NER: Terahertz Detection of Electron Spin Precession

本提案是对纳米科学和工程计划NSF 01-157的响应而收到的，属于NER类别。整个工作的重点是通过检测在外加磁场中运动的一组电子的磁偶极子所介导的太赫兹辐射的发射来直接检测电子自旋动力学。这个初步探索性项目的目标是确定在n掺杂的砷化镓和可能的半成像材料中，是否有可测量的太赫兹辐射是由n掺杂的砷化镓和可能的半成像材料中的自旋取向电子群产生的。超导分裂线圈磁体将被用来施加高达6.5特斯拉的磁场。太赫兹辐射强度的检测将使用液氦冷却测辐射热计，以避免电光或光导检测带来的对准困难。利用圆偏振飞秒脉冲的光激发将产生自旋取向的电子布居。为了获得足够大的群体以产生可检测的信号，将使用放大的脉冲，或者通过与自旋进动共振的激发来进行自旋放大。仅根据强度的测量，就可以确定最佳构型并研究饱和特性。这些结果将补充以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映自旋动力学的发射电场提供了背景。这将提供电子自旋动力学的直接探测器，而不存在当前使用的间接光学探测器(如法拉第或克尔旋转)中存在的模糊性。这样的直接探测器将回答有关自旋动力学的重要基本问题，自旋密度比目前技术所能探测的更大。这一结果将为开发基于电子自旋操纵的纳米技术设备提供必要的重要基础知识。此外，基于纳米技术在自旋操纵方面的进展，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.