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Chinese Physics Letters

Magneto-Optical Trapping of 88 Sr atoms with 689 nm Laser

Qiang Wang, Bai-Ke Lin, Yang Chun Zhao, Ye Li, Shaokai Wang, Wang Min-Ming, Erjun Zang, Tianchu Li, Zhanjun Fang

Published Mar 1, 2011• 10 citations
Publisher

Abstract

We report the experimental realization of strontium magneto-optical trap (MOT) operating on the intercombination transition 1 S 0 − 3 P 1 at 689 nm, namely red MOT. A 689 nm laser used for cooling and trapping is injection locked to a master laser, whose linewidth is narrowed to 150 Hz by locking to a high finesse optical reference cavity. 88 Sr atoms pre-cooled and trapped by the broad 1 S 0 − 1 P 1 transition at 461 nm are transferred to the red MOT with the help of a time sequence controller. The transfer ratio is about 20% and the red MOT's temperature is estimated to be less than 20 μK by the time-of-flight (TOF) image analysis.

DOI
10.1088/0256-307x/28/3/033201

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We report the experimental realization of strontium magneto-optical trap (MOT) operating on the intercombination transition 1 S 0 − 3 P 1 at 689 nm, namely red MOT. A 689 nm laser used for cooling and trapping is injection locked to a master laser, whose linewidth is narrowed to 150 Hz by locking to a high finesse optical reference cavity. 88 Sr atoms pre-cooled and trapped by the broad 1 S 0 − 1 P 1 transition at 461 nm are transferred to the red MOT with the help of a time sequence controller. The transfer ratio is about 20% and the red MOT's temperature is estimated to be less than 20 μK by the time-of-flight (TOF) image analysis.
Laser cooling 88^{88}88Sr to microkelvin temperature with an integrated-photonics system
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About 2/spl times/10/sup 7/ neutral strontium atoms have been loaded into a magneto-optical trap (MOT) that uses the narrow (/spl Gamma/=2/spl pi/ 7 kHz) intercombination line at 689 nm as the cycling transition. The atoms are second-stage laser cooled to /spl sim/10 /spl mu/K from an initial 5 mK atomic sample (/spl sim/5/spl times/10/sup 7/ atoms), generated in a vapor cell MOT that employs the strong (/spl Gamma/=2/spl pi/ 32 MHz) cycling transition at 461 nm. To demonstrate the low temperatures of these atoms, optical Ramsey spectroscopy is performed upon the /sup 1/S/sub 0/-/sup 3/P/sub 1/ transition using only two excitation pulses; the time dependence of the fringe contrast indicates an RMS velocity of 3 cm/s for the 689 nm MOT-cooled sample.
The secondary laser cooling of a cloud of strontium-88 atoms on the 1 S 0–3 P 1 (689 nm) intercombination transition captured into a magneto-optical trap has been demonstrated. We describe in detail the recapture of atoms from the primary trap operating on the strong 1 S 0–1 P 1 (461 nm) transition and determine the recapture coefficient κ, the number of atoms, and their temperature in the secondary trap as a function of experimental parameters. A temperature of 2 µK has been reached in the secondary trap at the recapture coefficient κ = 6%, which confirms the secondary cooling efficiency and is sufficient to perform metrological measurements of the 1 S 0–3 P 1 (698 nm) clock transition in an optical lattice.
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.
Abstract We outline an experimental setup for efficiently preparing a tweezer array of 88Sr atoms. Our setup uses permanent magnets to maintain a steady-state two-dimensional magneto-optical trap (MOT) which results in a loading rate of up to 108 s−1 at 5 mK for the three-dimensional blue MOT. This enables us to trap 2 × 106 88Sr atoms at 2 μK in a narrow-line red MOT with the 1S0 → 3P1 intercombination transition at 689 nm. With the Sisyphus cooling and pairwise loss processes, single atoms are trapped and imaged in 813 nm optical tweezers, exhibiting a lifetime of 2.5 min. We further investigate the survival fraction of a single atom in the tweezers and characterize the optical tweezer array using a release and recapture technique. Our experimental setup serves as an excellent reference for those engaged in experiments involving optical tweezer arrays, cold atom systems, and similar research.
We report the experimental realization of88Sr magneto-optical trap (MOT) operating at the wavelength of 461 nm and 689nm. The blue MOT is loaded via a 32 cm long spin-flip type Zeeman slower which enhances the MOT population by a factor of 44. We have trapped 1.6×10888Sr atoms with the use of 679nm and 707nm repumping laser. The88Sr cloud has a temperature of about 2.3 mK, measured by recording the time evolution of the absorption signal. The 689nm laser used in our experiment has a line width of about 200Hz. To optimize the transfer efficiency, the laser spectrum is broadened by frequency modulation technique to about 2 MHz. The transfer efficiency from blue MOT to red MOT is about 20%.