Abstract

One can apply two-tone frequency modulation spectroscopy techniques to the detection of gas-phase species by using laser light scattered from hard targets. High sensitivities are demonstrated, with a minimum detectable absorption of 10⁻⁴ possible with a simple apparatus. The effects of laser speckle on the FM signal are described, and we show that the detection signal-to-noise ratio can be improved by collecting an increased number of speckle cells.

© 1996 Optical Society of America

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