Two Schemes for Generating Efficient Terahertz Waves in Nonlinear Optical Crystals with a Mid-Infrared CO₂ Laser

Terahertz wave generation is explored on the basis of difference frequency generation in nonlinear optical crystals with a mid-infrared CO₂ laser. The phase−matching angle and the grating period of periodically inverted GaAs in the 100–1000 µm (0.3–3 THz) range are also investigated on the basis of the surface-emitted difference frequency generation. It is found that two schemes of phase-matching-applied collinear phase matching and phase-matching-applied non-collinear phase matching are efficient to obtain THz waves.