The dependence of the optimal electric biasing field and the diffraction efficiency on the thickness of the nematic thin film through the degenerate four-wave-mixing process is investigated. For relatively low optical pumps, the optimal bias monotonically increases with thickness, while the corresponding diffraction efficiency increases at first and then decays for a thickness even less than 150 µm, which is well within the phase-matching regime. For stronger pumps, the optimal bias can be doubly valued, and the curve of optimal bias versus thickness shows a closed loop. This behavior is unique to liquid crystals. The main mechanism is due to the twist effect of molecular orientation in addition to the scattering loss. Both the numerical and experimental results show these peculiar phenomena.
© 1993 Optical Society of America
Chen-Lung Kuo, J.-G. Wei, and Shu-Hsia Chen, "Unique behavior of thickness dependence in the nonlinear wave-mixing process with a nematic thin film," Opt. Lett. 18, 592-594 (1993)