4,133 research outputs found
Torque of guided light on an atom near an optical nanofiber
We calculate analytically and numerically the axial orbital and spin torques
of guided light on a two-level atom near an optical nanofiber. We show that the
generation of these torques is governed by the angular momentum conservation
law in the Minkowski formulation. The orbital torque on the atom near the fiber
has a contribution from the average recoil of spontaneously emitted photons.
Photon angular momentum and atomic spin angular momentum can be converted into
atomic orbital angular momentum. The orbital and spin angular momenta of the
guided field are not transferred separately to the orbital and spin angular
momenta of the atom
Good Code Sets from Complementary Pairs via Discrete Frequency Chips
It is shown that replacing the sinusoidal chip in Golay complementary code
pairs by special classes of waveforms that satisfy two conditions,
symmetry/anti-symmetry and quazi-orthogonality in the convolution sense,
renders the complementary codes immune to frequency selective fading and also
allows for concatenating them in time using one frequency band/channel. This
results in a zero-sidelobe region around the mainlobe and an adjacent region of
small cross-correlation sidelobes. The symmetry/anti-symmetry property results
in the zero-sidelobe region on either side of the mainlobe, while
quasi-orthogonality of the two chips keeps the adjacent region of
cross-correlations small. Such codes are constructed using discrete
frequency-coding waveforms (DFCW) based on linear frequency modulation (LFM)
and piecewise LFM (PLFM) waveforms as chips for the complementary code pair, as
they satisfy both the symmetry/anti-symmetry and quasi-orthogonality
conditions. It is also shown that changing the slopes/chirp rates of the DFCW
waveforms (based on LFM and PLFM waveforms) used as chips with the same
complementary code pair results in good code sets with a zero-sidelobe region.
It is also shown that a second good code set with a zero-sidelobe region could
be constructed from the mates of the complementary code pair, while using the
same DFCW waveforms as their chips. The cross-correlation between the two sets
is shown to contain a zero-sidelobe region and an adjacent region of small
cross-correlation sidelobes. Thus, the two sets are quasi-orthogonal and could
be combined to form a good code set with twice the number of codes without
affecting their cross-correlation properties. Or a better good code set with
the same number codes could be constructed by choosing the best candidates form
the two sets. Such code sets find utility in multiple input-multiple output
(MIMO) radar applications
Dynamical polarizability of atoms in arbitrary light fields: general theory and application to cesium
We present a systematic derivation of the dynamical polarizability and the ac
Stark shift of the ground and excited states of atoms interacting with a
far-off-resonance light field of arbitrary polarization. We calculate the
scalar, vector, and tensor polarizabilities of atomic cesium using resonance
wavelengths and reduced matrix elements for a large number of transitions. We
analyze the properties of the fictitious magnetic field produced by the vector
polarizability in conjunction with the ellipticity of the polarization of the
light field.Comment: see also Supplemental Materia
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