OPTICAL AND INFRARED LASERS Final Report December 1, 1972 to March 31, 1978 To: National Aeronautics and Space Administration Goddard Space Flight Center Greenbeld, Maryland 20771 NASA Research Grant NGL 22-009-741 M.I.T. Project OSP 80711 From: Professor Ali Javan Department of Physics Massachusetts Institute of Technology Cambridge, Massachusetts 02139 NASA-CR--15325) -OPTICAL AND INFRARED .N8-28437 LASERS Final Report, 1 Dec. 1972 - 31 ar. 1978 (Massachusetts Inst. of Tech.) fiS p'- Unclas HC A19/MF A01 CSCL 20E G3/36 25918 REPRODUCED B NATIONAL TECHNICAL I INFORMATION SERVICE 1 Augist 1978 U.S.DEPARTMENT OFCOMMERCE SPRINGFIELD. VA. 22161 MASSACHUSETTS INSTITUTE OF TECHNOLOGY DEPARTMENT OF PHYSICS CAMBRIDGE. MASSACHUSETTS 02139 August 8, 1978 NASA Scientific and Technical Information Facility P.O. Box 8757 Baltimore/Washington International Aitport Maryland 21240 Gentlemen: In compliance with the requirements of NASA Grant No. NGR 22-009­ 741, we submit two copies of the Final Technical Report covering the period December 1, 1972 to March 31, 1978. If you should need further information, please let me know. Sincerely yours, Ali Javan Francis W. Davis Professor of Physics Enclosures cc: N. McAvoy G. Wiseman D. Herlehy x/ NOTICE THIS DOCUMENT HAS BEEN REPRODUCED FROM THE BEST COPY FURNISHED US BY THE SPONSORING AGENCY. ALTHOUGH IT IS RECOGNIZED THAT CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED IN THE INTEREST OF MAKING AVAILABLE AS MUCH INFORMATION AS POSSIBLE. Table of Contents Papers appear in-the order listed below 1. D. Seligson, M. Ducloy, J.R.R. Leite, A. Sanchez and M.S. Feld, Quantum Mechanical Features of Optically Pumped CW FIR Lasers, J. of Quantum Electronics, QE-13, 468 (1977). 2. R.E. McNair, S.F. Fdighum, G.W. Flynn, M.S. Feld, Energy Storage and Vibrational Heating in CH F Following Intense Laser Excitation, Chem. Phys. Lett. 48, 241 (19)7). 3. R.E. McNair, R. Forber, S.F. Fulghum,G.W. Flynn, M.S. Feld and - BJ- Feldman, Energy Absorption and Vibrational Excitation by Intense Laser Pulses, (To be published). 4. A. Javan and A. Sanchez, Extension of Microwave Detection and Frequency Measuring Technologies into the Optical Region, Pro­ .ceedings of the Vail Conference, Plenum Press 1973. 5. A. Sanchez, S. K. Singh and A. Javan, Generation of Infrared Radiation in a Metal-to-Metal Point Contact Diode at Synthesized Frequencies of Incident Fields; A New High Speed Broad Band Light Modulator, Published in Applied Physics Letters. 6. T.W.iDucas and A. Javan, Measurement of Microwave Fine Structure in OH Infrared Transitions using Frequency Mixing with Metal-to- Metal Infrared Diodes, J.Chem. Phys. 60, 1677 (1974). 7. A. Sanchez, C.F. Davis, K.C.Liu and A. Javan, The MOM Tunneling Diode: Theoretical Estimate of its Performance at Microwave and Infrared Frequencies, J. Appl. Phys., (to be published, August 1978). 8. TW. Ducas, L.D. Geoffrion, R.M. Osgood, Jr. and A. Javan, Observa­ ] tion of Laser Oscillation in Pure Rotational Transitions of OH .and OD Free Radicals, Published in Appl. Phys. Letters. 9.fH.P.Grieneisen, J. Goldhar, N.A. Kurnit and A. Javan and H.S. Schlossberg, Observation of the Transparency of a Resonant Medium to Zero-Degree Optical Pulses, Published in Appl. Phys. Letters. 10. N. Skribanowitz, I.P. Herman, R.M. Osgood, Jr., M.S. Feld and A. Javan, Anistropic Ultra-High Gain Emission Observed in Rotational Transitions in Optically Pumped HF Gas, Published in Appl. Phys. Letts. Ic Table of Contents continued -­ 11. H.P. Grieneisen, J. Goldhar, and N.A. Kurnit, Observation of Zero-Degree Pulse Propagation in a Resonant Medium,- Proceedings of the 3rd Rochester Conference on Coherent and Quantum Optics, edited by L. Mandel and E. Wolf, Plenum Press 1973. 12. R.M. Osgood, Jr. and A. Javan, Measurement of Vibration- Vibration Energy Transfer Time in HF Gas, Published in Appl. Phys. Letters. 13. Measurement of V-V Transfer Rate from HF v = 3 Using Simul­ taneous Optical Pumping on the HF v = 2-l and v = 1-*O bands, Published in Appl. Phys. Lett. 14. N. Skribanowitz, M.J. Kelly and M.S. Feld, A New Laser Tech­ - nique for the Identification of Molecular Transitions, Published in Phys. Rev. A. 15. F. Keilmann, R.L. Sheffield, M.S. Feld and A. Javan, Optical isolation using a Doppler-Broadened Molecular Absorber, Appl. Phys..Lett., 23, 612 (1973). 16. J.G. Small, Infrared Frequency Synthesis and Precision Spectroscopy. 21Z This final report consists of selected papers describing research work performed in the MIT Optical and Infrared Laser Laboratory with the support of NASA Research Grant NGL 22-009-741. 1. D. Seligson, M. Ducloy, J.R.R. Leite, A. Sanchez and M.S. Feld Quantum Mechanical Features of optically Pumped CW FIR Lasers J. of Quantum Electronics, QE-13, 468 (1977) 4< 468 IEEE JOURNAL OF QUANTUM ELECTRONICS., VOL. QE-13, NO. 6, JUNE 1977 Quantum Mechanical Features of Optically Pumped CW FIR Lasers D. SELIGSON, MARTIAL DUCLOY, J. R. R. LEITE, A. SANCHEZ, AND M. S. FELD Abstract-Quantum mechanical predictions for the gain of an op- tion model. Some of the quantum mechanical predictions axe verified tically pumped CIV FIR laser axe presented for cases in which one or m CH 3OH. both of the pump and FIR transitions are pressure or Doppler broadened. The results ae compared to those based on the rate equa- G ENERATION of far infrared (FIR) laser radiation by means of optical pumping of molecules has received Manuscript received February 4, 1977. This work was supported in increasing attention over the past few years [1]. Analysis of" part by the U.S. Army Research Office (Durham), the National Aero­ nautics and Space Administration, the Universdade Federal de Per- the optical pumping process is usually based on rate equation nambuco and the CNPq-Brazil under grants to one of the authors (RE) treatments [2]. Such treatments neglect important con­ (J. R. R. L.), and an Alfred P. Sloan Fellowship (M.S.F.). tributions to the FIR gain due to multiple quantum processes D. Seligson, J. R. R. Leute, A. Sanchez, and M. S. Feld are with the Department of Physics and the Spectroscopy Laboratory, Massachu- and modulation of the time-dependent wave function. From i setts Institute of Technology, Cambridge, MA 02139. the quantum-mechanical (QM) point of view an optically - M.Ducloy was with the Department of Physics and the Spectroscopy pumped laser can be considered as a coupled three-level sys- 5 Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139. He is now wjth the Laboratoire de Physique des Lasers, Uni- tem interacting with applied radiation fields. It is well known versit4 Paris Nord, Villetaneuse, France. that in such systems-Raman-type processes [31 play-an impor- Copyright © 1977 by The Institute of Electrical and Electronics Engineers, Inc. Printed in U.S.A. Annals No. 706Q1.026 SELIGSON et a.: OPTICALLY PUMPED CW FIR LASERS 469 tant role. For example, double quantum transitions can occur 0 in which a molecule initially in the ground state undergoes a E,cosflI coherent transition to the lower level of the FIR transition by simultaneously absorbing a pump photon and emitting a FIR photon. Such processes can modify the gain and, in some E .sflat cases, give rise to directional anisotropy in the FIR laser emis­ sion [3], [4]. Accordingly, a complete understanding of the 2 quantum mechanical features makes it possible to optimize Fig. 1. Three-level system used to describe an optically pumped FIR the output characteristics of such lasers. For example, in one laser. The pump field resonates with the 2-0 transition, molecular case [5) ithas been possible to achieve gain and laser oscil- center frequency W,2, The FIR laser emission occurs at the 0-1 transition, molecular center frequency w 1 . lation in the. absence of population inversion. The way in which Raman-type processes manifest themselves depends on 92 = 2, k, whether one or both of the coupled transitions are pressure or Doppler broadened. In Sections I-III the predictions of the n 2 = f 2 - ek2 V, QM treatment for the gain of an optically pumped laser are = discussed for the various cases. Section IV presents some FIR i laser experiments in which QM features, not predicted by rate The frequencies i'1and 9 are those seen by the molecules in equations, are observed, their rest frames and are Doppler shifted by kI vand ekv,fe­ The theoretical model [6] considers a three-level system spectively. For copropagating (counterpropagating) beams we composed of a pump transition, 2-0, center frequency wd2, have c = +1(e = -1). Depending on whether pump and probe coupled to a FIR transition, 0-i, cdnter frequency w1, via the transitions are pressure or Doppler broadened, any of the cases common level, 0 (Fig. 1). It is assumed that in the absence of described in the following three sections can occur. the pump laser only the ground state, level 2, is populated (total population n2). The pump field, E2, at frequency f2,, I.HOMOGENEOUSLY BROADENED SYSTEMS can be arbitrarily large, but the field E,, frequency S21,gen- (HIGH-PRESSURE REGIME) crated at the 0-1 transition is considered to be weak [7]. When both transitions are pressure broadened (y>>ki,u) Different relaxation rates (y's) are included in the theory: pop- ihe velocity dependence at both pump and probe frequencies ulation decay (7o,71 ,72), polarization decay (-ol, 702),and may be neglected (i.e., 12'1 = 21, 22 = 922), so the factor in decay of the Raman coherence (7y2). The quantity of interest Jbrackets in (1)becomes velocity independent and the remain­ is the gain induced at the 0-1 transition by a weak probe field ing integration over W(u) gives unity.