A new two-wave-mixing interaction with gain through a Bi12SiO20 liquid-crystal light valve is presented. We show that the diffraction of a Pump beam in the direction of a weak signal leads to a net amplification of the signal beam, with no need for a phase shift between the interference pattern and the induced index grating. A two-wave-mixing gain of 10 and a 150-ms response time are obtained with a 8.8-mu m-thick liquid-crystal layer, a total intensity of the interacting beams of only 200 mu W/cm(2), and an ac external voltage of +/- 6 V. Image amplification is also demonstrated. (C) 1997 Optical Society of America.
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