Terahertz nonlinear detection and quantum optical studies by resonant two-photon transitions in semiconductor quantum wells

这个项目的目的是利用太赫兹(THz)波段的双光子跃迁来进行非线性光学光谱，并研究在1-7THz频率范围内的二阶相干和非线性极化率。我们的方法利用了包括三个能量等距导带的共振双光子吸收。与块状晶体相比，这种光学非线性的效率提高了六个数量级，使我们能够实现非常灵敏的二次型探测器，适合于极弱的太赫兹脉冲的自相关。这些探测器将用于研究飞秒钛宝石激光泵浦的光导太赫兹发射体的自相关，以及用于同步辐射泵浦红外光束线非相干太赫兹辐射的光子聚束的量子光学研究。这些辐射源的超短关联时间将使我们能够确定探测器的本征时间常数，从而获得关于子带间动力学的新信息，特别是关于远低于光学声子频率的弛豫和退相。另一个目标是研究III-V半导体中非线性磁化率的声子-极化子共振。

The aim of this project is exploiting two-photon transitions for nonlinear optical spectroscopy in the Terahertz(THz) regime, and to study second-order coherence and nonlinear susceptibility at frequencies in the range 1 – 7 THz. Our approach makes use of resonant two-photon absorption involving three energetically equidistant conduction subbands in GaAs/AlGaAs quantum wells. This optical nonlinearity is by six orders of magnitude more efficient as compared to bulk crystals and allows us to realize extremely sensitive quadratic detectors, suitable for autocorrelating extremely weak THz pulses. These detectors will be used for autocorrelation studies of photoconductive THz emitters pumped by femtosecond Ti: Sapphire lasers, and for quantum optical investigations of photon bunching of incoherent THz radiation from synchrotron-pumped infrared beamlines. The ultrashort correlation time of these radiation sources will allow us to determine intrinsic time constants of the detectors, thus gaining new information on intersubband dynamics, in particular on relaxation and dephasing well below the optical phonon frequencies. Another goal will be the study of phonon-polariton resonances of the nonlinear susceptibility in III-V semiconductors.