Polarimetric stellar interferometry by use of birefringent retarders

Murakami, Naoshi; Ohishi, N.; Nishikawa, Jun; Yoshizawa, M.

doi:10.1364/ao.48.005774

Cited by 1 publication

(1 citation statement)

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“…We define the instrument to be the equipment that resides in a central location and complements the light gathering and beam transport functions of the telescopes. We do not consider the case of scientific polarimetric interferometry (Rousselet-Perraut et al 1997;Murakami et al 2009). Neither do we address the impact of the birefringence of the optical trains of the telescopes; one can note that in practical terms such birefringence may be significant for precision polarimetry but has a negligible impact on fringe contrast.…”

Section: Introductionmentioning

confidence: 99%

A novel technique to control differential birefringence in optical interferometers

Lazareff

Bouquin

Berger

2012

A&A

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Context. Optical interferometers are subject to many atmospheric and instrumental artifacts that contribute to the degradation of their instrumental contrast, hence their performances. The differential birefringence is, among these effects, one of the trickiest to control, in particular for instrument using fibers, where it can be far larger than the one arising in the optical mirror trains. Several solutions have been tested in the past, ranging from polarization splitting to fiber tweaking. We adopt a new solution for the PIONIER instrument, a four-telescope (4T) combiner at the Very Large Telescope Interferometer (VLTI). Aims. We present a method to cancel the instrumental birefringence in an optical interferometer, allowing the joint detection of the fringe patterns of both polarizations, and substantial gains to be made in both signal-to-noise ratio and readout speed. Methods. A thin (2 mm) plate of birefringent material (LiNbO 3 ) is inserted in each of the four beams. The incidence angle of each plate is adjustable. This allows us to introduce a controlled amount of birefringence in each beam and to cancel the instrumental differential birefringence. We present our derivation of the induced birefringence versus incidence angle and discuss the design choices. Results. Our proposed solution is implemented in the Pionier instrument. Before correction, the instrumental birefringence was of order 5 μm (path length). The adjustment takes about one hour, results in a birefringence of less than 0.1 μm, and is stable for at least the duration of an observing run (several days). Conclusions. We demonstrate on an operational near-infrared interferometer a novel, simple, low-cost, and effective technique to control the differential birefringence. The predictability and stability of the correction make this technique ideal for an automated correction in the VLTI second generation instruments.

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Section: Introductionmentioning

confidence: 99%