Raab Jürgen, Lange Christoph, Boland Jessica L, Laepple Ignaz, Furthmeier Martin, Dardanis Enrico, Dessmann Nils, Li Lianhe, Linfield Edmund H, Davies A Giles, Vitiello Miriam S, Huber Rupert
Opt Express. 2019 Feb 4;27(3):2248-2257. doi: 10.1364/OE.27.002248.
Intersubband (ISB) transitions in semiconductor multi-quantum well (MQW) structures are promising candidates for the development of saturable absorbers at terahertz (THz) frequencies. Here, we exploit amplitude and phase-resolved two-dimensional (2D) THz spectroscopy on the sub-cycle time scale to observe directly the saturation dynamics and coherent control of ISB transitions in a metal-insulator MQW structure. Clear signatures of incoherent pump-probe and coherent four-wave mixing signals are recorded as a function of the peak electric field of the single-cycle THz pulses. All nonlinear signals reach a pronounced maximum for a THz electric field amplitude of 11 kV/cm and decrease for higher fields. We demonstrate that this behavior is a fingerprint of THz-driven carrier-wave Rabi flopping. A numerical solution of the Maxwell-Bloch equations reproduces our experimental findings quantitatively and traces the trajectory of the Bloch vector. This microscopic model allows us to design tailored MQW structures with optimized dynamical properties for saturable absorbers that could be used in future compact semiconductor-based single-cycle THz sources.
半导体多量子阱（MQW）结构中的子带间（ISB）跃迁有望用于开发太赫兹（THz）频率的可饱和吸收体。在此，我们利用亚周期时间尺度上的振幅和相位分辨二维（2D）太赫兹光谱，直接观测金属 - 绝缘体MQW结构中ISB跃迁的饱和动力学和相干控制。作为单周期太赫兹脉冲峰值电场的函数，记录了非相干泵浦 - 探测和相干四波混频信号的清晰特征。对于11 kV/cm的太赫兹电场振幅，所有非线性信号都达到明显的最大值，而对于更高的场强则减小。我们证明这种行为是太赫兹驱动的载流子 - 波拉比振荡的特征。麦克斯韦 - 布洛赫方程的数值解定量地再现了我们的实验结果，并追踪了布洛赫矢量的轨迹。这种微观模型使我们能够设计具有优化动力学特性的定制MQW结构，用于可饱和吸收体，这些吸收体可用于未来基于半导体的紧凑型单周期太赫兹源。
