Transformation of amplitude–phase characteristics of focused laser radiation with the aid of nonlinear optical effects in acetone and liquid nitrogen

An experimental study demonstrated that the relative intensity of stimulated backscattering, the efficiency of conversion into stimulated backscattering, and the transmission were largely determined by the position of a focal constriction of a lens focusing a laser pulse in an active medium. Focused pumping ensured that the intensity of a phase-conjugated wave and the conversion efficiency had optima at different positions of the focal constriction. The amplitude and phase of laser radiation focused in acetone changed considerably as a result of two-photon absorption and due to the hf Kerr effect. A nonlinear medium therefore made it possible to observe phase objects and inhomogeneities of strongly reflecting surfaces illuminated by laser pulses.