EGAS41 - Swansea University

41 st EGAS CP 179 Gdańsk 2009
Probing cold atoms using tapered optical fibres
M. Morrissey 1,2 , K. Deasy 1,2 , S. Nic Chormaic 2,3,∗
1 Department of Applied Physics and Instrumentation, Cork Institute of Technology, Rossa
Avenue, Bishopstown, Cork, Ireland
2 Photonics Centre, Tyndall National Institute, Prospect Row, Cork, Ireland
3 Physics Department, University College Cork, Cork, Ireland.
∗ Corresponding author: s.nicchormaic@ucc.ie
In this paper, we discuss the coupling of light emitted by cold rubidium atoms into
the guided mode of a tapered optical fibre [1,2]. Tapered fibres are promising tools for
manipulating and trapping cold atoms via the evanescent light field [3,4]. In order to fully
understand the processes present when a cold atom is close to the surface of an optical
fibre, the spontaneous emission rate of atoms near the fibre’s surface must be studied.
Fibres used in our work typically have diameters of ∼600 nm, with a transmission at 780
nm of ∼60% prior to installation into the vacuum chamber. A schematic of the setup is
shown in Fig. 1. Light coupled into the fibre is monitored using a single photon counting
module connected to one end. Using this technique, we have measured the profile of
the atom cloud by moving the cloud across the narrowest region of the tapered fibre and
recording the photon count rate. We have used a similar technique to measure the lifetime
and decay time of the atom cloud. Our results are compared to those obtained by imaging
the cloud directly onto a photodiode.
Figure 1: Schematic of the experimental setup
It is worth noting that the tapered fibre proves to be a more sensitive tool for few
atoms, giving an increased decay time of the cloud, thereby providing a method of
analysing density distributions in MOTs with a high degree of precision.
References
[1] J.M. Ward, D. O’Shea, B. Shortt, M. Morrissey, K. Deasy, S. Nic Chormaic, Rev. Sci.
Instrum. 1775, 083105 (2006)
[2] M. Morrissey, K. Deasy, Y. Wu, S. Nic Chormaic, arXiv:0903.2953
[3] K.P. Nayak, P.N. Melentiev, M. Morinaga, F. Le Kien, V.I. Balykin, K. Hakuta, Opt.
Express 15, 5431 (2007)
[4] G. Sagué, E. Vetsch, W. Alt, D. Meschede, A. Rauschenbeutel, Phys. Rev. Lett. 99,
163602 (2007)
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