Novel approach for the analysis of infrared photothermal microscopy data

We consider a photothermal microscope based on spatially resolved infrared (IR) radiometric measurement to perform thermal diffusivity measurements. The nonlinearity in the IR emission due the continuous temperature distribution and the finite resolution of the collecting optics makes the radiometric scan distorted with respect to the thermal wave distribution at the sample surface. These distortions, which are responsible for raising the phase signal profile and hence for a thermal diffusivity overestimate, are further enhanced in the case of a reduced spectral bandwidth (≈2–5 μm) as compared to the typical range 2–12 μm typically offered by common HgCdTe detectors. An approach to estimate thermal diffusivity for distorted data is presented here. The fundamental idea is constituted by the possibility of evaluating the quantities necessary for signal deconvolution directly from the experimental data obtained for properly selected conditions. The method is applied to measure the thermal diffusivity of transparent samples like BK7 glass by using a CO₂ laser as pump beam. © 2003 American Institute of Physics.