GaP,GaAs和PPLN晶体级联差频产生太赫兹辐射

Cascaded difference-frequency generation for THz in GaP,GaAs and PPLN crystals

研究周期极化磷化镓晶体(GaP)、砷化镓晶体(GaAs)和周期极化铌酸锂晶体(PPLN)准相位匹配级联差频产生太赫兹辐射,相较于差频过程,级联过程太赫兹辐射输出功率增大9.5倍。通过分析三波耦合方程,计算并比较晶体的波矢失配量、极化周期和太赫兹功率,结果显示,基于GaP晶体产生的太赫兹功率略大于GaAs晶体输出的功率;GaAs晶体的极化周期最小;PPLN晶体的波矢失配量和极化周期取值范围最小,而输出的太赫兹功率和转换效率最高。建立基于周期极化掺氧化镁铌酸锂晶体(MgO:PPLN)准相位匹配原理的宽调谐激光系统,分析吸收因子对输出太赫兹功率的影响,计算级联差频峰值功率和转换效率。十五阶峰值功率3.72 MW,泵浦光总能量到太赫兹辐射能量的转换效率是3.72%。

Terahertz（THz） generation by periodically poled Gallium Phosphide（GaP） crystal, periodically poled Gallium Arsenide（GaAs） crystal, and Periodically Poled Lithium Niobate（PPLN） crystal based on Quasi-Phase-Matched（QPM） cascaded Difference-Frequency Generation（DFG） is studied. Compared to DFG, THz power in cascading processes increase by 9.5 times, the cascading process contributes to efficient THz generation. The wave vector mismatch, polarization period and terahertz power of three crystals are calculated from the coupled wave equations, and the results are compared. The results show that terahertz power generated by GaP crystal is slightly higher than that generated by GaAs crystal. The polarization period of GaAs crystal is the smallest; so are the wave vector mismatch and polarization period range of PPLN crystal, however, its conversion efficiency is the highest. A widely tunable laser source system based on the general theory of QPM in MgO：PPLN crystal has been developed. Through analyzing the absorption factor on its output of the terahertz power in theory, the conversion efficiency of cascaded DFG is obtained. The infrared radiation is produced from cascading orders 15 with a maximum power of 3.72 MW. A maximum output conversion efficiency of 3.72% is generated. The research shows significance in experiments on cascaded DFG for terahertz radiation using periodically polarized GaP, periodically polarized GaAs and PPLN crystals.