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Journal of the Optical Society of America B

Journal of the Optical Society of America B


  • Vol. 2, Iss. 4 — Apr. 1, 1985
  • pp: 535–540

Gain dynamics in pulsed 12-μm NH3 lasers

H. D. Morrison, B. K. Garside, and J. Reid  »View Author Affiliations

JOSA B, Vol. 2, Issue 4, pp. 535-540 (1985)

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The dynamics of pulsed line-tunable NH3 lasers are investigated by measuring small-signal gain as a function of NH3 transition, NH3 concentration, and pump intensity. Under typical experimental conditions, it is shown that the rotational populations in NH3 thermalize and that consequently the relative gain distribution can be described by a ratio of vibrational populations. Peak gains of 20% cm−1 are reported for mixtures of 4% NH3 in N2 pumped by the 9R(30) CO2 laser line. Heating that is due to increased pump absorption reduces the gain in mixtures of higher NH3 concentrations. The experimental results are in good agreement with the predictions of a rate-equation model, which can be applied to optimize line-tunable NH3 lasers.

© 1985 Optical Society of America

H. D. Morrison, B. K. Garside, and J. Reid, "Gain dynamics in pulsed 12-μm NH3 lasers," J. Opt. Soc. Am. B 2, 535-540 (1985)

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  1. H. Tashiro, K. Suzuki, K. Toyoda, and S. Namba, "Wide-range line-tunable oscillation of an optically pumped NH3 laser," Appl. Phys. 21, 237–240 (1980).
  2. B. I. Vasil'ev, A. Z. Grasyuk, A. P. Dyad'kin, A. N. Sukhanov, and A. B. Yastrebkov, "High-power efficient optically pumped NH3 laser, tunable over the range 770–890 cm−1," Sov. J. Quantum Electron. 10, 64–68 (1980).
  3. N. Yamabayashi, T. Yoshida, K. Miyazaki, and K. Fujisawa, "Infrared multi-line NH3 laser and its application for pumping an InSb laser," Opt. Commun. 30, 245–248 (1979).
  4. N. Yamabayashi, K. Fukai, K. Miyazaki, and K. Fujisawa, "Resonant pumping far-infrared NH3 laser," Appl. Phys. B 26, 33–36 (1981).
  5. V. G. Averin, M. Akhrarov, G. S. Baronov, B. I. Vasil'ev, A. Z. Grasyuk, M. G. Morozov, E. P. Skvortsova, and A. B. Yastrebkov, "Dissociation of UF6 molecules involving excitation of combination modes by NH3–N2 laser radiation," Sov. J. Quantum Electron. 13, 189–194 (1983).
  6. H. D. Morrison, B. K. Garside, and J. Reid, "Dynamics of the optically pumped midinfrared NH3 laser at high pump power—Part I: inversion gain," IEEE J. Quantum Electron. QE-20, 1051–1060 (1984).
  7. S. M. Fry, "Optically pumped multi-line NH3 laser," Opt. Commun. 19, 320–324 (1976).
  8. C. Rolland, J. Reid, and B. K. Garside, "12 μm Raman lasers in NH3 pumped by low-power CO2 laser pulses," IEEE J. Quantum Electron. QE-18, 182–186 (1982).
  9. Ortho- NH3 consists of molecules with rotational quantum number K = 3n, and para -NH3 consist of molecules with K = 3n ±1.
  10. C. Rolland, J. Reid, and B. K. Garside, "Line-tunable oscillation of a cw NH3 laser from 10.7 to 13.3 μm," Appl. Phys. Lett. 44, 380–382 (1984).
  11. This is equivalent to setting the parameter t of Ref. 6 equal to its maximum value of t = 1.0.
  12. P. Minguzzi, M. Tonelli, A. Carrozzi, and A. Di Lieto, "Optoacoustic laser Stark spectroscopy in the ν2 band of 14NH3," J. Mol. Spectrosc. 96, 294–305 (1982).
  13. C. H. Townes and A. L. Schawlow, Microwave Spectroscopy (Dover, New York, 1975).
  14. V. S. Letokhov and A. A. Makarov, "Kinetics of excitation of molecular vibrations by infrared laser radiation," Sov. Phys. JETP 36, 1091–1096 (1973).
  15. For most of the pumping conditions that we examine, the relaxation rates are fast enough that the vibrational populations follow the variations in pump intensity after the peak of the pulse. As the pump absorption is saturated at intensities well below 950 kW/cm2 (see Section 4.C), changes in the intensity by as much as a factor of 2 have negligible effect on the gain calculation.
  16. To calculate temperature changes, we used heat capacities at constant volume of 29.0 J/(mol K) and 20.7 J/(mol K) for NH3 and N2, respectively, derived from W. Braker and A. L. Mossman, Matheson Gas Data Book, 5th ed. (Matheson Gas Products, East Rutherford, N.J., 1971).
  17. F. E. Hovis and C. B. Moore, "Temperature dependence of vibrational energy transfer in NH3 and H218O," J. Chem. Phys. 72, 2397–2402 (1980).
  18. Linear interpolation between rate coefficients provided by Hovis and Moore17 was employed to evaluate the V-T rates up to 398 K, the maximum temperature reported. For temperatures greater than 398 K the V-T rates were maintained equal to the values for 398 K.
  19. H. D. Morrison, J. Reid, and B. K. Garside, "16–21μm line-tunable NH3 laser produced by two-step optical pumping," Appl. Phys. Lett. 45, 321–323 (1984).

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