Pulsed and Doppler CO2 laser radar

Abstract

This paper discusses the design, construction, and performance tests of a feasibility model of a CO2 laser radar suitable for the simultaneous determination of velocity and range. The highly stable Q-switched CO2 laser transmitter features an intracavity Stark cell filled with methylchloride and a grating that tunes the laser to the P(26) line of the P branch of the 0 0°1-0 2°0 band at about 9.6 μm. By adjusting the gas pressure in the Stark cell the laser emits a train of Q-switched pulses riding on top of highly stable cw oscillation. For coherent detection we require that the generation of the Q-switched pulses does not destroy the frequency stability of the cw oscillation. Heterodyne experiments have been conducted by beating the return signal against another stable laser, and the results indicate that the instabilities have been held to less than 100 kHz thus allowing a velocity resolution of better than 1 knot. The use of the Stark effect in gases requires the match of an absorption line with a CO2 laser emission line. Two gases, methylchloride and difluoroethylene, have been used to Q switch a 20-W CO2 laser.