Third-order nonlinear optical effects exhibited by Gold-Platinum nanoparticles in a Titanium Dioxide thin solid film were induced by a two-wave mixing configuration with digitally-modulated irradiance profiles. The nanomaterials were prepared by a sol-gel method, and a spinning coating technique was employed for the preparation of the samples in thin film form. We used a Nd:YAG laser system at 532 nm wavelength and 4 nanosecond for the exploration of the thirdorder optical nonlinearities. The characterization of the morphology and optical transmittance was carried out by transmission electronic microscopy and UV-vis spectroscopy studies; respectively. A round continuously variable nonlinear refractive index was proposed to generate twisted light by nanosecond pulses in the sample. The system was designed with a randomly distributed density of the nanoparticles. This technique can be considered an alternative for performing ultrafast all-optical instrumentation functions.
Speckle fringe patterns modulated by the third-order nonlinear optical behavior of Gold-Platinum nanoparticles in rotation were analyzed by a two-wave mixing configuration. Random interference patterns derived by speckles were obtained by employing a Nd:YAG laser system featuring nanosecond pulses at 532 nm wavelength for the measurements. The nanostructured samples were prepared by a sol-gel method and contained in a water suspension. Transmission electronic microscopy, UV-vis spectroscopy and Energy-dispersive X-ray spectroscopy studies were undertaken in order to characterize the samples. The bimetallic nature of the nanoparticles gave origin to an optically anisotropic response related to nonlinear optics enhanced by plasmonic excitations. The orientation of the samples produced important changes in the ratio between the real and imaginary parts of the third-order nonlinear optical susceptibility. Gyroscopic properties of the samples confirmed the possibility to identify mechanical motion of the system through the evaluation of induced birefringence and multi-photonic absorption. Vectorial self-diffraction signals generated by two-wave mixing experiments were explored to reveal the mechanisms responsible for the nonlinearities observed. The nanoparticles were incorporated in randomly distributed cells in order to monitor their mechanical activity by recording speckle fringe patterns. A self-focusing effect resulting from a positive nonlinear refractive index in the nanoparticles allowed us manipulating the location of the speckle fringe pattern; and then, a focusing system dependent on irradiation was proposed for the observation of mechano-optical processes. Nonlinear optical interactions for performing ultrafast all-optical instrumentation functions can be contemplated.
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