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
(010.7340) Atmospheric and oceanic optics : Water
(300.0300) Spectroscopy : Spectroscopy
(300.1030) Spectroscopy : Absorption
(300.6260) Spectroscopy : Spectroscopy, diode lasers
(300.6380) Spectroscopy : Spectroscopy, modulation
Christopher S. Edwards, Geoffrey P. Barwood, Patrick Gill, Bernd Schirmer, Holger Venzke, and Adrian Melling, "Development of an IR Tunable Diode Laser Absorption Spectrometer for Trace Humidity Measurements at Atmospheric Pressure," Appl. Opt. 38, 4699-4704 (1999)