Generation of high-contrast narrow-band subpicosecond correlations from broadband stochastic fields

We demonstrate that two broadband stochastic fields generated by use of either parametric frequency conversion or stimulated Raman scattering can be mixed in a nonlinear crystal to produce an output spectrum with a pronounced narrow-band feature. This narrow-band feature, which we show is due to the phase-correlated nature of the beams, is present when the two broadband beams are delayed less than a coherence length relative to each other. We apply this technique to a novel measurement of the field cross-correlation function between two broadband stochastic fields with different center frequencies.