59,730 research outputs found
Optical Dipole Trapping beyond Rotating Wave Approximation: The case of Large Detuning
We show that the inclusion of counter-rotating terms, usually dropped in
evaluations of interaction of an electric dipole of a two level atom with the
electromagnetic field, leads to significant modifications of trapping potential
in the case of large detuning. The results are shown to be in excellent
numerical agreement with recent experimental findings, for the case of modes of
Laguerre-Gauss spatial profile.Comment: 13 pages, 2 figure
Surface optical vortices
It is shown how the total internal reflection of orbital-angular-momentum-endowed light can lead to the generation of evanescent light possessing rotational properties in which the intensity distribution is firmly localized in the vicinity of the surface. The characteristics of these surface optical vortices depend on the form of the incident light and on the dielectric mismatch of the two media. The interference of surface optical vortices is shown to give rise to interesting phenomena, including pattern rotation akin to a surface optical Ferris wheel. Applications are envisaged to be in atom lithography, optical surface tweezers, and spanners
Preliminary study of VTO thrust requirements for a V/STOL aircraft with lift plus lift/cruise propulsion
A preliminary assessment was made of the VTO thrust requirements for a supersonic (Type B) aircraft with a Lift plus Lift/Cruise propulsion system. A baseline aircraft with a takeoff gross weight (TOGW) of 13 608 kg (30,000 lb) was assumed. Pitch, roll, and yaw control thrusts (i.e., the thrusts needed for aircraft attitude control in the flight hover mode) were estimated based on a specified set of maneuver acceleration requirements for V/STOL aircraft. Other effects (such as installation losses, suckdown, reingestion, etc.), which add to the thrust requirements for VTO were also estimated. For the baseline aircraft, the excess thrust required for attitude control of the aircraft during VTO and flight hover was estimated to range from 36.9 to 50.9 percent of the TOGW. It was concluded that the total thrust requirements for the aircraft/propulsion system are large and significant. In order to achieve the performance expected of this aircraft/propulsion system, reductions must be made in the excess thrust requirements
Polarisation rotation of slow light with orbital angular momentum in ultracold atomic gases
We consider the propagation of slow light with an orbital angular momentum
(OAM) in a moving atomic medium. We have derived a general equation of motion
and applied it in analysing propagation of slow light with an OAM in a rotating
medium, such as a vortex lattice. We have shown that the OAM of slow light
manifests itself in a rotation of the polarisation plane of linearly polarised
light. To extract a pure rotational phase shift, we suggest to measure a
difference in the angle of the polarisation plane rotation by two consecutive
light beams with opposite OAM. The differential angle is
proportional to the rotation frequency of the medium
and the winding number of light, and is inversely proportional to the
group velocity of light. For slow light the angle should
be large enough to be detectable. The effect can be used as a tool for
measuring the rotation frequency of the medium.Comment: 5 pages, 1 figur
A Review of the Open Educational Resources (OER) Movement: Achievements, Challenges, and New Opportunities
Examines the state of the foundation's efforts to improve educational opportunities worldwide through universal access to and use of high-quality academic content
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Fungal community assembly in soils and roots under plant invasion and nitrogen deposition
Slow light in degenerate Fermi gases
We investigate the effect of slow light propagating in a degenerate atomic
Fermi gas. In particular we use slow light with an orbital angular momentum. We
present a microscopic theory for the interplay between light and matter and
show how the slow light can provide an effective magnetic field acting on the
electrically neutral fermions, a direct analogy of the free electron gas in an
uniform magnetic field. As an example we illustrate how the corresponding de
Haas-van Alphen effect can be seen in a neutral gas of fermions.Comment: Slightly updated. Phys. Rev. Lett. 93, 033602 (2004
Exact real-time dynamics of the quantum Rabi model
We use the analytical solution of the quantum Rabi model to obtain absolutely
convergent series expressions of the exact eigenstates and their scalar
products with Fock states. This enables us to calculate the numerically exact
time evolution of and for all regimes of the
coupling strength, without truncation of the Hilbert space. We find a
qualitatively different behavior of both observables which can be related to
their representations in the invariant parity subspaces.Comment: 8 pages, 7 figures, published versio
Illumination from space with orbiting solar-reflector spacecraft
The feasibility of using orbiting mirrors to reflect sunlight to Earth for several illumination applications is studied. A constellation of sixteen 1 km solar reflector spacecraft in geosynchronous orbit can illuminate a region 333 km in diameter to 8 lux, which is brighter than most existing expressway lighting systems. This constellation can serve one region all night long or can provide illumination during mornings and evenings to five regions across the United States. Preliminary cost estimates indicate such an endeavor is economically feasible. The studies also explain how two solar reflectors can illuminate the in-orbit nighttime operations of Space Shuttle. An unfurlable, 1 km diameter solar reflector spacecraft design concept was derived. This spacecraft can be packaged in the Space, Shuttle, transported to low Earth orbit, unfurled, and solar sailed to operational orbits up to geosynchronous. The necessary technical studies and improvements in technology are described, and potential environmental concerns are discussed
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