Physical Review Letters

Time-Resolved Studies of Ultracold Ionizing Collisions

Chad Orzel, Scott Bergeson, S. A. Kulin, S. L. Rolston

Published Jun 8, 1998• 21 citations

Abstract

Using 40 ns laser pulses, we probe the real-time dynamics of ultracold ionizing collisions in metastable xenon. We time resolve both shielding and enhancement effects, and observe the production of ${\mathrm{Xe}}_{2}^{+}$ molecular ions through associative ionization. We estimate the rate of molecule formation in excited-state collisions, and directly measure the role of both flux enhancement and excited state survival in the collisional enhancement process. Conceptually simple theoretical models are used to predict the dynamics of the collisional shielding.

DOI: 10.1103/physrevlett.80.5093

Related papers

Ultracold collisions and optical shielding in metastable xenon

Kalle‐Antti Suominen, Keith R. Burnett, Paul S. Julienne +5 more

Physical Review AMar 1, 199631 citations

Ultracold Collisions Observed in Real Time

S. D. Gensemer, P. L. Gould

Physical Review LettersFeb 2, 199841 citations

Photoassociation of atoms in ultracold collisions probed by wave-packet dynamics

Mette Machholm, Annick Giusti-Suzor, Frederick H. Mies

Physical Review ADec 1, 199450 citations

Optical Control of Ultracold Collisions in Metastable Xenon

M. Walhout, Uwe Sterr, Chad Orzel +2 more

Physical Review LettersJan 23, 199585 citations

Suppression and Enhancement of Collisions in Optical Lattices

John Lawall, Chad Orzel, S. L. Rolston

Physical Review LettersJan 19, 199816 citations

Dynamics of photoinduced collisions of cold atoms probed with picosecond laser pulses

Fredrik K. Fatemi, K. M. Jones, He Wang +2 more

Physical Review AAug 17, 200135 citations

Physical Review Letters

Time-Resolved Studies of Ultracold Ionizing Collisions

Chad Orzel, Scott Bergeson, S. A. Kulin, S. L. Rolston

Published Jun 8, 1998• 21 citations

Publisher

Abstract

Using 40 ns laser pulses, we probe the real-time dynamics of ultracold ionizing collisions in metastable xenon. We time resolve both shielding and enhancement effects, and observe the production of

{\mathrm{Xe}}_{2}^{+}

molecular ions through associative ionization. We estimate the rate of molecule formation in excited-state collisions, and directly measure the role of both flux enhancement and excited state survival in the collisional enhancement process. Conceptually simple theoretical models are used to predict the dynamics of the collisional shielding.

DOI: 10.1103/physrevlett.80.5093

Related papers

Ultracold collisions and optical shielding in metastable xenon

Kalle‐Antti Suominen, Keith R. Burnett, Paul S. Julienne +5 more

Collisions between laser-cooled metastable xenon atoms in the presence of laser fields provide a good experimental test for ultracold collision theories as the observed ionization can be directly linked to the atomic binary collisions. Hyperfine structure is not present for the even isotopes ${\mathrm{Xe}}^{132}$ and ${\mathrm{Xe}}^{136}$ , which simplifies the theoretical work. We present our results and show how these and the results presented in Walhout et al. [Phys. Rev. Lett. 74, 605 (1995)] can be interpreted with suitably adapted two-state models. Our approach suggests one possibility why the strong shielding of collisions predicted by the simple two-state model of Suominen et al. [Phys. Rev. A 51, 1446 (1995)] has not been achieved in the xenon experiment. \textcopyright{} 1996 The American Physical Society.Collisions between laser-cooled metastable xenon atoms in the presence of laser fields provide a good experimental test for ultracold collision theories as the observed ionization can be directly linked to the atomic binary collisions. Hyperfine structure is not present for the even isotopes ${\mathrm{Xe}}^{132}$ and ${\mathrm{Xe}}^{136}$, which simplifies the theoretical work. We present our results and show how these and the results presented in Walhout et al. [Phys. Rev. Lett. 74, 605 (1995)] can be interpreted with suitably adapted two-state models. Our approach suggests one possibility why the strong shielding of collisions predicted by the simple two-state model of Suominen et al. [Phys. Rev. A 51, 1446 (1995)] has not been achieved in the xenon experiment. \textcopyright{} 1996 The American Physical Society.

Physical Review AMar 1, 199631 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

Photoassociation of atoms in ultracold collisions probed by wave-packet dynamics

Mette Machholm, Annick Giusti-Suzor, Frederick H. Mies

Photoassociation in laser-assisted collisions of ultracold alkali atoms has been used recently to perform high-precision spectroscopy of very-long-range states. Rovibrational spectra close to the Na(3 $^{2}$ S)+ ${\mathrm{Na}}^{\mathrm{*}}$ (3 $^{2}$ ${\mathit{P}}_{3/2}$ ) dissociation limit have been obtained by monitoring an enhanced ${\mathrm{Na}}_{2}^{+}$ ion signal. We propose the use of pump-probe techniques to study the dynamics of the ionization process. At very large distances (typically 70 a.u.) two colliding Na atoms absorb a photon and form a coherent vibrational wave packet. We follow the packet in time and probe two possible mechanisms that are proposed to yield molecular ions: photoionization, where the second photon is absorbed at a small internuclear distance R directly ionizing the molecule, and associative ionization with excitation at intermediate R to the nuclear continuum of a doubly excited state followed by a half collision and autoionization at small R. The latter event can also lead to dissociation of the complex. The two mechanisms lead to distinct differences in the ion signals as a function of delay time between the pump and the probe pulses. Estimates of the ion rates to be expected in actual pump-probe experiments are given, which tend to favor the autoionization mechanism as the dominant reaction path.Photoassociation in laser-assisted collisions of ultracold alkali atoms has been used recently to perform high-precision spectroscopy of very-long-range states. Rovibrational spectra close to the Na(3 $^{2}$S)+${\mathrm{Na}}^{\mathrm{*}}$(3 $^{2}$${\mathit{P}}_{3/2}$) dissociation limit have been obtained by monitoring an enhanced ${\mathrm{Na}}_{2}^{+}$ ion signal. We propose the use of pump-probe techniques to study the dynamics of the ionization process. At very large distances (typically 70 a.u.) two colliding Na atoms absorb a photon and form a coherent vibrational wave packet. We follow the packet in time and probe two possible mechanisms that are proposed to yield molecular ions: photoionization, where the second photon is absorbed at a small internuclear distance R directly ionizing the molecule, and associative ionization with excitation at intermediate R to the nuclear continuum of a doubly excited state followed by a half collision and autoionization at small R. The latter event can also lead to dissociation of the complex. The two mechanisms lead to distinct differences in the ion signals as a function of delay time between the pump and the probe pulses. Estimates of the ion rates to be expected in actual pump-probe experiments are given, which tend to favor the autoionization mechanism as the dominant reaction path.

Physical Review ADec 1, 199450 citations

Optical Control of Ultracold Collisions in Metastable Xenon

M. Walhout, Uwe Sterr, Chad Orzel +2 more

Near-resonant light is used to modify the collision dynamics of magneto-optically trapped metastable xenon atoms. Enhanced collisional ionization occurs for a "control laser" tuned below resonance, greatly exceeding the predictions of existing models of trap loss very close to resonance. With the trapping laser off, control light tuned above resonance suppresses ionization by a factor of 8. With the trap light on, a suppression factor >30 is observed. Increases in the number and density of trapped atoms and in the trap lifetime attest to the utility of optical control of collisions.Near-resonant light is used to modify the collision dynamics of magneto-optically trapped metastable xenon atoms. Enhanced collisional ionization occurs for a "control laser" tuned below resonance, greatly exceeding the predictions of existing models of trap loss very close to resonance. With the trapping laser off, control light tuned above resonance suppresses ionization by a factor of 8. With the trap light on, a suppression factor >30 is observed. Increases in the number and density of trapped atoms and in the trap lifetime attest to the utility of optical control of collisions.

Physical Review LettersJan 23, 199585 citations

Suppression and Enhancement of Collisions in Optical Lattices

John Lawall, Chad Orzel, S. L. Rolston

In a three-dimensional optical lattice for metastable xenon we observe the dynamical effects of the optical potential on Penning ionizing collisions between atoms. Enhancement of collisions over that for free atoms is observed at short times after the atoms are loaded into the lattice. After the atoms thermalize and localize into the potential wells, we observe a suppression of the collisions by as much as a factor of 2. From our measurements and a simple model we are able to extract an estimate of the rate at which atoms ``hop'' between wells.In a three-dimensional optical lattice for metastable xenon we observe the dynamical effects of the optical potential on Penning ionizing collisions between atoms. Enhancement of collisions over that for free atoms is observed at short times after the atoms are loaded into the lattice. After the atoms thermalize and localize into the potential wells, we observe a suppression of the collisions by as much as a factor of 2. From our measurements and a simple model we are able to extract an estimate of the rate at which atoms ``hop'' between wells.

Physical Review LettersJan 19, 199816 citations

Dynamics of photoinduced collisions of cold atoms probed with picosecond laser pulses

Fredrik K. Fatemi, K. M. Jones, He Wang +2 more

Pump-probe experiments are performed in which cold colliding Na atoms are photoassociated to form ${\mathrm{Na}}_{2}$ molecules, and subsequently ionized. The experiments are performed in a regime where the pulsed photoassociation to an intermediate potential takes place at long range, and to several electronic, vibrational, and rotational states. A probe pulse then produces an ionization signal by further exciting these molecules to autoionizing doubly excited states. The time dependence of the ion signal shows a dramatic flux-enhancement effect on a nanosecond time scale due to the motion on the intermediate potentials. This time dependence can be viewed as monitoring the inward motion and dephasing of a population wave packet formed at long range.Pump-probe experiments are performed in which cold colliding Na atoms are photoassociated to form ${\mathrm{Na}}_{2}$ molecules, and subsequently ionized. The experiments are performed in a regime where the pulsed photoassociation to an intermediate potential takes place at long range, and to several electronic, vibrational, and rotational states. A probe pulse then produces an ionization signal by further exciting these molecules to autoionizing doubly excited states. The time dependence of the ion signal shows a dramatic flux-enhancement effect on a nanosecond time scale due to the motion on the intermediate potentials. This time dependence can be viewed as monitoring the inward motion and dephasing of a population wave packet formed at long range.

Physical Review AAug 17, 200135 citations

Using 40 ns laser pulses, we probe the real-time dynamics of ultracold ionizing collisions in metastable xenon. We time resolve both shielding and enhancement effects, and observe the production of

{\mathrm{Xe}}_{2}^{+}

{\mathrm{Xe}}^{132}

and

{\mathrm{Xe}}^{136}

, which simplifies the theoretical work. We present our results and show how these and the results presented in Walhout et al. [Phys. Rev. Lett. 74, 605 (1995)] can be interpreted with suitably adapted two-state models. Our approach suggests one possibility why the strong shielding of collisions predicted by the simple two-state model of Suominen et al. [Phys. Rev. A 51, 1446 (1995)] has not been achieved in the xenon experiment. \textcopyright{} 1996 The American Physical Society.

^{2}

S)+

{\mathrm{Na}}^{\mathrm{*}}

^{2}

{\mathit{P}}_{3/2}

) dissociation limit have been obtained by monitoring an enhanced

{\mathrm{Na}}_{2}^{+}

ion signal. We propose the use of pump-probe techniques to study the dynamics of the ionization process. At very large distances (typically 70 a.u.) two colliding Na atoms absorb a photon and form a coherent vibrational wave packet. We follow the packet in time and probe two possible mechanisms that are proposed to yield molecular ions: photoionization, where the second photon is absorbed at a small internuclear distance R directly ionizing the molecule, and associative ionization with excitation at intermediate R to the nuclear continuum of a doubly excited state followed by a half collision and autoionization at small R. The latter event can also lead to dissociation of the complex. The two mechanisms lead to distinct differences in the ion signals as a function of delay time between the pump and the probe pulses. Estimates of the ion rates to be expected in actual pump-probe experiments are given, which tend to favor the autoionization mechanism as the dominant reaction path.

Pump-probe experiments are performed in which cold colliding Na atoms are photoassociated to form

{\mathrm{Na}}_{2}

molecules, and subsequently ionized. The experiments are performed in a regime where the pulsed photoassociation to an intermediate potential takes place at long range, and to several electronic, vibrational, and rotational states. A probe pulse then produces an ionization signal by further exciting these molecules to autoionizing doubly excited states. The time dependence of the ion signal shows a dramatic flux-enhancement effect on a nanosecond time scale due to the motion on the intermediate potentials. This time dependence can be viewed as monitoring the inward motion and dephasing of a population wave packet formed at long range.