High-field-seeking Rydberg atoms orbiting a charged wire

H. Ko and S. D. Hogan

Phys. Rev. A 89, 053410 – Published 12 May 2014

Abstract

Pulsed supersonic beams of helium atoms in the high-field-seeking $52 p$ Rydberg state have been guided while following helical trajectories in the electrostatic field of a charged wire suspended along the axis of a grounded cylindrical metallic tube. The operation of this electrostatic wire guide for samples in high-field-seeking Rydberg-Stark states has been investigated with dc and pulsed electric potentials applied to the wire while the guided atoms were detected by pulsed electric-field ionization. The acceptance of the guide has been determined through numerical particle trajectory simulations.

Received 19 February 2014

DOI:https://doi.org/10.1103/PhysRevA.89.053410

Authors & Affiliations

H. Ko and S. D. Hogan

Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT England, United Kingdom

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Issue

Vol. 89, Iss. 5 — May 2014

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Images

Figure 1
(a) Schematic diagram of the experimental apparatus (not to scale). E1 and E2 represent the metallic electrodes surrounding the Rydberg photoexcitation region, while E3 is the electrode to which a pulsed electric potential is applied to ionize the Rydberg atoms. (b) Example of a typical helical trajectory along the wire guide (solid red curve) of a He Rydberg atom in the $52 p$ state.
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Figure 2
Calculated trajectories of He atoms in the $52 p$ state, moving in the electric field of a cylindrical capacitor the center wire of which is suspended along the $z^{'}$ axis at $(x^{'}, y^{'}) = (0, 0)$ . In these calculations $R_{0} = 12.5$ mm, $r_{w} = 25 μ$ m, and $V_{c} = - 10$ V. For each trajectory the initial velocity of the atoms is $\vec{v}_{i}^{'} = (76, 0, 1948)$ m/s. In each panel trajectories for three initial positions are displayed. In panel (a) these are $(x^{'}, y^{'}) = (- 0.25, + 1.35)$ , $(0, + 1.35)$ , and $(+ 0.25, + 1.35)$ mm; in panel (b) these are $(x^{'}, y^{'}) = (- 0.25, + 1.0)$ , $(0, + 1.0)$ , and $(+ 0.25, + 1.0)$ mm and in each case are indicated by the red dash-dotted, solid blue, and green dashed curves, respectively. In each panel, contours of equal electric-field strength beginning at 10 V/cm and increasing in steps of 10 V/cm are indicated by the black circles.
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Figure 3
(a) Stark map of the triplet $n = 52$ Rydberg states of He for which $| m | = 1$ . The $52 p$ state used in the experiments is highlighted in red. (b) Experimentally measured Rydberg photoexcitation spectrum recorded in the presence of an electric field $F = 0.65$ V/cm [dashed vertical line in (a)].
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Figure 4
(a) He $^{+}$ time-of-flight distributions recorded with the guide off (solid black curve), a dc potential of $V_{c} = - 10$ V applied to the guide (blue dash-dotted curve), and a pulsed potential with a duration of $Δ t_{c} = 35 μ$ s and an amplitude of $V_{c} = - 10$ V applied to the guide (red dashed curve). (b) Calculated He atom spatial distributions at the position of pulsed electric-field ionization with (i) the guide off, and (ii) a pulsed potential with a duration of $Δ t_{c} = 35 μ$ s and an amplitude of $V_{c} = - 10$ V applied to the guide.
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Figure 5
(a,b) Representations of the spatial acceptance of the guide in the $x^{'}$ and $y^{'}$ dimensions, when $V_{c} = - 10$ V and $Δ t_{c} = 35 μ$ s, for He atoms in the $52 p$ state with initial velocities $\vec{v}_{i}^{'} = (v_{x^{'}}^{'}, v_{y^{'}}^{'}, v_{z^{'}}^{'})$ , where $v_{x^{'}}^{'} = v_{0} sin θ_{w} = 76$ m/s, $v_{y^{'}}^{'} = 0$ m/s, and $v_{z^{'}}^{'} = v_{0} cos θ_{w} = 1948$ m/s. In each panel, the black dash-dotted curve represents the hole of radius 1.5 mm in E2 that collimates the excited Rydberg atoms before they enter the guide. The red shaded region in (a) represents the initial positions from which the Rydberg atoms can travel through the guide without undergoing electric-field ionization. The blue shaded region in (b) represents the initial particle positions from which, after a flight time of $35 μ$ s, the orbital radius of the guided atoms is less than or equal to their initial orbital radius.
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Figure 6
Color maps representing experimentally recorded He $^{+}$ time-of-flight distributions following pulsed electric-field ionization. The time-of-flight distributions were recorded for pulsed guide potentials with (a) pulse durations ranging from $Δ t_{c} = 0$ to $45 μ$ s with the amplitude of the pulses held constant at $| V_{c} | = 10$ V and (b) pulse amplitudes ranging from $| V_{c} | = 0$ to 10 V with constant pulse durations of $Δ t_{c} = 35 μ$ s. The dashed vertical white line in each panel indicates the flight time associated with the peak of the time-of-flight distribution with the guide off. The color scale on the right is common to both (a) and (b).
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