A narrow-bandwidth (cw) phase-fluctuation laser-heterodyne interferometer for trace-gas detection is described. Performance was evaluated using both Stark-effect modulation and conventional beam chopping. Sensitivities of 10(-8) cm(-1) were obtained in both cases. However, when Stark-effect modulation was employed, the usual background signal caused by interfering absorbing species and windows could be subtracted from the overall signal. In this mode, a detection limit of 5 parts in 10(9) (ppb) NH(3) in air was obtained.
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Campillo et al. (1980) studied this question.
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