Bulletin of the American Physical Society

Light scattering from laser-trapped atoms

Robert A. Cline, Joseph D. Miller, M. R. Matthews, Daniel J. Heinzen

Published May 1, 1993• 0 citations

Abstract

We study a novel property of light scattering by Rb atoms confined in a far off-resonance optical dipole force trap. The trapping laser wavelength varies from 780 nm to 860 nm and its intensity is about 1 MW/cm{sup 2}. Spontaneous Raman scattering of photons from the trapping laser can change the ground-state hyperfine quantum number F of the atoms. We observe the relaxation time by measuring the population of the F=3 level after optically pumping the atoms into the F=2 level. Spontaneous photon scatter rates as low as 10{sup 3} s{sup -1} have been observed, corresponding to recoil heating rates below 1 mK/s. For detuning from resonance {Delta} greater than the excited-state fine-structure splitting the total scatter rate, including Rayleigh scattering, decreases as {Delta}{sup 2} while the spontaneous Raman scatter rate decreases as {Delta}{sup 4}. This is due to interference between the Raman scattering amplitudes from the two excited-state fine-structure levels in the Kramers-Heisenberg formula. Because Rayleigh scattering dominates, the atoms` F and M{sub F} quantum numbers are preserved even after many scattering events. This makes far off-resonance optical traps ideal for studies of state-selective collisions and collective phenomena.

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Bulletin of the American Physical Society

Light scattering from laser-trapped atoms

Robert A. Cline, Joseph D. Miller, M. R. Matthews, Daniel J. Heinzen

Published May 1, 1993• 0 citations

OpenAlex

Abstract

Related papers

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We study spin relaxation of optically trapped atoms that is due to light scattering from the trap laser. We observe relaxation times greater than 2 s for ground-state hyperfine-level populations of 85Rb atoms trapped in an optical dipole force trap operating as much as 65 nm to the red of the D1 line. The measured relaxation rate can be more than 100 times slower than the atoms’ total spontaneous scatter rate from the trap laser. This enhancement in atomic ground-state lifetime is due to an interference effect in spontaneous Raman scattering far from atomic resonance.We study spin relaxation of optically trapped atoms that is due to light scattering from the trap laser. We observe relaxation times greater than 2 s for ground-state hyperfine-level populations of 85Rb atoms trapped in an optical dipole force trap operating as much as 65 nm to the red of the D1 line. The measured relaxation rate can be more than 100 times slower than the atoms’ total spontaneous scatter rate from the trap laser. This enhancement in atomic ground-state lifetime is due to an interference effect in spontaneous Raman scattering far from atomic resonance.

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Daniel J. Heinzen, Robert A. Cline, M. R. Matthews +1 more

We have confined up to 10{sup 4} {sup 85}Rb atoms in an optical dipole force trap operating up to 65 nm from atomic resonance. For detunings greater than 16 nm, we obtained long confinement times, limited only by background gas collisions, without additional cooling. However, for trapping laser tunings between 4 nm and 16 nm to the red of the lowest Rb (D1) resonance, we observed a novel trap loss mechanism which results in much shorter-trap lifetimes. The trap loss rate is very sensitive to the laser wavelength, and exhibits a complex spectrum. This trap loss may arise from a photo-associative collisional process in which an initially free pair of colliding ground state atoms is promoted to a bound molecular excited state. The bound excited molecule could then be lost from the trap by photoionization, or by spontaneous decay to an untrapped ground state. The results of our preliminary experiments and of further experiments to clarify this novel trap loss process will be presented.We have confined up to 10{sup 4} {sup 85}Rb atoms in an optical dipole force trap operating up to 65 nm from atomic resonance. For detunings greater than 16 nm, we obtained long confinement times, limited only by background gas collisions, without additional cooling. However, for trapping laser tunings between 4 nm and 16 nm to the red of the lowest Rb (D1) resonance, we observed a novel trap loss mechanism which results in much shorter-trap lifetimes. The trap loss rate is very sensitive to the laser wavelength, and exhibits a complex spectrum. This trap loss may arise from a photo-associative collisional process in which an initially free pair of colliding ground state atoms is promoted to a bound molecular excited state. The bound excited molecule could then be lost from the trap by photoionization, or by spontaneous decay to an untrapped ground state. The results of our preliminary experiments and of further experiments to clarify this novel trap loss process will be presented.

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Far-off-resonance optical trapping of atoms

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We confine $^{85}\mathrm{Rb}$ atoms in an optical dipole force trap with a very large detuning from resonance of up to 65 nm. Confinement times of 200 ms, limited only by background-gas collisions, are obtained without additional cooling. A typical trap contains 1300 atoms at a temperature of 0.4 mK and a peak density of 8\ifmmode\times\else\texttimes\fi{} ${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. We measure spontaneous photon scatter rates of the trapped atoms to be less than 1.6\ifmmode\times\else\texttimes\fi{} ${10}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, corresponding to recoil heating rates below 0.6 mK/s. The far-detuned trap confines atoms with a strong, nearly conservative optical force and negligible atomic excitation.We confine $^{85}\mathrm{Rb}$ atoms in an optical dipole force trap with a very large detuning from resonance of up to 65 nm. Confinement times of 200 ms, limited only by background-gas collisions, are obtained without additional cooling. A typical trap contains 1300 atoms at a temperature of 0.4 mK and a peak density of 8\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. We measure spontaneous photon scatter rates of the trapped atoms to be less than 1.6\ifmmode\times\else\texttimes\fi{}${10}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, corresponding to recoil heating rates below 0.6 mK/s. The far-detuned trap confines atoms with a strong, nearly conservative optical force and negligible atomic excitation.

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Joseph D. Miller, Robert A. Cline, Daniel J. Heinzen

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Bulletin of the American Physical SocietyMay 1, 19930 citations

Effects of laser light on ultracold atom collisions

V. Sánchez-Villicaña

Measurements of the temperature dependence of trap loss collisions of laser-cooled rubidium atoms are presented. A significant suppression of the rate of collisions between ground- and excited-state atoms is observed for temperatures below $\\sim$70 $\\mu$ K. In such inelastic collisions, the atomic excitation takes place at long range and must survive against spontaneous decay to short range. Our results are consistent with recent predictions for the low temperature suppression of these collisions due to reduced survival of atomic excitation at low collision velocities.^ We report on measurements of trap loss collisions between ultracold Rb atoms which are confined in a magneto-optical trap. Both isotopes $\\sp{85}$ Rb and $\\sp{87}$ Rb have been studied over wide range of trap laser intensities and detunings. The trap loss collision rates exhibit variations over 3 orders of magnitude. We observe significant differences between the isotopes. At large detunings the ability of the trap to recapture products of the hyperfine-changing collisions is significantly diminished. This finding is supported by our numerical simulations of the recapture process. The trap loss rates due to collisions with room temperature background gas have also been measured.^ Using laser light tuned to a repulsive molecular potential, we have been able to suppress inelastic ground-state hyperfine changing collisions between ultracold $\\sp{87}$ Rb atoms. Adiabatic excitation to the repulsive curve alters the atomic trajectories and prevents the atoms from approaching close enough for the hyperfine change to occur. Experimental results show suppressions up to $\\sim$50% and are in reasonable agreement with a simple Landau-Zener model.^ Finally, we have observed a significant cooperative effect in ultracold trap loss collisions induced by two separate lasers. One laser, tuned close to the atomic resonance, excites the atom pair to an attractive potential at long range. The resulting acceleration and deflection give rise to an enhancement in the collisional flux of ground-state atoms reaching short range, as probed by a second laser. Enhancements up to a factor of $\\sim$3 have been observed. ^Measurements of the temperature dependence of trap loss collisions of laser-cooled rubidium atoms are presented. A significant suppression of the rate of collisions between ground- and excited-state atoms is observed for temperatures below $\\sim$70 $\\mu$K. In such inelastic collisions, the atomic excitation takes place at long range and must survive against spontaneous decay to short range. Our results are consistent with recent predictions for the low temperature suppression of these collisions due to reduced survival of atomic excitation at low collision velocities.^ We report on measurements of trap loss collisions between ultracold Rb atoms which are confined in a magneto-optical trap. Both isotopes $\\sp{85}$Rb and $\\sp{87}$Rb have been studied over wide range of trap laser intensities and detunings. The trap loss collision rates exhibit variations over 3 orders of magnitude. We observe significant differences between the isotopes. At large detunings the ability of the trap to recapture products of the hyperfine-changing collisions is significantly diminished. This finding is supported by our numerical simulations of the recapture process. The trap loss rates due to collisions with room temperature background gas have also been measured.^ Using laser light tuned to a repulsive molecular potential, we have been able to suppress inelastic ground-state hyperfine changing collisions between ultracold $\\sp{87}$Rb atoms. Adiabatic excitation to the repulsive curve alters the atomic trajectories and prevents the atoms from approaching close enough for the hyperfine change to occur. Experimental results show suppressions up to $\\sim$50% and are in reasonable agreement with a simple Landau-Zener model.^ Finally, we have observed a significant cooperative effect in ultracold trap loss collisions induced by two separate lasers. One laser, tuned close to the atomic resonance, excites the atom pair to an attractive potential at long range. The resulting acceleration and deflection give rise to an enhancement in the collisional flux of ground-state atoms reaching short range, as probed by a second laser. Enhancements up to a factor of $\\sim$3 have been observed. ^

Jan 1, 19960 citations

Hyperfine spectroscopy of optically trapped atoms

A Kaplan, M F Andersen, T Grünzweig +1 more

We perform spectroscopy on the hyperfine splitting of $^{85}$ Rb atoms trapped in far-off-resonance optical traps. The existence of a spatially dependent shift in the energy levels is shown to induce an inherent dephasing effect, which causes a broadening of the spectroscopic line and hence an inhomogeneous loss of atomic coherence at a much faster rate than the homogeneous one caused by spontaneous photon scattering. We present here a number of approaches for reducing this inhomogeneous broadening, based on trap geometry, additional laser fields, and novel microwave pulse sequences. We then show how hyperfine spectroscopy can be used to study quantum dynamics of optically trapped atoms.We perform spectroscopy on the hyperfine splitting of $^{85}$Rb atoms trapped in far-off-resonance optical traps. The existence of a spatially dependent shift in the energy levels is shown to induce an inherent dephasing effect, which causes a broadening of the spectroscopic line and hence an inhomogeneous loss of atomic coherence at a much faster rate than the homogeneous one caused by spontaneous photon scattering. We present here a number of approaches for reducing this inhomogeneous broadening, based on trap geometry, additional laser fields, and novel microwave pulse sequences. We then show how hyperfine spectroscopy can be used to study quantum dynamics of optically trapped atoms.

arXiv:physics/0409146Journal of Optics B Quantum and Semiclassical OpticsJul 11, 200518 citations

We confine

^{85}\mathrm{Rb}

atoms in an optical dipole force trap with a very large detuning from resonance of up to 65 nm. Confinement times of 200 ms, limited only by background-gas collisions, are obtained without additional cooling. A typical trap contains 1300 atoms at a temperature of 0.4 mK and a peak density of 8\ifmmode\times\else\texttimes\fi{}

{10}^{11}

${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. We measure spontaneous photon scatter rates of the trapped atoms to be less than 1.6\ifmmode\times\else\texttimes\fi{}

{10}^{3}

${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, corresponding to recoil heating rates below 0.6 mK/s. The far-detuned trap confines atoms with a strong, nearly conservative optical force and negligible atomic excitation.

\\mu

K. In such inelastic collisions, the atomic excitation takes place at long range and must survive against spontaneous decay to short range. Our results are consistent with recent predictions for the low temperature suppression of these collisions due to reduced survival of atomic excitation at low collision velocities.^ We report on measurements of trap loss collisions between ultracold Rb atoms which are confined in a magneto-optical trap. Both isotopes

\\sp{85}

Rb and

\\sp{87}

Rb have been studied over wide range of trap laser intensities and detunings. The trap loss collision rates exhibit variations over 3 orders of magnitude. We observe significant differences between the isotopes. At large detunings the ability of the trap to recapture products of the hyperfine-changing collisions is significantly diminished. This finding is supported by our numerical simulations of the recapture process. The trap loss rates due to collisions with room temperature background gas have also been measured.^ Using laser light tuned to a repulsive molecular potential, we have been able to suppress inelastic ground-state hyperfine changing collisions between ultracold

\\sp{87}

Rb atoms. Adiabatic excitation to the repulsive curve alters the atomic trajectories and prevents the atoms from approaching close enough for the hyperfine change to occur. Experimental results show suppressions up to $\\sim$50% and are in reasonable agreement with a simple Landau-Zener model.^ Finally, we have observed a significant cooperative effect in ultracold trap loss collisions induced by two separate lasers. One laser, tuned close to the atomic resonance, excites the atom pair to an attractive potential at long range. The resulting acceleration and deflection give rise to an enhancement in the collisional flux of ground-state atoms reaching short range, as probed by a second laser. Enhancements up to a factor of $\\sim$3 have been observed. ^

We perform spectroscopy on the hyperfine splitting of

^{85}

Rb atoms trapped in far-off-resonance optical traps. The existence of a spatially dependent shift in the energy levels is shown to induce an inherent dephasing effect, which causes a broadening of the spectroscopic line and hence an inhomogeneous loss of atomic coherence at a much faster rate than the homogeneous one caused by spontaneous photon scattering. We present here a number of approaches for reducing this inhomogeneous broadening, based on trap geometry, additional laser fields, and novel microwave pulse sequences. We then show how hyperfine spectroscopy can be used to study quantum dynamics of optically trapped atoms.