Abstract
The development of a laser diode absorption spectrometer that uses a strong water vapor absorption at 1393 nm is reported. Three spectroscopic techniques were compared in ≈0.4 m of laboratory air, namely, frequency modulation, wavelength modulation, and two-tone frequency modulation spectroscopy. The first two techniques use a single-frequency modulation at 9.2 GHz and 1 kHz, respectively, generated either by a phase modulator operating at 9.2 GHz or injection current modulation at 1 kHz. The two-tone method requires modulation at two frequencies, in this case 9.19 and 9.21 GHz. It is shown that the two-tone method should provide the highest sensitivity for a trace moisture detection system.
© 1999 Optical Society of America
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