Cascaded nonlinear difference-frequency generation of enhanced terahertz wave production

Cascaded nonlinear optical interactions are analyzed for their potential to overcome quantum-defect related limitations on the efficiency of terahertz wave difference-frequency generation. The dispersion of ZnTe permits phase-matched production of a series of Stokes lines from two initial near-infrared beams. As the pump beams run down the Stokes ladder, the number of terahertz photons continually increases. A potential improvement by a factor of 5 is demonstrated in a 0.26-cm-long crystal by use of 25-MW/mm2 pumps at a wavelength of 824 nm.