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Journal of Physics Conference Series

Studying Cold Potassium Rydberg Atoms with an AC-MOT

Matthew Harvey, John Chidowerem Agomuo, Ahmad Sakaamini, Andrew James Murray

Published Jul 1, 2017• 0 citations
Publisher

Abstract

A new method is described for the detection and study of cold Rydberg atoms. Cold atoms held in an AC-driven magneto optical trap (AC-MOT) are selectively laser excited to a Rydberg state in a stepwise process. Ions or electrons from interactions between Rydberg atoms are then electrostatically extracted and detected via a channel electron multiplier. The apparatus is capable of studying Rydberg atoms from n = 15 to n ∼ 220.

DOI
10.1088/1742-6596/875/3/022046

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A new method is described for the detection and study of cold Rydberg atoms. Cold atoms held in an AC-driven magneto optical trap (AC-MOT) are selectively laser excited to a Rydberg state in a stepwise process. Ions or electrons from interactions between Rydberg atoms are then electrostatically extracted and detected via a channel electron multiplier. The apparatus is capable of studying Rydberg atoms from n = 15 to n ∼ 220.
Results from measurement of the energy levels of ultra-cold Rydberg states of 39 K in an AC-Magneto-Optical Trap are presented. Rydberg atoms are produced by stepwise excitation from the laser-excited 4 2 P 1 / 2 states using a tunable blue dye laser. Energy level data for principal quantum numbers n = 18 up to n = 199 are reported. For n = 18 to n = 46 , the measured levels are in good agreement with the available data from the National Institute of Standards and Technology (NIST) list of atomic spectral lines. New values for the parameters in the Rydberg-Ritz formula were then calculated from a fit to the measured energy level data. Atomic transition energies for n = 47 to n = 199 are also reported for the first time. Shifts in the levels for excitation to both the 2 S 1 / 2 and 2 D 3 / 2 states at principal quantum number n > 100 are found when compared to calculations derived from the revised Rydberg-Ritz formula. These deviations are due to the greater probability of overlap between the wavefunctions of the excited atoms in the ensemble, resulting in strong interaction between the Rydberg atoms which are in close proximity. For n > 167, the D-state energies were unresolved.
ABSTRACTCandidate?s Names: John AgomuoDegree Title: PhDThesis Title: Excitation And Photoionization Of Laser-Cooled Atoms In The AC Driven Magneto-Optical Trap (AC-MOT), Using Resonant And Non-Resonant Radiation.Date: 19/12/2014Results of experiments involving the manipulation of atoms using laser radiation are presented. A high-density trap of potassium atoms was created using an AC-driven magneto-optical trap (AC-MOT), loaded from a Zeeman-slowed atomic beam. The AC-MOT was operated in a pulsed mode, with a trapping laser that was detuned by -4?, where ? is the natural line-width of the trapping transition. Under these conditions, the AC-MOT trapped an average of 3.63�0.02�?10?^8 atoms, which were cooled to a mean temperature of 275?K�33?K.Using the AC-MOT, the absolute photoionization cross-section of cold potassium atoms was determined using ionizing laser radiation at 450.4 nm obtained from a high-power diode laser. The measured photoionization cross-section from the 42P3/2 excited state was obtained by measuring the loss rate and the lifetime of the AC-MOT during the loading and decay processes. Using these methods, the cross section was determined to be 1.49�0.13 Mb, and 2.38�0.18 Mb respectively. Precise energy levels of high-n Rydberg states of potassium have also been measured using stepwise-excitation of the trapped atoms, with the intermediate state being the 42P1/2 state that was excited by resonant laser radiation at 389,286,368.12 MHz. Excitation from the 42P1/2 state to the n^2 S_(1/2) states was carried out using blue radiation from a dye laser, for transitions to Rydberg states with principal quantum numbers ranging from n = 18 to ~200. For excitation to the n^2 D_(3/2) states, transitions up to Rydberg states with n ranging from 18 to 167 were studied. Due to the strong interaction between Rydberg atoms, the measured energy levels deviated from their predicted theoretical values at high principal quantum numbers (n?130 for the S-states, and n?100 for the D-states). For principal quantum numbers greater than these values, the spectral lines were found to both broaden and shift in energy, and new features in the Rydberg spectra were observed. These new features have been attributed to the dipole-forbidden n2P1/2 and n2P3/2 states, which cannot be excited directly by the laser. These states must hence be excited due to interplay between the highly excited Rydberg atoms that is occurring due to their large effective size and close proximity in the AC-MOT.