We present theoretical and experimental results of the leading order angular correlations of second harmonic light generated inside random media, for both the transmission and reflection geometries. We find the striking result that correlations in reflection of the second harmonic light scales with the sample thickness L, in sharp contrast to the corresponding short-range correlation function in reflection of the fundamental light in the linear scattering regime, which scales with mean free path l*.

Phys. Rev. Lett.

de Boer, J., Lagendijk, A., Sprik, R., & Feng, S. (1993). Transmission and reflection correlations of second harmonic waves in nonlinear random media. Phys.Rev.Lett., 71, 3947–3950.