Changes in the nonlinear optical properties of a DKDP crystal under the influence of high-temperature photorefraction

The change in phase-matching conditions in second-harmonic generation in DKDP crystals under the influence of the photorefraction appearing because of additional illumination of a sample was investigated. Comparison of the results of a calculation carried out on the basis of a phenomenological model with experimental data revealed their fundamental disagreement. Direct measurements were made of the internal field in the sample induced on photorefraction. A relationship was observed between the phase-matching conditions and the spectroscopic properties of the photorefraction, because irradiation of the sample ensured the excitation of both the photorefraction and of nonlinear optical effects. The internal electric field strength up to 0.5 kV cm^-1, obtained for an energy density of the pulsed irradiation of the medium of 10 — 20 J cm^-2 indicates the necessity to take into account the internal field in the majority of situations when nonlinear optical effects are excited.