MRI: Development of an Agile Free-Electron-Laser-Powered Pulsed Electron Magnetic Resonance (FEL-EMR) Spectrometer

非技术描述：在高磁场下激发和检测电子的磁响应——高场电子磁共振（EMR）——是从生物学到量子信息科学等学科突破所需要的。所有的磁共振光谱仪都是基于这样一个事实：物质的组成部分——质子、大多数原子核和电子——的行为就像微小的磁铁，它们的强度是通过它们的磁矩来量化的。在许多医院部署的磁共振成像（MRI）光谱仪利用频率远低于1ghz的强大电磁辐射脉冲激发和探测大磁场中质子的磁矩。由于电子的磁矩比质子的磁矩大近700倍，高场EMR光谱仪必须使用频率超过100千兆赫（0.1太赫兹）的强大电磁辐射脉冲。由于产生如此强大的高频脉冲极其困难，高场EMR光谱仪的能力远远落后于MRI和其他核磁共振光谱仪。在这个项目中，加州大学圣巴巴拉分校的研究人员利用他们独特的强大的亚太赫兹电磁辐射源来建立一个灵活的自由电子激光驱动的EMR光谱仪。该光谱仪旨在对新型量子传感器候选材料的基本特性进行前所未有的研究；快速、节能的电子产品替代品；以及物质的奇异量子力学状态。本科生、研究生和博士后研究人员组成的多元化团队在开发最先进的科学仪器方面接受了独特的培训，这为科学和工程劳动力提供了极好的准备。技术描述：加州大学圣巴巴拉分校的自由电子激光器（FELs）是强大的、准连续波亚太赫兹和太赫兹电磁辐射的独特来源。一种新型的螺旋FEL结合“脉冲切片”技术，在140至500 GHz之间可调的频率下，提供峰值功率约为10 kW的脉冲。由该主要研究仪器项目支持的由fel驱动的EMR （FEL-EMR）光谱仪，设计用于在高达16.5特斯拉的磁场和1.6至300 K的样品温度下，在几纳秒内旋转自旋1/2种物质90度，实现顺磁、反铁磁和强相关自旋系统中的快速电子自旋操纵和读出。FEL-EMR谱仪的科学目标包括：优化顺磁造影剂的动态核极化增强核磁共振蛋白质；光学可寻址分子量子比特自旋相干性的测量反铁磁自旋电子学中阻尼和自旋输运的研究寻找难以捉摸的分馏磁体激发。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Description:Excitation and detection of the magnetic response of electrons at high magnetic fields -- high-field electron magnetic resonance (EMR) -- is needed for breakthroughs in disciplines ranging from biology to quantum information science. All magnetic resonance spectrometers are based on the fact that the building blocks of matter -- protons, most atomic nuclei, and electrons --behave like tiny magnets whose strength is quantified by their magnetic moments. Magnetic resonance imaging (MRI) spectrometers deployed in many hospitals excite and detect the magnetic moments of protons in large magnetic fields using powerful pulses of electromagnetic radiation at frequencies well below 1 GHz. Because the magnetic moments of electrons are nearly 700 times larger than those of protons, high-field EMR spectrometers must use powerful pulses of electromagnetic radiation with frequencies above 100 GHz, or 0.1 THz. Due to the extreme difficulty of generating such powerful, high-frequency pulses, the capabilities of high-field EMR spectrometers lag far behind those of MRI and other nuclear magnetic resonance spectrometers. In this project, researchers at the University of California at Santa Barbara leverage their unique sources of powerful sub-THz electromagnetic radiation to build an agile free-electron-laser-powered EMR spectrometer. This spectrometer is designed to enable unprecedented studies of the basic properties of candidates for new classes of quantum sensors; fast, energy-efficient alternatives to electronics; and exotic quantum mechanical states of matter. The diverse team of undergraduates, graduate students, and post-doctoral researchers receive unique training in developing state-of-the-art scientific instrumentation, which is excellent preparation for the science and engineering workforce.Technical Description:The free-electron lasers (FELs) at the University of California at Santa Barbara are unique sources of powerful, quasi-continuous wave sub-THz and THz electromagnetic radiation. A new helical FEL in combination with "pulse slicing" technology delivers pulses with peak powers of about 10 kW at frequencies that are tunable between 140 and 500 GHz. The FEL-powered EMR (FEL-EMR) spectrometer, supported by this Major Research Instrumentation project, is designed to rotate spin-1/2 species by 90 degrees in a few nanoseconds at magnetic fields up to 16.5 Tesla and sample temperatures between 1.6 and 300 K, enabling rapid electron spin manipulation and read-out in paramagnetic, antiferromagnetic, and strongly correlated spin systems. The scientific targets of the FEL-EMR spectrometer include the optimization of paramagnetic contrast agents for dynamic nuclear polarization-enhanced nuclear magnetic resonance of proteins; the measurement of spin coherence in optically addressable molecular qubits; the investigation of damping and spin transport in antiferromagnetic spintronics; and searches for elusive excitations of fractionalized magnets.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.