Thermal Background Suppression in Rayleigh-Type Nondegenerate Four-Wave Mixing Based on Field-Correlation Effects

We apply the principle of field-correlation to the thermal background suppression of the Rayleigh-type nondegenerate four-wave mixing spectra,which have been employed for the measurement of ultrafast longitudinal time in the frequency-domain recently. Conditions, under which contributions from the thermal grating can be neglected,are given and numerical results that illustrate the validity of this method are presented.