We report the experimental results of the optical beam self-focusing and soliton formation in a photorefractive Fe doped lithium niobate (LN:Fe) crystal caused by a pyroelectric effect. The laser beam at 632.8 nm wavelength and with power of 5 mW and a 10 mm length LN:Fe crystal with the controlled temperature in the range of 10–45C are used. The time evolution of the soliton formation shows approximately two times decrease of the optical beam diameter to ~60 m with simultaneous bending of ~140 m opposite to the crystalline C+-axis. The physical model is developed to explain the experimental results. The generated curvilinear waveguiding channels in the crystal are long-living making them promising for applications.
We report the trapping of dielectric micro-particles of CaCO3 via dielectrophoretic forces on the surface of Fe doped LiNbO3 (LN:Fe) crystal with recorded volume holographic grating which provides quasi-periodic space-charge electric field distribution on the crystal surface. The non-diffracting Bessel beam approach was used for optical induction of holographic grating by 20÷40 mW power Bessel beam at 532 nm wavelength in photorefractive Y-cut LN:Fe crystal providing the Bessel lattice periodicity of ~40 m and hologram size on the crystal surface of 4 mm. This approach provides the induction of high contrast 2D periodic distribution of electric field on the crystal surface and high quality 2D patterning of microparticles. The particles are trapped on the crystal surface in the areas of refractive index maxima of the Bessel lattice. The physical model was developed to explain the experimental results. The photovoltaic approach of trapping and manipulation of micro- and nanoparticles is promising for applications in photonics, integrated optics and biotechnology.
We report for the first time a regular optical patterns formation in a laser beam propagating through a Fe doped lithium niobate (LN:Fe) crystal. The process was controlled by pyroelectric effect resulting in self-localization of the regular optical pattern in a single light spot with reduced size and displacement relative to the input beam. The experiments were performed with the use of single mode laser radiation at 632.8 nm wavelength and with beam powers of 0.5 ÷ 10 mW. The LN:Fe sample with 0.03 wt% concentration of Fe and 10 mm lengths along beam propagation was used in the experiments. The switching of the pyroelectric effect in the process was achieved by gradual heating of the crystal in the temperature range of 10 ÷ 42 °C during 130 s. The observed phenomenon of optical patterns formation is explained with the light induced complex refractive index variation with a central minimum (negative lens) and symmetric side maxima (positive lenses) due to photovoltaic effect. Light-induced complex lens produces beam defocusing from the beam center and focusing on the periphery. Mutual interference of the beams leads to the regular light patterns formation. The switching of pyroelectric effect results in the space-charge field modification in the crystal, asymmetric positive lens formation and light self-localization.
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