Thermal effects in photothermal spectroscopy and photothermal imaging

The effect of thermal parameters on photothermal spectroscopy and photothermal imaging for certain types of spatially heterogeneous samples has been studied. Results have been obtained for both photoacoustic and photothermal deflection modes of detection. Specific attention has been paid to optical saturation in samples whose properties exhibit gradual spatial changes and to the dependence of the photothermal signal on the individual thermal parameters. Most photothermal spectroscopy has been done using thermally homogeneous samples, and most photothermal imaging using optically saturated samples. In this paper, these limitations are relaxed, and the photothermal signal is assumed to depend simultaneously on gradual spatial variations in the optical absorption coefficient, thermal conductivity, and thermal capacity of the sample.