The application of external feedback in the laser spectroscopy of nonlinear media

A new spectroscopic technique to gain information on the nonlinear constants of optical materials is presented. This technique is made possible due to the point that the application of an external controlled negative feedback (CNF) circuit to an intracavity nonlinear cell results in the generation of extended boundaries of the stability for the laser beam. This effect is analyzed using a semiclassical set of equations that govern laser oscillation. Measurements are made on systems containing either an instantaneous CNF circuit or an integrating CNF circuit. The integrating CNF circuit produces a maximum in the measurement accuracy. The suitability of the technique is experimentally verified with a KD*P multicomponent photorefractive medium. The method has been generalized for application to nonlinear-optic and photorefractive materials including cases when the effect is a product of several subsystem actions.