Ben Ofori-Okai

Ben Ofori-Okai, a spectroscopist at the SLAC National Accelerator Laboratory, has some big questions about what’s happening at the center of planets. The secret lives of high-pressure and high-temperature environments hold the key to scientists’ long-standing questions about the evolution of our universe and even the elusive chemistry within nuclear reactors. To explore these exotic conditions, Ofori-Okai is taking spectroscopy to the extreme.

Ofori-Okai specializes in a field called terahertz spectroscopy, which measures the vibrational energy of molecules as they interact with and emit terahertz radiation. This region of the electromagnetic spectrum, which lies roughly between infrared and microwave wavelengths, captures distinct vibrational modes of molecules that other spectroscopic measurements miss. For example, chemists can use terahertz spectra to reveal the chemical composition of molecular mixtures that might be indistinguishable by nuclear magnetic resonance or infrared spectroscopy, Ofori-Okai says. Yet chemists have been slow to adopt terahertz spectroscopy because “it’s been traditionally very hard to make and measure terahertz radiation,” he says. Now Ofori-Okai is helping fill the terahertz gap.

Ofori-Okai took his first forays into spectroscopy as an undergraduate at Yale University. After an initial stint pursuing a degree in mathematics, he switched his major to chemistry. One organic chemistry seminar stands out in his memory. The professor was giving an introductory lecture on the fundamental principles of spectroscopy and used the photoactivation of 1,3-butadiene as an example. As the professor wrote the wave functions to explain this mechanism on the board, Ofori-Okai realized that his mathematics background gave him the skills to both recognize the physics behind these problems and solve the equations that describe these chemical phenomena. “It all clicked for me at once,” Ofori-Okai says. This insight led him to pursue undergraduate spectroscopy research, which laid the foundation for his career in physical chemistry.

After graduating from Yale in 2009, Ofori-Okai began his doctoral work at the Massachusetts Institute of Technology, where he eventually joined the lab of spectroscopist Keith A. Nelson. At the time, terahertz spectroscopy was still a nascent field with limited applications for laboratory chemists, Nelson says. While it might take a matter of seconds for a chemist to capture ultraviolet spectra of a material, each terahertz measurement required timescales on the order of 10 min or more, making these experiments prohibitively time consuming for routine use. Ofori-Okai’s work has helped speed up that data-gathering process. “I spent a whole bunch of my PhD figuring out how to make terahertz sources more efficient,” he says. At the same time, he was able to develop methods that could capture myriad measurements with a single burst of radiation, rapidly expediting the time needed to perform experiments. Ofori-Okai’s contributions to fundamental terahertz spectroscopy research have helped facilitate the technology’s wider use today, Nelson says.

Ofori-Okai is now a Panofsky Fellow at SLAC working with a team of plasma physicists who use terahertz spectroscopy to study materials in extreme conditions. By reducing the time requirements for terahertz spectroscopy, Ofori-Okai has opened the door to studying irreversible changes in materials. For example, he collected spectra of molecules transitioning through all the phases of matter to become plasma. “I’ve actually started to do experiments where the whole point is to do spectroscopy on a thing that’s blowing up,” he says. These reactions happen under conditions far outside 0 ˚C and 101 kPa—what chemists call standard temperature and pressure. When it comes to the rest of our universe, the term standard is a “misnomer,” he says. By expanding scientists’ instrumental capabilities to include exotic environments beyond human experience, Ofori-Okai’s methods are giving researchers some of their first glimpses into the hidden chemistry at Earth’s core and tantalizing clues about how planets form.

Ofori-Okai stands out to Nelson for both his fearlessness in asking questions and his innate respect for colleagues who come to him for advice. This quality of “confidence without a trace of arrogance” is evident in Ofori-Okai’s persistence in tackling tough problems through productive collaborations, Nelson says.

“Big things happen when you have people who want to be helpful and don’t even care about getting most of the credit. They just want to see the thing succeed,” Ofori-Okai says. “That’s a big part of who I am as a person.”