture composition the CO2 : W2 : He = 1:3:6 mix has been found to give the highest electrooptical efficiency. The ' beam divergence of about 2. mrad allowed to focus the beam well enough for trial tests of laser cutting and welding.

116 THU-P-16

HIGH FREQUENCY TURBULENCE DIAGNOSTIC

David Chuchem, Bach Vu, and James Moran Avco Research Laboratory-Textron, Everett Mass

Extensive work has been done by many researchers in measuring atmospheric turbulence statistics. However, relatively few measurements have been performed at the high frequency end of the Kolmogorov spectrum. This is due. mainly to limitations of diagnostic apparatus usually used in this field. We have set up a small aspirating tunnel to simulate flow turbulence for testing purposes. Turbulent index of refraction fluctuations are generated in the test channel by injecting jets of carbon dioxide into the air flow-stream. Optical diagnostic techniques are used to measure optical scintillations. From these we calculate the frequency spectra of index of refraction fluctuations. Thermal anemometry measurements will be performed simultaneously in the flow stream at the low frequency end of,the spectrum so that the optical diagnostic data can be "anchored" to conventionally measured results. With the optical diagnostic we expect to be able to measure sub-millimeter scale sizes.

117 THU-P-17

PLASMA CONTROL DURING WELDING PROCESS AT HIGH POWER AND LOW TARGET VELOCITY

P.Savorelli - Politecnico di Torino - Turin - Italy D.Cru6tani, M.Ciboldi - RTH - Vico Canaveee - Italy

Laser welding at low traslation speed of the workpiece and high optical power shows a lowering of efficiency (1), as shown in figure. It is believed (2) that the problem arises from inadequate plasma control by conventional cover gas techniques. In order to investigate the plasma behaviour, and its possible control, many different process configurations were tested. These included oscillating beam (3), oblique positio- ning of the workpiece combined cover gas jets. Measurement of the absorbed and reflected energy and high speed cinematography were used in order to correlate plasma behaviour and process results.

REFERENCES 1) A.V.La Rocca et al. Analisi sperimentale dei fenoraeni di interazione del fascio laser sui materiali metallici. Relazione CNR. 2) J.F.Ready. Industrial Application of Lasers, 1976 Academic Press Inc. New York. 3) Y.Arata, 1982 patent N. 57-27819

(h)/mm)

118 THU-P-18

DIAGNOSTICS OF HIGH POWER LASER BEAMS

W. Jueptner, R.Rothe, Th. Kreis, G. Sepold Bias, Bremen, FRG

The laser beam material processing has a big potentiality to be automated. Nevertheless, the laser beam must be controlled by on-line diagnostic systems for power and/or intensity. Additionally, the interaction area should be surveyed, e.g. to control the plasma appearance by measuring the light emission. In the paper, different systems for these diagnostics are to be reported. Future technical aspects will be discussed.

119 THU-P-19 INFLUENCE OF PROCESSING CONDITIONS ON SURFACE MELTING OF STEELS

M.Carbucicchio, G.Lenzi, Department of Physics, University of Parma, Italy G.Palorabarini, G.Sambogna, Institute of Metallurgy, Univer- sity of Bologna, Italy

In the field of material processing by means of power lasers, increasing interest is directed towards treatments involving rapid surface melting and cooling. In the present work, the influence exerted by atmosphere and anti- reflection coating on phase composition and morphology of laser melted steels, was investigated for a medium carbon, a low-alloy medium carbon and a high-carbon alloy steel. The samples were either graphite-coated or phosphatized, and then treated either in air or under a helium stream. The laser transformed surface regions were studied by X-ray diffraction, surface Mossbauer analyses, metallography, microhardness tests and fractography. For the same processing conditions, considerably greater melting depths were observed on the high carbon steel. Generally, the solidified zones showed polyphasic structures, with predominantly dendritic morphologies, and were constituted mainly by austenite, cementite and martensite. Depending on atmosphere, anti-reflection coating and base alloy composition, differences were observed in proportions and morphology of the phases constituting the solidified regions, and interpreted on the basis of carbon availabi- lity. The amount of carbon supplied by the steel, in fact, can be either increased by a suitable coating, or lowered by oxidizing phenomena due to atmosphere.

120 THU-P-20

GENERATION AND APPLICATION OF A PULSED CO^LASER OF HIGH AVERAGE POWER

Z .Mucha, S.Milller, J. H. Schafer, J. Uhlenbusch ,W.Viol Institute of Physics II, University of Dusseldorf W.Germany An oscillator-arnplifier system with a maximum cw power of 3kW is chopped mechanically(f=0-70kHz) by means of a chopper wheel delivering pulse energy of 40mJ and pulse power of 4 0kW. In a second experiment a TEA laser was used to study the amplification of pulses with a cw amplifier. The mechanically chopped laser system was employed to investigate the interaction between metal targets and laser pulses of high repetition rates. A GeAu detector in combination with a high speed camera and a spectroscopic set-up allow diagnostics of the time dependent development of the laser power and the observation of the region near laser focus. The experiments show a strong reaction of reflected laserlight on the oscillator-amplifier- system resulting in a spiking output up to 1MHz repetition rate. The pictures of the high speed camera and the spectroscopy give information about the metal vapour plasma and the ootical discharge in the ambient eras.

121 THU-P-21 HIGH POWER CW-DISCHARGE MULTI kHzREPETITION RATE Q-SWITCH CO2 -LASERS.

C. d1 Ambrosio,W. Fuss»W.E. Schmid, K.L. Kompa Max-Planck-Institut fur Quantenoptik 8046 Garching bei Munchen, Germany The goal of this study is to provide an IR-Laser for laser chemistry (isotope seperation) or for some specfal applications in material processing. The following properties are desir- able: - high average power (several hundred watts) - high peak power (several hundred kilowatts) - single pulse energy ca 50 mJ - nearly cw-laser efficiency - repetiton rates up to kO kHz - 1ine tunabi1ity - changing average power at constant peak power - good beam guality - 10^ to 10'^ pulses without replacing parts

8 As lifetime of TEA C02-lasers is limited to 10 -109 pulses, we use an oscillator-amplifier concept with cw-longitudinal discharge. Electrooptical and mechanical Q-switching is applied. Switching speed requirements are discussed. Laser powers up to 300 W at 20 kHz repetition rate have been achieved so far. The pulses have been applied to laser isotope seperation of sulfur (SFg) and carbon (CHCIF,),

122 FRIDAY. t2 SEPTEMBER 1986 FRI-INV

SHORT WAVELENGTH CHEMICAL LASERS

S. J. Davis Physical Sciences Inc. Research Park, Andover, MA, 01810, Essex

For more than a decade there has been interest in developing short wavelength chemical laser systems. Such lasers would have a vide variety of potential applications including hi

125 FRI-0

THE C + N20—*CN(A,X) + NO REACTION : A POSSIBLE CANDIDATE FOR A NEAR INFRARED ELECTRONIC TRANSITION CHEMICAL LASER ?

L. TORCHIN, P. PRIGENT, H. BRUNET LABORATOIRES DE MARCOUSSIS, C.R.C.G.E. Route de Nozay 91460 MARCOUSSIS - FRANCE This paper will summarize a three-year effort devoted to study the excited products of the C + N2O reaction. Preli- minary experiments had shown that very fast energy exchan- ges induce a Boltzmann distribution between the coupled le- 2 vels of the A IIi (v'=l-5) and X2£+ (v"=4-8) electronic states. A new method was then derived to measure the electronic branching ratio between these states. Carbon atoms were electrically produced in medium pressure (=:15 Torr) highly diluted He-CO mixtures. 30 % of the CN radicals were measured in the A^II state, the vibrational temperature of the equilibrated levels being 5800 K. A total population inversion was observed between the (A, v'=0) and (X, v"=l) levels, but the CN densities were too low for lasing. These densities were multiplied by a 5.7 factor by lowering the pressure of the discharge to 3.5 Torr. This is still a factor of 10 too low. The next step consisted in the use of hollow-cathode discharges. The vibrational temperature was then found to be above 10 000 K, and this, together with the direct observation of luminescence from high-lying levels of the carbon atom, suggest that the cyanide radical is formed not only by reacting nitrous oxide with the C(3p) fundamen- tal state, but also with metastable levels. A complete description of the hollow cathode discharge results will be presented, together with preliminary experiments on the chemical production of atomic carbon.

126 FRI-0

LUMINESCENCE STUDIES OF SOLID AND GAS-PHASE TETRAMETHYL- DIOXETANE: POTENTIAL FOR A VISIBLE CHEMICAL LASER

Margaret A. Tolbert, Mark Spencer, and Michel J. Rossi SRI International, Chemical Physics Laboratory Menlo Park, CA 94025 USA

Tetramethyldloxetane(TMDX), C6H12O2, is a relatively high vapor pressure solid which undergoes highly exother- mic unlmolecular decomposition under light emission according to the following reaction: TMDX + .253A + .75AQ where A is acetone (C3H6O). Solid TMDX Is an explosive which detonates under intense blue light emission. Our approach to a visible chemical laser makes use of two novel reactions which are important at high densities. Solid samples of the title compound were detonated both thermally and by IR radiation from the unfocussed output of a TEA laser at J.0.247 [im> The chemiluminescence was analyzed using an OMA system , and was found to be a composite of thermalized triplet and singlet acetone emission, with the maximum generally found at 440 nm. Identification of the emitting species under solid-state decomposition conditions Is afforded by time resolved emission studies using a conventional photomultiplier detection system. The relative quantum yield of singlet- versus-triplet emission under various decompostion conditions will be discussed. Since model calculations on the basis of kinetic rate equations predict final temperatures around 1000 to 1200 K for the detonating pure sample, the high temperature luminescence of gas-phase TMDX was Investigated using the technique of laser-powered- homogeneous pyrolysis (LPHP). The high temperature emission spectrum, the quantum yield of singlet-versus-triplet emission as well as the ensuing slow decomposition of triplet-excited acetone will be presented.

127 FRI-0

COMBUSTION-DRIVEN C.W. HBr CHEMICAL LASER

F. VOIGNIER LABORATOIRES DE MARCOUSSIS, C.R.C.G.E. Route de Nozay 91460 MARCOUSSIS - FRANCE

Present techniques to produce efficient c.w. HBr chemical laser based upon the pumping reactions H + Br2 +-HBr* + Br and Br + HI -*• HBr* + I are limited because of the difficul- ties to provide high H or Br atoms concentrations. We will report the operation of a Br + HI pumped chemical laser using a copious source of low pressure Br atoms. Br atoms are thermally produced in a conventional HF/DF combustion- driven chemical laser. Fluorine and hydrogen bromide diluted in helium are reacted in a combustor. For a F2/HBr ratio of 0.5 and a pressure of 0.7 atm. the stagnation temperature in the plenum conditions is about 1600 K and there are only HF, Br and Br2 produced in the combustor. The basic laser hardware consists of a combustor-nozzle assembly and an optical cavity. The 20 x 1 cm matrix hole nozzles provides the expansion of the Br atoms flow and its mixing with HI. The flow rates (in mole/sec.) of F2, HBr, He and HI are 0.032, 0.062, 0.112 and 0.041 respectively. The cavity pressure is 2.5 Torr. For these operating conditions a maximum HBr multiline output power of 25 W has been obtained. Lasing occurs in the 4.1 - 4.2 /urn region on four vibration-rotation transitions : Pi(5) to P|(8). Chemiluminescent emission measurements indicate a rotational gas temperature of 300 K and a vibrational temperature of 6000 K. A complete description of the experiment will be presented and several improvements which should result in higher output power will be suggested.

128 FRI-0

HBr cw COMBUSTION-DRIVEN LASER

R. A. Meinzer and G. M. Dobbs United Technologies Research Center East Hartford, Connecticut 06108

Since cv combustion-driven lasing has been demonstrated with two hydrogen halides, HF and HC1, an investigation was performed to demonstrate lasing with a third hydrogen halide, HBr. As a result of this investigation, combustion-driven HBr lasing was demonstrated. The lasing output spanned the 4.0 to 4.8 micron region and the highest observed vibrational-rotational transitions correspond to the v=4 to v=3 transitions. A measurement of the vibrational population in the various vibrational levels (v 0) was made via chemiluminescent emission measurements. At the optimum conditions, the lasing power was 1.5 watts. The overall performance potential of the HBr laser cannot be predicted at the present time, however, some qualitative assessments can be made. On the basis of^the chemiluminescent emission measurements, the number of v * 3 HBr molecules per cc is 4 x 10 . This concentration is approximately an order of magnitude smaller than that which is measured in the other hydrogen halide systems. If the static pressure of the HBr laser is increased, then the concentration per cc should increase. This increase is made more probable by the relatively long relaxation rates for the HBr molecule. Comparison of the HBr-HBr relaxation rates to those which have been measured for HF-HF collisions indicates that the HBr relaxation rate is 100 times slower. Therefore, the vibrationally excited HBr medium should not decay very rapidly. Comparison of the active medium lengths which are achieved in the HF and HC1 lasers supports this contention. Details of the hardware, gas composition, rection mechanism, lasing spectrum and chemiluminescent emission measurements will be described.

129 POST-DEADLINE PAPERS VIBRATIONAL RELAXATION RATES CF CD2 (001) WITH MRIOUS CDLLI- SICN PARTNERS FOR T<300 K

S. H« Bauer, J. F. Caballero, R. Curtis and J. R. Wiesenfeld, Department of Chemistry, Cornell University, Ithaca, New York 14853

Population decay rates of O32(001), due to self- collisions and to encounters with ten other species [(CH3)^J, (CH3)£>, up, CS2, HC1, N^, CCS, NO, O2, and N2] were measured as a function of temperature by recording the decay in fluorescence of 002 {(001) -»• (000)}. The (001) level was overpopulated by exposing mixtures of CD2 with various collision partners, to narrow pulses of 9.4 jjn radiation from a mechanically chopped CD2 cw laser, which selectively pumped the thermal populations of CO2 {(100) + (020)}. The lowest attained temperatures ranged from 190-240K, and were limited mostly by the population of C02{(100) + (020)}. While, in general, the log of the probability for collisional deactivation is linear when plotted against T"1/3 for T>400 K, significant departures appear at lower temperatures. In a sub- stantial fraction of cases the probability rises with decreasing temperature after passing through a minimum. In qeneral, the probability for collisional deactivation is higher for polyatomics compared to diatomics, and is lowest for those molecules which possess no dipole moment.

133 AUTHOR INDEX

135 Author Page Author Aberman, Z. 72 Flusberg, A. 113 Agmon, P. 99 Fontaine, B.L. 55 , 80 Aguillon, F. 62 Forestier, B.M. 55 , 80 Autric, M. 68 Fuj ioka, T. 50, 86 , 87 Bacis, R. 29 Fuss, W. 122 Badziak, J. 46 Gastaud, M. 40, 115 Baker, H.J. 79 Georges, E. 30,31 Bar to, J.L. 56 Gevaudan, A. 80 Basting, D. 95 Giesen, A. 38 Bauer, S.H. 41, 133 Go 1ub, I. 114 Baumert, R. 97 Guenther, A.H. 37 Berger, M. 60 Hafl, Th. 42 Beyer, E. 66 Hanko, L. 102 Biblarz, O. 56 Hart, G.A. 81 Bigio, I.J. 35 , 61 Hashimoto, K. 96 Birch, S.F. 93 Hennig, W. 52 Bobin, J.L. 43 Herziger, G. 66 Bohn, W.L. 42 Hoch, E. 99 Bournot, Ph. 68 Hor ioka,- K. 69 Bousselet, P. 115 Hugel, H.E. 38, 52 , 82 Bradburn, G.R. 45 Hugenschmidt, M. 94 Brun, R. 112 Hut in, G. 115 Brunet, H. 40, 47, 126 Imbert, M. 112 Brunne, M. 48, 85, 106 I ssartier, P. 55 Caballero, J.F. 133 Iyoda, M. 50 Campargue, R. 62 J-oeckle, R. 70 Carbucicchio, M. 120 Joly, V. 104 Cassady, P.E. 93 Jueptner, W. 39, 119 Cefalas, A.C. 78 Kaizerman, S. 57 Cenian, A. 49, 85, 107 Kali sky, Y. 51 Chauvet, Ph. 47 Kanazawa, H. 69, 84, 86 Chiu, N.-S. 41 Kasuya, K. 69 Chuchem, D. 51, 117 Katz, D. 99 Ciboldi, M. 118 Kompa, K.L. 122 Cruciani, D. 118 Konefal, J. 65, 116 Curtis, R. 133 Kopeika, N.S. 109 d'Ambrosio, C. 122 Koren, M. 72 David, D. 31, 104 Korff, D. 113 Da v i s, S.J. 103, 125 Kottler 60 Dobbs, CM. 129 Kramer, R. 66 Dorko, E.A. 102 Kreis, Th. 119 Dubicki, A. 46 Kubota, H. 58 Dufresne, D. 68 , 91 Kukiello, P. 116 Duignan, M.T. 36 Kuwabara, K. 98 Durran. D.A. 110 La Rocca, A.V. 92 Erez, G. 114 Lando,' M. 53 Fausse, A. 104 Lebehot, A. 62 Feldman, B.J. 36 Lenzi, G. 120 Feltham, A.M. 79 Leporcq, B. 30,, 31 Fishman, D. 71 Lilenfeld, H.V. 45

137 Author Page Author Page Loosen, P. 66 SIiwinski, G. 116 Mabru, M. . 40. 47 Sontag, A. 70 Makowsk i, A. 85 Spalding, I.J. 100 Margalith, E. 63 Spencer, D. J. 110 Marquet, L. 27 Spencer, M. 127 Maruyama, T. 84 Spindler, G. 59 Masuda, W. 54 Spyrou, S. 78 Matsuzaka, M. 58 Stanco, J. 116 Mayerhofer, W. 52 , 59 Steen, W. M. 101 Mclver, J.K. 37 Sugawara, H. 98 Meinzer, R.A. 129 Taira, T. 86 Moran, J. 117 Takemori, S. 98 Mucha, Z. 121 Tamura, H. 69 Mu11e r , S. 121 Temkin, A.Ya. 108 Nachshon, Y. 57 Terry, P.J. 93 Nicolaides, C.A. 78 Terunuma, K. 50, 87 Noguchi, A. 87 Thomas, S.J. 61 Nowack, R. 52 Tolbert, M.A. 127 Ogawahara, N. 54 Torchin, L. 47, 112, 126 Palombar ini, G. 120 Uhlenbusch, J. 121 Palumbo, L.J. 81 Verdier, C. 30, 31 Per ram, G.P. 103 Vigliano, P. 68 Pigache, D. 31,, 55 Viol, W. 121 Pons, A. 115 Voignier, F. 128 Prigent, P. 126 Vu, B. . 117 Rabczuk, G. 64, 116 Wacholder, E. 57 Rokni, M. 53 Wada, A. 98 Rossi, M. J. 127 Waichman, K. 51 Rothe, R. 39, 119 Walter, B. 67, 105 Rousseau, J. 62 Walter, R.F. 81,111 Rozenberg, Z. 53 Watanabe, K. 86 Rozkwitalski, Z. 116 Watanuki, T. 58 Saito, H. 54, 84 , 86, 87 Webb, C.E. 28 Sambogna, G. 120 Whitney, W.T. 36 Sasaki, K. 98 Wiesenfeld, J.R. 133 Satani, R. 84 Wilcox, C.F. 41 Sato, S.-I. 50, -86, 87 WiIdermuth, E. 38 Sato, Sh. 58 Wolf, P.J. 102, 103 Sauerbrey, R. 77 Yackerson, N. 109 Savorelli, P. 118 Yamaguchi, S. 58, 84 Schaffer, J.H. 121 Yatsiv, S. 83 Schall, W.O. 59 Yogev, A. 44 Schmid, W.E. 122 Yokozawa, T. S4 Schuocker, D. 67, 92, 105 Yuasa, M. 84 Sent is, M.L. 55, 80 Zaremba, R. 116 Sepold, G. 39, 119 Zeitoun. D. 112 Shachrai, A. 71, 99 Zinman, Y. 99 Shapiro, M. 44 Shuker, R. 114 Skordoulis, C. 78

138