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arXiv:1903.07798

Characterizing the Optical Trapping of Rare Isotopes by Monte Carlo Simulation

David H. Potterveld, Fromm, S. A., Bailey, K. G., Michael Bishof, Booth, D. W., Matthew Dietrich, Greene, J. P., Roy J. Holt, Kalita, M. R., W. Korsch, Lemke, N. D., Peter Mueller, O'Connor, T. P., Parker, R. H., Tenzin Rabga, Singh, J. T.

Published Mar 19, 2019• 2 citations
arXivHTMLPDF

Abstract

Optical trapping techniques are an efficient way to probe limited quantities of rare isotopes. In order to achieve the highest possible measurement precision, it is critical to optimize the optical trapping efficiency. This work presents the development of a three-dimensional semi-classical Monte Carlo simulation of the optical trapping process and its application to optimizing the optical trapping efficiency of Radium for use in the search of the permanent electric dipole moment of $^{225}$Ra. The simulation includes an effusive-oven atomic beam source, transverse cooling and Zeeman slowing of an atomic beam, a three-dimensional magneto-optical trap, and additional processes such as collisions with residual gas molecules. We benchmark the simulation against a well-characterized $^{88}$Sr optical trap before applying it to the $^{225}$Ra optical trap. The simulation reproduces the relative gains in optical trapping efficiency measured in both the $^{88}$Sr and $^{225}$Ra optical traps. The measured and simulated values of the overall optical trapping efficiencies for $^{88}$Sr are in agreement; however, they differ by a factor of $30$ for $^{225}$Ra. Studies of several potential imperfections in the apparatus or systematic effects, such as atomic beam source misalignment and laser frequency noise, show only limited effects on the simulated trapping efficiency for $^{225}$Ra. We rule out any one systematic effect as the sole cause of the discrepancy between the simulated and measured $^{225}$Ra optical trapping efficiencies; but, we do expect that a combination of systematic effects contribute to this discrepancy. The accurate relative gains predicted by the simulation prove that it is useful for testing planned upgrades to the apparatus.

DOI
10.48550/arxiv.1903.07798

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Optical trapping techniques are an efficient way to probe limited quantities of rare isotopes. In order to achieve the highest possible measurement precision, it is critical to optimize the optical trapping efficiency. This work presents the development of a three-dimensional semi-classical Monte Carlo simulation of the optical trapping process and its application to optimizing the optical trapping efficiency of Radium for use in the search of the permanent electric dipole moment of 225^{225}225Ra. The simulation includes an effusive-oven atomic beam source, transverse cooling and Zeeman slowing of an atomic beam, a three-dimensional magneto-optical trap, and additional processes such as collisions with residual gas molecules. We benchmark the simulation against a well-characterized 88^{88}88Sr optical trap before applying it to the 225^{225}225Ra optical trap. The simulation reproduces the relative gains in optical trapping efficiency measured in both the 88^{88}88Sr and 225^{225}225Ra optical traps. The measured and simulated values of the overall optical trapping efficiencies for 88^{88}88Sr are in agreement; however, they differ by a factor of 303030 for 225^{225}225Ra. Studies of several potential imperfections in the apparatus or systematic effects, such as atomic beam source misalignment and laser frequency noise, show only limited effects on the simulated trapping efficiency for 225^{225}225Ra. We rule out any one systematic effect as the sole cause of the discrepancy between the simulated and measured 225^{225}225Ra optical trapping efficiencies; but, we do expect that a combination of systematic effects contribute to this discrepancy. The accurate relative gains predicted by the simulation prove that it is useful for testing planned upgrades to the apparatus.
We report theoretical studies of an ef ficient accumulation of 225 Ra atoms in a magneto-optical trap (MOT) from an atomic beam. The number of atoms in the trap is limited due to the large leakage into metastable D states from the cooling transition and the loss mechanism from collisions with the background gases and with other elements in the atomic beam. We propose a setup consisting of an ef ficient Zeeman slower, an optical atomic beam de flector, and an EggMOT, which provides a large capture velocity, e.g. the Zeeman slower capture velocity of 581 ms 1 and the MOT capture velocity of 46 ms 1 . Furthermore, the pure slow atomic beam produced by the optical atomic beam de flector can maximize the number of trapped atoms and their lifetime in a ultra high vacuum chamber by minimizing the collisional loss. Our proposed setup allows for the search for a permanent electric dipole moment based on laser-cooled and trapped radium atoms with improved sensitivity.
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We present an experimental, numerical, and analytical study of strontium magneto-optical trap (MOT) loading from a cold atomic beam in a configuration optimized for high numerical aperture optical tweezers. Our approach orients the beam flow along the MOT symmetry axis to reduce the experimental complexity and maximize the overall optical access into the scientific region of study. We use a moving molasses technique to enable this configuration and show that its performance depends critically on metastable-state shelving (to 5s5p 3P2) during the atom transfer to the three-dimensional (3D) MOT. Furthermore, we find that the parameters for optimal transfer efficiency are bounded by dark-state loss (to 5s5p 3P0) in the trap region where repumping is present. These observations are verified to great degree of accuracy using both our developed analytical and numerical models. The corresponding 3D simulation tool is used to perform a comprehensive study of the trap loading dynamics, beginning at the oven exit and ending at the 3D MOT, demonstrating its effectiveness in optimizing an effusive oven experiment.
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We demonstrate a technique for transferring 226{}^{226}226Ra atoms from a three-dimensional magneto-optical trap (MOT) into a standing wave optical dipole trap (ODT) in an adjacent chamber. The resulting small trapping volume (120 $\ensuremath{\mu}$m in diameter) allows for high control of the electric and magnetic fields applied to the atoms. The atoms are first transferred to a traveling-wave optical dipole trap, which is then translated 46 cm to a science chamber. The atoms are subsequently transferred into an orthogonal standing-wave ODT by application of a one-dimensional MOT along the traveling-wave axis. For each stage, transfer efficiencies exceeding 60% are demonstrated.
We have magneto-optically trapped the nine stable isotopes of xenon. Using the Zeeman slowing method to decelerate a beam of xenon atoms in the metastable 6s 3/2 [3/2]2{]}_{2}]2​ state (notation representing nl Jcore{\mathit{J}}_{\mathrm{core}}Jcore​ [K=Jcore{\mathit{J}}_{\mathrm{core}}Jcore​+l]J{]}_{\mathit{J}}]J​), we load our trap to a collisionally limited density of more than 1010{10}^{10}1010 atoms/cm3{\mathrm{cm}}^{3}cm3. The two odd isotopes are trapped without a repumping frequency, even though they have hyperfine structure. The sensitivity of the trapping process to the laser frequency is exploited to make accurate measurements of the isotope shifts for the 6s 3/2 [3/2]2{]}_{2}]2​\ensuremath{\rightarrow}6p 3/2 [5/2]3{]}_{3}]3​ laser-cooling transition and of the hyperfine constants for 131Xe^{131}\mathrm{Xe}131Xe.