Date of Award

1-1991

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Engineering Physics

Supervisor

J. Reid

Abstract

An experimental and theoretical study of the dynamics of NH₃ lasers is presented. The significant achievements of this work are summarized below. In initial experiments, a pulsed transversely-excited CO₂ laser operating on the 9R(30) transition is used to optically pump mixtures of NH₃ in buffer gas. A simple oscillator/amplifier system allows the performance of the NH₃ amplifier in the 11 μm region to be characterized. Small-signal gain coefficients of >10%/cm are measured on the aQ(3,3) transition at 10.8 μm, while pump conversion efficiencies of ~50% are shown to occur under saturation conditions. The NH₃ laser system is described by a rate-equation model, which is validated by comparison with experiment over a wide range of operating conditions. Measurements are made for NH₃ concentrations ranging from 0.05 to 0.2%, for Ar, N₂ and He buffer gas pressures from 170 to 700 Torr, and for gas temperatures from 200 to 300 K. Optically pumped NH₃ is shown to be a versatile and efficient system for the amplification of mid-infrared radiation. The rate-equation model is used to aid in the design of a simple and efficient NH₃ laser. This laser is tuned over more than 70 vibrational band transitions between 10.08 and 14.14 μm. Output energies greater than 1 J per pulse are achieved on several of the strongest lines. In a non-selective cavity an energy conversion efficiency of greater than 35% is obtained with a maximum output energy of 4.6 J. Optically pumped NH₃ is shown to be a flexible and efficient system for the downconversion of CO₂ radiation to the 10-14 μm region. In other experiments, it is shown that optically pumped high pressure mixtures of NH₃ in N₂ are efficient, broadband amplifiers of pulsed CO₂ radiation. In a dilute NH₃ mixture at 6 atmospheres and 200 K, a single pass gain of 150 (21.8 dB) is measured for the 10P(34)CO₂ transition. Gain is observed in NH₃ at pressures as high as 10 atmospheres. Experimental measurements are made for a range of wavelengths in the 10.7 μm region, and the results compared with calculations based on a simplified rate-equation model. The operation of a two-step optically pumped NH₃ laser (using two CO₂ lasers) is examined. Output is obtained from 16-22 μm. Experimental measurements made at 200 K and 300 K are compared to calculations based on an extended rate-equation model. As a result of this work it was shown that a single CO₂ pump laser can be used to obtain 16-22 μm lasing at 200 K.

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