121 research outputs found
Manifestation of the van der Waals surface interaction in the spontaneous emission of atoms into an optical nanofiber
We study the spontaneous emission of atoms near an optical nanofiber and analyze the coupling efficiency of the spontaneous emission into a nanofiber. We also investigate the influence of the van der Waals interaction of atoms with the surface of the optical nanofiber on the spectrum of coupled light. Using, as an example, Rb-85 atoms we show that the van der Waals interaction may considerably extend the red wing of the spontaneous emission line and, accordingly, produce a well-defined asymmetry of the spontaneous emission spectrum coupled into an optical nanofiber
Doppler cooling with coherent trains of laser pulses and tunable "velocity comb"
We explore the possibility of decelerating and Doppler cooling of an ensemble
of two-level atoms by a coherent train of short, non-overlapping laser pulses.
We develop a simple analytical model for dynamics of a two-level system driven
by the resulting frequency comb field. We find that the effective scattering
force mimics the underlying frequency comb structure. The force pattern depends
strongly on the ratio of the atomic lifetime to the repetition time and pulse
area. For example, in the limit of short lifetimes, the frequency peaks of the
optical force wash out. We show that laser cooling with pulse trains results in
a "velocity comb", a series of narrow peaks in the velocity space
Atom microtraps based on near-field Fresnel diffraction
We propose and present a quantitative analysis of neutral atom microtraps based on optical near fields produced by the diffraction of a laser wave on small apertures in a thin screen. We show that near-field atom microtraps are capable of storing atoms in micron-sized regions, with estimated trap lifetimes of about 1 s, when using a moderate laser intensity of about 10 Wâcm2. The depth of the proposed Fresnel atom microtraps is about 0.1 mK. An array of such atom microtraps could have applications to site-selective manipulation of cold atoms
Spectral distribution of atomic fluorescence coupled into an optical nanofibre
We analyse the lineshape of the fluorescence emitted by a cloud of optically excited cold atoms and coupled into an optical nanofibre. We examine the efficiency of the fluorescence coupling and describe the asymmetry of the lineshape caused by the redshifts arising from both the van der Waals and Casimir-Polder interaction of the atoms with the surface of the optical nanofibre. We compare the contributions of the van der Waals and Casimir-Polder redshifts and show that the lineshape of the fluorescence coupled into an optical nanofibre is, basically, influenced by the van der Waals redshift and is characterized by a long tail on the red side of the spectrum. We conclude that a measurement of the lineshape of the coupled fluorescence could be used to characterize the strength of the interaction of atoms with dielectric surfaces and for the detection of atoms using nanofibres
Trapping of a microsphere pendulum resonator in an optical potential
We propose a method to spatially confine or corral the movements of a
micropendulum via the optical forces produced by two simultaneously excited
optical modes of a photonic molecule comprising two microspherical cavities. We
discuss how the cavity enhanced optical force generated in the photonic
molecule can create an optomechanical potential of about 10 eV deep and 30 pm
wide, which can be used to trap the pendulum at any given equilibrium position
by a simple choice of laser frequencies. This result presents opportunities for
very precise all-optical self-alignment of microsystems.Comment: 13 pages, 3 figure
Theory of an optical dipole trap for cold atoms
The theory of an atom dipole trap composed of a focused, far red-detuned, trapping laser beam, and a pair of red-detuned, counterpropagating, cooling beams is developed for the simplest realistic multilevel dipole interaction scheme based on a model of a (3+5)-level atom. The description of atomic motion in the trap is based on the quantum kinetic equations for the atomic density matrix and the reduced quasiclassical kinetic equation for atomic distribution function. It is shown that when the detuning of the trapping field is much larger than the detuning of the cooling field, and with low saturation, the one-photon absorption (emission) processes responsible for the trapping potential can be well separated from the two-photon processes responsible for sub-Doppler cooling atoms in the trap. Two conditions are derived that are necessary and sufficient for stable atomic trapping. The conditions show that stable atomic trapping in the optical dipole trap can be achieved when the trapping field has no effect on the two-photon cooling process and when the cooling field does not change the structure of the trapping potential but changes only the numerical value of the trapping potential well. It is concluded that the separation of the trapping and cooling processes in a pure optical dipole trap allows one to cool trapped atoms down to a minimum temperature close to the recoil temperature, keeping simultaneously a deep potential well
Laser nanotraps and nanotweezers for cold atoms: 3D gradient dipole force trap in the vicinity of Scanning Near-field Optical Microscope tip
Using a two-dipole model of an optical near-field of Scanning Near-field
Optical Microscope tip, i. e. taking into account contributions of magnetic and
electric dipoles, we propose and analyze a new type of 3D optical nanotrap
found for certain relations between electric and magnetic dipoles. Electric
field attains a minimum value in vacuum in the vicinity of the tip and hence
such a trap is quite suitable for manipulations with cold atoms.Comment: 9 pages, 6 figure
Doppler cooling of three-level -systems by coherent pulse trains
We explore the possibility of decelerating and Doppler cooling an ensemble of
tree-level -type atoms by a coherent train of short, non-overlapping
laser pulses. We show that -atoms can be Doppler cooled without
additional repumping of the population from the intermediate ground state. We
derive analytical expression for the scattering force in the quasi-steady-state
regime and analyze its dependence on pulse train parameters. Based on this
analysis we propose a method of choosing pulse train parameters to optimize the
cooling process.Comment: 22 pages, 6 figure
Focusing of atoms with strongly confined light potentials
Focusing of atoms with light potentials is studied. In particular, we
consider strongly confined, cylindrical symmetric potential, and demonstrate
their applications in both red and blue-detuned focusing of atoms. We also
study the influence of aberrations, and find that a resolution of 1 nm should
in principle be possible.Comment: 23 pages, 9 figures, Submitted to Optics Communication
Dissipative light field as a way to create strongly localized structures for atom lithography
Generally, the conditions for deep sub-Doppler laser cooling do not match the
conditions for the strong atomic localization that takes a place in deeper
optical potential and, in consequence, leads to larger temperature. Moreover,
for a given detuning in a deep optical potential the secular approximation
which is usually used for quantum description of laser cooling becomes no more
valid. Here we perform an analysis of atomic localization in optical potential
based on a full quantum approach for atomic density matrix. We also show that
the laser cooling in a deep far-off detuned optical potential, created by a
light field with a polarization gradient, can be used as an alternative method
for forming high contrast spatially localized structures of atoms for the
purposes of atom lithography and atomic nanofabrication. Finally, we perform an
analysis of the possible limits for the width and the contrast of localized
atomic structures that can in principle be reached by this type of the light
mask.Comment: 4 figure
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