Papers by Keyword: Second-Harmonic Generation

Abstract: The kinetics of the orientation of Disperse Red 1 (DR1) molecules embedded in nanostructured Polymethylmetacrylate (PMMA) films was studied under the effect of an intense constant electric poling field. The changes in the orientation distribution of the DR1 molecules were followed by Second Harmonic Generation (SHG) measurements. The SHG signal was recorded as function of time at three different temperatures. We focused on both, the signal increases under the presence of the poling field and the signal decays without the poling field. The studied PMMA films were nanostructured by the incorporation of ionic surfactants as the Sodium Dodecyl Sulfate (SDS) and the Cetyl Trimethyl Ammonium Bromide (CTAB) during their preparation. The kinds of nanostructures obtained in the films were determined by means of X-ray diffraction (XRD) measurements. Substantial differences in signal intensity and in growth and decay rates between amorphous and nanostructured films were found.

Abstract: Tellurite glasses exhibit attractive optical properties such as high refractive index, high transmittance in the infrared-to-visible region, and large third-order nonlinear susceptibility. Poled tellurite glasses also show second-harmonic generation (SHG) as revealed by the present authors. However, there exist many unresolved problems in second-harmonic generation of oxide glasses; SH intensity is low and it decays at room temperature. In this work, the effect of Al2O3 addition on SH intensity and its decay has been explored for thermally poled sodium tellurite glasses. The decay rate of SH intensity is reduced by the addition of Al2O3. The result is similar to those reported for phosphate and silicate glasses containing Al2O3. Also, the glasses poled at a voltage of 4 kV manifest optimum poling temperature lower than that for the same glasses poled at 3 kV.

Abstract: Monovalent silver ions have been introduced in a sodium niobium borophosphate glass by poling the glass under heating and high voltage. A silver thin film electrode was previously deposited on the glass surface and put in contact with the anode. Second harmonic generation (SHG) has been obtained after the thermal poling treatment. The SHG signal has been studied through an analysis of transmitted polarized Maker-fringe patterns. The transmitted current curves during poling are registered and compared to the curves obtained from poling of the natural glass by the use of ndoped silicon anode. It indicates a complex space-charge-migration process during the poling treatment resulting in modification of the nonlinear SHG glasses signal profile.

Abstract: Transparent fresnoite(Ba2TiSi2O8) glass-ceramics considered as a new type of non-linear optical materials have been prepared by controlled heat treatment in the system xK2O-(33.3-x)BaO-16.7TiO2-50SiO2(0≤x≤20 mol%), and optical properties were investigated. The glassy nature was analyzed by differential thermal analyses. The transparency of glass-ceramics was variable and controllable by the processing parameters like time and temperature. The transparent glass-ceramics showed second harmonic generation (SHG) when irradiated by a 1064nm laser beam (Nd:YAG). The SHG intensity was compared with a Y-cut α-quartz plate.

Abstract: Shorter pulse duration and higher power lasers have accelerated the development of frequency conversion technique using nonlinear optical crystals for laser precision microfabrications. Previous theoretical studies concerning frequency conversion supposed one-pulse irradiation; accordingly, the influence of the temperature change of crystal induced by laser absorption was not considered, although practical frequency conversions are used with repetitive irradiation. Therefore, researches and developments of harmonic generation with repetitive irradiation have been approached experimentally or empirically. In this study, second harmonic generation considering laser absorption was analyzed theoretically. Output second harmonic pulse shape influenced by repetitive irradiation was evaluated, supposing that the intensity distribution of input pulse was temporal- and spatial-Gaussian. It was quantitatively revealed that a beam profile of output second harmonic pulse, especially generated by high input intensity, is distorted temporally and spatially even during extremely short time-ranges of one pulse. Our analysis suggests the possibility that this pulse distortion influences on processing accuracy.

Abstract: Homogeneous crystal lines were fabricated at the surface of 8Sm2O3.37Bi2O3.55B2O3 glass by irradiations of cw Nd: YAG laser (λ=1064 nm) with laser powers of 0.7-0.9 W and laser scanning speeds of 3-5 μm/s. It was confirmed from micro-Raman scattering spectra that the lines consist of nonlinear optical SmxBi1-xBO3 crystals showing second harmonic generations. The curved crystal lines with bending angles of 0∼90° were successfully written by just changing laser scanning directions. The light (λ=632.8 nm) transmission was confirmed for a crystal line (length: 850 μm) with two bending angles of ±30o, where significant light scattering losses were not observed at the bending points. We propose that the curved crystal lines written by YAG laser irradiations have a high potential for applications in optical waveguides.