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24 September 1987Stable Lasers In Dynamic Environments
Short term laser frequency stability is an important parameter affecting target velocity resolution of a coherent laser radar (ladar) system. This paper presents CO2 laser design considerations which affect frequency stability, measures the frequency sensitivity of the laser to various stimuli, and evaluates performance of an actively stabilized, unmodulated output CO2 laser. A frequency modulated acousto-optic modulator is used to produce a control beam which is passed through a low pressure SF6 gas cell and the laser is locked to the resultant saturated absorption peak. This investigation demonstrated laser frequency instability for periods up to 50 msec of less than ±500 Hz when the piezoelectric transducer (PZT) drive voltage was off, and about ±900 Hz when the laser was free running with voltage applied to the PZT. When a 90 dB, 200 Hz acoustic disturbance was applied, the frequency instability was less than ±4.3 kHz and ±2.8 kHz when the laser was free running and locked, respectively.