Abstract
Imaging ultracold atomic gases close to surfaces is an important tool for the detailed analysis of experiments carried out using atom chips. We describe the critical factors that need be considered, especially when the imaging beam is purposely reflected from the surface. In particular we present methods to measure the atom-surface distance, which is a prerequisite for magnetic field imaging and studies of atom surface-interactions.
Highlights
We only consider imaging with resonant light.Microtraps created above microfabricated surfaces, or atom chips [1–3], are a promising approach towards the precise manipulation of ultracold atoms
As the cloud becomes smaller, important components of the scattered wave occupy a larger angular spread relative to the direction of the plane wave. As long as this spread is small compared to the angle between the imaging beam and the atom chip surface, all the light propagates away from the mirror: a lens will reconstruct the true wavefront in the object plane
The input imaging beam is sent through an optical fibre and reflected from the atom chip surface
Summary
Microtraps created above microfabricated surfaces, or atom chips [1–3], are a promising approach towards the precise manipulation of ultracold atoms. Ultracold atoms held in close proximity to the chip surface are versatile probes for atom-surface interactions [17], local magnetic fields [18–23] and current flow irregularities [24]. Atoms are held and manipulated at short distances (a few microns) from the chip surface. A main measurement tool is absorption imaging [35] and a thorough understanding of the disturbances caused by the close by atom chip surface is essential for the analysis of experiments. We describe the key ingredients for imaging atomic clouds close to a surface and give examples of specific implementations. We cover three different scenarios, two of which involve reflecting the imaging beam from the atom chip surface, where reflecting at grazing incidence produces a standing wave
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