review research
rhombus4
Powerful infrared lasers promise a simpler,
lightweight alternative to the systems for
launching multiple flares, which is the current
approach for deflecting heat-seeking anti-aircraft
missiles. CREDIT: US Marine Corps
Pranalytica’s novel design pushes up
mid IR laser power
US researchers claim to have broken the record for the single facet output power
from a quantum cascade laser (QCL).
T
he team from Pranalytica, Harvard University, and Patel says that this two-resonance condition leads to very
the University of California, Los Angeles, has fast removal of electrons from the lower laser level,
fabricated a 4.6 µm QCL with a non-resonant extraction preventing electrons backscattering into it. Stopping this
design that delivered 3W at 293K. The laser, which from happening is beneficial, because it prevents a
incorporates a highly strained InGaAs/AlInAs active region, decrease in population inversion that would degrade laser
produced a peak wall-plug efficiency of 12.7 percent. performance. However, the penalty paid by this design is
its lack of flexibility, because layer thicknesses in the
Funding from the Defense Advanced Research Projects active region are dictated by the resonance condition and
Agency (DARPA) assisted the development of this laser, the desired laser transition energy.
which could aid directed infrared countermeasures, such
as deflecting heat-seeking missiles. In addition, this QCL Pranalytica overcomes this weakness with a non-resonant
could aid free space optical communications and provide extraction approach that uses parallel non-resonant
a battery-powered source for infrared target illumination. transitions to realize fast carrier extraction from the lower
laser level. Non-resonant transitions are slower than the References
Corresponding author Kumar Patel, who is Pranalytica’s resonant one, but multiple paths mean that the total A. Lyakh et al.
CEO, explains that the team’s design differs from the lifetime in the lower laser level is essentially the same. 2009 Appl.
majority of today’s QCLs, which employ a two-phonon Phys. Lett.
resonance approach. In this more common design, a Two major benefits result from the non-resonant design, 95 141113
radiative electron transition between upper and lower according to Patel: it enables higher continuous-wave R. Maulini et al.
laser levels is followed by two consecutive, non-radiative output powers and wall-plug efficiencies; and it allows 2009 Appl.
transitions involving resonant interaction with longitudinal greater freedom in QCL design, which can also lead to Phys. Lett.
optical phonons. improved performance. The researchers have also been 95 121112
November / December 2009 www.compoundsemiconductor.net 41
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