Optical Vortex Generation in Nematic Liquid Crystal Light Valves
R. Barboza, U. Bortolozzo, G. Assanto, and S. Residori
Mol. Cryst. Liq. Cryst. 572 (1), 24-30 (2013)
Abstract:A nematic liquid crystal light valve (LCLV) is made by using a photosensitive material as one of the cell-confining walls. The liquid crystals (LCs) are homeotropically aligned and with a negative anisotropy; therefore, they naturally produce topological defects when they reorient under the application of an electric field. In our work, we show that by sending circularly polarized light beams onto the photosensitive wall of the light valve, it is possible to locally induce the reorientation and to generate vortex-like defects that remain, each stable and trapped at the chosen location. We demonstrate the ability of the system to create optical vortices with opposite topological charge that, consistently with angular momentum conservation, both derive from the same defect created in the LC texture.The efficiency of the spin-to-orbital angular momentum conversion is measured as a function of the system control parameters, namely the low-frequency electric field applied to the light valve and the intensity of the optical beam inducing the matter defect.