Laboratory demonstration of a broadband six-level phase mask coronagraph.

The six-level phase mask (SLPM) can be used in a focal plane as an efficient coronagraph [Opt. Express 22, 1884 (2014)]. It has several advantages: high-contrast imaging in broadband with small inner working angle; easy fabrication at low cost by photolithography and reactive ion etching processes; easy implementation with no need of pupil apodization. We present in this paper the first laboratory results demonstrating the high performance of a SLPM with an unobscured pupil. The on-axis attenuation reaches 2 × 10 at λ = 800 nm and is better than 10 over a 10% spectral bandwidth and better than 10 over a 20% bandwidth. Finally, the detection of a planet can be achieved down to 1 λ/D.