Forward and backward Terahertz-wave difference-frequency generations from periodically poled lithium niobate

We report terahertz-wave generation in the wavelength range of 190 similar to 210 and 457 similar to 507 mu m from forward and backward difference frequency generations, respectively, in a 3.2-cm long multi-grating periodically poled lithium niobate (PPLN) crystal. The grating period of the PPLN crystal varies form 63 to 70 mu m in 1-mu m increments. The extraordinary refractive index of lithium niobate in the THz-wave range was precisely deduced from the quasi-phase-matching condition of the difference frequency generations. (C) 2008 Optical Society of America.