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arXiv:1310.3239 · New Journal of Physics

Buffer gas loaded magneto-optical traps for Yb, Tm, Er and Ho

Boerge Hemmerling, Garrett K. Drayna, Eunmi Chae, Aakash Ravi, John M. Doyle

Published Jun 30, 2014• 34 citations
arXivHTMLPDF

Abstract

Direct loading of lanthanide atoms into magneto-optical traps (MOTs) from a very slow cryogenic buffer gas beam source is achieved, without the need for laser slowing. The beam source has an average forward velocity of 60– and a velocity half-width of , which allows for direct MOT loading of Yb, Tm, Er and Ho. Residual helium background gas originating from the beam results in a maximum trap lifetime of about 80 ms (with Yb). The addition of a single-frequency slowing laser applied to the Yb in the buffer gas beam increases the number of trapped Yb atoms to with a loading rate of . Decay to metastable states is observed for all trapped species and decay rates are measured. Extension of this approach to the loading of molecules into a MOT is discussed.

DOI
10.1088/1367-2630/16/6/063070

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Direct loading of lanthanide atoms into magneto-optical traps (MOTs) from a very slow cryogenic buffer gas beam source is achieved, without the need for laser slowing. The beam source has an average forward velocity of 60– and a velocity half-width of , which allows for direct MOT loading of Yb, Tm, Er and Ho. Residual helium background gas originating from the beam results in a maximum trap lifetime of about 80 ms (with Yb). The addition of a single-frequency slowing laser applied to the Yb in the buffer gas beam increases the number of trapped Yb atoms to with a loading rate of . Decay to metastable states is observed for all trapped species and decay rates are measured. Extension of this approach to the loading of molecules into a MOT is discussed.
Molecular magneto-optical traps (MOTs) are loaded from cryogenic buffer gas beam (CBGB) sources, which produce a large flux of cold molecules. However, only a small fraction of this flux is slowed and captured. Here, we investigate and optimize one of these CBGB sources through a combination of experiment and simulation to maximize the number of molecules loaded into a MOT of CaF molecules. We experimentally determine the range of molecule velocities from the source that are successfully slowed and captured in the MOT, and perform a systematic study of buffer gas source geometries to identify designs that maximize MOT loading. Our observations agree well with Monte Carlo simulations, which provide physical insight into the dynamics within the source and explain how source geometry influences the subset of molecules that are ultimately trapped. These results provide practical design guidelines for optimizing cryogenic buffer gas beam sources used in laser cooling experiments.
We present the properties of a magneto-optical trap (MOT) of CaF molecules. We study the process of loading the MOT from a decelerated buffer-gas-cooled beam, and how best to slow this molecular beam in order to capture the most molecules. We determine how the number of molecules, the photon scattering rate, the oscillation frequency, damping constant, temperature, cloud size and lifetime depend on the key parameters of the MOT, especially the intensity and detuning of the main cooling laser. We compare our results to analytical and numerical models, to the properties of standard atomic MOTs, and to MOTs of SrF molecules. We load up to molecules, and measure a maximum scattering rate of s −1 per molecule, a maximum oscillation frequency of 100 Hz, a maximum damping constant of 500 s −1 , and a minimum MOT rms radius of 1.5 mm. A minimum temperature of 730 μ K is obtained by ramping down the laser intensity to low values. The lifetime, typically about 100 ms, is consistent with a leak out of the cooling cycle with a branching ratio of about . The MOT has a capture velocity of about 11 m s −1 .
We study the properties of a cryogenic buffer gas source that uses a low-temperature two-stage buffer gas cell to produce very slow beams of ytterbium monofluoride molecules. The molecules are produced by laser ablation inside the cell and extracted into a beam by a flow of cold helium. We measure the flux and velocity distribution of the beam as a function of ablation energy, helium flow rate, cell temperature, and the size of the gap between the first and second stages of the cell. We also compare the velocity distributions from one-stage and two-stage cells. The one-stage cell emits a beam with a speed of about 82 m s − 1 and a translational temperature of 0.63 K. The slowest beams are obtained using the two-stage cell at the lowest achievable cell temperature of 1.8 K. This beam has a peak velocity of 56 m s − 1 and a flux of 9 × 10 9 ground-state molecules per steradian per pulse, with a substantial fraction at speeds below 40 m s − 1 . These slow molecules can be decelerated further by radiation pressure slowing and then captured in a magneto-optical trap. Published by the American Physical Society 2024
We report on building a pulsed source of cold Tm atoms and loading of the narrow-line magneto-optical trap (MOT) from the cold atomic beam. We achieve the loading rate of the first-stage MOT in the primary chamber up to 108 atoms/s and obtain a cold atomic beam with the mean longitudinal velocity ∼10 m/s and an angular spread of 18 mrad in a pulsed mode. In this regime, we can form a cold atomic beam with up to 5 × 106 atoms at a 5 Hz repetition rate. We also introduce a novel method to enhance the capture velocity of the narrow-line MOT by incorporating an additional axial cooling beam and achieve loading efficiency η = 10% of the second-stage MOT in the science chamber. Our approach could be extended to other atomic species with similar properties, such as Sr, Yb, Dy, and Er, serving as a convenient alternative for the traditional 2D-MOT schemes. Providing rapid loading of the MOT in the science chamber, it would reduce preparation time of the atomic ensemble leading to a shorter dead time in spectroscopy experiments and a higher repetition rate.
We have directly loaded a cryogenic beam of molybdenum atoms into a magneto-optical trap. By chirping the detuning of the trapping lasers, we were able to enhance the number of atoms loaded into the trap by more than a factor of 2. We optimize the trapped samples for atom number, temperature, and lifetime by varying the laser-cooling parameters. The laser-cooled molybdenum atoms are subsequently transferred to a magnetic trap where we achieve vacuum-limited lifetimes of 100 ms. Comparison of magneto-optical trap and magnetic trap lifetimes allow us to extract partial decay rates of the $z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}\ensuremath{\rightarrow}a{\phantom{\rule{0.16em}{0ex}}}^{5}{D}_{4}$ and $z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}\ensuremath{\rightarrow}a{\phantom{\rule{0.16em}{0ex}}}^{5}{D}_{3}$ transitions. We also provide measurements of the isotope shifts for the $a{\phantom{\rule{0.16em}{0ex}}}^{7}{S}_{3}\ensuremath{\rightarrow}z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}$ transition with up to four times better precision than previously reported. Finally, we discuss the prospect of applying the chriped magneto-optical trap to produce laser-cooled samples of MgF.
We report an efficient trapping of rare-earth-metal Yb atoms with a high-power violet laser diode (LD). An injection-locked violet LD with a 25-mW frequency-stabilized output was used for the magneto-optical trapping (MOT) of fermionic as well as bosonic Yb isotopes. A typical number of $4\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms for 174Yb{}^{174}\mathrm{Yb}174Yb with a trap density of $\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{8}{\mathrm{cm}}^{\ensuremath{-}3}$ was obtained. A 10-mW violet external-cavity LD was used for the one-dimensional slowing of an effusive Yb atomic beam without a Zeeman slower resulting in a 35-fold increase in the number of trapped atoms. The overall characteristics of our compact violet MOT, e.g., the loss time of 1 s, the loading time of 400 ms, and the cloud temperature of 0.7 mK, are comparable to those in previously reported violet Yb MOTs, yet with a greatly reduced cost and complexity of the experiment.