基于双温耦合模型的太赫兹晶体损伤阈值分析

飞秒激光通过非线性光学整流效应产生太赫兹(THz)波时,THz波转换效率会随着飞秒激光功 率的增大而明显提高。然而,飞秒激光功率过高会造成非线性晶体损伤,进而影响THz波的 产生及输出, 因而对飞秒激光作用下非线性晶体的损伤阈值进行研究具有重要意义。本文在经典的双温模 型基础上,引 入电子激发、载流子吸收等电离过程的影响,建立了飞秒激光作用下非线性THz晶体损伤 阈值的预估模 型。采用有限差分法,数值模拟了飞秒激光辐照下THz晶体的温度场变化,并据此对 晶体损伤阈值进行 预估。在此基础上,分析比较了LiNbO₃、ZnTe和ZnSe 3种THz晶体的损伤 阈值随激光脉宽的变化规 律。结果表明,晶体的禁带宽度和比热容越大 ,晶体的损伤 阈值就越大；LiNbO₃晶体因其具有更高的损伤阈值,在产生高功率THz波方面 具有更大的优势。

Analysis on damage threshold of terahertz crystals based on two-temperature coupling model

The conversion efficiency of terahertz (THz) wave generated in nonline ar optical rectification is obviously improved with the increase of femtosecond laser power.However,the nonlinear crystals tend to be damaged under high-power femtosecond lasers,which seriously affects the generation and output of THz wave.Therefore,it is of great significance to study the damage threshold of nonlinear crystals irr adiated by femtosecond lasers.In this paper,based on the classic two-temperature coupling model,the influence of io nization process,including electronic excitation and carrier absorption,has been taken into account,and th e prediction model of damage threshold of nonlinear terahertz crystals under femtosecond lasers has been furt her built up.The variation of the temperature field of terahertz crystals irradiated by femtosecond lasers has bee n numerically simulated by the finite-difference method,and the damage threshold of terahertz crystals has bee n estimated.On the basis,the variations of damage thresholds of LiNbO₃,ZnTe and ZnSe crystals with the puls e width of femtosecond lasers have been analyzed and compared.The results show that the forbidden band width and specific heat capacity of the crystal significantly affect the damage threshold.In addition,the damag e threshold is higher for nonlinear terahertz crystals with larger forbidden band width and heat capacity.Consequent ly,LiNbO_3crystal is superior in generating high-power THz wave due to its higher damage threshold.