Radiation of THz electromagnetic waves from semiconductor microcavity polaritons

本课题研究了半导体微腔中激子极化子的太赫兹电磁波辐射。特别地，我们着重展示了由腔极化子产生的太赫兹波辐射的实验证据。另一个目的是利用太赫兹波观测作为探针来研究腔极化子的相干动力学。所得结果可总结如下：1。通过我们系统的实验研究，有条件地得出太赫兹波是由激子居群的章动辐射出来的，与谐振激励下腔极子的正模振荡有关。我们发现太赫兹波的频率略高于两个极化模之间的能量差所期望的频率。这种偏差是由于在反射光谱中观测到的能量差与极化子系统的本征模式（正常）模式之间的差异造成的。对量子阱施加高内电场的情况下，观察到太赫兹波的阻尼率增加。我们发现更快的阻尼与激子线的展宽有关。此外，发现在强激励下阻尼率变得更高。随着腔内Q值的减小，我们还观察到振荡在太赫兹波中的衰减速度更快。特别是，只有一个周期，但相当强的太赫兹波发射被观察到。结果表明，高q腔中振荡太赫兹信号是由激子群的章动引起的。我们提出了一种基于体体半导体微腔中激发功率有效利用的半导体表面太赫兹电磁波辐射增强新方案。与现成的散装InAs相比，我们证明了太赫兹波辐射的一个数量级以上的增强，而现成的散装InAs被认为是太赫兹波辐射的最佳材料。少

In this project, we studied the radiation of THz electromagnetic waves from exciton-polariton in semiconductor microcavities. In particular, we focused on demonstrating the experimental evidences of THz-wave radiation from cavity polaritons. Another aim has been the investigation of coherent dynamics of cavity polaritons using the THz wave observation as a probe. The obtained results can be summarized as follows.1. Through our systematic experimental study, it was condidentially concluded that the THz wave is radiated from the nutation of exciton population, associated with the normal mode oscillation of cavity-polaritons under resonant excitation.2. We found that the frequency of the THz-wave is slightly higher than that expected from the energy difference between the two polariton modes. Such a deviation was shown to result from the difference between the energy differences observed in reflection spectra and the eigen (normal) modes of the polariton system, through the experiment and … More theoretical considerations.3. Increases of damping rates of the THz-waves were observed for the case that a high internal electric field is applied to the quantum wells. We showed that the faster damping is relevant to the broadening of exciton lines. Also, the damping rates were found to become higher under intense excitations.4. With the decrease of the cavity Q value, we also observed the faster damping of the oscillation in the THz-wave. In particular, only a single cycle, but rather strong THz-wave emission was observed. The results are the other manifestation that the oscillatory THz signals in high-Q cavities are due to the nutation of exsciton populations.5. We proposed a new scheme for the enhancement of THz electromagnetic wave radiation from semiconductor surfaces based on the efficient use of excitation power in bulk semiconductor microcavities. We demonstrated more than one-order of magnitude enhancement of the THz-wave radiation in comparison with off-the shelf bulk InAs which has been believed to be the best material for the THz-wave radiation. Less