The achromatic chessboard, a new concept of a phase shifter fornulling interferometryIII. Experimental performances

摘要

Context. Dark fringe interferometry in the thermal infrared is one way to detect directly a planet orbiting a star, and so tocharacterize the planet's atmosphere through spectroscopy. This method demands a phase shift of π~1 in one arm of theinterferometer. In order to detect various bio-tracers gases, a broad wavelength range (6-18 urn)~(2-3) is necessary, thereforean achromatic phase shift of n is required. The achromatic device presented here is a phase shifter made of two cellularmirrors, 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 setupand the very first results.Methods. In a first step, we have consolidated the theoretical ground and in a second step we developed an optical benchin 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 nullingand achromatism: in spite of an error on one cell of the prototype, it provides a nulling of 2.10~(-3) at one wavelength, andthis 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.