High-efficiency terahertz wave generation combined with optimized cascaded difference frequency generation and optical parametric oscillator

Abstract

We propose a high-efficiency scheme to generate THz waves combined with optimized cascaded difference frequency generation (OCDFG) and optical parametric oscillator (OPO) consisting of a periodic poled lithium niobate (PPLN) crystal or an aperiodic poled lithium niobate (APPLN) crystal at 100 K. The phase mismatches of the OCDFG are decreased in cascaded Stokes processes and increased in cascaded anti-Stokes processes respectively by setting desirable poling periods along the APPLN crystal length. By setting the reflectance of the OPO cavity mirrors, pump energies are transferred to the cascaded Stokes waves rather than the cascaded anti-Stokes waves. As a result, the cascaded Stokes processes are greatly enhanced and the cascaded anti-Stokes processes are greatly weakened simultaneously through the combination of OCDFG and OPO. Theoretical calculations show that optical-to-THz energy conversion efficiencies in excess of 40 % can be achieved when the pump intensity is 10 MW/cm2 at 100 K. The scheme can be applied to the generation of pulsed, quasi-continuous or continuous THz waves.