A quasi-phase-matching technique for efficient optical mixing and frequency doubling

Abstract

A detailed theory is presented of the second‐order nonlinear optical interaction in a sequence of crystal lamellae oriented to give quasi‐phase‐matching. The efficiency of second‐harmonic and sum‐frequency generation is analyzed with respect to the orientation of the crystal axes, plate thickness, input intensities, transmission coefficients, dispersion in the intervening medium, and number of lamellae. An energy conserving modification of the small‐signal approximation is introduced. To overcome the Fresnel reflection losses the use of antireflection coatings, optical contacting, and Brewster‐angle incidence is considered with the latter approach emerging as the most promising. A series of experiments are described where 10.6‐μ laser radiation is frequency doubled in a sequence of GaAs plates using Brewster‐angle incidence. The conversion efficiency is investigated as a function of crystal orientation, intensity, and number of plates, and good agreement is found between theory and experiment.