Dynamics of atoms in a femtosecond optical dipole trap

Laser Physics, 2005

Theoretical study and computer simulation results for the stochastic dynamics of atoms localized in an optical dipole trap are presented. This dynamics is governed by the optical trap potential, cooling due to the Doppler effect, and heating due to the emission and absorption of virtual photons, i.e., due to the resonant dipole-dipole interactions (RDDI). It is shown that the RDDI becomes essential for closely spaced atoms, but the effect can be significantly improved by irradiating the atoms in the trap with an additional resonance probe laser beam. By varying both the optical dipole trap parameters and intensity of the probe laser field, the role of RDDI in the atomic dynamics in the trap is clarified in detail.

ICONO 2001: Quantum and Atomic Optics, High-Precision Measurements in Optics, and Optical Information Processing, Transmission, and Storage, 2002

Theoretical study and computer simulation results for stochastic dynamics of two atoms trapped in an optical dipole trap under action of a probe resonant radiation are presented. The radiation force correlations resulting from our model lead, in addition to cold collisions, to a tendency for atoms escape in pairs from the trap.

Journal of Physics: Conference Series, 2007

We discuss the results of measurements of the temperature and density distribution of cold Rubidium atoms trapped and cooled in an optical dipole trap formed by focussed CO2 laser beams at a wavelength of 10.6 µmfrom a cold, collimated and intense atomic beam of flux 2 × 10 10 atoms/s produced using an elongated 2D + MOT. A large number of rubidium atoms (≥ 10 10) were trapped in the MOT and the number density of atoms were further increased by making a temporal dark MOT to prevent density-limiting processes like photon rescattering by atoms at the trap centre. Subsequently, between 10 7 to 10 8 cold atoms at a temperature below 30 µK were transferred into a Quasi-Electrostatic trap (QUEST) formed by focussed CO2 laser beams at the MOT centre. Both single beam and crossed dual beam dipole traps were studied with a total output power of 50 W from the CO2 laser with focal spot sizes less than 100 microns. Various measurements were done on the cold atoms trapped in the dipole trap. The total atom number in the dipole trap and the spatial atom number density distribution in the trap was measured by absorption imaging technique. The temperature was determined from time-of-flight (TOF) data as well as from the absorption images after ballistic expansion of the atom cloud released from the dipole trap. The results from measurements are used to maximize the initial phase-space density prior to forced evaporative cooling to produce a Bose-Einstein Condensate.

We report on studies of simultaneous trapping of 85 Rb atoms in a magneto-optical trap ͑MOT͒ and onedimensional optical lattice. Using Raman pump-probe spectroscopy, we observe the coexistence of two atomic fractions: the first consists of free, unbound atoms trapped in a MOT and the second is localized in the micropotentials of the optical lattice. We show that recoil-induced resonances allow not only temperature determination of the atomic cloud but, together with vibrational resonances, can also be used for real-time, nondestructive studies of the lattice loading and of the dynamics of systems comprising unbound and bound atomic fractions.

Applied Physics B, 2020

Atoms trapped in the evanescent field around a nanofiber experience strong coupling to the light guided in the fiber mode. However, due to the intrinsically strong positional dependence of the coupling, thermal motion of the ensemble limits the use of nanofiber trapped atoms for some quantum tasks. We investigate the thermal dynamics of such an ensemble by using short light pulses to make a spatially inhomogeneous population transfer between atomic states. As we monitor the wave packet of atoms created by this scheme, we find a damped oscillatory behavior which we attribute to sloshing and dispersion of the atoms. Oscillation frequencies range around 100 kHz, and motional dephasing between atoms happens on a timescale of 10 µs. Comparison to Monte Carlo simulations of an ensemble of 1000 classical particles yields reasonable agreement for simulated ensemble temperatures between 25 µK and 40 µK.

Physical Review A, 2008

The interaction of near-resonant laser radiation with atoms immersed in a magnetic B-field is calculated using a Quantum Electro-Dynamic (QED) model. In this model, the magnetic field is assumed to produce a small perturbation such that the degeneracy of the magnetic sub-states is lifted while maintaining the usual quantum numbers that define the states (the Zeeman effect). The laser radiation is considered to have a narrow bandwidth and to be temporally and spatially coherent. The model produces three general coupled differential equations that describe the state populations and their relative coherences, and the optical coherences between levels coupled by the laser radiation. The model can therefore be directly applied to different experiments ranging from atom trapping and cooling experiments, through to collision experiments carried out in magnetic and laser fields. PACS No. 34.80.Dp 1.0 Introduction. The application of laser radiation to atomic or molecular targets immersed in magnetic fields is now widely used in many different experiments. Such experiments include the production of slow atoms from effusive sources in a Zeeman slower, and the cooling and trapping of atoms to micro-Kelvin temperatures in a Magneto-Optical Trap (MOT) [1]. New collision experiments have also been performed where atoms are prepared in an excited state within a magnetic field produced by a Magnetic Angle Changing (MAC) device [2]

Journal of the Optical Society of America B

We systematically studied the storage time of 87 Rb atoms in an optical dipole trap (ODT) formed by a multimode fiber laser. Storage time is an important parameter in cold atom experiments. If atoms are prepared in the hyperfine state jF 2i, hyperfine-state-changing collisions can transfer these atoms from jF 2i to jF 1i, whereby the released kinetic energy leads to considerable trap loss. In most ODT experiments, atoms are prepared in the hyperfine state jF 1i. However, two-photon Raman transitions induced by high-power multimode fiber lasers can optically pump these atoms from jF 1i to jF 2i, and the following hyperfine-state-changing collision results in the trap loss. In this work, our experimental data indicate that both the two-photon Raman transition and the hyperfine-state-changing collision can be inhibited if the atoms are prepared in the single Zeeman sublevel of jF 2;m 2i (or jF 2;m −2i) and an auxiliary magnetic field is applied.

Physical Review A, 2009

Rubidium atoms prepared by evaporative cooling in an optical dipole trap are used in Stern-Gerlach type experiments. The analysis of the magnetic state distribution in the trap and during free fall demonstrates the possibility of ejecting all atoms with m F 0 from the optical dipole trap. This is achieved by applying an appropriately located inhomogeneous magnetic field. We investigate the dynamics of this cleaning process, and record the temporal history of atom positions under the combined action of magnetic field and dipole-trap potential. The experimental findings are fully supported by realistic numerical simulations of the atomic dynamics. We show that analysis of the ejected atoms provides a means for nondestructive thermometry of a trapped atom cloud.

Physical Review A, 2006

We report on studies of simultaneous trapping of 85 Rb atoms in a magneto-optical trap ͑MOT͒ and onedimensional optical lattice. Using Raman pump-probe spectroscopy, we observe the coexistence of two atomic fractions: the first consists of free, unbound atoms trapped in a MOT and the second is localized in the micropotentials of the optical lattice. We show that recoil-induced resonances allow not only temperature determination of the atomic cloud but, together with vibrational resonances, can also be used for real-time, nondestructive studies of the lattice loading and of the dynamics of systems comprising unbound and bound atomic fractions.

Journal de Physique IV (Proceedings), 2004

We present a brief overview of optical trapping experiments of individual neutral atoms. Then we describe in more details an experiment using a very small optical dipole trap, that is designed to store and manipulate individual atoms. Due to the very small dipole trap volume, a "collisional blockade" mechanism locks the average number of trapped atoms on the value 0.5 over a large range of loading rates. We study this regime experimentally, and we describe methods to measure the oscillation frequencies and the temperature of a single atom in the trap with a high accuracy.