NER: Terahertz Detection of Electron Spin Precession

该提案是响应纳米科学与工程倡议，计划征求NSF 01-157，在NER类别。 整体工作的重点是直接检测电子自旋动力学的传感器介导的磁偶极子的电子在施加的磁场中进动人口的太赫兹辐射的发射。 这个初步探索项目的目标是确定可测量的太赫兹辐射是否是由n型掺杂GaAs中的自旋取向电子的光学激发群体以及可能的半磁性材料（如CdMnTe）产生的。 超导分裂线圈磁体将用于施加高达6.5特斯拉的磁场。 太赫兹辐射强度的检测将通过使用液氦冷却测辐射热计来完成，以避免电光或光电导检测所带来的对准困难。 自旋取向的电子的人口将产生由圆偏振飞秒脉冲的光激发。 为了获得足够大以产生可检测信号的群体，将使用放大脉冲或通过与自旋进动共振的激发的“自旋放大”。仅基于强度的测量，可以确定最佳配置并研究饱和特性。这些结果将补充以前的研究使用法拉第旋转，并提供背景使用更复杂的检测太赫兹辐射来测量发射的电场，这反映了自旋动力学。这将提供电子自旋动力学的直接探测，而没有目前使用的间接光学探测（例如法拉第或克尔旋转）中存在的模糊性。这样的直接探测将回答关于更大的自旋密度的自旋动力学的重要基本问题，而不是用现有技术探测。 这些结果将为基于电子自旋操纵的纳米技术器件的开发提供重要的基础知识。 此外，它们还可以为基于纳米技术自旋操纵进步的太赫兹辐射源提供基础。

This proposal was received in response to the Nanoscale Science and Engineering Initiative, Program Solicitation NSF 01-157, in the NER category. The overall effort focuses on direct detection of electron spin dynamics by sensing the emission of terahertz radiation mediated by the magnetic dipole of a population of electrons precessing in an applied magnetic field. The goal of this initial exploratory project is to determine if measurable terahertz radiation is produced from an optically excited population of spin-oriented electrons in n-doped GaAs and possibly semimagnetics such a CdMnTe. A superconducting split-coil magnet will be used to apply fields upto 6.5 Tesla. Detection of the radiated intensity of the terahertz will be done by using a liquid helium cooled bolometer to avoid the alignment difficulties presented by electrooptic or photoconductive detection. The population of spin-oriented electrons will be generated by optical excitation with circularly-polarized femtosecond pulses. To obtain populations that are sufficient large to generate a detectable signal, either amplified pulses, or "spin amplification" by excitation that is resonant with the spin precession will be used. Based on measurement of the intensity alone, the optimum configuration can be determined and saturation characteristics studied. These results will complement prior studies made using Faraday rotation and provide the background for using more sophisticated detection of the terahertz radiation to measure the emitted electric field, which reflects the spin dynamics. This will provide a direct probe of the electron spin dynamics without the ambiguities present in the currently used indirect optical probes such as Faraday or Kerr rotation. Such a direct probe will answer important basic questions about spin dynamics for larger spin densities than can be probed with current techniques. The results will provide important fundamental knowledge necessary for the development of nanotechnology devices based on the manipulation of electron spins. In addition, they could provide the basis for a source of terahertz radiation based on advances in spin manipulation using nanotechnology.