Tapered optical fibers as tools for probing magneto-optical trap characteristics

Abstract

We present a novel technique for measuring the characteristics of a magneto-optical trap (MOT) for cold atoms by monitoring the spontaneous emission from trapped atoms coupled into the guided mode of a tapered optical nanofiber. We show that the nanofiber is highly sensitive to very small numbers of atoms close to its surface. The size and shape of the MOT, determined by translating the cold atom cloud across the tapered fiber, is in excellent agreement with measurements obtained using the conventional method of fluorescence imaging using a charge coupled device camera. The coupling of atomic fluorescence into the tapered fiber also allows us to monitor the loading and lifetime of the trap. The results are compared to those achieved by focusing the MOT fluorescence onto a photodiode and it was seen that the tapered fiber gives slightly longer loading and lifetime measurements due to the sensitivity of the fiber, even when very few atoms are present.

Contributed Review: Optical micro- and nanofiber pulling rig

“…Evanescent waves in optical waveguides have received great attention recently due to the advantage of optical coupling with systems such as microresonators, [1][2][3] cold atoms, [4][5][6][7][8] their use in optical sorting, 9,10 their ability to form microcavities themselves, [11][12][13] and to support cavities. [14][15][16] Of the many available waveguide types, the tapered optical fiber -otherwise known as the optical micro-or nanofiber (MNF) -is an important device in these research fields because it is relatively easy to fabricate, produces a strong evanescent field, and can be directly integrated into existing fiber optic systems.…”

Optical Nanofibers

“…(2012), low loss, and promise of improved atom-light interaction Alton et al (2011);Le Kien et al (2005b); ; Goban et al (2012); Wuttke et al (2012) have led to increased interest in the physics community. Optical micro-or nanofibers are used for sensing and detection Knight et al (1997); Nayak et al (2007), and coupling light to resonators Knight et al (1997); Kakarantzas et al (2002); Spillane et al (2003); Louyer et al (2005); Morrissey et al (2009);Fujiwara et al (2012), NV centers Schröder et al (2012), or photonic crystals Thompson et al (2013); Sadgrove et al (2013).…”

“…Morrissey et al (2009) uses the nanofiber to measure several characteristics of a magneto-optical trap (MOT): cloud shape, cloud size, atom loading rate, and atom number. In another experiment, Russell et al (2012) measure sub-Doppler temperatures of an atom cloud by dithering the magnetic trapping field to extract the trap frequency.…”

Manipulating Cold Atoms with Optical Fibres

“…The TNF is mounted inside an ultra-high vacuum MOT chamber using electrical feedthroughs attached to a vacuum flange. Tapered region of the fibre is held in an U-shaped mount, ensuring that the thinnest section of the fibre is centred in MOT chamber 31 . Other than anti-Helmholtz coils, pairs of smaller coils are also used to spatially overlap the cold cloud with the waist region of TNF.…”

“…A basic MOT set-up 29,30 was used to create a cold cloud of 85 Rb atoms near the waist region of TNF 31 . Three pairs of mutually perpendicular, opposite circularly polarized and retroreflecting laser beams, all intersecting at a point produce optical force necessary for cooling the atoms.…”