Context. To characterize their atmospheres in order to find evidences of life, one has to detect directly
photons from the exoplanets to measure their spectra. One possible technique is dark fringe
interferometry that needs an achromatic π phase shift in one arm of the interferometer. We have
conceived a phase shifter made of two cellular mirrors, in which each cell position and phase shift is
specific, so that the behaviour of the nulling with respect to wavelength is flat within a broad range.
Aims. We want to validate experimentally two versions of this achromatic phase shifter: a transmissive
one in bulk optics and a reflective one using a segmented deformable mirror. What we present in this
paper are the last results obtained in the lab.
Methods. We built an optical bench in the visible that allows us to test the principle and characterize
the performances and the limits of this phase shifter.
Results. We tested several transmissive and one reflective phase shifter and obtained, for instance, an
attenuation of about 2.10-3 for a white source (from 430 to 830 nm) that proved the achromatic
behavior of the phase shifter. The preliminary performances and limitations are analyzed.
Context. Dark fringe interferometry in the thermal infrared is one way to detect directly a planet orbiting a star, and so to
characterize the planet's atmosphere through spectroscopy. This method demands a phase shift of π1 in one arm of the
interferometer. In order to detect various bio-tracers gases, a broad wavelength range (6-18 μm)2-3 is necessary, therefore
an achromatic phase shift of π is required. The achromatic device presented here is a phase shifter made of two cellular
mirrors, in which each cell induces a specific phase shift.
Aims. We wish to demonstrate that this theoretical concept is experimentally valid. We present in this paper the setup
and the very first results.
Methods. In a first step, we have consolidated the theoretical ground and in a second step we developed an optical bench
in the visible domain to test the concept and measure the performances of this device.
Results. The preliminary experimental tests show evidences that such a device is working as expected in terms of nulling
and achromatism: in spite of an error on one cell of the prototype, it provides a nulling of 2.10-3 at one wavelength, and
this value is close to the expected value. Besides, a nulling of 1.10-2 in a 450 to 750 nm bandwidth: a hint that a perfect
device should be achromatic.
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