Loading of a krypton magneto-optical trap with two hollow laser beams in a Zeeman slower
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TOMS, MOLECULES, OPTICS
Loading of a Krypton MagnetoOptical Trap with Two Hollow Laser Beams in a Zeeman Slower1 S. Singh*, V. B. Tiwari, S. R. Mishra, and H. S. Rawat Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore452013, India *email: [email protected] Received April 11, 2014
Abstract—A significant enhancement in the number of cold atoms in an atomicbeamloaded 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 variablediameter 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 offaxis atoms in the atomic beam, resulting from the use of hollow beams in the Zeeman slower. DOI: 10.1134/S1063776114090209 1
1. INTRODUCTION
The laser cooling of noble gas atoms in the excited state is an attractive area of research to study cold atom collisions, ionization physics, nanolithography, and atom trap trace analysis (ATTA) [1, 2]. Compared to alkali atoms, which are cooled in the ground state, noble gas atoms are laser cooled in a metastable excited state. The excitation to this metastable state can be achieved by radiofrequency (RF) excitation [3, 4]. The metastable state atoms generated in the dis charge section are transported to the magnetooptical trap (MOT) chamber in the form of an atomic beam. Capturing these atoms in the MOT requires reducing the longitudinal velocity of the atoms in the atomic beam below the capture velocity of the MOT. A high flux of the slowed metastable atoms in the atomic beam is important for efficient loading of the MOT, which is a workhorse for many experiments including Bose Einstein condensation (BEC), atom optics, and atomic physics [5, 6]. The slowing of the atomic beam is conveniently achieved by using a Zeeman slower device [7], which is used as a decelerating unit for the atomic beam before its entry to the MOT chamber. The Zeeman slower decelerates the atoms through Doppler laser cooling of atoms in the presence of a spatially varying magnetic field. The deceleration results from the scattering force on an atom due to a laser beam propagating opposite to the atomic beam direction. The variation of the magnetic field in the Zeeman slower is kept in such a way that the Zeeman shift in the atomic transition frequency compensates the Doppler shift in the laser frequency for a moving 1 The article is published in the original.
atom. Thus, laser beam interacts resonantly with the atoms throughout the length of the Zeeman slower, which leads to effectively slowing the atomic beam for the loading of the MOT. In a Zeeman slower based atomicbeaml
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