Comprehensive Model for Randomly Phase-Matched Frequency Conversion in Zinc-Blende Polycrystals and Experimental Results for ZnSe

Second-order nonlinear interactions in disordered materials based on random phase matching suggest intriguing opportunities for extremely broadband frequency conversion. Here, we present a quantitative realistic model for random phase matching in zinc-blende polycrystals (ZnSe, ZnS, GaAs, GaP, etc.) that takes into account effects of random crystal orientation and grain-size fluctuations, and includes polarization analysis of the generated output. Our simulations are based on rigorous transformation of the second-order susceptibility tensor in randomly rotated coordinates-to account for random orientation of crystalline domains, and demonstrate a good agreement with our experimental data for ZnSe using a nanosecond lambda = 4.7 mu m source-in terms of variations of the strength and polarizations of the output fields. Also, it is revealed that random phase matching is most suitable for ultrafast (sub-100-fs) interactions with focused beams, e.g., second-harmonic generation, sum-and difference-frequency generation, and optical parametric oscillation, that typically require short (< 1 mm) interaction lengths, where disordered polycrystals can be on a par, in terms of conversion yield, with ideal quasi-phase-matched crystals.