154 research outputs found
Fundamental limitations to gain enhancement in periodic media and waveguides
A common strategy to compensate for losses in optical nanostructures is to
add gain material in the system. By exploiting slow-light effects it is
expected that the gain may be enhanced beyond its bulk value. Here we show that
this route cannot be followed uncritically: inclusion of gain inevitably
modifies the underlying dispersion law, and thereby may degrade the slow-light
properties underlying the device operation and the anticipated gain enhancement
itself. This degradation is generic; we demonstrate it for three different
systems of current interest (coupled resonator optical waveguides, Bragg
stacks, and photonic crystal waveguides). Nevertheless, a small amount of added
gain may be beneficial
Driving-induced population trapping and linewidth narrowing via the quantum Zeno effect
We investigate the suppression of spontaneous emission from a driven
three-level system embedded in an optical cavity via a manifestation of the
quantum Zeno effect. Strong resonant coupling of the lower two levels to an
external optical field results in a decrease of the exponential decay rate of
the third upper level. We show that this effect has observable consequences in
the form of emission spectra with subnatural linewidths, which should be
measurable using, for example, quantum dot--cavity systems in currently
obtainable parameter regimes. These results constitute a novel method to
control an inherently irreversible and dissipative process, and may be useful
in applications requiring the control of single photon arrival times and
wavepacket extent
Modulation response of quantum dot nanolight-emitting-diodes exploiting purcell-enhanced spontaneous emission
Modulation response of nanoLEDs and nanolasers exploiting Purcell enhanced spontaneous emission
Dephasing times in quantum dots due to elastic LO phonon-carrier collisions
Interpretation of experiments on quantum dot (QD) lasers presents a
challenge: the phonon bottleneck, which should strongly suppress relaxation and
dephasing of the discrete energy states, often seems to be inoperative. We
suggest and develop a theory for an intrinsic mechanism for dephasing in QD's:
second-order elastic interaction between quantum dot charge carriers and
LO-phonons. The calculated dephasing times are of the order of 200 fs at room
temperature, consistent with experiments. The phonon bottleneck thus does not
prevent significant room temperature dephasing.Comment: 4 pages, 1 figure, accepted for Phys. Rev. Let
Associations between health-related quality of life, physical function and fear of falling in older fallers receiving home care
Falls and injuries in older adults have significant consequences and costs, both personal and to society. Although having a high incidence of falls, high prevalence of fear of falling and a lower quality of life, older adults receiving home care are underrepresented in research on older fallers. The objective of this study is to determine the associations between health-related quality of life (HRQOL), fear of falling and physical function in older fallers receiving home care
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