Abstract

Optical radar techniques using heterodyne detection require coherent frequency-controlled laser operation. In laser oscillators, frequency drift is caused by change in the index of refraction within the resonator. Pulsed CO₂ lasers can have significant intrapulse chirp due to three time varying sources of refractive index: thermally induced gas density variations, electron plasma density, and anomalous dispersion when operating off line center. Previous work has focused on the first two of these effects.^1,2 Since the anomalous dispersion effect is dependent on the frequency shift off line center, this source of chirp can be controlled somewhat by judicious use of off-line-center operation, which can partially compensate for the effect of the other chirp sources. Using a computer simulation of the fields within both stable and unstable resonators, a quantification of the frequency drift dependent on an appropriate average of the index of refraction within the resonator has been accomplished.

© 1986 Optical Society of America