Multi-stage four-quadrant phase mask: achromatic coronagraph for space-based and ground-based telescopes
R. Galicher1,2, P. Baudoz2 and J. Baudrand2
Luth, CNRS, Observatoire de Paris,
5 place Jules Janssen,
2 Lesia, Observatoire de Paris, CNRS and University Denis Diderot Paris 7, 5 place Jules Janssen, 92195 Meudon, France
Received: 8 February 2011
Accepted: 28 March 2011
Context. Less than 3% of the known exoplanets were directly imaged for two main reasons. They are angularly very close to their parent star, which is several magnitudes brighter. Direct imaging of exoplanets thus requires a dedicated instrumentation with large telescopes and accurate wavefront control devices for high-angular resolution and coronagraphs for attenuating the stellar light. Coronagraphs are usually chromatic and they cannot perform high-contrast imaging over a wide spectral bandwidth. That chromaticity will be critical for future instruments.
Aims. Enlarging the coronagraph spectral range is a challenge for future exoplanet imaging instruments on both space- and ground-based telescopes.
Methods. We propose the multi-stage four-quadrant phase mask that associates several monochromatic four-quadrant phase mask coronagraphs in series. Monochromatic device performance has already been demonstrated and the manufacturing procedures are well-under control since their development for previous instruments on VLT and JWST. The multi-stage implementation simplicity is thus appealing.
Results. We present the instrument principle and we describe the laboratory performance for large spectral bandwidths and for both pupil shapes for space- (off-axis telescope) and ground-based (E-ELT) telescopes.
Conclusions. The multi-stage four-quadrant phase mask reduces the stellar flux over a wide spectral range and it is a very good candidate to be associated with a spectrometer for future exoplanet imaging instruments in ground- and space-based observatories.
Key words: instrumentation: high angular resolution / techniques: high angular resolution / methods: laboratory / methods: numerical
© ESO, 2011