SCATTERINGS | NEWS
Andrew Campbell, Northwestern University Claire Gmachl research group, Princeton University
OSA Fellow Peter Q. Liu of
Manijeh Razeghi Princeton Univer-
in her Northwest- sity works in the
ern University lab. optics lab.
Quantum Cascade Lasers Gain Ef ciency
Q uantum cascade
lasers (QCLs) have
much potential in the
graduate student and lead author of the
second paper. ese QCLs demonstrate
signiﬁcantly increased coupling between
mid-infrared spectral contact pad the injector ground level and the active
onto one of
region, but their low energy eﬃciency the lasers.
laser region by removing the barrier
has limited their application prospects. between the injector and the active
Two separate U.S. research teams have region. e Northwestern design incor-
fabricated QCLs that signiﬁcantly boost porates the traditional injection barrier.
“wall plug eﬃciency,” or the ratio of the Since the Princeton-Hopkins QCLs
power the laser emits to the power that operate close to the 4.55-µm absorption
the device consumes. peak of carbon monoxide, these lasers
At Northwestern University, OSA Fel- might someday be useful in CO detec-
low Manijeh Razeghi and her colleagues tors, Liu said.
made a 4.85-µm-wavelength pulsed QCL Even at 300 K, the Princeton-Hop-
with a wall plug eﬃciency of 53 percent kins QCLs showed wall plug eﬃciency
at an operating temperature of 40 K of roughly 15 percent, which is still
(Nature Photon. 4, 99). e authors among the best recorded values, Liu
Claire Gmachl research group, Princeton University
wrote in their abstract, “In other words, said. By contrast, the Northwestern
we demonstrate a quantum cascade laser researchers designed their QCLs with a QCLs measured only about 5 percent
that produces more light than heat.” single-well injector, speciﬁcally made for eﬃcient at room temperature.
e second group of researchers from low temperatures, that creates a thermal e need for cryogenic operating
Princeton University, Johns Hopkins forward ﬁlling eﬀect. ey also managed temperatures would make QCL-based
University and AdTech Optics Inc. built to reduce the voltage defect at turn-on devices much more expensive than
a series of pulsed QCLs that attained and turn-oﬀ stages of operation, which instruments that run in shirtsleeve envi-
40 to 50 percent wall plug eﬃciency at led directly to a lower operating voltage— ronments. “People are not interested in
temperatures of 160 K or lower (Nature another factor in boosting eﬃciency. low-temperature applications,” Liu said.
Photon. 4, 95). eir QCLs had emissions e Princeton-Hopkins QCL consists e Princeton-Hopkins team would like
in the 4.5- to 4.7-µm spectral region. of InGaAs and AlInAs layers on an InP to tweak their devices to demonstrate the
e Northwestern team sought to substrate. e lasers are tiny: roughly same kind of wall plug eﬃciency during
demonstrate the highest possible wall plug 3 mm long, 15 µm wide and less than continuous wave operation.
eﬃciency in pulsed-mode operation. e 10 µm high, said Peter Q. Liu, a Princeton —Patricia Daukantas
6 | OPN Optics & Photonics News www.osa-opn.org