Physical Review A

Laser-induced ultracold Rb(5 S1/2 )+Rb(5 P1/2 ) collisions

M. G. Peters, Dominikus Hoffmann, Joseph D. Tobiason, Thad G Walker

Published Aug 1, 1994• 35 citations

Abstract

Measurements of collisional loss of optically trapped Rb atoms are presented for excitation of the colliding atoms by light tuned near the 5${\mathit{S}}_{1/2}$\ensuremath{\rightarrow}5${\mathit{P}}_{1/2}$ transitions of $^{85}\mathrm{Rb}$ and $^{87}\mathrm{Rb}$. Using the ${\mathit{P}}_{1/2}$ state allows the effects of spontaneous emission on excited-state collisions to be studied with minimal complications arising from hyperfine structure. The shapes of the collision spectra are nearly identical for the two isotopes and are consistent with a simple model for the role of spontaneous emission during the collision.

DOI: 10.1103/physreva.50.r906

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Physical Review A

Laser-induced ultracold Rb(5 S1/2 )+Rb(5 P1/2 ) collisions

M. G. Peters, Dominikus Hoffmann, Joseph D. Tobiason, Thad G Walker

Published Aug 1, 1994• 35 citations

Publisher

Abstract

Measurements of collisional loss of optically trapped Rb atoms are presented for excitation of the colliding atoms by light tuned near the 5

{\mathit{S}}_{1/2}

\ensuremath{\rightarrow}5

{\mathit{P}}_{1/2}

transitions of

^{85}\mathrm{Rb}

and

^{87}\mathrm{Rb}

. Using the

{\mathit{P}}_{1/2}

state allows the effects of spontaneous emission on excited-state collisions to be studied with minimal complications arising from hyperfine structure. The shapes of the collision spectra are nearly identical for the two isotopes and are consistent with a simple model for the role of spontaneous emission during the collision.

DOI: 10.1103/physreva.50.r906

Related papers

The effects of hyperfine interactions on collisions between optically trapped atoms

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The authors report measurements of excited state collision rates of optically trapped {sup 85}Rb and {sup 87}Rb. The collision rates have been measured in the vicinity of the P{sub 3/2} and P{sub 1/2} states of both isotopes. By studying the collision rates as a function of the frequency of light used to cause the collisions, they obtain collision spectra that reveal the importance of hyperfine interactions on the collision dynamics. In certain frequency ranges the collision rates for the two isotopes are nearly identical, while in others they find substantially reduced rates for {sup 87}Rb (large hyperfine interaction) as compared to {sup 85}Rb (small hyperfine interaction). For the P{sub 1/2} states, where hyperfine splittings are large compared to the characteristic frequency scales for these collisions, the shapes of the spectra more closely correspond to those expected from simple models that neglect hyperfine interactions.The authors report measurements of excited state collision rates of optically trapped {sup 85}Rb and {sup 87}Rb. The collision rates have been measured in the vicinity of the P{sub 3/2} and P{sub 1/2} states of both isotopes. By studying the collision rates as a function of the frequency of light used to cause the collisions, they obtain collision spectra that reveal the importance of hyperfine interactions on the collision dynamics. In certain frequency ranges the collision rates for the two isotopes are nearly identical, while in others they find substantially reduced rates for {sup 87}Rb (large hyperfine interaction) as compared to {sup 85}Rb (small hyperfine interaction). For the P{sub 1/2} states, where hyperfine splittings are large compared to the characteristic frequency scales for these collisions, the shapes of the spectra more closely correspond to those expected from simple models that neglect hyperfine interactions.

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Effects of laser light on ultracold atom collisions

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Comparison of trap-loss collision spectra for Rb85 and Rb87

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Role of spontaneous emission in ultracold two-color optical collisions

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Trap-loss collisions of 85 Rb and 87 Rb : Dependence on trap parameters

S. D. Gensemer, V. Sánchez-Villicaña, K. Y. N. Tan +2 more

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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Light-induced collisions of ultracold rubidium atoms

Dominikus Hoffmann

In this dissertation I present a variety of experiments on collisions between ultra-cold rubidium atoms. These collisions take place in light-force atom traps, where temperatures below 1 mK are reached. At these low temperatures weak, long-range interactions between the atoms are important, and collision times are long. Consequently, the absorption and spontaneous emission of photons plays an important role in determining the collision dynamics. The collisions studied in this dissertation involve excitation of the atoms to a state where the relatively strong dipole-dipole interaction with another atom results in attraction (or repulsion) after which spontaneous emission may take place. The resulting energy transfer in such a collision can eject the atoms from the trap. We have observed such collisions in both stable isotopes of rubidium. If the excitedstate is involved, the two isotopes behave quite di ff erently. This makes clear the importance of hyperfine interactions in the collision dynamics. In contrast, for the excited-state such di ff erences disappeare, because the hyperfine interaction is strong enough to eliminate hyperfine mixing of the potentials. Another collision process involved collisions with a repulsive dipole-dipole interaction. This experiment gives strong support for a Landau-Zener treatment of the excitation process. These collisions enabled the measurement of the trap depth. Finally, collisions between rubidium atoms that have undergone a two-step excitation by two near-infrared photons produce violet fluorescence as a signature of the collision. We have observed this e ff ect. The data shows unexpected features, which warrant further investigation. P3 2 ⁄In this dissertation I present a variety of experiments on collisions between ultra-cold rubidium atoms. These collisions take place in light-force atom traps, where temperatures below 1 mK are reached. At these low temperatures weak, long-range interactions between the atoms are important, and collision times are long. Consequently, the absorption and spontaneous emission of photons plays an important role in determining the collision dynamics. The collisions studied in this dissertation involve excitation of the atoms to a state where the relatively strong dipole-dipole interaction with another atom results in attraction (or repulsion) after which spontaneous emission may take place. The resulting energy transfer in such a collision can eject the atoms from the trap. We have observed such collisions in both stable isotopes of rubidium. If the excitedstate is involved, the two isotopes behave quite di ff erently. This makes clear the importance of hyperfine interactions in the collision dynamics. In contrast, for the excited-state such di ff erences disappeare, because the hyperfine interaction is strong enough to eliminate hyperfine mixing of the potentials. Another collision process involved collisions with a repulsive dipole-dipole interaction. This experiment gives strong support for a Landau-Zener treatment of the excitation process. These collisions enabled the measurement of the trap depth. Finally, collisions between rubidium atoms that have undergone a two-step excitation by two near-infrared photons produce violet fluorescence as a signature of the collision. We have observed this e ff ect. The data shows unexpected features, which warrant further investigation. P3 2 ⁄

Jan 1, 19960 citations

Measurements of collisional loss of optically trapped Rb atoms are presented for excitation of the colliding atoms by light tuned near the 5

{\mathit{S}}_{1/2}

\ensuremath{\rightarrow}5

{\mathit{P}}_{1/2}

transitions of

^{85}\mathrm{Rb}

and

^{87}\mathrm{Rb}

. Using the

{\mathit{P}}_{1/2}

\\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 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 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.