Coronagraph contrast demonstrations with the high-contrast imaging testbed

Abstract

Predictions of contrast performance for the Eclipse coronagraphic telescope are based on computational models that are tested and validated with laboratory experience. We review recent laboratory work in the key technology areas for an actively-corrected space telescope designed for extremely high-contrast imaging of nearby planetary systems. These include apodized coronagraphic masks, precision deformable mirrors, and coronagraphic algorithms for wavefront sensing and correction, as integrated in the high contrast imaging testbed at JPL. Future work will focus on requirements for the Terrestrial Planet Finder coronagraph mission.

10^-7 contrast ratio at 4.5 lambda/D: New results obtained in laboratory experiments using nano-fabricated coronagraph and multi-Gaussian shaped pupil masks

“…[3] the experimental bench-mounted optics had no focal plane obscuration and used a prolate spheroidal pupil mask manufactured by laser cutting, and yet in ref. [22] there was a precisely made apodized coronagraph. Both had optical systems that incorporated a deformable mirror in the imaging section which made it possible to interactively reduce wavefront errors to something below 1.8 nm rms.…”

“…This could be caused by one of two effects: (1) the absence of dynamic wavefront error minimization in the final imaging optics (which all come after the UnISIS AO corrections) unlike [3,22], or (2) that the bright star light was simply scattering from various optical elements including the edges of the pupil mask. We decided to address point two by introducing a hard-stop focal plane mask of 2.5λ/D that will affectively prevent the transmission of unneeded light from the central star fully recognizing that the scattered light from the hard stop might introduce its own subsidiary effects.…”

“…However, realizing contrast levels of 10 -9 to 10 -10 is proving to be a challenging task even in a laboratory environment with a laser source as the artificial star (see for eg. [3,22]). The major challenges are: a) fabricating masks with edge rms errors better than λ /4 in order minimize scattered light from the edges; b) minimizing scattered light from optical components in the detection system; and c) minimizing the rms error in the wavefront itself [13][14] to reduce the effects of speckles.…”

Planet Formation Instrument for the Thirty Meter Telescope

“…A second solution is to use a single DM to carve out a half-dark hole in the image plane. It has been shown (Trauger et al 2004) that, in monochromatic light, by use of the correct control algorithm a DM can be used to correct for intensity errors if the contrast is allowed to increase in half of the image plane. A third solution is to install another DM in the system, but not at a pupil, to allow control of phase and amplitude errors as is described in Section 11.3 .…”

High-Contrast Imaging using Adaptive Optics for Extrasolar Planet Detection

“…To combat amplitude errors, HCIT uses a speckle nulling algorithm to correct phase and amplitude errors affecting a half dark hole region [75]. They have demonstrated 2 × 10 −9 contrast with speckle nulling and a Lyot coronagraph [75].…”