Intrinsic complications in the analysis of optical-pump, terahertz probe experiments

A general formalism is presented for the interpretation of experiments in which a laser pulse (or pump pulse) creates charge carriers that are subsequently probed by a broadband THz pulse (or probe pulse). The time dependence of the sample properties is described in terms of the conductivity (, ), where the dependence on frequency describes the intrinsic properties of the charge carriers and the dependence on pump-probe delay describes their population dynamics. It is shown that there are significant complications in obtaining this quantity from experimental data for values comparable to the charge carrier response time. Also, in transient THz absorption experiments, fast dynamics in the measured signals may be observed that do not necessarily reflect sample dynamics.