Generation of time-reversed wave fronts by nonlinear refraction*

We describe a nonlinear method for generating, nearly instantaneously, a time-reversed replica of any monochromatic-beam wave pattern. The method employs the interaction of the incident beam, of arbitrary wave front, with counter-propagating plane “pump” waves in a homogeneous, transparent, nonlinear medium. Media are shown to exist in which time-reversed waves can be generated with high efficiency using available laser pump sources.