Enhanced nonlinear optical effects in rotationally twinned crystals

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Abstract
We have produced continuously tunable infrared radiation between 4 and 21 μm by mixing the outputs of a ruby laser and a ruby−pumped dye laser in a single rotationally twinned ZnSe crystal. The peak output power of 5 W at 4 μm is approximately 250 times larger than the power obtained from an untwinned ZnSe crystal of comparable length. This enhancement is attributable to randomly spaced rotational twin planes perpendicular to the direction of propagation. Regularly spaced twins should produce an enhancement proportional to the square of the number of twin planes.