Abstract: Optical breakdown in a transparent, non-linear medium used for optical phase conjugation or the like is induced by interaction with the medium of a strong laser beam propagating therethrough, resulting from electron avalanche breakdown and plasma formation. Application of an electrical potential to electrodes disposed across the laser focal volume in the medium causes optically and/or electrically ionized impurities to be removed from the non-linear medium and attached to the electrodes, thereby purifying the medium and raising the optical breakdown threshold. The threshold may be further raised by adjusting the electric potential to a magnitude at which free electrons are removed from the laser focal volume either during an optical pulse or before the arrival of subsequent pulses.

Abstract: An apparatus and method for creating a time-reversed replication of an optical wave front. More specifically, an apparatus and method is disclosed in which a non-linear medium having counter-propagating monochromatic optical waves passing therethrough generates a time-reversed replica of an incident wave, the generation being due to non-linear refraction within the medium. As a monochromatic light-ray beam source irradiates an inhomogeneous, nonabsorbing medium, (e.g., a frosted pane of glass), the wave front of the source beam is broken up during transmission therethrough so that any image information contained within the source beam is unrecognizable from the other side of the frosted glass. According to the present invention, this unrecognizable image, when directed into the non-linear medium containing the counter-propagating optical waves is reflected back as a time-reversed wave due to the non-linear refraction of the medium.

Abstract: An optical harmonic microscope assembly and an examination method which provides for focusing lased coherent light as an incident beam onto a specimen, disposing the optical path of a microscope and the incident beam at a relative angle in a range which is at least as broad as 0.degree.-90.degree., blocking the fundamental frequency of the lased light and viewing light of a harmonic of said fundamental frequency generated by nonlinear diffraction by said specimen.