Physical Review Letters

Electron Collisions with Laser Cooled and Trapped Metastable Helium Atoms: Total Scattering Cross Sections

L. J. Uhlmann, R. G. Dall, Andrew G. Truscott, Maarten D. Hoogerland, K. G. H. Baldwin, Stephen J. Buckman

Published May 3, 2005• 36 citations

Abstract

Absolute measurements of total scattering cross sections for low energy (5-70 eV) electrons by metastable helium (2(3)S) atoms are presented. The measurements are performed using a magneto-optical trap which is loaded from a laser-cooled, bright beam of slow He(2(3)S) atoms. The data are compared with predictions from convergent close coupling and R matrix with pseudostate calculations, and we find good agreement between experiment and theory.

DOI: 10.1103/physrevlett.94.173201

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Physical Review Letters

Electron Collisions with Laser Cooled and Trapped Metastable Helium Atoms: Total Scattering Cross Sections

L. J. Uhlmann, R. G. Dall, Andrew G. Truscott, Maarten D. Hoogerland, K. G. H. Baldwin, Stephen J. Buckman

Published May 3, 2005• 36 citations

Publisher

Abstract

DOI: 10.1103/physrevlett.94.173201

Related papers

Experiments with a Metastable Helium Atomic Trap

M. Colla

In this work I report on the development of a Magneto Optic Trap (MOT) for metastable helium atoms (He*). The metastable helium atoms are produced in a discharge nozzle source and collimated, slowed and compressed to provide a slow bright beam for loading the trap. The trap confines approximately 107 atoms, has a diameter of about 3 mm and with temperature approximately 1 mK. The trap is used for intra-trap and electron-atom scattering experiments. The results from these two experiments are reported. The electron scattering experiment is unique and employs a He* MOT for the first time, in combination with a new diagnostic technique (Phase Modulation Spectroscopy) to measure the trap loss. The results of these experiments have yielded the first total electron-metastable atom collision cross section measurements at intermediate (10-100 eV) electron energies.In this work I report on the development of a Magneto Optic Trap (MOT) for metastable helium atoms (He*). The metastable helium atoms are produced in a discharge nozzle source and collimated, slowed and compressed to provide a slow bright beam for loading the trap. The trap confines approximately 107 atoms, has a diameter of about 3 mm and with temperature approximately 1 mK. The trap is used for intra-trap and electron-atom scattering experiments. The results from these two experiments are reported. The electron scattering experiment is unique and employs a He* MOT for the first time, in combination with a new diagnostic technique (Phase Modulation Spectroscopy) to measure the trap loss. The results of these experiments have yielded the first total electron-metastable atom collision cross section measurements at intermediate (10-100 eV) electron energies.

Jan 1, 20060 citations

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K. G. H. Baldwin, L. J. Uhlmann, R. G. Dall +2 more

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Optically trapped atoms are in many ways ideal replacements for atomic beams for scattering experiments. In a typical such experiment, a particle beam ejects atoms from the trap at a rate {Gamma} = {sigma}{phi}, where {phi} is the particle flux density and {sigma} the scattering cross section. {Gamma} is easily measured from trap decay transients. Since the trapped atoms have neV kinetic energies, the method is sensitive to extremely small momentum transfers. Since the beam flux is measured, the absolute target density is not required, removing an important source of error for most atomic beam experiments. At Wisconsin the authors have integrated an electron beam with a magneto-optical trap and performed electron-scattering experiments on Rb atoms in the range of 10-1000 eV. In the first experiment they measured total cross sections for scattering from the 5s state by lowering the capture velocity of the trap below the recoil velocity of the scattered atoms. In the second experiment they isolated the total ionization cross section by operating the trap such that virtually all elastically and inelastically scattered atoms were captured by the trap. These experimental results will test new theoretical methods for calculating total and ionization cross sections. Straightforward extensions ofmore » these methods should allow similar measurements using excited-state atoms (5p, 5d) as well. The techniques should also be readily adaptable to the important case of the metastable noble gases.« lessOptically trapped atoms are in many ways ideal replacements for atomic beams for scattering experiments. In a typical such experiment, a particle beam ejects atoms from the trap at a rate {Gamma} = {sigma}{phi}, where {phi} is the particle flux density and {sigma} the scattering cross section. {Gamma} is easily measured from trap decay transients. Since the trapped atoms have neV kinetic energies, the method is sensitive to extremely small momentum transfers. Since the beam flux is measured, the absolute target density is not required, removing an important source of error for most atomic beam experiments. At Wisconsin the authors have integrated an electron beam with a magneto-optical trap and performed electron-scattering experiments on Rb atoms in the range of 10-1000 eV. In the first experiment they measured total cross sections for scattering from the 5s state by lowering the capture velocity of the trap below the recoil velocity of the scattered atoms. In the second experiment they isolated the total ionization cross section by operating the trap such that virtually all elastically and inelastically scattered atoms were captured by the trap. These experimental results will test new theoretical methods for calculating total and ionization cross sections. Straightforward extensions ofmore » these methods should allow similar measurements using excited-state atoms (5p, 5d) as well. The techniques should also be readily adaptable to the important case of the metastable noble gases.« less

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Measurement of low-energy total absolute atomic collision cross sections with the metastable P23 state of neon using a magneto-optical trap

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We present total absolute collision cross sections for neon in the $^{3}P_{2}$ metastable state with ground state, thermal atoms and molecules using a recently developed experimental technique. The technique utilizes a magneto-optical trap (MOT) and involves the measurement of MOT population dynamics to determine the cross section. Collision cross section measurements are presented for metastable neon in the $^{3}P_{2}$ state with He, Ne, Ar, ${\mathrm{H}}_{2}$ , ${\mathrm{O}}_{2}$ , and ${\mathrm{N}}_{2}$ . The average thermal energy of the collision ranges from $11\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}27\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ . The measurements made using this technique have small errors, of the order of 10% of the measured cross section; the technique is capable of producing benchmark collision cross sections.We present total absolute collision cross sections for neon in the $^{3}P_{2}$ metastable state with ground state, thermal atoms and molecules using a recently developed experimental technique. The technique utilizes a magneto-optical trap (MOT) and involves the measurement of MOT population dynamics to determine the cross section. Collision cross section measurements are presented for metastable neon in the $^{3}P_{2}$ state with He, Ne, Ar, ${\mathrm{H}}_{2}$, ${\mathrm{O}}_{2}$, and ${\mathrm{N}}_{2}$. The average thermal energy of the collision ranges from $11\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}27\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. The measurements made using this technique have small errors, of the order of 10% of the measured cross section; the technique is capable of producing benchmark collision cross sections.

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Homonuclear ionizing collisions of laser-cooled metastable helium atoms

R. J. W. Stas, J. M. McNamara, W. Hogervorst +1 more

We present a theoretical and experimental investigation of homonuclear ionizing collisions of laser-cooled metastable $(2\phantom{\rule{0.2em}{0ex}}^{3}S_{1})$ helium atoms, considering both the fermionic $^{3}\mathrm{He}$ and bosonic $^{4}\mathrm{He}$ isotopes. The theoretical description combines quantum threshold behavior, Wigner's spin-conservation rule, and quantum-statistical symmetry requirements in a single-channel model, complementing a more complete close-coupling theory that has been reported for collisions of metastable $^{4}\mathrm{He}$ atoms. The model is supported with measurements (in the absence of light fields) of ionization rates in magneto-optically trapped samples that contain about $3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms of a single isotope. The ionization rates are determined from measurements of trap loss due to light-assisted collisions combined with comparative measurements of the ion production rate in the absence and presence of trapping light. Theory and experiment show good agreement.We present a theoretical and experimental investigation of homonuclear ionizing collisions of laser-cooled metastable $(2\phantom{\rule{0.2em}{0ex}}^{3}S_{1})$ helium atoms, considering both the fermionic $^{3}\mathrm{He}$ and bosonic $^{4}\mathrm{He}$ isotopes. The theoretical description combines quantum threshold behavior, Wigner's spin-conservation rule, and quantum-statistical symmetry requirements in a single-channel model, complementing a more complete close-coupling theory that has been reported for collisions of metastable $^{4}\mathrm{He}$ atoms. The model is supported with measurements (in the absence of light fields) of ionization rates in magneto-optically trapped samples that contain about $3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms of a single isotope. The ionization rates are determined from measurements of trap loss due to light-assisted collisions combined with comparative measurements of the ion production rate in the absence and presence of trapping light. Theory and experiment show good agreement.

arXiv:cond-mat/0601414Physical Review AMar 14, 200623 citations

We present total absolute collision cross sections for neon in the

^{3}P_{2}

metastable state with ground state, thermal atoms and molecules using a recently developed experimental technique. The technique utilizes a magneto-optical trap (MOT) and involves the measurement of MOT population dynamics to determine the cross section. Collision cross section measurements are presented for metastable neon in the

^{3}P_{2}

state with He, Ne, Ar,

{\mathrm{H}}_{2}

{\mathrm{O}}_{2}

, and

{\mathrm{N}}_{2}

. The average thermal energy of the collision ranges from

11\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}27\phantom{\rule{0.3em}{0ex}}\mathrm{meV}

. The measurements made using this technique have small errors, of the order of 10% of the measured cross section; the technique is capable of producing benchmark collision cross sections.

We present a theoretical and experimental investigation of homonuclear ionizing collisions of laser-cooled metastable

(2\phantom{\rule{0.2em}{0ex}}^{3}S_{1})

helium atoms, considering both the fermionic

^{3}\mathrm{He}

and bosonic

^{4}\mathrm{He}

isotopes. The theoretical description combines quantum threshold behavior, Wigner's spin-conservation rule, and quantum-statistical symmetry requirements in a single-channel model, complementing a more complete close-coupling theory that has been reported for collisions of metastable

^{4}\mathrm{He}

atoms. The model is supported with measurements (in the absence of light fields) of ionization rates in magneto-optically trapped samples that contain about $3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms of a single isotope. The ionization rates are determined from measurements of trap loss due to light-assisted collisions combined with comparative measurements of the ion production rate in the absence and presence of trapping light. Theory and experiment show good agreement.