The effectiveness of mixing differently polarized light waves at uniaxial nonlinear crystals

General expressions for the nonlinear interaction coefficients are obtained for three methods of mixing light waves at uniaxial crystals in the phase matching directions. Comparison of these coefficients enables one to choose the most effective method of mixing waves. Such a comparison is carried out for the generation of the difference frequency at a lithium niobate crystal and of the sum frequency at a KDP crystal in mixing the radiations of ruby and neodymium lasers.