Pulsed electron paramagnetic resonance spectroscopy powered by a free-electron laser

• Published in: Nature (London) 2012-09, Vol.489 (7416), p.409-413
• Main Authors: Takahashi, S., Brunel, L.-C., Edwards, D. T., van Tol, J., Ramian, G., Han, S., Sherwin, M. S.
• Format: Article
• Language: English
• Subjects: 639/301/1019/1020/1087; 639/766/930/527; Advantages; Allyl Compounds - chemistry; Benzene - chemistry; Cyclic N-Oxides - chemistry; Diamond - chemistry; Electromagnetism; electron and ion optics; Electron paramagnetic resonance; Electron Spin Resonance Spectroscopy - instrumentation; Electron Spin Resonance Spectroscopy - methods; Electrons; Exact sciences and technology; Fourier Analysis; Free electron lasers; Free Radicals - chemistry; Fundamental areas of phenomenology (including applications); Humanities and Social Sciences; Infrared, submillimeter wave, microwave and radiowave instruments, equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Laser beams; Lasers; letter; Magnetic fields; multidisciplinary; Nanocomposites; Nanomaterials; Nanostructure; Nitrogen Oxides - chemistry; NMR; Nuclear magnetic resonance; Observations; Physics; Radiation by moving charges; Science; Science (multidisciplinary); Semiconductors; Solar cells; Spectrometers; Spectroscopy; Spectrum analysis; Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipments and techniques; Temperature; Time Factors
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature11437

A free-electron laser is used to power a pulsed electron paramagnetic resonance spectrometer at 240 GHz, demonstrating a range of experimental possibilities such as the manipulation of spin-1/2 systems with 6-ns pulses and the measurement of ultrashort decoherence times. Pulsed EPR spectroscopy The technique of electron paramagnetic resonance (EPR) spectroscopy probes unpaired electrons and can provide valuable information on dynamic local structure in biological systems, optoelectronic devices and fundamental quantum systems. Like nuclear magnetic resonance, EPR spectroscopy becomes more powerful at high magnetic fields and frequencies, and using uses pulses rather than continuous waves. Overcoming a major bottleneck in producing powerful pulses at frequencies above 100 gigahertz, the authors use a free-electron laser to power a pulsed spectrometer at 240 gigahertz. This enables them to demonstrate a range of new experimental possibilities, such as the manipulation of spin-1/2 systems with 6 nanosecond pulses and ultrashort decoherence times. Electron paramagnetic resonance (EPR) spectroscopy interrogates unpaired electron spins in solids and liquids to reveal local structure and dynamics; for example, EPR has elucidated parts of the structure of protein complexes that other techniques in structural biology have not been able to reveal 1 , 2 , 3 , 4 . EPR can also probe the interplay of light and electricity in organic solar cells 5 , 6 , 7 and light-emitting diodes 8 , and the origin of decoherence in condensed matter, which is of fundamental importance to the development of quantum information processors 9 , 10 , 11 , 12 , 13 . Like nuclear magnetic resonance, EPR spectroscopy becomes more powerful at high magnetic fields and frequencies, and with excitation by coherent pulses rather than continuous waves. However, the difficulty of generating sequences of powerful pulses at frequencies above 100 gigahertz has, until now, confined high-power pulsed EPR to magnetic fields of 3.5 teslas and below. Here we demonstrate that one-kilowatt pulses from a free-electron laser can power a pulsed EPR spectrometer at 240 gigahertz (8.5 teslas), providing transformative enhancements over the alternative, a state-of-the-art ∼30-milliwatt solid-state source. Our spectrometer can rotate spin-1/2 electrons through π/2 in only 6 nanoseconds (compared to 300 nanoseconds with the solid-state source). Fourier-transform EPR on nitrogen impurities in diamond demonstrates excit