Marie Claire Chelini, Trinity Communications
At the same time that Mike Krzyzewski was starting his Duke career, a freshman named Henry Everitt stepped foot on campus for the first time.
Forty years later, as Coach K was getting ready for his retirement tour, Everitt’s undergrad research project in the Physics department has become a key piece in an apparatus promising to revolutionize the way we collect and transmit information.
No bigger than a shoebox, this ground-breaking device is a widely tunable terahertz laser, with applications ranging from medicine to national security. At the center of it lies a crude-looking copper pipe. Everitt invented that pipe for his undergraduate research project.
“My whole career has been bookended by a piece of copper,” said Everitt. “I’m mighty proud of it.”
“Copper-pipe” doesn’t sound particularly innovative, but in the ‘80s this small device certainly was.
No bigger than a pen, it has a pinhole-sized opening on one end and a plunger similar to a syringe’s at the other. It holds captive molecules of methyl fluoride gas that, when excited by a source of radiation, emit electromagnetic waves. By moving the plunger back and forth inside this pipe, Everitt can tune the frequency of the terahertz radiation being emitted, like an organ player choosing which notes to play.
“This was something of a breakthrough in building little terahertz lasers,” said Frank De Lucia, Everitt’s advisor at Duke, now an emeritus professor of physics at Ohio State University.
Shorter than microwaves but longer than infrared, terahertz electromagnetic waves have challenged physicists and engineers for decades.
The laundry list of potential uses for terahertz radiation is impressive. It could send signals or transfer data with speeds that are orders of magnitude greater than our fastest Wi-Fi, it can be used in medical scanning devices to detect cancer and it can be used to detect and identify chemical substances hidden from the naked eye, whether they are in a cardboard box or in the center of a galaxy.
When shone upon with a terahertz laser, many chemical molecules reveal a unique spectral fingerprint — they shine in a peculiar way. By cataloguing these fingerprints, researchers have built a lexicon of molecules and can use it to detect and recognize substances. Telescopes can use terahertz lasers to identify the chemical nature of interstellar clouds, and, since terahertz waves can penetrate opaque layers, security agencies can use similar lasers in devices able to detect danger better than your best bomb-sniffing dogs.
The catch? Harnessing terahertz wavelengths isn’t easy. But, 40 years ago, Everitt knocked on just the right door to do carve that path.
Like many Trinity undergrads, soon after coming to Duke Everitt started looking for research opportunities. De Lucia, then a Physics professor at Duke, offered him a summer job working on ways to make lasers by exciting gas molecules and forcing them to emit light.
At the time, terahertz lasers were bulky beasts. To emit terahertz waves, molecules had to be excited by an even more monstrous, and potentially dangerous, source of infrared radiation called a CO2 laser. To change the frequency emitted by the terahertz laser, researchers had to change the gas being used, making any tuning a slow and complicated process. De Lucia was working on developing smaller and safer terahertz lasers, and Everitt was enlisted to help.
The summer project grew into an undergrad honors thesis, which grew into a Ph.D. dissertation. Everitt had originally left Duke for his Ph.D., but found he really wanted to come back.
“He was well positioned to go to graduate school in a number of places, and he chose the University of Wisconsin, since that was a very good school,” De Lucia said. “About Christmas time I get a phone call, and it’s Henry. ‘Can I come home? It's too cold up here.’”
By the time Everitt defended his Ph.D. at Duke in 1990, he and De Lucia had developed terahertz lasers with a smaller and smaller footprint. But they still couldn’t get rid of the need for CO2 lasers.
Fast forward five years, and despite great advances, terahertz lasers remained bulky and difficult to use. They were the size of kitchen table, and still required a change in the laser gas to emit different frequencies. The field of infrared lasers, on the other hand, was about to take a major leap forward when a team led by Federico Cappaso, then at AT&T Bell Labs, developed a new technology to emit a wide range of infrared waves: the quantum cascade laser.
Everitt, at the time a program manager at the Army Research Office and an adjunct professor in the Physics department, managed the project and its DARPA funding.
Although quantum cascade lasers were still in their infancy, Everitt started thinking ahead: quantum cascade lasers could be the long-awaited replacement for the CO2 lasers used to power up terahertz lasers.
“I told Federico, ‘Look, someday, when these quantum cascade lasers are ready for prime time, let's try to pair them with my terahertz laser concept,’” Everitt said.
Fast forward another 20 years, and Everitt, now a white-haired senior technologist for optical sciences in the DEVCOM Army Research Lab, ran into Capasso, now a professor at Harvard, at a meeting.
“I said, ‘Hey Federico, quantum cascade lasers are now commercially available, maybe we ought to start thinking about that idea we talked about 20 years ago,’” Everitt said. “He thought that was a fine idea. I still had my old copper pipe laser from Duke, so I shipped all my stuff to Harvard, and we got it to work!”
In 2019, the team published their first paper, describing a shoebox-sized terahertz laser operable at room temperature. It was a revolutionary first step: CO2 lasers were no longer required, and the terahertz laser frequencies could be tuned without changing gas inside of the device.
It still had two big limitations, though: the new, compact laser worked by exciting molecules of laughing gas, which is tricky to handle, and emitted only a relatively narrow band of the terahertz spectrum. Being able to tune a laser to a wide range of frequencies would make it more versatile: longer frequencies can allow for signals to travel further, while short frequencies help ensure they remain contained to a certain area.
Earlier this year the team published an improved version of the same laser, able to transmit a much wider range of wavelengths, using the same methyl fluoride laser gas that Everitt used as an undergrad.
“It took us from the construction of that copper pipe laser in 1983, in the Duke Physics machine shop, which only worked at one terahertz frequency, until 2021, when we made the methyl fluoride laser work at more than 120 frequencies, for that whole thing to come full circle,” Everitt said.
Forty years is a very long time. For basic research, though, it may be just how long a project needs to come to fruition.
“Physics is a very basic science, so you're starting close to zero,” De Lucia said. “A lot of times you don't know exactly what you're exploring, but what Henry has done is to take an original concept and continue to refine it, which may take many years.”
Finding support for such long projects isn’t a given, though.
“Scientific research often takes a long time,” Everitt said. “It takes patience, it takes purpose, it takes serendipity. You can't just throw money at a problem, turn the crank and expect revolutionary concepts to come out the other end on a schedule.”
“Duke is a great incubator for cutting-edge work and I was lucky to be a part of that,” he added.
Everitt’s undergrad research in fact belongs to a longer Duke legacy that began in 1946 with the arrival of a renowned physicist named Walter Gordy. During World War II, Gordy worked to use microwaves (wavelengths longer than terahertz) to improve radar technology. De Lucia, Everitt’s advisor, joined Gordy’s lab at Duke as a graduate student in 1964, then became a Duke professor himself, and later chair of the Physics department.
Under De Lucia’s supervision, Everitt built upon Gordy’s work and brought it back to the field of radar technologies: Seventy-five years after Gordy’s arrival at Duke, one of the most promising applications of this portable new terahertz laser is to build next-generation, high-resolution radars.
And it all started with an undergraduate research project.
“I owe it all to Frank De Lucia, Walter Gordy and to Duke for hiring such great mentors, and for giving undergraduate researchers a chance to do science,” he said.