Journal of the Optical Society of America B

Magneto-optical trapping and ultracold collisions of potassium atoms

R. S. Williamson, Thad G Walker

Published Aug 1, 1995• 47 citations

Abstract

We present measurements of loading and loss rates for a vapor-cell optical trap of the two naturally occurring potassium isotopes 39K and 41K. The unresolved excited-state hyperfine structure makes trapping of K fundamentally different from trapping of the other alkalis and leads to an enhanced loading rate. We measure the loading rate as a function of laser intensity, beam size, and detuning and find that the results are in reasonable agreement with a simple rate-equation model for the loading process. The dependence of the loss rate on trapped-atom density determines the contribution to the loss rates from excited-state collisions. We find a substantial difference between the collisional loss rates for the two isotopes.

DOI: 10.1364/josab.12.001393

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Journal of the Optical Society of America B

Magneto-optical trapping and ultracold collisions of potassium atoms

R. S. Williamson, Thad G Walker

Published Aug 1, 1995• 47 citations

Publisher

Abstract

DOI: 10.1364/josab.12.001393

Related papers

Comparative investigation of 39K and 40K trap loss rates: alternative loss channel at low light intensities

Giovanni Carlo Modugno, G. Roati, M. Inguscio +4 more

We report a comparative investigation of trap loss rates in a magneto-optical trap for two potassium isotopes, 39K and 40K, as a function of trap light intensity. The isotopes present a quite similar behavior for the loss rates at high intensities, and a sudden increase of the loss rates at low intensities is present in both cases. While for 39K such increase can be explained assuming that the major contribution to the losses comes from Hyperfine Changing Collisions, a different loss mechanism must be considered for 40K, which has an inverted ground state hyperfine structure. The experimental results of both isotopes are well reproduced by an alternative model based on radiative escape as the dominant loss mechanism.We report a comparative investigation of trap loss rates in a magneto-optical trap for two potassium isotopes, 39K and 40K, as a function of trap light intensity. The isotopes present a quite similar behavior for the loss rates at high intensities, and a sudden increase of the loss rates at low intensities is present in both cases. While for 39K such increase can be explained assuming that the major contribution to the losses comes from Hyperfine Changing Collisions, a different loss mechanism must be considered for 40K, which has an inverted ground state hyperfine structure. The experimental results of both isotopes are well reproduced by an alternative model based on radiative escape as the dominant loss mechanism.

arXiv:physics/0105015May 4, 20010 citations

Measurement of the collisional trap loss rate in magneto-optically trapped {sup 7}Li and {sup 6}Li

Nicholas W. M. Ritchie, Yangyang Xiao, E. Abraham +1 more

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We report on measurements of trap-loss collisions between ultracold Rb atoms that are confined in a magneto-optical trap. Both isotopes, ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb},$ have been studied over a wide range of trap laser intensities and detunings. The trap-loss collisional rate constant exhibits variations over three orders of magnitude. At low intensities and/or large detunings, the trap loss is dominated by ground-state hyperfine-changing collisions, while at high intensities and small detunings, collisions involving excited atoms are more important. We see significant differences between the isotopes in both regimes. At large detunings, the ability of the trap to recapture products of a hyperfine-changing collision 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. A surprisingly large increase in this rate is seen when the confining power of the trap is reduced.We report on measurements of trap-loss collisions between ultracold Rb atoms that are confined in a magneto-optical trap. Both isotopes, ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb},$ have been studied over a wide range of trap laser intensities and detunings. The trap-loss collisional rate constant exhibits variations over three orders of magnitude. At low intensities and/or large detunings, the trap loss is dominated by ground-state hyperfine-changing collisions, while at high intensities and small detunings, collisions involving excited atoms are more important. We see significant differences between the isotopes in both regimes. At large detunings, the ability of the trap to recapture products of a hyperfine-changing collision 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. A surprisingly large increase in this rate is seen when the confining power of the trap is reduced.

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Comparison of trap-loss collision spectra for Rb85 and Rb87

Paul Feng, Dominikus Hoffmann, Thad G Walker

We present measurements of excited-state trap-loss collisions of optically trapped $^{85}\mathrm{Rb}$ and $^{87}\mathrm{Rb}$ atoms as a function of the frequency of the light used to excite the colliding atom pairs. For detunings outside the excited-state hyperfine structure, the trap-loss rates are found to be the same for the two isotopes. For detunings inside the excited-state hyperfine structure, $^{87}\mathrm{Rb}$ collisions occur at a substantially lower rate than those of $^{85}\mathrm{Rb}$ . The spectra make it clear that the long-range dynamics of the collisions are strongly modified by the excited-state hyperfine structure, and that the dynamics are different for the two isotopes.We present measurements of excited-state trap-loss collisions of optically trapped $^{85}\mathrm{Rb}$ and $^{87}\mathrm{Rb}$ atoms as a function of the frequency of the light used to excite the colliding atom pairs. For detunings outside the excited-state hyperfine structure, the trap-loss rates are found to be the same for the two isotopes. For detunings inside the excited-state hyperfine structure, $^{87}\mathrm{Rb}$ collisions occur at a substantially lower rate than those of $^{85}\mathrm{Rb}$. The spectra make it clear that the long-range dynamics of the collisions are strongly modified by the excited-state hyperfine structure, and that the dynamics are different for the two isotopes.

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Optical trapping of cold fermionic potassium for collisional studies

G. Roati, W. Jastrzȩbski, Andrea Simoni +2 more

We report on trapping of fermionic ${}^{40}\mathrm{K}$ atoms in a red-detuned standing-wave optical trap, loaded from a magneto-optical trap. Typically, unpolarized samples of ${10}^{6}$ atoms are loaded at a density of ${10}^{12}{\mathrm{cm}}^{\ensuremath{-}3}$ and a temperature of $65\ensuremath{\mu}\mathrm{K},$ and trapped for more than 1 s. The optical trap appears to be the proper environment for performing collisional measurements on the cold atomic sample. In particular, we measure the spherically averaged elastic collision rate by detecting the rethermalization following an intentional parametric heating of the atoms. We also measure spherically averaged inelastic two-body collision rates for atoms in the ground hyperfine states, through detection of trap losses.We report on trapping of fermionic ${}^{40}\mathrm{K}$ atoms in a red-detuned standing-wave optical trap, loaded from a magneto-optical trap. Typically, unpolarized samples of ${10}^{6}$ atoms are loaded at a density of ${10}^{12}{\mathrm{cm}}^{\ensuremath{-}3}$ and a temperature of $65\ensuremath{\mu}\mathrm{K},$ and trapped for more than 1 s. The optical trap appears to be the proper environment for performing collisional measurements on the cold atomic sample. In particular, we measure the spherically averaged elastic collision rate by detecting the rethermalization following an intentional parametric heating of the atoms. We also measure spherically averaged inelastic two-body collision rates for atoms in the ground hyperfine states, through detection of trap losses.

arXiv:physics/0010065Physical Review AApr 16, 200118 citations

We report on measurements of trap-loss collisions between ultracold Rb atoms that are confined in a magneto-optical trap. Both isotopes,

{}^{85}\mathrm{Rb}

and

{}^{87}\mathrm{Rb},

have been studied over a wide range of trap laser intensities and detunings. The trap-loss collisional rate constant exhibits variations over three orders of magnitude. At low intensities and/or large detunings, the trap loss is dominated by ground-state hyperfine-changing collisions, while at high intensities and small detunings, collisions involving excited atoms are more important. We see significant differences between the isotopes in both regimes. At large detunings, the ability of the trap to recapture products of a hyperfine-changing collision 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. A surprisingly large increase in this rate is seen when the confining power of the trap is reduced.

We have studied heteronuclear and homonuclear excited-state--ground-state collisions by loading both

^{85}\mathrm{Rb}

and

^{87}\mathrm{Rb}

into a far off resonant trap (FORT). Because of the relatively weak confinement of the FORT, we expect the hyperfine structure of the different isotopes to play a crucial role in the collision rates. This dependence on hyperfine structure allows us to measure collisions associated with long-range interatomic potentials of different structures, such as long and short ranged; or such as purely attractive, purely repulsive, or mixed attractive and repulsive. We observe significantly different loss rates for different excited-state potentials. Additionally, we observe that some collisional channels' loss rates are saturated at our operating intensities

(15\phantom{\rule{0.3em}{0ex}}\mathrm{mW}∕{\mathrm{cm}}^{2})

. These losses are important limitations in loading dual isotope optical traps.

We present measurements of excited-state trap-loss collisions of optically trapped

^{85}\mathrm{Rb}

and

^{87}\mathrm{Rb}

atoms as a function of the frequency of the light used to excite the colliding atom pairs. For detunings outside the excited-state hyperfine structure, the trap-loss rates are found to be the same for the two isotopes. For detunings inside the excited-state hyperfine structure,

^{87}\mathrm{Rb}

collisions occur at a substantially lower rate than those of

^{85}\mathrm{Rb}

. The spectra make it clear that the long-range dynamics of the collisions are strongly modified by the excited-state hyperfine structure, and that the dynamics are different for the two isotopes.

We report on trapping of fermionic

{}^{40}\mathrm{K}

atoms in a red-detuned standing-wave optical trap, loaded from a magneto-optical trap. Typically, unpolarized samples of

{10}^{6}

atoms are loaded at a density of ${10}^{12}{\mathrm{cm}}^{\ensuremath{-}3}$ and a temperature of $65\ensuremath{\mu}\mathrm{K},$ and trapped for more than 1 s. The optical trap appears to be the proper environment for performing collisional measurements on the cold atomic sample. In particular, we measure the spherically averaged elastic collision rate by detecting the rethermalization following an intentional parametric heating of the atoms. We also measure spherically averaged inelastic two-body collision rates for atoms in the ground hyperfine states, through detection of trap losses.