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Annual Meeting Optical Society of America

Deceleration of atoms with a fluctuating laser field

Reginaldo de Jesus Napolitano, Vanderlei Salvador Bagnato

Published Jan 1, 1991• 0 citations

Abstract

In a recent publication1 we have analyzed the stability of the deceleration process of atoms in the Zeeman tuning technique2 by looking at the velocity profile of the atoms along the magnetic field. When the velocity [v(z)] follows the field profile [B(z)] we refer to this as adiabatic following of atoms because the absorption is adiabatically adjusted to each position so that v(z) follows B(z). This situation does not hold everywhere; in fact, at points where the absorption cannot be adiabatically adjusted the velocity ceases to follow the field interrupting the deceleration. The existence of fluctuations on the laser field produces dramatic changes on the expected behavior of the atoms during the deceleration. We have made numerical simulation and analytical investigation where v(z) is obtained for cases where the laser field has frequency and amplitude fluctuations produced by Markovian and Gaussian stochastic processes. In both cases, the deceleration is dependent on the spectral densities of the fluctuations. The process seems to be more sensitive to amplitude than to frequency fluctuation. These results are important in determining the desired characteristics of the laser source on atoms deceleration experiments.

DOI: 10.1364/oam.1991.tuvv5

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In a recent publication1 we have analyzed the stability of the deceleration process of atoms in the Zeeman tuning technique2 by looking at the velocity profile of the atoms along the magnetic field. When the velocity [v(z)] follows the field profile [B(z)] we refer to this as adiabatic following of atoms because the absorption is adiabatically adjusted to each position so that v(z) follows B(z). This situation does not hold everywhere; in fact, at points where the absorption cannot be adiabatically adjusted the velocity ceases to follow the field interrupting the deceleration. The existence of fluctuations on the laser field produces dramatic changes on the expected behavior of the atoms during the deceleration. We have made numerical simulation and analytical investigation where v(z) is obtained for cases where the laser field has frequency and amplitude fluctuations produced by Markovian and Gaussian stochastic processes. In both cases, the deceleration is dependent on the spectral densities of the fluctuations. The process seems to be more sensitive to amplitude than to frequency fluctuation. These results are important in determining the desired characteristics of the laser source on atoms deceleration experiments.

We present a study on the process of atomic deceleration in the Zeeman tuning technique when a fluctuating laser is used. The characterization of the deceleration is made through the analysis of velocity trajectories (k v(z)) from integration of the averaged equation of motion obtained from the Bloch optical equations. Atomic motion described from an accelerated frame of reference aids the analysis of the process. It is shown that the capability of an atom to follow a magnetic field profile is more sensitive to amplitude than to phase fluctuations. The analysis presented here permits evaluation of laser quality beam on optical deceleration of atoms.

We report on the use of a stimulated Raman transition in a slowed atomic beam to produce a narrow velocity distribution of atoms in a selected electronic state, which could be used for atomic collisions studies in the low temperature regime(1). The velocity selection is part of the deceleration process and in this sense it is unique. The atomic beam is decelerated by the radiation pressure force exerted on the atoms by a counter- propagating laser beam. The resonance condition is maintained along the deceleration path because the changing Doppler shift is compensated by Zeeman tuning the electronic sublevels(2) with a spatialy inhomogneous magnetic field. At the end of the slowing process, the initial Maxwell-Boltzman distribution is compressed to a narrow velocity distribution (Δv ~ 50 m/s), centered close to v = 0. This velocity bunching(3) increases considerably the number of atoms in each velocity class, allowing the use of velocity selection techniques as a feasible way of studying low velocity collisions.

A production of low velocity and monoenergetic atomic beams would increase the resolution in spectroscopic studies and many other experiments in atomic physics. Laser Cooling uses the radiation pressure to decelerate and cool atoms. The effusing from a glow discharge metastable argon atomic beam is affected by a counterpropagating laser light tuned to the cycling transition in argon. The Zeeman shift caused by a spatially varying magnetic field compensates for the changing Doppler shift that takes the atoms out of resonance as they decelerated. Deceleration and velocity bunching of atoms to a final velocity that depends on the detuning of the laser relative to a frequency of the transition have been observed. Time-of-Flight (TOF) spectroscopy is used to examine the velocity distribution of the cooled atomic beam. These TOF studies of the laser cooled atomic beam demonstrate the utility of laser deceleration for atomic-beam "velocity selection".