Temperature variation and wave front distortions due to temperature rise and thermal stress, in rotationally symmetric and isotropic optical elements irradiated by periodically repeated short pulses, have been calculated. The analytical expressions of the periodically varying temperature distributions have been obtained by making full use of the periodicity of the pulsed laser system. For the case that the diameter of optical element is considerably larger than the thickness and the temperature variation along the thickness direction is negligibly small, the plain approximation has been used to estimate the phase distortions. The results have shown that the polarization independent phase distributions due to thermal deformations of the optical element may be a problem of concern, especially if one considers the fact that the phase distortions of the light wave may be accumulated after passing through several optics.
A theoretical analysis is presented for third-harmonic generation (THG) in KDP for type I/ type II angle-detuning scheme of high-intensity laser to produce third harmonic radiation near 0.35μm. The effects of the third-order nonlinear susceptibilities (χ<sup>(3) </sup> ), transverse walk-off and diffraction, especially, the effects of third-order nonlinearity and the phase variations on the frequency conversion have been discussed. A split-step algorithm based on the Fast Fourier Transform and fourth-order Runge-Kutta integrator is used. The results shown that the third-order nonlinear interactions decreases the tripling efficiency, and increases of the modulate strength of the output intensity of 3ω radiation. However, adjusting the angular detuning can compensate effectively the effects of third- order nonlinearity. Furthermore 3ω conversion efficiency will drop with the increase of the degree of phase variations, and the improve 3ω conversion efficiency can suppress the 3ω wave amplitude ripples.
Based on our model, a program designed by us can give the distributions of temperature, stress and refractive index inside the laser medium of diode-pumped rod laser. Some displayed results obtained by simulation are in excellent agreement with experimental results reported in the literature.