Albert Niessner

Coronagraph contrast demonstrations with the high-contrast imaging testbed

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.

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

The Vector Vortex Coronagraph (VVC) is an attractive internal coronagraph solution to image and characterize exoplanets. It provides four key pillars on which efficient high contrast imaging instruments can be built for ground- and space-based telescopes: small inner working angle, high throughput, clear off-axis discovery space, and simple layout. We present the status of the VVC technology development supported by NASA. We will review recent results of the optical tests of the second-generation topological charge 4 VVC on the actively corrected High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory (JPL). New VVC contrast records have been established.

Taking the vector vortex coronagraph to the next level for ground- and space-based exoplanet imaging instruments: review of technology developments in the USA, Japan, and Europe

The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at Palomar and in the laboratory at JPL, and Hokkaido University. Manufacturing technologies for devices covering wavelength ranges from the optical to the mid-infrared, have been maturing quickly. We will review the current status of technology developments supported by NASA in the USA (Jet Propulsion Laboratory-California Institute of Technology, University of Arizona, JDSU and BEAMCo), Europe (University of Li`ege, Observatoire de Paris- Meudon, University of Uppsala) and Japan (Hokkaido University, and Photonics Lattice Inc.), using liquid crystal polymers, subwavelength gratings, and photonics crystals, respectively. We will then browse concrete perspectives for the use of the VVC on upcoming ground-based facilities with or without (extreme) adaptive optics, extremely large ground-based telescopes, and space-based internal coronagraphs.

High-contrast imaging testbed for the Terrestrial Planet Finder coronagraph

One of the architectures under consideration for Terrestrial Planet Finder (TPF) is a visible coronagraph. To achieve TPF science goals, the coronagraph must have extreme levels of wavefront correction (less than 1 /spl Aring/ rms over controllable spatial frequencies) and stability to get the necessary suppression of diffracted starlight (10/sup -10/ contrast). The High Contrast Imaging Testbed is the TPF platform for laboratory validation of key coronagraph technologies, as well as demonstration of a flight-traceable approach to coronagraph implementation. Various wavefront sensing approaches are under investigation on the testbed, with wavefront control provided by a precision high actuator density deformable mirror. Diffracted light control is achieved through a combination of an occulting or apodizing mask and stop; many concepts exist for these components and are explored. Contrast measurements on the testbed establishes the technical feasibility of TPF requirements, while model and error budget validation are demonstrate implementation viability. This paper describes the current testbed design and preliminary experimental results.

Phase-Induced Amplitude Apodization (PIAA) coronagraph testing at the High Contrast Imaging Testbed

We present the current status of our testing of a phase-induced amplitude apodization (PIAA) coronagraph at the Jet Propulsion Labs High Contrast Imaging Testbed (HCIT) vacuum facilities. These PIAA optics were designed to produce a point-spread function containing a region whose intensity is below 10-9 over a 20-percent fractional bandpass, comparable to the requirements for direct imaging of exoplanets from space. The results presented here show contrast levels of 4×10-7 in monochromatic light, with an inner working angle of 2.4 λ/D. The instrumentation is described here, as well as the testing procedures, wavefront control, and results.

Laboratory demonstrations of high-contrast imaging for space coronagraphy

Space coronagraphy is a promising method for direct imaging of planetary systems orbiting the nearby stars. The High Contrast Imaging Testbed is a laboratory facility at JPL that integrates the essential hardware and control algorithms needed for suppression of diffracted and scattered light near a target star that would otherwise obscure an associated exo-planetary system. Stable suppression of starlight by a factor of 5×10−10 has been demonstrated consistently in narrowband light over fields of view as close as four Airy radii from the star. Recent progress includes the extension of spectral bandwidths to 10% at contrast levels of 2×10−9, with work in progress to further improve contrast levels, bandwidth, and instrument throughput. We summarize recent laboratory results and outline future directions. This laboratory experience is used to refine computational models, leading to performance and tolerance predictions for future space mission architectures.

Laboratory demonstration of Phase Induced Amplitude Apodization (PIAA) coronagraph with better than 10-9 contrast

We present coronagraphic images from the Phase Induced Amplitude Apodization (PIAA) coronagraph on NASAs High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Lab, showing contrasts of 5×10−10 averaged from 2-4 λ/D, in monochromatic light at 808 nm. In parallel with the coronagraph and its deformable mirror and coronagraphic wavefront control, we also demonstrate a low-order wavefront control system, giving 100× rms suppression of introduced tip/tilt disturbances down to residual levels of 10−3 λ/D. Current limitations, as well as broadband (10% fractional bandpass) preliminary results are discussed.

Demonstration of extreme wavefront sensing performance on the TPF high-contrast imaging testbed

The Terrestrial Planet Finder (TPF) high contrast imaging testbed (HCIT) facilitates the investigation into the diversity of engineering challenges presented by the goal of direct exo-planet detection. For instance, HCIT offers a high-density deformable mirror to control the optical wavefront errors, a configurable coronagraph to control the diffracted light, and translatable cameras for measuring the focal and pupil planes before and after the coronagraph. One of the principle challenges for a coronagraphic space telescope is the extreme level of wavefront control required to make the very faint planet signal reasonably detectable. A key component, the extremely accurate sensing of the wavefront aberrations, was recently shown to be achievable using a sufficiently constrained image-based approach. In this paper, we summarize the experimental performance a focus-diverse phase-retrieval method that uses symmetrically defocus point-spread function measurements that are obtained about the coronagraph occulter focal plane. Using the HCIT, we demonstrate the high level of wavefront sensing repeatability achieved with our particular choices of focus diversity, data fidelity and processing methodologies. We compare these results to traceable simulations to suggest a partitioning of the error sources that may be limiting the experimental results.

Wavefront Amplitude Variation of TPF's High Contrast Imaging Testbed: Modeling and Experiment

Knowledge of wavefront amplitude is as important as the knowledge of phase for a coronagraphic high contrast imaging system. Efforts have been made to understand various contributions to the amplitude variation in Terrestrial Planet Finders (TPF) High Contrast Imaging Testbed (HCIT). Modeling of HCIT with as-built mirror surfaces has shown an amplitude variation of 1.3% due to the phase-amplitude mixing for the testbeds front-end optics. Experimental measurements on the testbed have shown the amplitude variation is about 2.5% with the testbeds illumination pattern having a major contribution to the low order amplitude variation.

A High-Availability, Distributed Hardware Control System Using Java

Two independent coronagraph experiments that require 24/7 availability with different optical layouts and different motion control requirements are commanded and controlled with the same Java software system executing on many geographically scattered computer systems interconnected via TCP/IP. High availability of a distributed system requires that the computers have a robust communication messaging system making the mix of TCP/IP (a robust transport), and XML (a robust message) a natural choice. XML also adds the configuration flexibility. Java then adds object-oriented paradigms, exception handling, heavily tested libraries, and many third party tools for implementation robustness. The result is a software system that provides users 24/7 access to two diverse experiments with XML files defining the differences.