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Abstract
In this work, the laser-intensity-modulation method (LIMM), e.g. the determination of the spatial polarization profile from the pyroelectric current spectrum caused by the interaction of thermal waves generated by an intensity modulated laser and the unknown polarization distribution, is applied for investigation of sputtered PZT thin films on a thermally coupled bulk silicon substrate or a thermally isolating membrane, respectively. To investigate thin films with a thickness of about 1 μm the modulation frequency of the laser was extended up to 2 MHz. The reconstruction of the spatial polarization distribution requires to solve a Fredholm's integral equation of the first kind which is a so called “ill-posed” problem. For deconvolution of the inverse LIMM problem several approaches like power series trial functions and Lagrange polynomials are used and compared with the original Fourier series approach for LIMM introduced by S.B. Lang. To obtain a non-oscillating solution of the inverse LIMM-problem the Tikhonov regularization method is used.
