Pulsed illumination of a sample, e.g., of a biological tissue, causes a sudden temperature\nincrease of light absorbing structures, such as blood vessels, which results in an outgoing acoustic\nwave, as well as heat diffusion, of the absorbed energy. Both of the signals, pressure and temperature,\ncan be measured at the sample surface and are used to reconstruct the initial temperature or pressure\ndistribution, called photoacoustic or photothermal reconstruction respectively. We have demonstrated\nthat both signals at the same surface pixel are connected by a temporal transformation. This allows\nfor the calculation of a so-called acoustical virtual wave from the surface temperature evolution\nas measured by an infrared camera. The virtual wave is the solution of a wave equation and can\nbe used to reconstruct the initial temperature distribution immediately after the excitation pulse.\nThis virtual wave reconstruction method was used for the reconstruction of inclined steel rods in\nan epoxy sample, which were heated by a short pulse. The reconstructed experimental images\nshow clearly the degradation of the spatial resolution with increasing depth, which is theoretically\ndescribed by a depth-dependent thermographic point-spread-function.
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