Woerner Michael, Ghalgaoui Ahmed, Reimann Klaus, Elsaesser Thomas
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany.
J Chem Phys. 2021 Apr 21;154(15):154203. doi: 10.1063/5.0047700.
Nonlinear two-dimensional terahertz (2D-THz) spectroscopy at frequencies of the emitted THz signal different from the driving frequencies allows for exploring the regime of (off-)resonant even-order nonlinearities in condensed matter. To demonstrate the potential of this method, we study two phenomena in the nonlinear THz response of bulk GaAs: (i) The nonlinear THz response to a pair of femtosecond near-infrared pulses unravels novel fourth- and sixth-order contributions involving interband shift currents, Raman-like excitations of transverse-optical phonon and intervalence-band coherences. (ii) Transient interband tunneling of electrons driven by ultrashort mid-infrared pulses can be effectively controlled by a low-frequency THz field with amplitudes below 50 kV/cm. The THz field controls the electron-hole separation modifying decoherence and the irreversibility of carrier generation.
在与驱动频率不同的发射太赫兹（THz）信号频率下进行的非线性二维太赫兹（2D-THz）光谱，能够探索凝聚态物质中（非）共振偶数阶非线性的机制。为了证明该方法的潜力，我们研究了块状砷化镓非线性太赫兹响应中的两种现象：（i）对一对飞秒近红外脉冲的非线性太赫兹响应揭示了涉及带间位移电流、横向光学声子的类拉曼激发和价带间相干的新型四阶和六阶贡献。（ii）由超短中红外脉冲驱动的电子的瞬态带间隧穿可以被幅度低于50 kV/cm的低频太赫兹场有效控制。太赫兹场通过改变退相干和载流子产生的不可逆性来控制电子-空穴分离。
