Frequency-modulated impulse response photothermal detection through optical reflectance. 1: Theory

The 3-D theory of impulse response photothermal detection in opaque (i.e., photothermally saturated) solids through the dependence of the surface temperature optical reflectance on the mathematical equivalent of an optical impulse (the Green's function) is presented. The theory is extended to include the effects of the finite spatial extent of the photothermal laser source. Explicit expressions for the time-dependent temperature field have been obtained in the experimentally important cases of semi-infinite solids and solids of finite thickness in contact with thermally insulating or conducting backings.