Vector vortex coronagraph: first results in the visible

Abstract

We report the status of JPL and JDSU ongoing technological developments and contrast results of the vector vortex coronagraph (VVC) made out of liquid crystal polymers (LCP). The first topological charge 4 VVC was tested on the high contrast imaging testbed (HCIT) around 800 nm, under vacuum and with active wavefront control (32x32 Xinetics deformable mirror). We measured the inner working angle or IWA (50% off-axis transmission) at ∼ 1.8λ/d. A one-sided dark hole ranging from 3λ/d to 10λ/d was created in polarized light, showing a mean contrast of ∼ 2 × 10 −7 over a 10% bandwidth. This contrast was maintained very close in (3 λ/d) in a reduced 2% bandwidth. These tests begin to demonstrate the potential of the LCP technology in the most demanding application of a space-based telescope dedicated to extrasolar planet characterization. The main limitations were identified as coming from incoherent sources such as multiple reflections, and residual chromaticity. A second generation of improved masks tackling these issues is being manufactured and will be tested on the HCIT in the coming months.

Recent results of the second generation of vector vortex coronagraphs on the high-contrast imaging testbed at JPL

“…After the very first test in 2008, 8 this second pass using an improved second-generation VVC of topological charge 4 achieved a two orders of magnitude gain in contrast both monochromatically and over a 10% bandpass ‡ . We expect the third and subsequent generations of devices in the making to be intrinsically achromatic over 20% bandwidth (thanks to a 3-layer design, see Ref.…”

“…1, these proceedings) was used but the process was optimized to answer identified weaknesses of the gen-1 prototype. Indeed, the VVC tested in 2008 performed well (best contrast result of ∼ 10 −7 ) but was limited by several factors, 8 summarized here:…”

“…1), following the promising test of the first generation of charge 4 VVC in 2008. 8 The same liquid crystal polymer technology (LCP, see Ref. 1, these proceedings) was used but the process was optimized to answer identified weaknesses of the gen-1 prototype.…”

SPICES a small space coronagraph to characterize giant and telluric planets in reflected light

“…Our goal is to implement a more promising technique, the Self Coherent Camera [5], which for now has a lower Technology Readiness Level but will allow a better discrimination of planets and speckles [2] while it requires little modification in a coronagraph. We chose the Vector Vortex Coronagraph (VVC), a derivation of the phase mask concept which can be made potentially achromatic on a ∼50% bandwidth [10]. The backend instrument is a microlenses based integral field spectrograph (IFS) similar to those developed now on the ground for SPHERE and GPI [1].…”

High-charge and multiple-star vortex coronagraphy from stacked vector vortex phase masks

“…Future giant telescopes will require the management of pointing noise/errors, lower order aberrations, and finite spatial extension of the source, which implies the development of higher order vortex masks. Their realization is especially difficult for subwavelength gratings [6,11], while liquid crystal polymers allow easier fabrication of a vector vortex phase mask of the order higher than two [12].…”