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

Abstract

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 $\ensuremath{\sigma}(\ensuremath{\omega},\ensuremath{\tau})$, where the dependence on frequency $\ensuremath{\omega}$ describes the intrinsic properties of the charge carriers and the dependence on pump-probe delay $\ensuremath{\tau}$ describes their population dynamics. It is shown that there are significant complications in obtaining this quantity from experimental data for $\ensuremath{\tau}$ 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.