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A Nitrogen-Laser-Pumped Dye Laser System ? ' A

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A Nitrogen-Laser-Pumped Dye Laser System ? ' A Mr. 'Ian S. NAME OF AUTHOR/NOI# DE L'AUTEUR, GORDON h A Nitrogen-Laser-Pumped Dye . - T %tE OF THESIS/TfTRE DE LA TH& Phission is haQy (panted to ths NATIONAL LlEWW OF L'autwisetiim rst, par !a pr~*(nte:KCOI~@ 4 ,le ~UOTH~- -. 2 -, )-->- >CANADA m rnicrdilrn hi-4 mi s adto lend or ael l wisr WENATIONALE LJU-CANADA dr &rd&er cett* th&m at af the film. de pr4ter w ds VS~Rdes exonpl~jresdu film. The euB## reserves other publication raw,and neithgr the L'sutew se @serve fes eutrtw &&Is do puliHc&tion; ni la - thesis M* extbisiw extpzts from it mybe printed or olheii thdsenl de longs eqreits aGP cslt~ine doivent &re impritnds A NITROGEN- LASER-PUMPED - - * OF T~ REQUIREMENTS FOR THE DE6mE OF MASTER OF SCIENCE* in the Dapartnent A> -A .. is my not be reproduced in whole or in part, by photocopy or other means, without @rmission of the author. % . APPROVAL . \ . I '\ Name : Ian Sydney 'Gordon Degree : ast tar of Science t -~itl$of Themis : A Nf trogen Laser Pumped Dye Lmer - Examining Cowttee : Chairman: Be ?. Clayman .,- J. C. Irwin Senior Supervisor 0 8 I hereby grant to Uproa F -ty th~ r- , ' my thesis or d'ieeertation (the ti of "whgch =--below) to usen of the Simon Freser university Libr,ary, and to make partial or einglc @ copies only for such users or in response to a request from the library : of any other university, or other educational iitstitutim, on i'te 'own s behalf or for one of fts usere. I further agree that permisatcan for A - m7riprripre-cFpTing of this thesis for scholarly purposes &y be granted by me or the Dean of Graduate Studies. It is understood that copying without my written permission. Title of ihedis/~issertstion: *A Nitrogen-Laser-Pumped Dye Laser system ? ' a (signature ) Pfr. Ian S. Gordon I +. > 1 (date) I , , P .... ,. STRACT . ~ 11. % , A fiitrogen-'l~ser~pu~~peddye laser system has been ,.- .\ designed. constructed, and evaluated. me nitrogen laser ? # -ou'tput was in the form of pubes whose width between the half-pawer points wds about. 9 nsec. The nitrogen laser Y gave a peak power of 500 kW in each pulse and at the average parer of 38 xWwa.8 obtained, The nitrogen-laser , , was in turn used to pump a dye laser; The dye laaer, ---- -- -- -- with Rhodamine 60 as the active medium, gave a maximum " i 4 . v average pqJer output of approximately .064 mW. The d= laser system has been used t'og perform preliminary Rman scattering experiments'on ZnSe and ZnTe. The fizst-order ,I . Raqan spectra of both ccrmpbunds have been obtained and I ' \ in addition a very brief investigation of the Resonant I -. ZnTe has been Raman effect in carried out. The- fettsibitity of usingsoch &laseraystera for Raman scatteringexpeziments ' - is discussed and poeshle improvements suggested. e pleasure working with , him.A Thankrr are due to Frank Wick . ' e and-others in the machina shop twit weill aa Wally Hall kn the P /'ronicshop. USO, thank you' T.B. B for stixnulaeing -Y/ c. many usef 4% discussions. I also thank my colleagues, ---- many valuable Acknowl '?dgment is made to'the National Research Council Assistantships, aild to J.Q. lmii who provided f inanciai P"" assistance through his .grant. i d Table of Contents I Abstract - iv 1'- Acknowledgements * a - ~istof Tables vii k , , \ . List of Figures + vifi d Chapter 1 Introduction 1. \ Chapter 2 The.Pulsed Molecular Nitrogen -Laser 6 0 - er Tr*si#$ons in "the Nitrogen ' 6 .2 The Rate Equations for the 8 U i -- - 'Inversion Criterion 11 ' 2.4 Power Output 14 2.5 The Nitrogen-Helium, ~aser I 2.6 Descript~onZofthe Nitrogen Laser q. I_ 2,6a The Laser Box , 20 a . .. - 2.6b The ~iectrodea 22 2.6~'The Gas Supplr system 24 A t I I 2.6d The Electrical Circuit L 0 . - 2-?+ De.tmztora 27 I * ~07 + 2; 8 ~ischar~eCharacteristics of the 27 Nitrogen Lasee 2.9 Output Energy of the'gitrogen Yes29 $ b. r Chapter 3 Tuneable pulsed Dye Lasers 37 - -. < -". 3.1 t he Dye ~olecule 37 - Pr= 3.2 Light Ab$Mpti% by Dyes ' 38 i , 3.3 Dye Laser.Stirnulation Wfth a -43 Pulsed Molecular Nitrogen Laser i .3.4 The Description of the Dye.~saer , 44 ' 3.4a The Dye Cell F 46 3.5 The Output of the Dyepaset 51 * r 3.6 Dye8 52 I - Etfrapted---Sc-- --- --- 4.1 ~ntxoductiona 56 ' 4.2 The Apparatp , 56 4 4.3 Results 60 ?\ f e h 4.4 Resonant Rman Effect 63 4 1 .Chapter 5 Cone lusion's - 69 List of References - 72 9 '. 4" \ 7 4i- d / - -- - --- ---A- - -- -- A- - L % v --- - - - --- - --- - - - -- -- - - - - - - - - - w Table * ,. Page I The Lasing Limits and Laser output for Dyes Used LIST; OF FIGURES - - d Figure Page An Energy Level Diagram of the Nitrogen 7 Molecule P SP' The Pump cycle of Nitrogen Molecules 9 Calculated Laser Power Density Using the 12 Saturation~~pproximation~- . The,.Laser Box Cross-Section, 23 ' -- - -- --7 T--- u------L-~ - - A- -ALL w- The Electrical Circuit- f ?he Bias Circuit for the Phototube 28 -- - - -- - - T& Dependence of Pulse-Energy P-~=sNEF- - -31- The Dependence of Pulse Energy on Repetition Rate with a ~ctrogenFlow 0of 3 Litets pet Minut * *. The Dependence of Pulse Energy on Repetition ' 33 t Rate with a ~itrogenFlow of 5 Liters per Minute The Dependence of Average Power Output on 34' ~epetitionRate 36 Pulse Shape Measurement fi s 37 7 The Molecule Butadiene ,. Eigenstates of a Typical Dye Molecule wdth 42 Radiative and Non-Radiative Transitions . A Simple Tuneable Dye Laser. 44 The Pump Cycle of Dye Molecules '45 The Layout of the Dye -Laser 47 - - - - - - - The Frame of t* Dye Cel& t ,-46 - -- Cr -- Relative Laaer Intensityas a L'unction or 53 * davelength for Rhodamine 66 and 7-Diethylamino-4-Methylcoumkfin Page Sek-up for Scattering Experiments '. 57 A Ranfan Spectr of ZnSe at Roqn Temperatare ,, '61 dkSpectra '7 o ZnTe at Roam Temperature+ -,62 Scattering Amplitude as a Function of the Rdduced Resonance Enesg)', Ai The Absorption yge in undbped\ ZnTe at.300 K - ? . 'he ideal light'source for luminescence and light ,scatterlYng studies would provide an arbitrarily istense, m&ochromatic beamwhose frequency could be varied continuously throughout the electro-magnetic spectruxu.' dssc~veryin 1966 (Schaf , 1973, p. 1) of the dye laser , I - i provides an approximate equivalence in the visible - - - ----- - --- 2 - - - ---- -- --- - -- - -- region of thqfspectrum. Witha suitable selection of A *i = \ dyes and excitation source, the laser can be tuned e throughout the visible spectrum. At present, there are , eseentially three types of dye lasers. classijied .acc&ding * & to the type of excitation, These three sources of * excitation are the flashlamp. cw argon ion lasers , and % the nitrogen laser. One podsibility of pumping a dye laser is to use a f lashlamp. Thbe, however, are not very efficient for several reasons. First oT all, they pr0duce.a lot of light which 4s not of a suitable wavelength to pump the dye; only a fraction the light produced can be of P--- -- - --- - -- - - - - - -- used for this puzpose, It is also-necessary to filter A~ ---*.--- out phot&herai~ally active wavelength; which will decom- 'pose the- me, Secondly, itcis an extended, diffuse - *. g 5'A 7 risetime of the pulse is slow, In the dye rnolecules,~' 1 1 i I a the maximum population of the excited state responsible 2 ii i f + for thelaser tranjiition can be reachid before the & I. intensity of the f lashlamp is a mqximum: Furthermore, 5, f - 9 [ there are many problems associated with flashlamps in general, These include a lack of pulse to pulse repro- - >" - - - - -- -- -- -> cw lasers, Until very recently, 'cw lasers operated only a., a., down to the green, so that they were unable to pump t the ; dyes to lower wavelepgths. Recently, however, an .argon laser operating in the ultra-violet has became a comerckally available. At present this is the most , I efficient and noise fre&itation source for use with h dye lasers but it is- very expensive and has a rather I short lifetime. \ FI t The third excitatiog aource for dyes is the nitrogen L e 11 laser. Until recentlyr this was the only laser which b I operated in the near ultra-violet with a reasonqble - -- ---- power output; ~hestrong lirX6f thiCliisF i* at-%~2 - . p-pppp . ma iind is thus well suited for pumping dyes. ~T~trogen.. d T- laser output is in the form of zt pulse lasthg for about c' -8 I 10 . se&nda, - d"so - that with a typical peak Gwer of 100 kilowatts and pulse repetition rate of 100 pulses per ~ second, a cw output of .lwatts is obtained. This laaer can be built of readily available materials, and the gases required, .nitrogen and helium, are readily available. Furthemre, the durability of the laser. is very good. L. There are two main disadvantages of this particular '1 A A- -- excitation- -- -- source.- - - -Firstly, the-- laser-- -- -- produces--- a---A large - - P amount of electrical noise interferes with any - 'sursounding equipment, difficult to separate low. ?.An output of .1 watts, wheh combi&ed with a dye laser efficiency of somewhat less than 101, yields an output of less than 10 milliwatts. Thus, to obtain results from a scattering experiment, qui- a sophisticated detection procedure is required. These two main dis- -advantages, however, are.also shared with the flashlamp r* -4 excitation source. The nitrogen laser has many advantages over the flashlamp; its output beam is monochromatic and collimated 9 to allow easy focussing, its risetime is short, and its ..
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