Modeling aspects for high precision absorption measurements

Abstract

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