6 research outputs found
Optical bistability in one dimensional doped photonic crystals with spontaneously generated coherence
We investigate optical bistability in a multilayer one-dimensional photonic
crystal where the central layer is doped with -type three level atoms.
We take into account the influence of spontaneously generated coherence when
the lower atomic levels are sufficiently close to each other, in which case
Kerr-type nonlinear response of the atoms is enhanced. We calculate the
propagation of a probe beam in the defect mode window using numerical nonlinear
transfer matrix method. We find that Rabi frequency of a control field acting
on the defect layer and the detuning of the probe field from the atomic
resonance can be used to control the size and contrast of the hysteresis loop
and the threshold of the optical bistability. In particular we find that, at
the optimal spontaneously generated coherence, three orders of magnitude lower
threshold can be achieved relative to the case without the coherence.Comment: 9 pages, 7 figure
RETRATO EN EL PATIO [Material gráfico]
INCLUIDAS EN EL PEQUEÑO ÁLBUM FOTOGRÁFICO FAMILIAR DE LA COLECCIÓN LUIS SUÁREZ GALVÁNCopia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
Graphene-Based Adaptive Thermal Camouflage
In nature, adaptive coloration has
been effectively utilized for
concealment and signaling. Various biological mechanisms have evolved
to tune the reflectivity for visible and ultraviolet light. These
examples inspire many artificial systems for mimicking adaptive coloration
to match the visual appearance to their surroundings. Thermal camouflage,
however, has been an outstanding challenge which requires an ability
to control the emitted thermal radiation from the surface. Here we
report a new class of active thermal surfaces capable of efficient
real-time electrical-control of thermal emission over the full infrared
(IR) spectrum without changing the temperature of the surface. Our
approach relies on electro-modulation of IR absorptivity and emissivity
of multilayer graphene via reversible intercalation of nonvolatile
ionic liquids. The demonstrated devices are light (30 g/m<sup>2</sup>), thin (<50 μm), and ultraflexible, which can conformably
coat their environment. In addition, by combining active thermal surfaces
with a feedback mechanism, we demonstrate realization of an adaptive
thermal camouflage system which can reconfigure its thermal appearance
and blend itself with the varying thermal background in a few seconds.
Furthermore, we show that these devices can disguise hot objects as
cold and cold ones as hot in a thermal imaging system. We anticipate
that, the electrical control of thermal radiation would impact on
a variety of new technologies ranging from adaptive IR optics to heat
management for outer space applications
Graphene-Based Adaptive Thermal Camouflage
In nature, adaptive coloration has
been effectively utilized for
concealment and signaling. Various biological mechanisms have evolved
to tune the reflectivity for visible and ultraviolet light. These
examples inspire many artificial systems for mimicking adaptive coloration
to match the visual appearance to their surroundings. Thermal camouflage,
however, has been an outstanding challenge which requires an ability
to control the emitted thermal radiation from the surface. Here we
report a new class of active thermal surfaces capable of efficient
real-time electrical-control of thermal emission over the full infrared
(IR) spectrum without changing the temperature of the surface. Our
approach relies on electro-modulation of IR absorptivity and emissivity
of multilayer graphene via reversible intercalation of nonvolatile
ionic liquids. The demonstrated devices are light (30 g/m<sup>2</sup>), thin (<50 μm), and ultraflexible, which can conformably
coat their environment. In addition, by combining active thermal surfaces
with a feedback mechanism, we demonstrate realization of an adaptive
thermal camouflage system which can reconfigure its thermal appearance
and blend itself with the varying thermal background in a few seconds.
Furthermore, we show that these devices can disguise hot objects as
cold and cold ones as hot in a thermal imaging system. We anticipate
that, the electrical control of thermal radiation would impact on
a variety of new technologies ranging from adaptive IR optics to heat
management for outer space applications