Signal Enhancement in Photothermal Imaging Produced by Three Dimensional Heat Flow

The development of photoacoustic microscopy (SPAM)(1,2) has provided a means of studying the surface and subsurface features of solids including subsurface voids or layer disbonding which modify the efficiency of thermal diffusion into the sample. We have recently introduced a new method of thermal imaging(2) which shares some of the features of SPAM but, rather than acoustic detection, uses the "mirage effect"(4) or deflection of an optical probe beam to determine the sample surface temperature distribution.(5) A theory of photothermal imaging has recently been developed for homogeneous samples(6) (i.e., samples containing no thermal diffusion boundaries important to the experiment). This development includes a full treatment of 3-dimensional diffusion in the sample and the gas. The theoretical results are in good agreement with those obtained experimentally.