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CRC Press eBooks

Channeling of Atoms in a Standing Wave

V. I. Balykin, Vladilen S Letokhov

Published Apr 23, 2020• 0 citations
Publisher

Abstract

This chapter provides a brief review of the recent theoretical and experimental results of channeling of atoms in the standing wave. It considers the channeling (one dimensional localization) of atoms in two configurations of the laser fields: a monochromatic and a bichromatic one dimensional laser fields. A quasi resonant monochromatic laser field creates a spatially periodic potential field with a period equal to a half of the wavelength. When atomic beam crosses standing wave and atoms have a low enough kinetic energy, they are guided into the channels where they move along the channel and oscillate in the transverse direction. To detect this channeling the atoms have been chosen themselves as probes of their position. A scheme of a cooling of atoms through their channeling is based on the adiabatic lowering the standing wave intensity.

DOI
10.1201/9780429333378-5

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Journal of Optics B Quantum and Semiclassical Optics•Apr 1, 2003•3 citations
This chapter provides a brief review of the recent theoretical and experimental results of channeling of atoms in the standing wave. It considers the channeling (one dimensional localization) of atoms in two configurations of the laser fields: a monochromatic and a bichromatic one dimensional laser fields. A quasi resonant monochromatic laser field creates a spatially periodic potential field with a period equal to a half of the wavelength. When atomic beam crosses standing wave and atoms have a low enough kinetic energy, they are guided into the channels where they move along the channel and oscillate in the transverse direction. To detect this channeling the atoms have been chosen themselves as probes of their position. A scheme of a cooling of atoms through their channeling is based on the adiabatic lowering the standing wave intensity.
We have investigated the localization of atoms in two configurations of laser fields: monochromatic and bichromatic standing waves. A quasi resonant monochromatic laser field creates a spatially periodic potential field with period equal to half of the wavelength. If the atomic kinetic energy is less than the height of the potential wells then atoms could be trapped in the wells. The motion of atoms in a standing wave is governed by the gradient force, friction force, and momentum diffusion. We studied one dimensional localization of sodium atoms in such a standing wave, as well as the influence of friction and diffusion on the motion of these atoms. The effect of accumulation of atoms at the bottom of potential wells (nodes of a standing wave) was observed. This leads to a new scheme of laser cooling of atoms with a minimum temperature below the Doppler limit.
The effect of the dipole force and its fluctuation on the motion of Li atoms in an intense, one-dimensional, near-resonant standing light wave has been investigated, both theoretically and experimentally. The duration of the interaction of the atoms with the standing wave was varied from several tens of spontaneous emission lifetimes to several hundred. For a standing wave frequency blue-detuned from resonance, diffusive heating can dominate the time-averaged dissipative dipole force so that there is no steady-state momentum distribution. However, for sufficiently large blue detunings the rate of diffusion is so slow that the resulting distribution approaches a quasi-steady state. For red detunings the diffusion is balanced with the force and a true steady-state is achieved. A Monte Carlo method based on the density matrix equations in the dressed-state representation is applied to simulate the atomic motion. The dynamics of atom channeling is studied. One of the important applications of this investigation is adiabatic laser cooling of atoms. Lithium atoms channeled in the nodes of an intense standing wave radiation field are cooled to near the recoil limit, a single photon's momentum hbark\\hbar{k}hbark, by adiabatically reducing the radiation intensity. The final momentum distribution has a narrow component with a root mean squared momentum of 2 hbark\\hbar{k}hbark in one-dimension. The data are compared with the results obtained by the Monte Carlo method. This process may be useful for cooling and increasing the phase-space density of atoms confined in a magnetic trap.
The interaction of a beam of two level atoms with a standing wave laser field has been the subject of extensive investigation in recent times. A standing wave perpendicular to an atomic beam allows the manipulation of the transverse velocity distribution. The interaction of an atomic beam with a strong standing wave laser field has been systematically investigated by both theoretical simulation and experiment in this thesis. We have developed a numerical model based on a continued fraction solution for the light pressure forces to simulate the near perpendicular interaction of an atomic beam with a strong standing wave laser field. The reshaping of the transverse spatial profile of an atomic beam by a perpendicular, near resonant, standing wave laser field is investigated for red detunings using a longitudinal velocity selective detection system. The experimental dependence of the reshaped profile on the longitudinal and transverse atomic velocities agrees well with a continued fraction solution for the light force. In particular, a regime is found where channelling of the atoms near the antinodes of the standing wave produces a central peak in the spatial distribution of the atomic beam in the far field which have also been observed elsewhere.
We present numerical calculations of the evolution of an atomic wave packet in the optical potential created by a laser standing wave. These calculations do not rely on the Raman-Nath approximation, and fully account for transverse atomic motion within the standing wave. Our results show that atomic dynamics is important even for very brief interactions, and that the wave packet can become well localized during and shortly after the interaction. We propose several atomic beam splitters and deflectors which make use of this effect. This effect may also have repercussions for recent proposals to measure the position of an atom in a standing wave by monitoring the phase shift of the optical field; these schemes require that the field does not act back on the atom to alter its position wave function. A standing wave can also localize the wave packet in momentum space, which we show can be used to cool an atomic beam in one transverse dimension.
We report the results of an experimental study on the interaction of cooled cesium atoms with the optical field of two standing waves having different wavelengths (852 and 894 nm) and opposite circular polarizations. The spatial modulation of the superposition of the two optical potentials and the polarization properties of this configuration are expected to produce cooling of the atoms and a spatial modulation of their density with the periodicity of the beat of the two wavelengths. We performed temperature measurements of the cesium sample and observed the density distribution of the atoms for several configurations of the standing wave by means of time-of-flight absorption imaging and fluorescence imaging techniques. Experimentally we could not observe a pronounced density modulation on the length scale of the superperiod. Reasons for this are revealed by a one-dimensional numerical simulation including the complexity of the full Zeeman structure of the cesium atoms. That simulation reproduces the experimental results for the temperatures and spatial confinement.