Thermally nonlinear laser photoacoustic tomography

The formation of a laser photoacoustic response in an inhomogeneous medium is considered taking into account the temperature dependence of the coefficient of thermal expansion. It is shown that in the one-dimensional or three-dimensional cases in the presence of individual absorbing centres (spherical particles), the shape of the photoacoustic response is the wavelet transform of the spatial distribution of heat sources. The parameters (level) of the wavelet expansion are determined by the characteristics of the laser pulse. The possibility of multiscale wavelet analysis of the medium structure is demonstrated by the example of a numerical model. The possibility of direct visualisation of individual cells in biological tissues is discussed.