We have observed violet photon emission resulting from energy-pooling collisions between ultracold Rb atoms illuminated by two colors of near-resonant infrared laser light. We have used this emission as a probe of doubly excited state ultracold collision dynamics. We have observed the lowest saturation intensity for light-induced ultracold collisions seen to date which we identify as due to depletion of incoming ground state flux. We have also varied the detuning of the lasers which allows us to clearly identify the effect of spontaneous emission and optical shielding.We have observed violet photon emission resulting from energy-pooling collisions between ultracold Rb atoms illuminated by two colors of near-resonant infrared laser light. We have used this emission as a probe of doubly excited state ultracold collision dynamics. We have observed the lowest saturation intensity for light-induced ultracold collisions seen to date which we identify as due to depletion of incoming ground state flux. We have also varied the detuning of the lasers which allows us to clearly identify the effect of spontaneous emission and optical shielding.

Physical Review LettersJul 27, 19989 citations

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

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

M. G. Peters, Dominikus Hoffmann, Joseph D. Tobiason +1 more

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.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.

Physical Review AAug 1, 199435 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

Collisions of ultracoldtrapped atoms

Paul S. Julienne, Frederick H. Mies

Collisions of ultracold atoms can now be investigated in the laboratory at temperatures below 0.001 K. Such collisions are qualitatively different in many ways from collisions at normal energies, where T ≫ 1 K, because of the long time and distance scales associated with such collisions. Spontaneous emission can strongly modify collision dynamics of excited-state species produced by near-resonant optical excitation if the temperature is less than the characteristic temperature TS, where the collision time is comparable with the spontaneous-emission lifetime. We also estimate the temperature TQ that is characteristic of the onset of quantum threshold behavior, where the WKB approximation fails to apply as the de Broglie wavelength becomes large. We find that TQ is generally larger than TD, the Doppler cooling limit, except for collisions controlled by long-range potentials varying as 1/R3.TQ may be larger or smaller than TS. Expressions for estimating the magnitude of rate coefficients in the T → 0 limit are given. As an example, a model for the threshold behavior of Penning ionization of two He 3S1 metastable atoms is given, and the threshold rate coefficient is estimated to be >5 × 10−10 cm3 sec−1.Collisions of ultracold atoms can now be investigated in the laboratory at temperatures below 0.001 K. Such collisions are qualitatively different in many ways from collisions at normal energies, where T ≫ 1 K, because of the long time and distance scales associated with such collisions. Spontaneous emission can strongly modify collision dynamics of excited-state species produced by near-resonant optical excitation if the temperature is less than the characteristic temperature TS, where the collision time is comparable with the spontaneous-emission lifetime. We also estimate the temperature TQ that is characteristic of the onset of quantum threshold behavior, where the WKB approximation fails to apply as the de Broglie wavelength becomes large. We find that TQ is generally larger than TD, the Doppler cooling limit, except for collisions controlled by long-range potentials varying as 1/R3.TQ may be larger or smaller than TS. Expressions for estimating the magnitude of rate coefficients in the T → 0 limit are given. As an example, a model for the threshold behavior of Penning ionization of two He 3S1 metastable atoms is given, and the threshold rate coefficient is estimated to be >5 × 10−10 cm3 sec−1.

Journal of the Optical Society of America BNov 1, 1989191 citations

Ultracold Collisions Observed in Real Time

S. D. Gensemer, P. L. Gould

In laser-induced collisions between ultracold atoms, the combination of low velocities and long-range interactions results in collision times which can exceed the excited-state lifetime. We use a cooperative effect between two lasers to explicitly observe this time dependence. The first laser, tuned near resonance, excites the atom pair at long range and enhances the collisional flux available for short-range excitation by a second, far-detuned laser. Using pulsed excitation, we find this collisional process to take place on a ${10}^{\ensuremath{-}6}\mathrm{s}$ time scale, in reasonable agreement with trajectory simulations.In laser-induced collisions between ultracold atoms, the combination of low velocities and long-range interactions results in collision times which can exceed the excited-state lifetime. We use a cooperative effect between two lasers to explicitly observe this time dependence. The first laser, tuned near resonance, excites the atom pair at long range and enhances the collisional flux available for short-range excitation by a second, far-detuned laser. Using pulsed excitation, we find this collisional process to take place on a ${10}^{\ensuremath{-}6}\mathrm{s}$ time scale, in reasonable agreement with trajectory simulations.

Physical Review LettersFeb 2, 199841 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}

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.

\\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. ^