Abstract
We have studied two-beam-coupling processes related to the generation of optical axis gratings in liquid crystals (LCs) due to the electromagnetic torque acting on the orientation of LCs in superimposed laser beams with spatially modulated polarization. Such gratings result in efficient coupling between the laser beams controlled by the frequency shift introduced between the beams at infrasound frequencies. Larger than 80% efficiency of energy transfer from a pump to a signal beam is reported at power density levels of the laser beams at . The distinction between pump and signal beams is relative, since the sign of the frequency shift rather than the power ratio between the beams determines the direction of energy transfer. The experiments were performed for radiation at a wavelength; high optical nonlinearity and low absorption make LCs suitable for use in visible and near-IR spectra, particularly in high-power laser systems. We have characterized the main fundamental features of the process of recording dynamic orientation gratings, plotting the gain spectra for several LCs and verifying the good quality of the amplified signal beam even for a strongly distorted pump. The obtained results set the groundwork for a variety of novel opportunities and applications that include combining high-power laser beams and wavelength division multiplexing at an ultranarrow interval of frequencies of the order of .
© 2006 Optical Society of America
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