Longitudinal deviation from phase matching in the generation of a second harmonic of cw laser radiation

An analysis is made of new effects which occur in the generation of a second harmonic of cw laser radiation and are associated with thermal self-interaction. It is shown that a longitudinally inhomogeneous heating of a crystal by an absorbed laser beam reduces the size of the stimulated emission region and lowers the efficiency of a frequency doubler. This effect can be compensated by inhomogeneous (over the length) heating of the doubler crystal. The results of numerical calculations, in which allowance is also made for the diffraction spreading of beams, are in good agreement with the experimental data.