Focusing characteristics of a 4 πparabolic mirror light-matter interface
Alber et al. Journal of the European Optical Society-Rapid
Publications
Focusing characteristics of a 4π parabolic mirror light-matter interface
Lucas Alber 0 1 3 4
Martin Fischer 0 1 3 4
Marianne Bader 0 1 3 4
Klaus Mantel 1 4
Markus Sondermann 0 1 3 4
Gerd Leuchs 0 1 2 3 4
0 Department of Physics, Friedrich-Alexander University Erlangen-Nürnberg (FAU) , Staudtstraße 7/B2, 91058 Erlangen , Germany
1 Max-Planck-Institute for the Science of Light , Staudtstr. 2, 91058 Erlangen , Germany
2 Department of Physics, University of Ottawa , 75 Laurier Avenue East, ON K1N 6N5 Ottawa , Canada
3 Department of Physics, Friedrich-Alexander University
4 Erlangen-Nürnberg (FAU) , Staudtstraße 7/B2, 91058 Erlangen , Germany
Background: Focusing with a 4π parabolic mirror allows for concentrating light from nearly the complete solid angle, whereas focusing with a single microscope objective limits the angle cone used for focusing to half solid angle at maximum. Increasing the solid angle by using deep parabolic mirrors comes at the cost of adding more complexity to the mirror's fabrication process and might introduce errors that reduce the focusing quality. Methods: To determine these errors, we experimentally examine the focusing properties of a 4π parabolic mirror that was produced by single-point diamond turning. The properties are characterized with a single 174Yb+ ion as a mobile point scatterer. The ion is trapped in a vacuum environment with a movable high optical access Paul trap. Results: We demonstrate an effective focal spot size of 209 nm in lateral and 551 nm in axial direction. Such tight focusing allows us to build an efficient light-matter interface. Conclusion: Our findings agree with numerical simulations incorporating a finite ion temperature and interferometrically measured wavefront aberrations induced by the parabolic mirror. We point at further technological improvements and discuss the general scope of applications of a 4π parabolic mirror.
Atom-photon coupling; Free space; Quantum optics; Ion trapping; 4Pi parabolic mirror; 4Pi microscopy; Confocal microscopy
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Background
Free space interaction between light and matter is
incorporated as a key technology in many fields in
modern science. The efficiency of interaction influences
measurements and applications ranging from various kinds
of fundamental research to industrial applications. New
innovations and new types of high precision
measurements can be triggered by improving the tools needed for
a light-matter interface. To achieve high interaction
probability with a focused light field in free space, an
experimental scheme using parabolic mirrors for focusing onto
single atoms has been developed in recent years [1–3].
This scheme relies on mode matching of the focused
radiation to an electric dipole mode (cf. Ref. [4] and citations
therein).
Focusing in free-space experiments is usually done with
state-of-the-art lens based imaging systems [5–8]. Single
lenses, however, suffer from inherent drawbacks like
dispersion induced chromatic aberrations, optical
aberrations, and auto-fluorescence, respectively. Most of these
limitations can be corrected to a high degree by precisely
assembling several coated lenses in a lens-system, e.g. in a
high numerical aperture (NA) objective. Although solving
some problems, multi-lens-systems induce new problems
such as short working distances, low transmission for
parts of the optical spectrum, the need for immersion
fluids, and high costs, respectively. Therefore, multi-lens
systems are often application specific providing best
performance only for the demands that are most important
for the application.
Mirror based objectives are an alternative to lens-based
systems and can overcome some of these problems. The
improvement is based on a mirror’s inherent property of
being free from chromatic aberrations. The nearly
wavelength independent behavior also leads to a homogeneous
reflectivity for a large spectral window. Comparing the
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
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reflectivity of mirrors to the transmission of lens based
objectives, mirrors can sometimes also surpass lens-based
systems. But surprisingly, they are rarely used when high
interaction efficiency is required. This lack in application
may be due to the fact that reflecting imaging systems,
like the Cassegrain reflector, cannot provide a high NA.
A high NA is however needed for matching the emission
pattern of a dipole, which spans over the entire solid angle.
The limitation in NA consequently constitutes a
limitation in the maximum achievable light-matter cou (...truncated)