Low-power (106-μm) laser-beam amplification by thermal-grating-mediated degenerate four-wave mixing in a nematic liquid-crystal film

Abstract

We present a detailed theoretical analysis of degenerate four-wave mixing by a laser-induced thermal grating in a nematic liquid-crystal film. In particular, we show that the coupling of the (strong) pump beam to the first-order diffracted beam can give rise to substantial amplification of a (weak) probe beam. Experimental verification of this effect with a CO2 laser beam is also made. A probe-beam gain of greater than 20 can easily be observed in a 120-μm film with a pump intensity of the order of a few watts per square centimeter.