Thermo-Optical Spectrophotometries in Analytical Chemistry

I. INTRODUCTION A. Background The incorporation of lasers as light sources in analytical spectroscopic instrumentation has resulted in spectacular detection limits. These detection limits arise from several unique properties of laser radiation. As an example, the spectral purity and high power of the laser facilitates detection of individual gas phase atoms with isotopic resolution by both fluorescence and ionization techniques.1−3 The temporal coherence of the laser has been used to discriminate signals generated by very fast scatter processes from relatively slower luminescence relaxation.4, 5 In addition, the spatial coherence of the laser allows measurement by thermo-optical techniques of very small absorbance, the subject of this review. A recent review in this journal considered the related technique of photoacoustic spectroscopy, another high-sensitivity absorbance method.6