Proceedings Article | 10 August 2010
Proc. SPIE. 7731, Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave
KEYWORDS: Coronagraphy, Lenses, Reflection, Beam splitters, Interferometers, Stars, Exoplanets, Fringe analysis, Spherical lenses, Phase shifts
In 1996, Jean Gay and Yves Rabbia presented their Achromatic Interferential Coronagraph (AIC) for detecting
and imaging faint companions (ultimately exoplanets) in the neighboring of a star. As presented then,
the Michleson-like Interferometer configuration of the AIC hardens its insertion into an existing (coaxial) optical
train, the output beam of the AIC being delivered at right angle from the input beam. To overcome this, they
reconfigured the AIC into a compact and fully axial coronagraph, the CIAXE, which main feature consists of
using two thick lenses machined in the same optical material. For the CIAXE to deliver the output beam along
the same axis as the input beam, the two lenses are coaxially disposed on the optical axis and are separated, at
their common spherical contact surface by a thin air gap acting like a beam splitter. We have set up a laboratory
experiment aiming at validating the principle of the concept. Our first step was to equalize the thicknesses of the
two lenses, so as to make zero the optical path difference between both arms. For this, the (residual) value of the
OPD has been evaluated and then the lenses have been re-machined so as to decrease as far as technologically
possible, the thicknesses mismatch. As a second step, a micro-controlled rotation around the common curvature
center of the spherical surfaces of the lenses is applied. This allows a fine tuning of the residual OPD at the
required accuracy level. Are presented here test bench, steps and results.
