Experimental and Theoretical Investigation of Ultrafast Coherent Phenomena in Semiconductors

在本计画中，我们将以理论与实验合作的方式研究半导体非平衡多体效应。我们将尝试在半导体中首次观察到强飞秒脉冲的拉比振荡（RO）和共振传播。拉比振荡和共振脉冲传播，甚至自诱导透明（SIT），已经在原子系统中被观察到，但尚未在半导体中被观察到。我们的多体计算预测了当飞秒激光脉冲短于消相T2时间时，在半导体中可以看到RO。此外，与原子系统相比，这些计算预测了半导体中强脉冲传播和自诱导透明度的显著变化。我们的目标之一是在GaAs-AlGaAs多量子阱样品中对调谐到激发共振的脉冲进行相互关联实验，以验证这些预测并证明差异在半导体和原子系统中的SIT之间。我们计划在确定的条件下定量地研究量子阱以及块状材料中的载流子弛豫和减相。从理论上讲，我们最近在体半导体中发现了一种新的无阻尼声等离子体模式，适合非平衡载流子分布。根据我们的计算，相关的超快载流子-载流子散射和脱相对于本征材料，n和p掺杂材料应该有显著的不同。由于低动量态的电子主要负责声学等离激元阻尼。在半导体增益区进行光谱烧孔，并利用烧孔的宽度来测量偏振减相时间。这些测量结果将与我们的计算结果进行比较，将得到有关载流子弛豫和减相速率的重要信息。

In this project we will investigate the semiconductor nonequilibrium many-body effects in a theory- experiment collaborative effort. We will attempt to demonstrate the first observation of Rabi oscillations (RO) and resonant propagation of strong femtosecond pulses in a semiconductor. Rabi oscillations and resonant pulse propagation, even self-induced transparency (SIT), have been seen in atomic systems, but have not yet been observed in semiconductors. Our many-body calculations have predicted that RO may be seen in semiconductors when femetosecond laser pulses shorter than the dephasing T2 times are employed. Also, these calculations predict significant modifications of strong pulse propagation and self-induced transparency in semiconductors, as compared to atomic systems. One of our goals is to perform cross- correlation experiments for pulses tuned to the excition resonance in a GaAs-AlGaAs multiple quantum well sample to verify these predictions and demonstrate the differences between SIT in semiconductors versus atomic systems. We plan to quantitatively investigate carrier relaxation and dephasing in quantum wells as well as in bulk materials under well- defined conditions. Theoretically, we recently found a new undamped acoustic plasmon mode in bulk semiconductors for suitable nonequilibrium carrier distributions. According to our calculations, the related ultrafast carrier-carrier scattering and dephasing should be significantly different for intrinsic, n- and p- doped materials, since the electrons in low momentum states are primarily responsible for the acoustic plasmon damping. Spectral hole burning in the gain region of semiconductors will be performed, and polarization dephasing times will be measured using the width of the burned holes. These measurements, which will be compared with our calculations, should yield important information on carrier relaxation and dephasing rates.