Phase-mask coronagraphs are known to provide high contrast imagingcapabilities while preserving a small inner working angle, which allowssearching for exoplanets or circumstellar disks with smaller telescopes or atlonger wavelengths. The AGPM (Annular Groove Phase Mask, Mawet et al. 2005) isan optical vectorial vortex coronagraph (or vector vortex) induced by arotationally symmetric subwavelength grating (i.e. with a period smaller than{\lambda}/n, {\lambda} being the observed wavelength and n the refractive indexof the grating substrate). In this paper, we present our first mid- infraredAGPM prototypes imprinted on a diamond substrate. We firstly give anextrapolation of the expected coronagraph performances in the N-band (~10{\mu}m), and prospects for down-scaling the technology to the most wanted L-band (~3.5 {\mu}m). We then present the manufacturing and measurement results,using diamond-optimized microfabrication techniques such as nano-imprintlithography (NIL) and reactive ion etching (RIE). Finally, the subwavelengthgrating profile metrology combines surface metrology (scanning electronmicroscopy, atomic force microscopy, white light interferometry) withdiffractometry on an optical polarimetric bench and cross correlation withtheoretical simulations using rigorous coupled wave analysis (RCWA).
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