The "crowning" career achievement of a senior technologist at the U.S. Army Combat Capabilities Development Command Aviation & Missile Center has the potential to transform the way the Warfighter conducts covert operations in theater.

Science magazine published "Widely Tunable Compact Terahertz Gas Lasers," introducing a revolutionary new laser concept conceived by Dr. Henry Everitt, senior technologist for CCDC AvMC's Weapons Development and Integration Directorate. The research, performed in collaboration with a team of scientists co-led by professors Federico Capasso of Harvard University and Steven Johnson of the Massachusetts Institute of Technology, demonstrates a new technique for generating terahertz waves based on the quantized rotational motion of molecules.

Dubbed the "laughing gas laser" because it uses nitrous oxide, the laser generates extremely high frequency "terahertz" radiation - combining the best of microwaves and infrared radiation. At such a high frequency, the terahertz region holds significant promise because the bandwidths are much greater than current wireless technologies, and the resolution is much finer than possible with our best radars. However, more powerful sources of frequency tunable radiation are needed to achieve these advantages, and the laser reported in Science is tunable over an enormous frequency range, yet can fit inside a shoebox.

"Getting a publication in one of the two top science journals in the world - Science or Nature - is the crowning achievement for many people's careers, and certainly I will claim that," Everitt said. "This is the biggest highlight of my career in terms of the quality of the journal and the importance of the work. I had this idea 25 years ago, but scientific discovery takes a long time. The Army deserves a lot of credit for allowing me the freedom to explore this."

The scientific breakthrough could benefit the Army's modernization priorities for networks and future vertical lift, as it opens up new options for secure communications and landing radar, Everitt said.

Terahertz radiation can't travel very far because the atmosphere absorbs the radiation, but its range can be adjusted simply by tuning the frequency. Most terahertz lasers are poorly tunable, but Everitt and his fellow scientists demonstrated that almost any molecule, not just laughing gas, can be made to lase with tremendous tunability. That means they can choose how far the waves travel before they are absorbed, thus controlling who can hear the communications or how far the radar can look.

"The ability to have a compact tunable source at these terahertz frequencies will allow us to do covert communications," said Everitt. "It's very secure because the atmosphere creates an adjustable 'cone of silence' around the terahertz transmitter; the signals only propagate as far as we want. Terahertz radiation has extremely high bandwidths so you can put a lot of information on this laser and it will propagate tens of meters, hundreds of meters, but then nobody beyond that will have any idea that you even have a radio or radar. That's the big payoff for the Army, and it's particularly relevant to the network modernization priorities that we have a source that is intrinsically covert."

Everitt's team was funded, in part, through two cooperative agreements with the Army Research Office, an element of CCDC's Army Research Laboratory. One of those agreements is through Institute for Soldier Nanotechnologies at Massachusetts Institute of Technology. Established in 2002, the interdisciplinary research center's focused nanoscience research creates opportunities for new materials and phenomena that directly advance Army modernization efforts.

"This work is the result of a fantastic interinstitutional collaboration weaving together expertises in laser physics, quantum mechanics and terahertz technology. It has led to the first high performance terahertz laser by creatively combining the advantages of molecular and quantum cascade lasers," said Capasso, the Robert Wallace Professor of Applied Physics at Harvard's School of Engineering and Applied Sciences, and co-senior author of the paper.

CCDC AvMC core technical competencies depend upon a preeminent, multidisciplinary, adaptive workforce that conducts leading edge research, development, and life cycle engineering, while promoting discovery and innovation across government, academia and industry.

"Dr. Everitt's dedication to solving the Army's hardest problems and his focus on novel technologies help to enable revolutionary modernization for the Army's next generation of warfighters," said Barry Pike, director for AvMC WDI.

The laughing gas laser requires a special type of infrared laser to convert infrared wavelengths to terahertz radiation. Everitt, who started working on terahertz lasers 35 years ago when he was an undergraduate at Duke University, was waiting for the right infrared laser to pair with his molecular laser. Capasso invented the quantum cascade infrared laser in 1994, and the breakthrough came in October 2018 at Harvard when their two laser concepts were brought together.

"I knew we had something big when that happened," Everitt said. "My colleagues at MIT and I had been working on the theory for almost 10 years, so we knew it had to work. How appropriate that the laser finally came to life on Halloween!"

Terahertz technology has the potential to provide a variety of benefits to current technologies, to include: higher resolution of radar images, the ability to go through objects, and an inherent ability to avoid radio frequency interference. The new technology will "open the doors for other new technologies," according to Paul Chevalier with the Capasso Group at the Harvard John A. Paulson School of Engineering and Applied Sciences.

"The implications of this discovery are significant since the THz part of the electromagnetic spectrum have been underutilized due to the lack of appropriate sources," said Chevalier, who was part of the experimental work with Everitt. "The THz region is still very rich for various fields such as security and communication."

--
The CCDC Aviation & Missile Center, formerly known as the Aviation & Missile Research, Development and Engineering Center (AMRDEC), is part of the U.S. Army Combat Capabilities Development Command, which conducts responsive research, development and life cycle engineering to deliver the aviation and missile capabilities the Army depends on to ensure victory on the battlefield today and tomorrow. Through collaboration across the command's core technical competencies, CCDC leads in the discovery, development and delivery of the technology-based capabilities required to make Soldiers more lethal to win our nation's wars and come home safely. CCDC is a major subordinate command of the U.S. Army Futures Command.