Abstract

Recent advances in tunable laser diodes and their availability at multiple wavelengths in the near-IR has opened a new era of spectroscopic gas concentration measurement techniques. By adjusting temperature and injection current, the laser diode can be tuned to the wavelength of a molecular resonance of interest, and the absorption can be measured and used to obtain concentration. The injection current can also be modulated, allowing for synchronous detection schemes such as wavelength and frequency modulated spectroscopy (WMS and FMS) which effectively bypass the large 1/f noise component of the laser diode.1-4 In this paper, a new WMS technique is presented which measures phase due to the anomalous dispersion around a resonance for trace gas detection.

© 1998 Optical Society of America