Abstract

Recently, mid-infrared photon-echo spectroscopy was used for the first time to measure the homogeneous vibrational linewidth hidden in an inhomogeneously broadened absorption line.¹ In this experiment the intense ultrashort mid-infrared pulses of a free-electron laser were used. However, the time resolution in photon-echo experiments is not determined by the pulse duration, but by the coherence time of the pulses. Hence, time-resolved photon-echo spectroscopy can be performed with incoherent pulses that are much longer than the homogeneous dephasing time constant T₂ but have a shorter coherence time. Here we report on the first application of incoherent mid-infrared pulses to perform photon-echo spectroscopy on molecular vibrations.

© 1997 Optical Society of America