New laser could be used for applications in imaging, security or communications


Researchers have taken a big step to bring terahertz frequencies out of their hard-to-reach region of the electromagnetic spectrum and into everyday applications. In a new paper, researchers present a first-of-its-kind terahertz laser that is compact, operates at room temperature, and can produce 120 individual frequencies covering the range of 0.25 to 1.3 THz, far wider than previous terahertz sources. .

The laser could be used in a range of applications, such as skin and breast cancer imaging, drug detection, airport security and very high capacity optical wireless links.

The research, conducted by a team from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in collaboration with the DEVCOM Army Research Lab and DRS Daylight Solutions, is published in APL Photonics.

“This is a breakthrough technology for generating terahertz radiation,” said Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Researcher of Electrical Engineering at SEAS and senior author of the paper. “With its compactness, efficiency, wide tuning range and room temperature operation, this laser has the potential to become a key technology to bridge the terahertz gap for imaging, security or communications applications.”

The terahertz frequency range – which lies in the middle of the electromagnetic spectrum between microwaves and infrared light – has remained elusive for applications because most terahertz sources are either very large, inefficient, or rely on devices at low temperatures to produce those elusive frequencies with limited tuning.

In 2019, the Capasso group, in collaboration with MIT and the US military, developed a prototype that proved that terahertz frequency sources could be compact, room temperature, and widely tunable by combining a quantum cascade laser pump with a nitrous oxide molecular laser.

The new research more than triples the adjustment range of this prototype. Among other advances, the new laser replaces nitrous oxide with methyl fluoride, a molecule that reacts strongly with optical fields.

“This compound is really good at absorbing infrared and emitting terahertz,” said Arman Amirzhan, a graduate student at SEAS and first author of the paper. “By using methyl fluoride, which is non-toxic, we have increased the laser’s efficiency and tuning range.”

“Methyl fluoride has been used as a terahertz laser for nearly 50 years, but it generates only a few laser frequencies when pumped by a bulky carbon dioxide laser,” said Henry Everitt, senior army technologist. American for Optical Sciences, and co-author of the paper. “The two innovations we report, a compact laser cavity pumped by a quantum cascade laser, combine to give methyl fluoride the ability to laser hundreds of lines.”

This laser already has the potential to be one of the most compact terahertz lasers ever designed and researchers are aiming to make it even more compact.

“A device under one cubic foot will allow us to target this frequency range for even more applications in short-range communications, short-range radar, biomedicine and imaging,” said Paul Chevalier, research associate at SEAS and principal investigator of the team.

“The combination of mature and compact quantum cascade lasers with molecular laser gain media has resulted in a very robust THz laser platform with a wide range of applications from basic research to molecular detection and imaging. THz, to THz communications and security and beyond,” said Timothy Day, senior vice president and general manager of DRS Daylight Solutions and co-author of the article.

The article was co-authored by Jeremy Rowlette, H. Ted Stinson, and Michael Pushkarsky. This work was partially supported by the US Army Research Office (contracts W911NF-19-2-0168, W911NF-20-1-0157).


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