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

非技术描述：激发和检测电子在强磁场中的磁响应--高场电子磁共振(EMR)--是从生物学到量子信息科学等学科的突破所必需的。所有的磁共振光谱仪都是基于这样一个事实，即物质的组成部分--质子、大多数原子核和电子--的行为就像微小的磁铁，其强度是由它们的磁矩来量化的。部署在许多医院的磁共振成像(MRI)光谱仪使用频率远低于1 GHz的强大电磁辐射脉冲来激发和检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 GHz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来源，建造了一台灵活的自由电子激光供电的EMR光谱仪。这台光谱仪的设计目的是使人们能够前所未有地研究新型量子传感器的候选对象的基本性质；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。由本科生、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，这为科学和工程工作人员做好了极好的准备。技术说明：加州大学圣巴巴拉分校的自由电子激光器(FEL)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。一种新的螺旋自由电子激光与“脉冲切片”技术相结合，以140-500 GHz可调的频率提供峰值功率约为10kW的脉冲。这台由自由电子激光驱动的EMR(FEL-EMR)光谱仪由该重大研究仪器项目支持，设计用于在高达16.5特斯拉的磁场和1.6至300K的样品温度下，在几纳秒内将自旋1/2粒子旋转90度，从而在顺磁、反铁磁和强关联自旋系统中实现快速电子自旋操纵和读出。FEL-EMR光谱仪的科学目标包括：为蛋白质的动态核极化增强核磁共振优化顺磁造影剂；测量光学可寻址分子量子比特中的自旋相干性；研究反铁磁性自旋电子学中的衰减和自旋输运；以及搜索难以捉摸的分数磁激发。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.