Andreas Kuhnert

Demonstration of high contrast in 10% broadband light with the shaped pupil coronagraph

The Shaped Pupil Coronagraph (SPC) is a high-contrast imaging system pioneered at Princeton for detection of extra-solar earthlike planets. It is designed to achieve 10-10 contrast at an inner working angle of 4λ/D in broadband light. A critical requirement in attaining this contrast level in practice is the ability to control wavefront phase and amplitude aberrations to at least λ/104 in rms phase and 1/1000 rms amplitude, respectively. Furthermore, this has to be maintained over a large spectral band. The High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Lab (JPL) is a state-of-the-art facility for studying such high contrast imaging systems and wavefront control methods. It consists of a vacuum chamber containing a configurable coronagraph setup with a Xinetics deformable mirror. Previously, we demonstrated 4x10-8 contrast with the SPC at HCIT in 10% broadband light. The limiting factors were subsequently identified as (1) manufacturing defects due to minimal feature size constraints on our shaped pupil masks and (2) the inefficiency of the wavefront correction algorithm we used (classical speckle nulling) to correct for these defects. In this paper, we demonstrate the solutions to both of these problems. In particular, we present a method to design masks with practical minimal feature sizes and show new manufactured masks with few defects. These masks were installed at HCIT and tested using more sophisticated wavefront control algorithms based on energy minimization of light in the dark zone. We present the results of these experiments, notably a record 2.4×10-9 contrast in 10% broadband light.

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.

Multichannel averaging phasemeter for picometer precision laser metrology

The Micro-Arcsecond Metrology (MAM) team at the Jet Propulsion Laboratory has developed a precision phasemeter for the Space Interferometry Mission (SIM). The current version of the phasemeter is well-suited for picometer accuracy distance measurements and tracks at speeds up to 50 cm/sec, when coupled to SIMs 1.3 micron wavelength heterodyne laser metrology gauges. Since the phasemeter is implemented with industry standard FPGA chips, other accuracy/speed trade-off points can be programmed for applications such as metrology for earth-based long-baseline astronomical interferometry (planet finding), and industrial applications such as translation stage and machine tool positioning. The phasemeter is a standard VME module, supports 6 metrology gauges, a 128 MHz clock, has programmable hardware averaging, and maximum range of 232 cycles (2000 meters at 1.3 microns).

Hybrid Lyot coronagraph for wide-field infrared survey telescope-astrophysics focused telescope assets: occulter fabrication and high contrast narrowband testbed demonstration

Abstract. Hybrid Lyot coronagraph (HLC) is one of the two operating modes of the WFIRST-AFTA coronagraph instrument. It produces starlight suppression over the full 360-deg annular region and thus is particularly suitable to improve the discovery space around WFIRST-AFTA targets. Since being selected by the National Aeronautics and Space Administration in December 2013, the coronagraph technology is being matured to technology readiness level 5 by September 2016. We present the progress of HLC key component fabrication and testbed demonstrations with the WFIRST-AFTA pupil. For the first time, a circular HLC occulter mask consisting of metal and dielectric layers is fabricated and characterized. Wavefront control using two deformable mirrors is successfully demonstrated in a vacuum testbed with narrowband light (<1-nm bandwidth at 516 nm) to obtain repeatable convergence below 8×10−9 mean contrast in the 360-deg dark hole with a working angle between 3λ/D and 9λ/D with arbitrary polarization. We detail the hardware and software used in the testbed, the results, and the associated analysis.

Technology development towards WFIRST-AFTA coronagraph

NASA’s WFIRST-AFTA mission concept includes the first high-contrast stellar coronagraph in space. This coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. In this paper we present the plan for maturing coronagraph technology to TRL5 in 2014-2016, and the results achieved in the first 6 months of the technology development work. The specific areas that are discussed include coronagraph testbed demonstrations in static and simulated dynamic environment, design and fabrication of occulting masks and apodizers used for starlight suppression, low-order wavefront sensing and control subsystem, deformable mirrors, ultra-low-noise spectrograph detector, and data post-processing.

Phase induced amplitude apodization (PIAA) coronagraphy: recent results and future prospects

The Phase Induced Amplitude Apodization (PIAA) concept uses aspheric optics to apodize a telescope beam for high contrast imaging. The lossless apodization, achieved through geometrical redistribution of the light (beam shaping) allows designs of high performance coronagraphs, ideally suited for direct imaging of exoplanets similar to Earth around nearby stars. The PIAA coronagraph concept has evolved since its original formulation to mitigate manufacturing challenges and improve performance. Our group is currently aiming at demonstrating PIAA coronagraphy in the laboratory to 1e-9 raw contrast at 2 λ/D separation. Recent results from the High Contrast Imaging Testbed (HCIT) at NASA JPL and the PIAA testbed at NASA Ames demonstrate contrasts about one order of magnitude from this goal at 2 λ/D. In parallel with our high contrast demonstration at 2λ/D, we are developing and testing new designs at a complementary testbed at NASA Ames, and solving associated technical challenges. Some of these new PIAA designs have been tested that can further mitigate PIAA manufacturing challenges while providing theoretically total starlight extinction and offering 50% throughput at less than 1 λ/D. Recent tests demonstrated on the order of 1e-6 contrast close to 1 λ/D (while maintaining 5e-8 contrast at 2 λ/D).

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.

Performance of TPF's high-contrast imaging testbed: modeling and simulations

The performance of the high-contrast imaging testbed (HCIT) at JPL is investigated through optical modeling and simulations. The analytical tool is an optical simulation algorithm developed by combining the HCITs optical model with a speckle-nulling algorithm that operates directly on coronagraphic images, an algorithm identical to the one currently being used on the HCIT to actively suppress scattered light via a deformable mirror. It is capable of performing full three-dimensional end-to-end near-field diffraction analysis on the HCITs optical system. By conducting extensive speckle-nulling optimization, we clarify the HCITs capability and limitations in terms of its contrast performance under various realistic conditions. Considered cases include non-ideal occulting masks, such as a mask with parasitic phase-delay errors (i.e., a not band-limited occulting mask) and one with damped ripples in its transmittance profiles, as well as the phase errors of all optics. Most of the information gathered on the HCITs optical components through measurement and characterization over the last several years at JPL has been used in this analysis to make the predictions as accurate as possible. Our simulations predict that the contrast values obtainable on the HCIT with narrow-band (monochromatic) illumination at 785nm wavelength are Cm=1.58x10-11 (mean) and C4=5.11x10-11(at 4λ/D), in contrast to the measured results of Cm~6×10-10 and C4~8×10-10, respectively. In this paper we report our findings about the monochromatic light performance of the HCIT. We will describe the results of our investigation about the HCITs broad-band performance in an upcoming paper.

Toward 10 10 contrast for terrestrial exoplanet detection: demonstration of wavefront correction in a shaped-pupil coronagraph

The Shaped Pupil Coronagraph (SPC) is a high-contrast imaging system pioneered at Princeton for detection of extra-solar earthlike planets. It is designed to achieve 10-10 contrast at an inner working angle of 4λ/D. However, a critical requirement in attaining this contrast level in practice is the ability to control wavefront phase and amplitude aberrations to at least λ/104 in rms phase and 1/1000 rms amplitude, respectively. Furthermore, this has to be maintained over a large spectral band. The High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Lab (JPL) is a state-of-the-art facility for studying high contrast imaging systems and fine wavefront control methods. It consists of a vacuum chamber containing a configurable coronagraph setup with a Xinetics deformable mirror. In this paper, we present the results of testing Princetons SPC in JPLs HCIT. In particular, we present the achievement of 4x10-8 contrast using a speckle nulling algorithm, and demonstrate that this contrast is maintained across wavelengths of 785, 836nm, and for broadband light having 10% bandwidth around 800nm.