A leap forward for terahertz lasers
New laser could be used for applications in imaging, security, or communications

Date:
January 26, 2022
Source:
Harvard John A. Paulson School of Engineering and Applied Sciences
Summary:
Researchers have taken a major step towards bringing terahertz
frequencies out of their hard-to-reach region of the electromagnetic
spectrum and into everyday applications. Researchers demonstrate
a first- of-its-kind terahertz laser that is compact, operates at
room temperature and can produce 120 individual frequencies spanning
the 0.25 - 1.3 THz, far more range than previous terahertz sources.



FULL STORY ========================================================================== Researchers have taken a major step towards bringing terahertz frequencies
out of their hard-to-reach region of the electromagnetic spectrum and
into everyday applications. In a new paper, the researchers demonstrate
a first-of-its-kind terahertz laser that is compact, operates at room temperature and can produce 120 individual frequencies spanning the 0.25
-- 1.3 THz, far more range 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 ultrahigh-capacity optical wireless links.

The research, conducted by a team from at 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 leap-ahead technology for generating terahertz radiation,"
said Federico Capasso, the Robert L. Wallace Professor of Applied Physics
and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS
and senior author of the paper. "Thanks to 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 applications in imaging, security, or communications." The terahertz
frequency range -- which sits in the middle of the electromagnetic
spectrum between microwaves and infrared light -- has remained difficult
to reach for applications because most terahertz sources are either very
bulky, inefficient, or rely on low-temperature devices to produce these
elusive frequencies with limited tuning.

In 2019, the Capasso Group, in collaboration with MIT and the U.S. Army, developed a prototype that proved terahertz frequency sources could
be compact, room temperature and widely tunable by combing a quantum
cascade laser pump with a nitrous oxide molecular laser.



==========================================================================
The new research more than triples the tuning range of that
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 increased the
efficiency and tuning range of laser." "Methyl fluoride has been used
as a terahertz laser for almost 50 years, but it only generates a couple
of laser frequencies when pumped by a bulky carbon dioxide laser," said
Henry Everitt, the U.S. Army's senior technologist 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 lase on hundreds of lines." This laser already
has the potential to be one of the most compact terahertz lasers ever
designed and the researchers aim to make it even more compact.

"A less than a cubic foot device will enable us to target this frequency
range for even more applications in short-range communications,
short-range radar, biomedicine and imaging," said Paul Chevalier,
a research associate at SEAS and lead researcher of the team.

"The combination of mature, 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 fundamental research, to THz molecular detection and imaging, THz communications and security and beyond," said Timothy Day, Senior Vice President and General Manager of DRS Daylight Solutions and co-author of the paper.

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

========================================================================== Story Source: Materials provided by Harvard_John_A._Paulson_School_of_Engineering_and_Applied
Sciences. Original written by Leah Burrows. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Arman Amirzhan, Paul Chevalier, Jeremy Rowlette, H. Ted Stinson,
Michael
Pushkarsky, Timothy Day, Henry O. Everitt, Federico Capasso. A
quantum cascade laser-pumped molecular laser tunable over 1 THz. APL
Photonics, 2022; 7 (1): 016107 DOI: 10.1063/5.0076310 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220126122438.htm

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