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A spectrally composite reconstruction approach for improved resolution of pulsed photothermal temperature profiling in water-based samples

We report on the first experimental evaluation of pulsed photothermal radiometry (PPTR) using a spectrally composite kernel matrix in signal analysis. Numerical studies have indicated that this approach could enable PPTR temperature profiling in watery tissues with better accuracy and stability as compared to the customary monochromatic approximation. By using an optimized experimental set-up and image reconstruction code (involving a projected ν-method and adaptive regularization), we demonstrate accurate localization of thin absorbing layers in agar tissue phantoms with pronounced spectral variation of a mid-infrared absorption coefficient. Moreover, the widths of reconstructed temperature peaks reach 14–17% of their depth, significantly less than in earlier reports on PPTR depth profiling in watery tissues. Experimental results are replicated by a detailed numerical simulation, which enables analysis of the broadening effect as a function of temperature profile amplitude and depth.