Mollow triplet emission and high-harmonic generation involving isolated impurity atoms of semiconductors in a strong terahertz field

该提案要求为在圣巴巴拉的加州大学（UCSB）进行短期研究访问提供资金，以便利用该大学的自由电子激光器（FEL）对半导体中的孤立掺杂剂原子进行原子物理类型的实验。该提案的两个主题是莫洛三重态-在强准连续太赫兹场中拉比振荡的频率模拟，以及由电荷载流子产生的高次谐波，这些电荷载流子在电离后在振荡场中加速，并与掺杂剂离子发生共振。这些主题的强烈动机与气体的原子物理学的模拟现象，其中值得注意的是高次谐波的观测的双折射现象代表了阿秒物理学的热门研究领域的基础。孤立的原子嵌入在宿主晶体中的结果是，非线性光学效应（具有相当长的相干时间）发生在比自由原子低得多的场强和光子能量下。由于缺乏合适的辐射源和测量技术，过去很难对这种现象进行研究。在我们先前研究的基础上，我们打算利用UCSB-FEL的独特性质来观察上述效应。这些特性是自由电子激光的长太赫兹脉冲的非常小的带宽，这有利于单个量子态的寻址和新产生的边带的观察，以及可访问的低辐射频率（低至几百GHz），这支持在载波离子电离时产生高次谐波。

This proposal asks for funding for a short research visit at the University of California at Santa Barbara (UCSB) in order to perform atomic-physics-type experiments on isolated dopant atoms in semiconductors with the university's free-electron laser (FEL). The proposal's two topics are the Mollow triplets-the frequency analogue of Rabi oscillations in a strong quasi-continuous terahertz field, and the generation of higher harmonics by charge carriers which, after ionization, are accelerated in the oscillating field and recollide with the dopant ions. These topics are strongly motivated by analog phenomena of atomic physics with gasses, where notably the observation of higher harmonics by the recollision phenomenon represents the foundation for the hot research field of attosecond physics. The embedding of isolated atoms in a host crystal has the consequence that nonlinear optical effects (with rather long coherence times) occur at much lower field strength and photon energy than in free atoms. Such phenomena could hardly be studied in the past for a lack of suitable radiation sources and measurement techniques. Building on our prior studies, we intend to take advantage of the UCSB-FEL's unique properties for the observation of the effects addressed above. These properties are the very small bandwidth of the FEL's long THz pulses which are favorable for the addressing of individual quantum states and the observation of newly generated sidebands, and the low radiation frequencies accessible (down to a few hundred GHz) which support the generation of high orders of the harmonics upon carrier-ion recollision.