Absolute Electron-Impact Ionization Cross Section Measurements Using a Magneto-Optical Trap

Schappe, R. Scott; Walker, Thad; Anderson, L. W.; Lin, Chun C.

doi:10.1103/physrevlett.76.4328

Cited by 56 publications

(36 citation statements)

References 25 publications

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“…These measurements involve collisions of trapped neutral particles with neutral atoms and molecules [20][21][22][23][24], electron beams [25][26][27], and trapped ions [28][29][30]. Photoionization cross sections have also been investigated though measurements of trap loss rates [31][32][33].…”

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Trap-depth determination from residual gas collisions

et al. 2011

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We present a method for determining the depth of an atomic or molecular trap of any type. This method relies on a measurement of the trap loss rate induced by collisions with background gas particles. Given a fixed gas composition, the loss rate uniquely determines the trap depth. Because of the "soft" long-range nature of the van der Waals interaction, these collisions transfer kinetic energy to trapped particles across a broad range of energy scales, from room temperature to the microkelvin energy scale. The resulting loss rate therefore exhibits a significant variation over an enormous range of trap depths, making this technique a powerful diagnostic with a large dynamic range. We present trap depth measurements of a Rb magneto-optical trap using this method and a different technique that relies on measurements of loss rates during optical excitation of colliding atoms to a repulsive molecular state. The main advantage of the method presented here is its large dynamic range and applicability to traps of any type requiring only knowledge of the background gas density and the interaction potential between the trapped and background gas particles.The particle loss rate from a trap is one of the primary observables for probing the collisional physics of trapped gases. Measurements of trap loss are routinely made in a variety of experiments to deduce elastic and inelastic collision cross sections for intratrap collisions and for collisions between trapped species and externally introduced particles. Trap depth often plays an important role in the interpretation of these measurements. A well-studied example of this is the large intensity-dependent variation displayed by the two-body intratrap loss-rate coefficient for atoms trapped in a magnetooptical trap (MOT). This variation results from an interplay of trap depth and the energy imparted to trapped atoms due to hyperfine or fine structure changing collisions, as well as radiative escape [1][2][3][4][5][6][7][8][9][10][11][12]. More recently, inelastic and elastic collision rates in dipole traps have been of interest, particularly for metastable species [13,14]. The fraction of elastic collisions resulting in an evaporated atom depends on trap depth, which is a key parameter for evaporative cooling [13,15,16]. The lifetime dependence of a state-insenstive dipole trap on trap depth for cesium atoms has also recently been investigated [17]. Of course the most fundamental role of trap depth is that it be large enough to provide sufficient confinement, which has been an issue for experiments with buffer-gas-cooled atoms or molecules [18,19].In recent years there has been interest in making precision determinations of collision cross-sections from measurements of particle loss rates due to externally introduced particles. These measurements involve collisions of trapped neutral particles with neutral atoms and molecules [20][21][22][23][24], electron beams [25][26][27], and trapped ions [28][29][30]. Photoionization cross sections have also been investigated though mea...

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Trap-depth determination from residual gas collisions

et al. 2011

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“…(In photoionization the 3 =1 ratio is 15 times larger at 424 eV, easing the signal/background requirements.) The use of ultracold atom targets for electron scattering studies was pioneered for absolute ionization cross section measurements [28]. The basic strategy was to prepare a target of ultracold lithium atoms at the center of a time-of-flight (TOF) ion spectrometer.…”

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Triple Ionization of Lithium by Electron Impact

et al. 2003

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Ejection of the three electrons from lithium in a single electron collision has been observed for the first time. Triply charged lithium was observed in an ion time-of-flight spectrum following electron impact on a sample of ultracold, trapped lithium. The higher signal/background afforded by the trap environment made the observation of Li3+ possible. We measured the ratios of triple-to-double and double-to-single ionization at an impact energy of 1000 eV. The 3+/2+ ratio is approximately 0.001, a value 2 orders of magnitude lower than semiempirical predictions. We present a simple method that uses photoionization data combined with sum-rule analysis to predict the asymptotic charge-state ratios. The sum-rule predictions compare reasonably with experiment and shake calculations, but disagree sharply with the semiempirical estimates.

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“…The atoms are located far from the discharge source at the center of a 3D magneto-optical trap (MOT) which is loaded from a bright beam of He2 3 S atoms, also produced by laser-cooling techniques. Atom trap-based techniques have been used previously for electron collision studies, but not with metastable excited atomic species such as He2 3 S. Previous experiments have involved total cross section measurements on Rb [12] and Cs [13] and total ionization measurements on Rb [14]. A similar experimental approach has been used here, although the light mass and strong Penning ionization of the He atoms provides for substantially greater difficulties in maintaining significant metastable atom densities.…”

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

et al. 2005

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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.

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Absolute Electron-Impact Ionization Cross Section Measurements Using a Magneto-Optical Trap

Cited by 56 publications

References 25 publications

Trap-depth determination from residual gas collisions

Trap-depth determination from residual gas collisions

Triple Ionization of Lithium by Electron Impact

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

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