Second-harmonic generation and amplification in an isotropic medium

Summary form only given. It is generally accepted that a second harmonic signal cannot be generated or amplified in an isotropic material due to symmetry conditions that result in all even orders of the nonlinear susceptibility vanishing. In materials with nonvanis hing /spl chi//sup (2)/, dispersion also requires that the material be birefringent in order for the second harmonic process to be phase matched. We present a novel scheme in which amplification of a second harmonic signal can be accomplished in an isotropic material through use of the nonvanishing /spl chi//sup (5)/ of the material, and phase matching is satisfied by adjusting the angle between the signal and pump.