of scientists from Harvard
University and the University
of Leeds in the United Kingdom have created a terahertz
(THz) semiconductor laser that is much different than traditional THz
lasers – it releases less
divergent beams, which will be helpful to the areas of astronomy,
security screening and chemical sensing.
study was led by postdoctoral fellow Nanfang Yu and Federico Capasso
along with Robert L. Wallace, professor of Applied Physics at
Harvard's School of Engineering and Applied Sciences (SEAS) and
Vinton Hayes, senior research fellow in Electrical Engineering at
SEAS. This team of Harvard researchers collaborated with a team from
the University of Leeds, which was led by Edmund Linfield from the
School of Electronic and Electrical Engineering.
rays, or T-rays, can
detect items such as weapons inside of materials such as
clothing, plastic and paper. They are also used to find tiny
concentrations of interstellar chemicals, cracks within certain
materials and to image tumors without side effects. Though, the
problem with these rays is that their beams are "widely
divergent," making it difficult for conventional types of
terahertz lasers to perform the aforementioned tasks.
to Capasso, the teams of scientists were able to create beams with a
smaller divergence by developing an artificial optical structure,
which consists of the sculpting of sub-wavelength-wide grooves
(metamaterial), right on the facet of the
laser. This causes the device to emit beams at a frequency of 3
THz into the far-infrared, which is also known as the invisible part
of the spectrum.
which are artificial materials used to provide properties "not
readily available in Nature," were a very important part of the
study, since metamaterials being used in semiconductor devices has
been limited until now. They were only mainly intended for negative
refraction, high resolution imaging and cloaking. Metamaterials have
now successfully confined the THz light in the laser, ultimately
tightening the direction of the beams. These artificial materials
have also eliminated the need for traditional, bulky lenses through
the high concentration and efficient collection of power it creates
in the facet of the laser.
team was able to reduce the divergence angle of the beam emerging
from these semiconductor lasers dramatically, whilst maintaining the
high output optical power of identical unpatterned devices,"
said Linfield. "This type of laser could be used by customs
officials to detect illicit substances and by pharmaceutical
manufacturers to check the quality of drugs being produced and
research was published in Nature
quote: The challenge for researchers around the world has been to develop a portable laser that operates in the far-infrared (wavelengths of 8 to 12 microns). Every chemical has a unique "fingerprint" because it absorbs light of a specific frequency, and most CWAs fall in the 8 to 12 micron region.