In this paper, the nonlinear responses and optical properties modification in SK3 glass sample are investigated. The nonlinear responses measurements were performed by using of nonlinear transmission monitoring of 200 fs at 800 nm laser pulses. The optical power limiting threshold of the sample is measured to be about 40 mJ/cm^{2}. The decrease of transmitted intensity is about 63% compared to the theoretical linear transmission at 270 mJ/cm^{2} incident pulse energy. For prediction of the experimental nonlinear behavior results, a theoretical model based on three-photon absorption and absorption of free carriers is presented. By fitting of experimental data with theoretical model, three-photon absorption coefficient and free-carrier absorption cross-section are reported. The photo-induced optical properties modification of the SK3 sample is investigated also. The modifications that appear as darkening are observed below breakdown threshold intensity. To analyses of modified region sizes, the laser pulse energy accumulation model is applied.
In this paper, the photochromic oxide glass sample under interaction of 200 fs laser pulses at 800 nm wavelength is studied. Two types of laser-induced modifications, bleaching and darkening, are observed. The induced darkening is observed inside the bleached volume. The effect of incident laser shot number and pulse energy on the bleached and darkened area are investigated. The pulse energy accumulation model is applied to investigation of both bleached and darkened area sizes. The bleaching and darkening modification fluence threshold are determined for single and multi-shot laser pulses.
Two-photon spectroscopy has expanded the scope of studies of excited states of ions and has also enabled the examination of the validity of conventional theories. In this study, the direct theoretical calculation of the two-photon intraconfigurational crystal field transitions of ^{7}F_{6}(Γ_{1g}) → ^{5}D_{4} of Tb^{3+} in Cs_{2}NaTbCl_{6} has been performed, based on third-order perturbation theory including electric dipoles and spin-orbit coupling. The core 4f^{7} (^{8}S_{7/2}} Γ_{6}, Γ_{7}, Γ_{8}) and 4f^{7}(^{6}P_{7/2} Γ_{6}, Γ_{7}, Γ_{8}) states coupled with 5d(Γ_{3}, Γ_{5}) are taken as the intermediate states. The calculated transition intensity ratios are in good agreement with the experimental results. In particular the two-photon transition ^{7}F_{6}(Γ_{1g}) → ( Γ_{1g})^{5}D_{4} is allowed in third-order perturbation instead of the proposed fourth-order process by Ceulemans et al. using the Judd-Pooler-Downer model. The inconsistency between the two studies arises from the failure of application of the Judd-Ofelt closure approximation. The closure approximation does not only simplify the two-photon calculation but also sacrifices the physical accuracy by changing the selection rule of the two-photon transition from that of two electric dipole transitions to that of one electric quadrupole transition.
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