Abstract

Cascade THG proves to be a versatile tool probing the sign and value of all second order nonlinear tensor components. Generally the χ⁽²⁾ tensor form will allow all six types of effective nonlinearity, although only types allowed by dispersion are phase matchable. Cascade THG poses no such a limit to THG along phase matchable directions for SHG and SFG of any type. If all six types of effective nonlinearities are possible then we get for the F(β) function [1] for THG, resolved along the slow "s" and fast “f” directions, the dependencies from the table. The angle p stands for the input polarization direction and is measured from the "f" polarization direction and the a = sff / fff, b = sff / ssf, c = ssf / sss, d = sff / sss, e = ssf / fff stand for ratios of effective nonlinearities of two second order processes. Each of these functions will generate a typical pattern, very sensitive to the sign and the value of tensor components. Wave vector mismatch is a part of these ratios and should be accounted for at appropriate wavelengths. Most notable are the SFG cases that will generate a sixfold dependence when the d and e ratios are negative and a fourfold one when positive. They will always couple non-phase matchable components, whatever the type of SFG is.

© 1998 IEEE