Photorefractive Liquid Crystal Light Valve Research Articles

Squeezing of laser pulses in nonlinear-optical LC cell

Controllable compression of the temporal duration of light pulses takes place in a liquid crystal medium via self-action processes of beam mixing, namely, a dynamic Bragg grating formation by incoming light waves with their consequent self-diffraction on the same recorded grating. Wherein, the laser pulse duration should be comparable with the time relaxation constant of the medium while the extent of the temporal compression is controlled by the variation of the input pulse durations and the value of nonlocal response. Full Text: PDF ReferencesU. Bortolozzo, S. Residori and J. P. Huignard, "Beam coupling in photorefractive liquid crystal light valves", J. Phys. D: Appl. Phys. 41, 224007 (2008). CrossRef P. Guner and J.P. Huignard, Photorefractive Matrials and their Applications, 1, 2, and 3 (New York Springer) and references therein (2006). CrossRef S. Bugaychuk and E. Tobisch, "Single evolution equation in a light-matter pairing system", J. Phys. A: Math. Theor., 51 (12), 125201 (2018). CrossRef S. Bugaychuk and R. Conte, "Nonlinear amplification of coherent waves in media with soliton-type refractive index pattern", Phys. Rev. E 86, 026603 (2012). CrossRef A. Iljin, "Light-induced order modification – The way to speed up", Journal of Molecular Liquids 267, 38 (2018). CrossRef A. Iljin, "Transient Modulation of Order Parameter and Optical Non-Linearity in a Chiral Nematic Liquid Crystal", Mol. Cryst. Liq. Cryst. 543, 143 (2011). CrossRef D. Wei, A. Iljin, Z. Cai, S. Residori, and U. Bortolozzo, "Two-wave mixing in chiral dye-doped nematic liquid crystals", Opt. Lett. 37, 734 (2012). CrossRef S. Bugayhuk, A. Iljin, O. Lytvynenko, L. Tarakhan and L. Karachevtseva, Nanoscale Res. Lett., 12, 449 (2017). CrossRef

Beam coupling in photorefractive liquid crystal light valves

Photorefractive liquid crystal light valves (LCLVs) are hybrid devices that combine a nematic liquid crystal layer with a thin monocrystalline Bi12SiO20 (BSO) photorefractive crystal in the form of a cell wall. The device behaves as an optically addressed spatial light modulator, where the photoconductive layer is made of the BSO crystal. Differently from conventional types of spatial light modulators, usually working in retroreflective configuration, the photorefractive light valves work in transmission, thus allowing new applications related to the coupling of the optical beams when they pass through the liquid crystal layer. Here, we review some recent experiments of beam coupling in photorefractive LCLVs. After a characterization of the device in terms of its spatial resolution, which is related to the features of pattern formation in an optical feedback configuration, we present two-beam coupling and optical amplification in single pass experiments. Then, we develop a theoretical model by taking into account the Raman–Nath diffraction of the incoming beams over the thin liquid crystal layer. By using two or more light valves in cascade, we show, both experimentally and theoretically, that the two-wave mixing gain can be enhanced by the Talbot effect related to the multi-passage of the beams through the successive layers of the nematic liquid crystal. Finally, we show that self-pumped phase conjugation can be realized by placing the light valve in a tilted feedback configuration. In this case, the four-wave mixing is spontaneously created through the scattering of the signal beam onto the feedback induced grating.

NONLINEAR OPTICAL APPLICATIONS OF PHOTOREFRACTIVE LIQUID CRYSTAL LIGHT-VALVES

We show a novel nonlinear optical medium, which is formed by coupling a liquid crystal layer to a photoconductive crystal. We show that this medium allows the control of the liquid crystal birefringence in a local and dynamical way, so that large optical nonlinearities are obtained on a large transverse section. The properties of the photorefractive liquid crystal light-valves are used to implement transverse pattern formation, two-wave mixing amplification and phase conjugation.

Self-pumped phase conjugation in a liquid crystal light valve with a tilted feedback mirror

We report self-pumped phase conjugation in a photorefractive liquid crystal light valve with a tilted feedback mirror. This is a new scheme for the self-generation of a phase-conjugate replica and can in general be applied to thin nonlinear layers, opening the way to distortion-correction applications of thin media.

Pattern formation and direct measurement of the spatial resolution in a photorefractive liquid crystal light valve

In a photorefractive liquid crystal light valve, acting as a Kerr-like nonlinear optical medium, we show the appearance of optical patterns induced by a single mirror feedback. The spatial wavelength of the patterns scales with the distance between the mirror and the valve and the contrast of the patterns decreases for decreasing this distance. We use these properties to setup a new optical scheme for the measurement of the spatial resolution of the nonlinear device.