NER: Terahertz Detection of Electron Spin Precession

该提案是响应纳米尺度科学与工程倡议，项目招标NSF 01-157，在NER类别。整体的努力集中在直接检测电子自旋动力学，通过感应发射的太赫兹辐射介导的电子群体的磁偶极子在一个应用磁场。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由n掺杂GaAs中自旋取向电子的光激发群产生，以及可能的半成像，如CdMnTe。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的测热计来完成，以避免电光或光导检测所带来的校准困难。自旋取向电子的居群将由圆偏振飞秒脉冲光激发产生。为了获得足够大的种群以产生可探测的信号，要么使用放大脉冲，要么使用与自旋进动共振的激发“自旋放大”。仅根据强度的测量，就可以确定最佳配置并研究饱和特性。这些结果将补充先前使用法拉第旋转进行的研究，并为使用更复杂的太赫兹辐射检测来测量反射自旋动力学的发射电场提供背景。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（如法拉第或克尔旋转）中存在的模糊性。这样的直接探针将回答关于更大自旋密度的自旋动力学的重要基本问题，而不是用现有技术可以探测到的。这些结果将为开发基于电子自旋操纵的纳米技术器件提供重要的基础知识。此外，基于纳米技术自旋操纵的进步，它们可以为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.