Influences of self-induced thermal effects on phase matching in nonlinear optical crystals

In nonlinear optical crystals useful for second-harmonic generation, index inhomogeneities introduced by the self-induced temperature profile due to the laser beam influence the phase-matching conditions for nonlinear optical interaction. We have found that broadening of the width of the central peak, increase of asymmetry, shift of the maximum towards higher temperature, disappearance of the subsidiary structure in the second-harmonic power versus temperature, and the reduction of the conversion efficiency for second-harmonic generation may be caused. These effects depend upon the total absorbed power in the crystal, the birefringence variations due to temperature, the thermal conductivity, and the wavelength.