Photothermal spectroscopy using optical beam probing: Mirage effect

Abstract
Optical beam deflection near a heated surface was recently introduced as a method of photothermal spectroscopy. Photothermal spectroscopy (PTS) is closely related to photoacoustic spectroscopy (PAS) in its ability to measure optical properties of opaque solids and liquids. This paper develops a theory of this effect and compares this theory with extensive experimental observations. Both are in excellent agreement. The relationship between this form of PTS and PAS is explicitly developed. Applications to the measurement of thermal diffusivity of gases is described.