Controlling light by light: Optical modulation in chiral nematics

Nonlinear optics of chiral liquid-crystalline media have been in scope of o ur interest for several years. Our previous observations in the subject had already been reported. This paper discusses a possibility of utilising the nonlinear optical properties of liquid crystals for practical purposes. We discuss an idea of "in line" intensity measurements of laser beam. The ide a is based on two optical phenomena which are observed in liquid-crystallin e media possessing a periodically stratified structure: nonlinear optical e ffect and selective light reflection. The effects start to appear by activa ting light intensities of the order of MW/m(2), so the method can be potent ially applied at present to high-intensity light beams (corresponding laser power is approximately 0.1 W), although there are now also prospects to lo wer this value significantly.