Photothermal spectroscopy as a sensitive spectroscopic tool

Photothermal spectroscopy has emerged as a popular spectroscopic technique over the past decade because it is convenient and sensitive. It is convenient since a wide range of samples of all phases from highly opaque, light- scattering or reflective to highly transparent materials can be measured to some level of accuracy over a broad spectral range with little or no sample preparation. It is sensitive since, in principle, it is a 'zero background' technique, unlike the tradition extinction technique to measure absorption. However, in practice, various sources of noises become significant when the absorption approaches the part-per-million level or below, and various considerations of noise suppression and signal enhancement are essential to exploit photothermal spectroscopy, in particular, photoacoustic spectroscopy and probe-beam deflection spectroscopy. The authors consider here the physical basis for signal generation and enhancement, as well as noise sources and reduction schemes for pulsed and continuous-modulated excitations. Examples of experimental techniques are given to illustrate the points.