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.

我们提出了一种高效的方案来生成THz波，并结合了优化的级联差分频率生成（OCDFG）和光学参数振荡器（OPO），该振荡器由周期极化铌酸锂（PPLN）晶体或非周期性极化铌酸锂（APPLN）晶体组成。通过沿APPLN晶体长度设置所需的极化周期，可分别在级联的斯托克斯过程中减少OCDFG的相位失配，并在级联的反斯托克斯过程中增加OCDFG的相位失配。通过设置OPO腔镜的反射率，泵浦能量将转移到级联的斯托克斯波上，而不是级联的反斯托克斯波上。结果，通过OCDFG和OPO的组合，可以极大地增强级联的斯托克斯过程，同时极大地削弱级联的反斯托克斯过程。²，在100 K的方案可以应用到脉冲的，准连续或连续的THz波的产生。