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Abstract
Optical-pump-terahertz-probe (OPTP) experiments are widely employed to study the dynamics of photoexcited carriers in semiconductors. In these experiments, due to the long wavelength nature of terahertz (THz) probe radiation, the probe beam can be focused only to a spot size in the mm range. To ensure homogeneous excitation of the probed sample region, a significantly larger optical pump beam spot size must be used, which is often difficult to implement in the experiment. Frequently used experimental geometries employ beam paths that result in small pump beam spot sizes, leading to spectral distortions of the sample response, translating to uncertainties in calculated THz conductivities and fitted Drude conductivity models, for example. We investigate the influence of pump beam spot size on benchmark OPTP experiments and evaluate model calculations to estimate the induced deviations. We demonstrate the impact of this effect on the acquired data with different dependencies on the investigated sample and the employed experimental configuration. We can provide guidelines for optimal configurations for the most commonly employed experiments.
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