© 2026 Aqora Quantum S.A.S.

Terms Privacy Legal Notice

Bulletin of the American Physical Society

Electron-atom collisions: From Franck-Hertz experiment to atom traps

Chang-Chun Lin

Published May 1, 1996• 0 citations

Abstract

The key features of the cross sections for electron-impact excitation out of the ground levels of the rare-gas atoms are summarized and application of these cross section data is shown. This is followed by discussions of recent experiments on determination of electron-impact cross sections for excitation out of the metastable levels of He and Ar. The metastiable atom targets are produced by two different methods, i.e., hollow-cathode discharges and charge-exchange collisions of rare-gas ions with Cs atoms. The former method is simple but is limited to low electron energies because of the very small metastable concentration, whereas the latter method yields a fast target beam with predominantly metastable atoms allowing measurements up to the keV range. The measured cross sections show features very different from those of excitation out of the ground levels. Another new development in electron-atom collision is the use of atom traps for measuring ionization cross sections. The experiment is conducted by passing an electron beam pulse through magneto-optically trapped Rb atoms while the trap is momentarily turned off. Turning the trap back on immediately after the electron beam pulse recaptures the unionized atoms allowing only the ions to escape. The ionization cross section is determined bymore » measuring the electron beam current density at the trapped atom region and the fractional loss of trapped atoms due to the electron beam. This method avoids measurements of the absolute number of the target atoms and the overlap between the atomic and electron beams and therefore eliminates the major sources of uncertainty associated with the crossed-beam method for measuring ionization cross section.« less

Related papers

Electron-Scattering Measurements using a Magneto-Optical Trap

Thad G Walker

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.« less

Bulletin of the American Physical Society•May 1, 1996•0 citations

Electron Collision Cross-Sections Measured with the Use of a Magneto-Optical Trap

R. Scott Schappe, P Feng, L. W. Anderson +2 more

We present the first application of optically trapped atoms as targets for a scattering experiment. We report absolute total electron scattering cross-sections for ground-state Rb atoms in the range of 7-500 eV.

Europhysics Letters (EPL)•Feb 20, 1995•34 citations

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

L. J. Uhlmann, R. G. Dall, Andrew G. Truscott +3 more

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.

Physical Review Letters•May 3, 2005•36 citations

Electron-impact ionization cross sections out of the ground and 6P2 excited states of cesium

Michał Łukomski, Sean Sutton, W. Kedzierski +6 more

An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the ``trap loss'' technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs $6\phantom{\rule{0.2em}{0ex}}^{2}{P}_{3∕2}$ state between $7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and $400\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region $(<11\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

Physical Review A•Sep 21, 2006•27 citations

Electron collision studies of cesium using a magneto-optical trap.

J. A. MacAskill

Experiments involving a magneto-optical trap (MOT) as the target in electron impact cross section studies were carried out. The use of a MOT allows the kinematic properties of the target atoms, and their electronic states, to be controlled via operating parameters of the MOT's lasers. A MOT is capable of saturating the excited state of a gaseous target of atoms and provides a unique opportunity to measure exotic collision processes. Measurements use a trap-loss technique to relate the loss rate of atoms from the trap due to electron interactions to a collision cross section. Total scattering cross section measurements are given for the 62S 1/2 ground state and the 62P3/2 excited state of cesium. The excited state measurement is the first measurement of its kind. Total ionization cross sections are also presented for the both the 6 2S1/2 ground state and 62P3/2 excited state. The ionization cross sections are measured by adjusting the radiation force of the MOT lasers to damp the elastic scattering component of the total cross section. The ionization cross section for the excited state is the first experimental determination of its kind. Full details of the experimental apparatus and the analysis procedure are presented. The results of this experiment are combined with other experimental data and compared to the most recent calculations.Dept. of Physics. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2003 .M322. Source: Dissertation Abstracts International, Volume: 64-10, Section: B, page: 4996. Adviser: J. W. McConkey. Thesis (Ph.D.)--University of Windsor (Canada), 2003.

•Oct 1, 2003•1 citation

ELECTRONIC EXCITATION OF METASTABLE STATES OF RARE GAS ATOMS

A. A. Mityureva

The important role of the scientific school of Prof. I. Zapisochny in the study of electron-atom collisions and its determination of most important parameters in this field are emphasized. The processes of electron-impact excitation to and from the metastable states of rare gases atoms are examined. The methods of measurement of the cross sections for such processes are described and the influence of cascade population on the metastable cross sections discussed also. The cross section data are presented. Keywords: electron-atom collisions, metastable states,

Scientific Herald of Uzhhorod University Series Physics•Jul 4, 2013•0 citations

The key features of the cross sections for electron-impact excitation out of the ground levels of the rare-gas atoms are summarized and application of these cross section data is shown. This is followed by discussions of recent experiments on determination of electron-impact cross sections for excitation out of the metastable levels of He and Ar. The metastiable atom targets are produced by two different methods, i.e., hollow-cathode discharges and charge-exchange collisions of rare-gas ions with Cs atoms. The former method is simple but is limited to low electron energies because of the very small metastable concentration, whereas the latter method yields a fast target beam with predominantly metastable atoms allowing measurements up to the keV range. The measured cross sections show features very different from those of excitation out of the ground levels. Another new development in electron-atom collision is the use of atom traps for measuring ionization cross sections. The experiment is conducted by passing an electron beam pulse through magneto-optically trapped Rb atoms while the trap is momentarily turned off. Turning the trap back on immediately after the electron beam pulse recaptures the unionized atoms allowing only the ions to escape. The ionization cross section is determined bymore » measuring the electron beam current density at the trapped atom region and the fractional loss of trapped atoms due to the electron beam. This method avoids measurements of the absolute number of the target atoms and the overlap between the atomic and electron beams and therefore eliminates the major sources of uncertainty associated with the crossed-beam method for measuring ionization cross section.« less

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.« less

An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the ``trap loss'' technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs

6\phantom{\rule{0.2em}{0ex}}^{2}{P}_{3∕2}

state between

7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}

and

400\phantom{\rule{0.3em}{0ex}}\mathrm{eV}

. CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region

(<11\phantom{\rule{0.3em}{0ex}}\mathrm{eV})

where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

Experiments involving a magneto-optical trap (MOT) as the target in electron impact cross section studies were carried out. The use of a MOT allows the kinematic properties of the target atoms, and their electronic states, to be controlled via operating parameters of the MOT's lasers. A MOT is capable of saturating the excited state of a gaseous target of atoms and provides a unique opportunity to measure exotic collision processes. Measurements use a trap-loss technique to relate the loss rate of atoms from the trap due to electron interactions to a collision cross section. Total scattering cross section measurements are given for the 62S 1/2 ground state and the 62P3/2 excited state of cesium. The excited state measurement is the first measurement of its kind. Total ionization cross sections are also presented for the both the 6 2S1/2 ground state and 62P3/2 excited state. The ionization cross sections are measured by adjusting the radiation force of the MOT lasers to damp the elastic scattering component of the total cross section. The ionization cross section for the excited state is the first experimental determination of its kind. Full details of the experimental apparatus and the analysis procedure are presented. The results of this experiment are combined with other experimental data and compared to the most recent calculations.Dept. of Physics. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2003 .M322. Source: Dissertation Abstracts International, Volume: 64-10, Section: B, page: 4996. Adviser: J. W. McConkey. Thesis (Ph.D.)--University of Windsor (Canada), 2003.

The important role of the scientific school of Prof. I. Zapisochny in the study of electron-atom collisions and its determination of most important parameters in this field are emphasized. The processes of electron-impact excitation to and from the metastable states of rare gases atoms are examined. The methods of measurement of the cross sections for such processes are described and the influence of cascade population on the metastable cross sections discussed also. The cross section data are presented. Keywords: electron-atom collisions, metastable states,