Transformation of optical properties of crystal media (KGW, YVO4) exposed to quasi-continuous laser radiation in the range of the transmission band of the medium

We present data from an investigation of the properties of the blue (475 nm) and green (520–560 nm) emissions that arise from KGW and YVO₄ crystals upon excitation into the transmission band of the medium by continuous infrared laser radiation the power density of which is in the kilowatt range. As distinct from standard luminescence, the two emissions are narrowband, have a structure, and show a nonlinear character. In the case of blue emission, it is noted that, simultaneously with laser radiation, the crystal experiences a significant action of Raman generation. We demonstrate the excitation of the blue emission by the laser radiation alone and present its dynamic characteristics, showing that its intrinsic time differs from the corresponding times of the Raman and laser generations. Our results show that the green emission has an up-conversion nature with the several photons excitation of residual low-concentration erbium ions. We report that the band intensity ratio of the upconversion luminescence of erbium sharply changes with increasing excitation intensity. The nonlinear interaction that is developed in KGW is accompanied by transformation of the transmission. It is concluded that the investigated processes develop in undoped KGW and YVO₄ crystals as a result of a prolonged exposure of the medium to the laser radiation, which leads to a change in its properties.