Thin-sample limit for time-resolved terahertz spectroscopy

The retrieval of the primary (subpicosecond) photoproducts in small-band two-dimensional time-domain terahertz spectroscopy has succeeded only in a few model systems, due to the complicated correlation between the two time parameters. We show that the nature of the primary photoproducts is revealed upon differentiating the measured time-domain spectra with respect to the pump-probe delay. An analytical treatment is given in the thin-sample limit, which distinguishes unambiguously between excitons and free charge carriers. This treatment gives a fair description of the data even for thick samples, including the subpicosecond timescale. (C) 2010 American Institute of Physics. [doi:10.1063/1.3505340]