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Journal of Experimental and Theoretical Physics

Effect of Zeeman Slower Beam on Loading of a Krypton Magneto-Optical Trap

Sunita Singh, Vibhuti Bhushan Tiwari, Satya Ram Mishra, H. S. Rawat

Published Apr 1, 2018• 1 citation
Publisher

Abstract

We report the studies on the effect of Zeeman slower beam power on the loading rate and collision loss rate in an atomic beam loaded krypton magneto-optical trap (MOT). The results show that an increase in Zeeman slower beam power initially increases the MOT loading rate and reduces the background collision loss rate to increase the number of cold atoms in the MOT to an optimum value. With further increase in the Zeeman slower beam power, the number of cold atoms in the MOT decreases due to increased background collision loss rate and decrease in the trap loading rate. However, the cold collision loss rate is observed to remain unaffected by the variation in the Zeeman slower beam power. Therefore, the study emphasizes the need to optimize the Zeeman slower beam power to trap maximum number of cold atoms in an atomic beam loaded MOT.

DOI
10.1134/s1063776118040076

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We report the studies on the effect of Zeeman slower beam power on the loading rate and collision loss rate in an atomic beam loaded krypton magneto-optical trap (MOT). The results show that an increase in Zeeman slower beam power initially increases the MOT loading rate and reduces the background collision loss rate to increase the number of cold atoms in the MOT to an optimum value. With further increase in the Zeeman slower beam power, the number of cold atoms in the MOT decreases due to increased background collision loss rate and decrease in the trap loading rate. However, the cold collision loss rate is observed to remain unaffected by the variation in the Zeeman slower beam power. Therefore, the study emphasizes the need to optimize the Zeeman slower beam power to trap maximum number of cold atoms in an atomic beam loaded MOT.
A significant enhancement in the number of cold atoms in an atomic-beam-loaded magneto-optical trap (MOT) for metastable krypton atoms is observed when hollow laser beams are used in a Zeeman slower instead of a Gaussian laser beam. In the Zeeman slower setup, a combination of two hollow laser beams, i.e., a variable-diameter hollow beam generated using a pair of axicon lenses superimposed on a fixed-diameter hollow beam, has been used to reduce the longitudinal velocity of the atoms in the atomic beam below the capture speed of the MOT. The observed enhancement in the number of atoms in the MOT is attributed to reduced destruction of the atom cloud in the MOT and increased cooling of the off-axis atoms in the atomic beam, resulting from the use of hollow beams in the Zeeman slower.
We present a detailed experimental study of the physics involved in transferring atoms from a magneto-optical trap (MOT) to an optical dipole trap. The loading is a dynamical process determined by a loading rate and a density dependent loss rate. The loading rate depends on cooling and the flux of atoms into the trapping volume, and the loss rate is due to excited state collisions induced by the MOT light fields. From this study we found ways to optimize the loading of the optical dipole trap. Key ingredients for maximum loading are found to be a reduction of the hyperfine repump intensity, increased detuning of the MOT light, and a displacement of the optical dipole trap center with respect to the MOT. A factor of 2 increase in the number of loaded atoms is demonstrated by using a hyperfine repump beam with a shadow in it. In this way we load $8\ifmmode\times\else\texttimes\fi{}{10}^{6}{}^{85}\mathrm{Rb}$ atoms into a 1 mK deep optical dipole trap with a waist of $58 \ensuremath{\mu}\mathrm{m},$ which is 40% of the atoms initially trapped in the MOT.
To prepare cold lithium atoms for atomic interferometry experiments, we have carried out experimental researches on Zeeman deceleration and magneto-optical trap (MOT) of lithium atoms. We have also designed and implemented a compact adjustable Zeeman slower with an inner water cooling chamber, to decelerate the velocity of the 7Li atom beam from 600 m/s down to 60 m/s, and load them into the MOT. The loading rate is 5108 /s, the total trapped atom number is 1109 , and the lowest temperature of the atom cloud is 220 30 K. Then we investigate the dependence of lifetime of 7Li atoms in optical molasses on the detuning of trapping laser beams. The above results lay a foundation for further sub-Doppler cooling, optical trap based on evaporative cooling, and atomic interferometry experiments.
We report here an atomic beam loaded magneto-optical trap (MOT) for metastable krypton atoms in which the fluorescence signal from the atomic beam is used to lock the cooling laser frequency. The fluorescence signal is generated by exciting the metastable krypton atomic beam using a probe laser beam (i.e. part of the cooling laser beam) intersecting the atomic beam at an angle. A spectral shift in the fluorescence signal can be achieved by varying the angle between the probe laser beam and the atomic beam to obtain the desired frequency detuning to lock the cooling laser frequency. This has been used to optimize the number of cold atoms in the MOT. The dependence of the peak height and slope of the atomic beam fluorescence (ABF) locking signal on the RF power in the discharge tube and pressure in the observation chamber of the setup has been studied to correlate its effect on the number of atoms in the MOT.
Abstract We report simultaneous cooling and trapping of metastable 84 Kr ( 84 Kr*) and metastable 86 Kr ( 86 Kr*) atoms by overlapping the cooling laser beams for these different isotopes in the same region of a magneto-optical trap (MOT). Approximately 2 × 10 5 atoms of each isotope were trapped in this two isotope-MOT (TIMOT). We have investigated the heteronuclear collision trap loss rates for each isotope due to the presence of cold atoms of other isotope using the TIMOT loading curves. The two body heteronuclear loss rate coefficient (i.e. for the loss of 84 Kr* due to presence of 86 Kr*) and the reciprocal loss rate coefficient (i.e. for the loss of 86 Kr* due to presence of 84 Kr*) are measured to be (8.7 ± 0.8) × 10 −10 cm 3 s −1 and (8.8 ± 0.8) × 10 −10 cm 3 s −1 respectively for laser beam intensity values of 21 mW cm −2 (for cooling of 84 Kr*) and 64 mW cm −2 (for cooling of 86 Kr*). The dependence of heteronuclear cold collision loss rate on cooling laser beams intensity has also been studied and compared with homonuclear cold collision loss rate.
Magneto-optical traps (MOTs) based on the 626-nm, 136-kHz-wide intercombination line of Dy, which has an attractively low Doppler temperature of $3.3\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$, have been implemented in a growing number of experiments over the last several years. A challenge in loading these MOTs comes from their low capture velocities. Slowed atomic beams can spread out significantly during free flight from the Zeeman slower to the MOT position, reducing the fraction of the beam captured by the MOT. Here we apply a scheme for enhancing the loading rate of the MOT wherein atoms are Zeeman slowed to a final velocity larger than the MOT's capture velocity and then undergo a final stage of slowing by a pair of near-detuned beams addressing the 421-nm transition directly in front of the MOT. By reducing the free-flight time of the Zeeman-slowed atomic beam, we greatly enhance the slowed flux delivered to the MOT, leading to more than an order-of-magnitude enhancement in the final MOT population.