Abstract: A method for efficiently controlling sum frequency mixing and second harmonic generation within Q-switched laser oscillators. A nonlinear crystal is placed at either the intersection point of two otherwise independent laser oscillators (in the case of sum frequency mixing) or within a single laser resonator (in the case of second harmonic generator). During the build-up phase of the oscillator temporal development. (i.e., after the Q-switch has been opened but before the laser has reached threshold), a nonlinear optical crystal controlled by high voltage is employed to significantly reduce the efficiency of the frequency conversion process. In a preferred embodiment, the nonlinear optical crystal reduces the efficiency of the birefringent nonlinear optical process by spoiling the dephasing of the multi-wave interaction. After threshold has been reached in the resonant cavity, the conversion efficiency is increased at some desired rate.

Abstract: A general method which extends quadrature techniques to Type I nonlinear optical parametric interactions. In one embodiment, a pair of either uniaxial or biaxial birefringent nonlinear optical crystal elements are serially arranged and oriented so that each crystallographic axis in one conversion means is parallel to the corresponding axis in the second conversion means. Two colinear input fundamental laser fields with parallel polarizations propagate through both crystals, generating a sum-frequency output field. Between the two crystals, a harmonic waveplate is inserted that rotates only the polarization of the sum-frequency field generated in the first conversion means by 90.degree. about its propagation axis. The net polarization rotation of each of the two residual fundamental waves which remain after the interaction in the first conversion means is zero.