Terahertz parametric oscillator based on KTiOPO4 crystal

KTiOPO4 (KTP) crystal is used as the nonlinear medium in a surface-emitted terahertz-wave parametric oscillator for the first time. The oscillating Stokes beam propagates along the x axis of the KTP crystal, the pumping beam propagates with a small incident angle theta(ext) to the x axis, and the polarizations of the pumping beam, the Stokes beam, and the THz wave are along the z axis. When theta(ext) is changed from 1.250 degrees to 6.000 degrees, the THz wave is intermittently tuned from 3.17 to 3.44 THz, from 4.19 to 5.19 THz, and from 5.55 to 6.13 THz. The maximum output of the THz wave is 336 nJ, obtained at 5.72 THz with a pumping energy of 80 mJ. The two frequency gaps, from 3.44 to 4.19 THz and from 5.19 to 5.55 THz, are located in the vicinities of the A(1) modes of 134 and 178.7 cm(-1), which are strongly infrared absorbing. (C) 2014 Optical Society of America