Modeling aspects for high precision absorption measurements

摘要

Collinear photothermal deflection spectroscopy (PDS) is a widely used method for the spatially resolved determination ofthe optical attenuation coefficient. In this work we rigorously model the signal contributions in PDS on semiconductorsbelow the band gap energy. The dependencies of the PDS signal on selected experimental parameters (pump beamintensity, crossing angle, chopper frequency and distance from the pump beam focus) are computed and compared withprevious calculation results that are based on simplified assumptions. We find that for high pump beam intensities andsample materials with high two photon absorption coefficients beside the mirage effect nonlinear absorption mechanismshave a strong impact on the signal. Furthermore, we show that angular deflection effects can significantly enhance the PDSsignal. For example, the conical refractive index field due to the pump beam divergence leads to an angular deflection atreadout points outside the pump beam focus. Considering these additional signal contributions is crucial to determineproper absorption properties.