Abstract

Tunable diode laser spectroscopy (TDLS) is one of the most successful techniques for trace-gas environmental monitoring [1-3]. By modulating the light source at high frequency for suppressing the noise [2], frequency modulation or wavelength modulation TDLS can measure optical absorption in atomic or molecular samples with high resolution and sensitivity. Apart from these absorptive techniques, there exists a group of zero-background spectroscopic methods [3], e.g. laser-induced fluorescence spectroscopy, photo-acoustic spectroscopy, and polarization spectroscopy. Here a spectroscopic signal rises from a zero or low background with little noise and these methods therefore can achieve good signal-to-noise ratio (SNR) even without any modulation on the light source.

© 2009 IEEE