Influence of thermal self-interaction on second harmonic generation in beams with an elliptic cross section

An analysis is made of continuous generation of the second harmonic as a result of thermal self-interaction in beams with an elliptic cross section. It is shown that cylindrical focusing of the fundamental-frequency beam in the direction of noncritical phase matching makes it possible to compensate partly thermal self-interaction only when the beam power is much higher than the critical value. The efficiency of conversion to the second harmonic can also be increased by some misalignment of the wave vectors on the beam axis. In the case of generation in the direction of critical phase matching the efficiency of such optimization methods depends on the ratio of the temperature gradients of the refractive index at both (fundamental and second harmonic) frequencies. Dependences of the harmonic power on these parameters are investigated for different birefringence angles and recommendations are put forward on optimization of the process in a wide range of crystals.