科研之友
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摘要
Doped LiNbO3 crystal is one kind of photorefractive mediums which are used for optical storage. When light passes through LiNbO3 crystal, it will cause local refractive index change and form noise grating. The noise grating diffracts the incident light, transferring part of the light energy to the scattered light, namely, light-induced scattering. In recent years, the modulation instability, generation process and energy transfer efficiency of light scattering in LiNbO3 crystals have been widely studied. Since a single component of linearly polarized light is used for the incident, no variation of the polarization state of the outgoing light is observed. However, considering the difference of energy transmission efficiency between o-light and e-light, it is reasonable to guess that the polarization state of the outgoing light may change when another light is incident. According to our investigation, there is no research in this field. In this work, the variation of the polarization state of LiNbO3:Fe crystal during the light-induced scattering process is reported. The circularly polarized light is focused into a thin light sheet and irradiated on the crystal with the c-axis along the vertical direction. The light scattering phenomenon at different incident angles is studied. In the tens of minutes from the generation of the scattered light to the steady state, the scattered light mainly grows in the direction parallel to the c-axis, and there is also a component in the direction parallel to the light sheet. The growth rate of scattered light decreases with the increase of the incident angle. Further observation manifests that the circularly polarized light becomes ordinary elliptically polarized light after passing through the crystal, and the ellipticity varies with the incident angle. Combined with the noise grating formed in the crystal, the scattering model of circularly polarized light is established, and the reason and mechanism of polarization state change are analyzed through calculation. Qualitative analysis shows that the ellipticity of scattered light is related to the transmission coefficient τ and azimuth angle, and the left-handed or right-handed polarization state is also related to the phase difference δ between o-light and e-light. This discovery proposes a method to generate elliptically polarized light using the light-induced light-scattering properties of photorefractive crystals, which can be applied to optical storage and photonic lattice based on photorefractive materials.
