Rydberg atom spectroscopy enabled by blackbody radiation ionization

Xiaoxu Lu, Yuan Sun, and Harold Metcalf

Phys. Rev. A 84, 033402 – Published 6 September 2011

Abstract

We have excited helium atoms from their metastable 2 $^{3} S$ state to Rydberg states in the range $13 < n < 50$ in a two-step process via the 3 $^{3} P$ state using light at $λ = 389$ nm and 785–815 nm. Atoms in a thermal beam (100 K) cross partially overlapping laser beams of the appropriate frequencies in the counterintuitive order to exploit the high efficiency of stimulated rapid adiabatic passage. The interaction region is between two plates that can be used for Stark tuning in a few V/cm field or for field ionization. At fields much too low for field ionization, we observe signals attributed to ionization by blackbody radiation. Multiple tests confirm this attribution as the cause of ionization. For example, by heating the plates we observe the expected signal increases. Our experiments reinforce previous work where the interaction between Rydberg atoms and room temperature blackbody radiation is important for experiments.

Received 13 June 2011

DOI:https://doi.org/10.1103/PhysRevA.84.033402

Authors & Affiliations

Xiaoxu Lu, Yuan Sun, and Harold Metcalf

Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA

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Issue

Vol. 84, Iss. 3 — September 2011

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Images

Figure 1
A top view of the atomic beam setup shows the position of the plates, aperture, and detectors (all dimensions in cm). The dashed line is the beam, A indicates the source region, B is the collimating aperture, and E is the beam detector. The laser beams (L) cross the atomic beam at right angles and the crossing point can be moved along the beam direction by the extent of the the Stark tuning plates P. The detector was first at D but was later moved to C (see text).Reuse & Permissions
Figure 2
The excitation level scheme used in our experiments.Reuse & Permissions
Figure 3
This diagram of the interaction region shows the atomic beam passing between the field plates from left to right, the overlapped laser beams crossing it at angle $π / 2$ , and the ion detector. In earlier experiments the upper plate was solid and the detector was mounted at position A just downstream of the end of the plates. In later experiments the upper plate was replaced by one with an array of 30 holes 0.5 mm diam spaced by $\sim$ 4 mm arranged in a triangular array near its center (also shown), and the detector mounted at position B just above these holes. The laser beams can be moved relative to one another and along the He* beam by almost the full length of the plates.Reuse & Permissions
Figure 4
The dashed lines are energy eigenvalues calculated for the $n = 24$ Rydberg states with $m_{ℓ} = 0$ using the method of Ref. [27], and the dots show the location in frequency and field where we observed ion peaks. The solid horizontal lines indicate a few of the field scans with the laser frequency held fixed. The inset is a zoom near the low field region.Reuse & Permissions
Figure 5
The two lower curves show the decay of the ion signal from the 24S and 30S states (squares and circles, respectively) taken by moving the laser excitation region upstream from the 25-mm lattice of the holes in the upper plate. For these data the voltage between the plates was just enough to attract the ions through the holes, well below $E_{F I}$ . Since the peak of the atomic beam velocity distribution is at $\sim$ 1070 m/s, the 30-mm scale here corresponds to a flight time of $\sim$ 28 $μ$ s. The uppermost curve (triangles) is for the 30S state with the plates heated to about 380 K.Reuse & Permissions
Figure 6
Part (a) shows a few traces of the measured ionization current derived from Rydberg atoms exposed to both uv and ir light vs. ir frequency. The double peaks are separated by the uv Rabi frequency $Ω_{uv}$ and constitute the Autler-Townes splitting. Part (b) is a plot of the observed $Ω_{uv}$ vs. $\sqrt{P_{uv}}$ . The inset to part (b) shows the geometry of the two laser beams and the path of the most intense, central part of the atomic beam (see text).Reuse & Permissions

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