Optical Mixing with Different Relative Polarization of the Beams

Abstract

The phase‐matching condition (Δk=0) for optical mixing of electromagnetic waves with parallel k vectors can be attained for various directions in a crystal, if all combinations of direction of polarization for the primary and the generated beams are considered. The phase‐matching angles are calculated for the different possible combinations in KDP, ADP, and LiNbO₃ at several usual laser wavelengths. The relative strength of interaction for the different combinations for optical mixing is given. Furthermore the sensitivity of the phase‐matching condition upon the angle (θ) between the wave vectors (k) and the optical axis (dΔk/dθ or the ``mismatch gradient'') is calculated. The reciprocal mismatch gradient is an important quantity for calculating the conversion ratio in optical mixing of divergent beams. For some cases the numerical result for the relative strengths of interaction and the mismatch gradients lead to more conversion for divergent beams, if we consider combinations of the three interacting waves where two of them are extraordinary rays.