Coherent coupling in frequency-resolved pump-probe spectroscopy
We have studied the influence of coherent coupling on the transient spectra observed in optical pump-probe spectroscopy. If the pump and probe pulses have temporal overlap, a strong increase of the pump-probe signal occurs at probe frequencies close to the pump frequency. This leads to sharp peaks in the transient spectra, which might erroneously be interpreted as spectral holes. We derive an explicit expression for both the delay dependence and the probe-frequency dependence of the pump-probe signal for the case of a homogeneously broadened absorption band. As an illustration, we use this expression to estimate the effect of coherent coupling on vibrational pump-probe spectroscopy on the OH stretch band of hydrogen-bonded systems.