Laser-ing in on Molecules

By using this high-powered laser, which is based at the University of Californa, Santa Barbara, scientists were able to dramatically boost the effectiveness of EPR spectroscopy.

Led by USC Dornsife, a multiuniversity team has employed a high-powered laser to dramatically improve one of the tools scientists use to study the world at the atomic level. The team was able to use its amped-up electron paramagnetic resonance (EPR) spectrometer to study the electron spin of free radicals and nitrogen atoms trapped inside a diamond.

Allowing scientists to study tiny molecules at a high resolution, the improvement will pull back the veil that shrouds the molecular world.

The team, which includes researchers from USC Dornsife, the University of California, Santa Barbara (UCSB), and Florida State University, published its findings in Nature on Sept. 20.

“We developed the world’s first free-electron laser-powered EPR spectrometer,” said Susumu Takahashi, assistant professor of chemistry in USC Dornsife and lead author of the paper. “This ultra high-frequency, high-power EPR system gives us extremely good time resolution. For example, it enables us to film biological molecules in motion.”

By using a high-powered laser based at UCSB, the researchers were able to significantly enhance EPR spectroscopy, which uses electromagnetic radiation and magnetic fields to excite electrons. The excited electrons emit electromagnetic radiation that reveals details about the structure of the targeted molecules.

“Each electron can be thought of as a tiny magnet which senses the magnetic fields caused by atoms in its nanoneighborhood,” said Mark Sherwin, professor of physics and director of the Institute for Terahertz Science and Technology at UCSB. “With free-electron laser-powered EPR, we have shattered the electromagnetic bottleneck that EPR has faced, enabling electrons to report on faster motions occurring over longer distances than ever before. We look forward to breakthrough science that will lay foundations for discoveries like new drugs and more efficient plastic solar cells.”

EPR spectroscopy has existed for decades. Its limiting factor is the electromagnetic radiation source used to excite the electrons — it becomes more powerful with high magnetic fields and frequencies, and when targeted electrons are excited with pulses of power as opposed to continuous waves.

Until now, scientists performed pulsed EPR spectroscopy with a few tens of gigahertz (GHz) of electromagnetic radiation. Using the UCSB free electron laser, which emits a pulsed beam of electromagnetic radiation, the multi-university team was able to use 240 GHz of electromagnetic radiation to power an EPR spectrometer.

The research was funded by the National Science Foundation and the W. M. Keck Foundation.