Effects of optothermal nonlinearities on photothermal beam deflection

The usual theory of the photothermal probe beam deflection, which is normal ly used for the thermal characterization of solids, is based on the assumpt ion that the optical refractive index of the air surrounding the heated sam ple behaves linearly with the temperature. Here we study the effects of the nonlinear variation of the refractive index with higher air temperatures i n front of the sample. These optothermal nonlinearities become important, w hen the photothermal probe beam deflection is applied at higher temperature s to analyze the effects of thermal ablation and erosion of heated surfaces . Examples of measurements in front of a heated vertical plate are presente d and compared with theory. (C) 1999 American Institute of Physics. [S0021- 8979(99)05103-8].