Opt Express. 2022 Nov 21;30(24):43815-43825. doi: 10.1364/OE.467457.
In recent years, high-power, tunable terahertz (THZ) radiation sources have become the key areas of research in the world. The method of THZ waves by nonlinear optical difference frequency generation (DFG) has the advantages of wide tuning, high power, room temperature operation, and compact structure. However, the conversion efficiency of the current difference frequency method is low, which needs a trade-off between conversion efficiency and tuning range. We apply the nonlinear optical cascade difference frequency conversion theory based on stimulated Raman adiabatic passage (STIRAP) and propose a theoretical scheme to generate THZ waves. Numerical simulation investigates the cascaded difference frequency process of generating THZ waves with the help of the nonlinear medium lithium niobate (LN) crystal. The theoretical analysis shows that the maximum quantum conversion efficiency from signal laser to THZ waves is 43.2 % when the wavelength of the tuned signal laser varies between 1.044 - 1.065 µm with the fixed two pump laser wavelengths constant. The tunable THZ waves of 0.48 - 5.0 THz can be obtained and the maximum output intensity of THZ waves is 2.17 MW/cm, and the method is robust to temperature variations. It also provides a novel idea for the cascaded difference frequency generation of THZ waves.
近年来，高功率、可调谐太赫兹（THz）辐射源已成为世界范围内的研究热点。利用非线性光学差频产生（DFG）方法产生 THz 波具有调谐范围宽、功率高、室温工作和结构紧凑等优点。然而，目前差频方法的转换效率较低，需要在转换效率和调谐范围之间进行权衡。我们应用基于受激拉曼绝热过程（STIRAP）的非线性光学级联差频转换理论，提出了一种产生 THz 波的理论方案。数值模拟研究了利用非线性介质铌酸锂（LN）晶体产生 THz 波的级联差频过程。理论分析表明，当调谐信号激光的波长在 1.044-1.065 µm 之间变化，两个泵浦激光波长固定时，信号激光到 THz 波的最大量子转换效率为 43.2%。可以获得 0.48-5.0 THz 的可调谐 THz 波，THz 波的最大输出强度为 2.17 MW/cm，该方法对温度变化具有鲁棒性。该方法为 THz 波的级联差频产生提供了新的思路。
