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arXiv:2205.04054 · Journal of Physics B Atomic Molecular and Optical Physics

Narrow-line cooling of 87Rb using 5S 1 / 2 → 6P 3 / 2 open transition at 420 nm

Rajnandan Choudhury Das, Dangka Shylla, Arkapravo Bera, Kanhaiya Pandey

Published Dec 15, 2022• 14 citations
arXivHTMLPDF

Abstract

Abstract A magneto-optical trap (MOT) at narrow transition offers lower temperature and hence is the key for producing a high phase density atomic cloud and subsequently quantum degeneracy with a large number of atoms for many elements. In this paper, we describe the loading of 87Rb atoms in the MOT using a narrow open transition (5S 1 / 2 → 6P 3 / 2 ) at 420 nm (i.e. blue MOT) from the routinely implemented MOT using a broad cyclic transition (5S 1 / 2 → 5P 3 / 2 ) at 780 nm (i.e. IR MOT). Using the four times narrower transition, we have trapped around 108 atoms in the MOT with a typical temperature of around 54 μ K. We have also studied the behavior of the blue MOT with various parameters such as hold time, detuning, and power of trapping and repumper beams.

DOI
10.1088/1361-6455/acabf0

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Bulletin of the American Physical Society•Feb 27, 2012•0 citations
Abstract A magneto-optical trap (MOT) at narrow transition offers lower temperature and hence is the key for producing a high phase density atomic cloud and subsequently quantum degeneracy with a large number of atoms for many elements. In this paper, we describe the loading of 87Rb atoms in the MOT using a narrow open transition (5S 1 / 2 → 6P 3 / 2 ) at 420 nm (i.e. blue MOT) from the routinely implemented MOT using a broad cyclic transition (5S 1 / 2 → 5P 3 / 2 ) at 780 nm (i.e. IR MOT). Using the four times narrower transition, we have trapped around 108 atoms in the MOT with a typical temperature of around 54 μ K. We have also studied the behavior of the blue MOT with various parameters such as hold time, detuning, and power of trapping and repumper beams.
We report continuous loading of 87Rb^{\text{87}}\mathrm{Rb}87Rb atoms in a magneto-optical trap (MOT) at narrow linewidth, 420-nm 5S1/25{S}_{1/2}5S1/2​, $F=2\ensuremath{\rightarrow}6{P}_{3/2}$, F=3F=3F=3 blue transition (blue MOT). Continuous loading of the blue MOT is achieved by superimposing the blue laser beam inside a hollow core of infrared (IR) laser beam driving the broad 5S1/25{S}_{1/2}5S1/2​, $F=2\ensuremath{\rightarrow}5{P}_{3/2}$, F=3F=3F=3 transition at 780 nm. We typically load $\ensuremath{\sim}{10}^{8}$ atoms in the blue MOT in 2.5 s. We characterize the continuous loading of the blue MOT with various parameters such as magnetic-field gradient, detuning, power and diameter of the blue MOT beam, and diameter of the hollow core (spot) inside the IR MOT beam. We observe that the blue laser beam should overfill the spot of the IR laser beam. This is because the blue laser cools the atoms to a lower temperature even in the presence of the broad IR laser, i.e., in the overlapped region, and hence helps in loading. To support the experimental result, we also present the theoretical framework for cooling atoms in the presence of two lasers driving two different transitions simultaneously. This method of continuous loading of the blue MOT can be useful to produce a continuous atomic beam of cold Rb atoms.
We present our technique to create a magneto-optical trap (MOT) for dysprosium atoms using the narrow-line cooling transition at 626 nm to achieve suitable conditions for direct loading into an optical dipole trap. The MOT is loaded from an atomic beam via a Zeeman slower using the strongest atomic transition at 421 nm. With this combination of two cooling transitions we can trap up to 2.0·10(8) atoms at temperatures down to 6 μK. This cooling approach is simpler than present work with ultracold dysprosium and provides similar starting conditions for a transfer to an optical dipole trap.
Laser cooling has become a powerful tool for producing quantum gases and has enabled the study of a wide range of phenomena only accessible at ultracold temperatures. This thesis will describe the implementation and characterization of a magneto-optical trap (MOT) for laser cooling strontium to microkelvin temperatures operating on the narrow 689nm transition (the “red” MOT). The red MOT is the second cooling stage required to create quantum degenerate gases of strontium, bridging the temperatures and densities produced by the first cooling stage (the 461 nm “blue” MOT) and the shallow conservative traps for evaporation to quantum degeneracy.
We have used the narrow 2 S 1/2 [arrow right] 3 P 3/2 transition in the ultraviolet (UV) to laser cool and magneto-optically trap (MOT) 6 Li atoms. Laser cooling of lithium atoms is usually performed on the 2 S 1/2 [arrow right] 2 P 3/2 (D2) transition, where temperatures of twice the Doppler limit, or ∼300 μ K for lithium, are achieved. The linewidth of the UV transition is seven times narrower than the D2 line, resulting in a lower Doppler limit. We show that a MOT operating on the UV transition reaches temperatures as low as 59 μ K. We load 6 million atoms from this UV MOT into a 1070 nm optical dipole trap (ODT). We show that the light shift of the UV transition in the ODT is small and blue-shifted, facilitating efficient loading. Evaporative cooling of a two spin-state mixture of 6 Li in the ODT produces a quantum degenerate Fermi gas with 3 million atoms in only 11 seconds.
We report an experimental study of peak and phase-space density of a two-stage magneto-optical trap (MOT) of 6Li^{6}\mathrm{Li}6Li atoms, which exploits the narrower $2{S}_{1/2}\ensuremath{\rightarrow}3{P}_{3/2}$ ultraviolet (UV) transition at 323 nm following trapping and cooling on the more common D2D2D2 transition at 671 nm. The UV MOT is loaded from a red MOT and is compressed to give a high phase-space density up to $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. Temperatures as low as $33\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{K}$ are achieved on the UV transition. We study the density limiting factors and in particular find a value for the light-assisted collisional loss coefficient of $1.3\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ cm3{\mathrm{cm}}^{3}cm3/s for low repumping intensity.
Low-temperature, high-density magneto-optical trapping of potassium using the open 4S →\rightarrow→ 5P transition at 405\,nm
We report the laser cooling and trapping of neutral potassium on an open transition. Fermionic 40K is captured using a magneto-optical trap (MOT) on the closed 4S1/2 → 4P3/2 transition at 767 nm and then transferred, with high efficiency, to a MOT on the open 4S1/2 → 5P3/2 transition at 405 nm. Because the 5P3/2 state has a smaller linewidth than the 4P3/2 state, the Doppler limit is reduced from 145 μK to 24 μK, and we observe temperatures as low as 63(6) μK. The density of trapped atoms also increases, due to reduced temperature and reduced expulsive light forces. We measure a two-body loss coefficient of β = 1.4(1) × 10−10 cm3/s near saturation intensity, and estimate an upper bound of 8 × 10−18 cm2 for the ionization cross section of the 5P state at 405 nm. The combined temperature and density improvement in the 405 nm MOT is a twenty-fold increase in phase-space density over our 767 nm MOT, showing enhanced precooling for quantum gas experiments. A qualitatively similar enhancement is observed in a 405 nm MOT of bosonic 41K.