A novel technique to control differential birefringence in optical interferometers: Demonstration on the PIONIER-VLTI instrument

• Published in: Astronomy and astrophysics (Berlin) Vol. 543; p. 1
• Main Authors: Lazareff, B, Le Bouquin, J-B, Berger, J-P
• Format: Journal Article
• Language: English
• Published: 01.07.2012
• Subjects: Indexing in process
• ISSN: 0004-6361; 1432-0746

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. The authors adopt a new solution for the PIONIER instrument, a four-telescope combiner at the Very Large Telescope Interferometer. A thin plate of birefringent material is inserted in each of the four beams. The incidence angle of each plate is adjustable. This allows them to introduce a controlled amount of birefringence in each beam and to cancel the instrumental differential birefringence. Their proposed solution is implemented in the Pionier instrument. Before correction, the instrumental birefringence was of order 5 mu m.