Design and performance simulations of mid-IR AGPMs for ELT/METIS applications

• The direct detection of exoplanets requires the use of dedicated, highcontrast imaging instruments. In this context, vector vortex coronagraphs(VVCs) are considered to be among the most promising solutions to reachhigh contrast at small angular separations. They feature a small innerworking angle (down to 0.9 lambda/D), high throughput, clear off-axis360° discovery space, and are simple to implement. The AGPM (AnnularGroove Phase Mask) is an implementation of the vortex phase mask, whichprovides achromaticity over an appreciable spectral range thanks to the useof sub-wavelength gratings. The grating profile can be optimized based onthe rigorous coupled wave analysis (RCWA) to achieve a quasi-achromaticphase shift up to a very broad band (L+M band: 3.5-5.1μm). These deviceshave been manufactured onto CVD diamond substrates, using reactiveion etching. In this communication, I will first present the latest RCWAConference 9605: Techniques and Instrumentationfor Detection of Exoplanets VIIR eturn to Contents +1 360 676 3290 · help@spie.org 631simulations performed in the L, M and N spectral bands, and for somecombinations of these bands. The resulting optimized AGPMs could beperfectly integrated in the E-ELT/METIS instrument, which aims at detectingand characterizing exoplanets by direct imaging. The target contrast forMETIS is <1e-4 at 2 lambda/D (~40 mas in L band), which translates into apeak rejection rate of few hundreds for the AGPMs. Secondly, the opticalpropagation within the METIS instrument will be studied to determine theperformances of a vortex coronagraph at the focus of METIS. In particular,the effect of the central obstruction, spiders, missing E-ELT segments,and pointing jitter will be analysed, together with the sensitivity to tip-tilt.Finally, the atmosphere and the AO contributions will be considered toobtain more realistic results.

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Publikations- och innehållstyp

ref (ämneskategori)

kon (ämneskategori)