Dear Editor,

please find enclosed a manuscript on an investigation towards improving the
light-atom coupling in a conceptually simple focusing experiment. 

This work is in line with an effort to better understand the coupling between
radiative modes of a single point-like emitter, and a strongly focused optical
mode. In recent years, there have been several efforts to accomplish strong
atom-light interaction with this approach, typically involving either lenses
with a large numerical aperture, Fresnel zone plates, or parabolic
mirrors.

However, several of such experiments observed a discrepancy between
experimentally observed and theoretically expected interaction strength. A
common suspicion, at least for the single emitters in free space, was a
limited localization due to residual motion of an atom.

In this work, we estimate the influence of this residual motion on the
coupling strength, and find that with common laser cooling techniques, the
light-atom coupling is actually not limited by the residual dislocation of the
atom, but most likely by imperfections in the focusing element.

The better understanding of the influence of the temperature on the light-atom
interaction, and a focusing element with a larger numerical aperture led to an
observed extinction 17% of a light mode by a single atom - to our knowledge a
record for single emitters in free space, which allow a very clean treatment
of the optical field.

We feel that the manuscript could be interesting to the audience of Physical
Review A, and therefore ask for your kind consideration.

With Best Regards on behalf of all authors,

Christian Kurtsiefer