外尔半金属TaAs中太赫兹电场诱导的二次谐波产生  

Terahertz-Field-Induced Second Harmonic Generation in Weyl Semimetal TaAs

作　　者：彭湃 李治林[1] 汪信波 Peng Pai;Li Zhilin;Wang Xinbo(Institute of Physics,Chinese Academy of Sciences,Beijing 100190,China;Department of Physics,Tsinghua University,Beijing 100084,China)

机构地区：[1]中国科学院物理研究所,北京100190 [2]清华大学物理系,北京100084

出　　处：《中国激光》2023年第17期191-199,共9页Chinese Journal of Lasers

基　　金：国家自然科学基金(11974414)。

摘　　要：使用强场太赫兹泵浦二次谐波产生探测、研究外尔半金属TaAs中的三阶非线性响应过程。当泵浦太赫兹电场沿着TaAs(112)晶面的不同晶向时,强场太赫兹诱导的光学二次谐波信号展现出了不同的响应,这可以用泵浦太赫兹电场引入的三阶非线性极化来定量地解释,其中较大的zzzz分量可能起着重要的作用。Objective In recent years,significant attention has been paid to the nonlinear response of Weyl semimetals,in which either the inversion or time-reversal symmetry is broken.For example,it was confirmed that the second-order optical responses in the type-I Weyl semimetal TaAs,including the shift and injection current and second-harmonic generation(SHG),relate to the topological effects of Weyl semimetals.Remarkably,Dirac or Weyl semimetals have been proposed to support divergently large current-induced SHG when the Fermi level is located near the Dirac/Weyl points.Such current-induced SHG components have been demonstrated in TaAs using an optically pumped shift current.Compared to the optical pump,the terahertz(THz)pump is advantageous because extremely strong THz fields such as 1‒80 MV/cm can be applied without a significant heating effect.In this study,we used the intense THz generated by the tilted wavefront method as the pump beam and the SHG probe to explore the TaAs third-order nonlinear response.Methods A Ti sapphire femtosecond laser amplifier generates 35 fs pulses with a central wavelength of 800 nm,repetition rate of 1 kHz,and single-pulse energy of 7 mJ.95%laser energy was employed to generate THz radiation from a MgO-doped LiNbO3 crystal(doping concentration of MgO is 5%)using tilted wavefront technique.The THz radiation generated with 0.8 THz center frequency(pump beam)was focused on the sample surface using three off-axis parabolic mirrors.A pair of wire-grid polarizers was used to attenuate the THz field and change polarization.The remaining weak laser pulse(probe beam)was used to generate SHG from the sample.The probe pulses were focused on the sample surface through a hole in the last off-axis parabolic mirror at near-normal incidence.Polarization of the probe pulses was rotated using a half-wave plate.The SHG signal generated at approximately 400 nm was delivered through several bandpass filters and detected using a photomultiplier tube.The SHG polarization was filtered using a wideband wire-g

关 键 词：非线性光学 强场太赫兹 二次谐波产生 外尔半金属 

分 类 号：O436[机械工程—光学工程]