Abstract

Frequency chirps within the output pulse of CO₂ lasers limit their usefulness in coherent detection systems. We present an in-depth study of the mechanisms responsible for the intrapulse chirp, so that it may be controlled by suitable laser design. Since on the timescale of a few μs the resonator is mechanically rigid (see below), these frequency variations must arise from refractive index changes within the cavity. Such changes may arise from laser action¹ as well as from discharge induced effects²,³; to avoid confusion the processes associated with the discharge are described first by observing refractive index changes in CO₂-free discharges which cannot lase under our experimental conditions. The method used was to insert the TEA discharge within the resonator of a cw CO₂ laser whose operating frequency was monitored by heterodyning with a cw CO₂ local oscillator. The index changes arising within the discharge thus give rise to frequency changes exactly as would result from the same phenomena in a TEA laser. The beat signal is recorded and the temporal variation of beat frequency extracted from the positions of the zero crossings.

© 1983 Optical Society of America