A
tiny terahertz laser is the first to reach three key performance goals at once:
high power, tight beam, and broad frequency tuning. Credit: Ali Khalatpour,
MIT.
Researchers
have achieved a tiny high-power narrow-beam laser that operates in the
terahertz frequencies. These frequencies are beyond visible light, and the
lasers have potential in many imaging and scanning applications. But previous
terahertz lasers required bulky laboratory equipment to stay cool enough to
function. The new devices are the first terahertz laser devices to reach three
key performance goals at once—high power, tight beam, and broad frequency
tuning—in a design that can work outside a laboratory.
The laser
achieves three key performance metrics simultaneously. As a result, it offers
increased power, reduced noise, and increased resolution. This enables more
reliable and lower cost applications in chemical sensing and medical imaging.
The laser works outside of laboratory conditions, enabling new remote
applications. For example, NASA has selected lasers from this research to fly
on the Galactic/Extragalactic Spectroscopic Terahertz Observatory. In this
mission, the laser will help NASA
A photonic
wire laser (PWL) is a type of laser built on a semiconductor chip, has
nanometer-sized bore and a millimeter length cavity. Several can be
side-by-side on a chip integrated with surrounding high-speed electronics.
Coupling multiple adjacent PWLs can synchronize the light beams to emit at the
same or multiple wavelengths and combine their power.
Many
applications require the ability to electrically tune laser frequency, at high
output power with a tight optical beam pattern. Realizing all three of these performance
metrics at the same time is a challenging task because the width of a PWL is
much smaller than its wavelength. This results in a large fraction of the
propagating waves moving outside the solid core of the wire and coupling with
an adjacent laser. Scientists at the Center for Integrated Nanotechnologies, a
DOE Office of Science user facility, were able to exploit this unique feature
of photonic laser wires to achieve the elusive combination of performance
features simultaneously. They used multiple wire lasers which were phase
locked, meaning that the lasers’ oscillations were synchronized. This approach
was inspired by a type of conjugation in chemistry where adjacent molecules are
coupled. By placing pairs of these photonic wires in an array, the researchers
combined the output of the pairs to produce a single, high-power beam with
minimal beam divergence. Adjusting the individual coupled lasers allows tuning
the laser over a broad frequency range.
The new
scheme achieved three critical performance metrics simultaneously: tunable
laser frequency, high power output, and tight beam pattern. This ability can
improve resolution and fidelity in measurements in chemical sensing and medical
imaging (e.g., cancer imaging and brain imaging). There are much broader
applications as well. For example, the NASA Galactic/Extragalactic ULDB
Spectroscopic Terahertz Observatory (GUSTO) will fly with selected lasers from
this collaboration. The observatory will detect and measure carbon, oxygen, and
nitrogen emissions from the interstellar medium, the matter and radiation
between stars, to provide insight into star birth and evolution and help map
more of the Milky Way and nearby Large Magellanic Cloud galaxies.