  In this letter we address the numeric inversion of optoacoustic signals to
initial stress profiles. Therefore we put under scrutiny the optoacoustic
kernel reconstruction problem in the paraxial approximation of the underlying
wave-equation. We apply a Fourier-series expansion of the optoacoustic Volterra
kernel and obtain the respective expansion coefficients for a given
"apparative" setup by performing a gauge procedure using synthetic input data.
The resulting effective kernel is subsequently used to solve the optoacoustic
source reconstruction problem for general signals. We verify the validity of
the proposed inversion protocol for synthetic signals and explore the
feasibility of our approach to also account for the diffraction transformation
of signals beyond the paraxial approximation.
