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

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.