Dana H. Lynch

Laboratory demonstration of high-contrast imaging at inner working angles 2 λ/D and better

Coronagraph technology is advancing and promises to enable direct imaging and spectral characterization of extrasolar Earth-like planets in the 2020 decade with a telescope as small as 1.5m. A small Explorer-sized telescope can also be launched in the 2010 decade capable of seeing debris disks as dim as tens of zodis and potentially a few large planets. The Phase Induced Amplitude Apodization (PIAA) coronagraph makes such aggressive performance possible, providing high throughput and high contrast close to the diffraction limit. We report on the latest results from a testbed at NASA Ames that is focused on developing and testing the PIAA coronagraph. This laboratory facility was built in 2008 and is designed to be flexible, operated in an actively thermally stabilized air environment, and to complement collaborative efforts at NASA JPLs High Contrast Imaging Testbed. For our wavefront control we are using small Micro-Electro- Mechanical-System deformable mirrors (MEMS DMs), which promise to reduce the size of the beam and overall instrument, a consideration that becomes very important for small telescopes. We describe our lab progress and results, which include (as of August 2011): the demonstration of 1.9x10-8 average raw contrast in a dark zone from 2.0 - 3.4 λ/D and of 1.2x10-6 contrast from 1.5-2.0 λ/D (in monochromatic light); the testing of the next-generation reflective PIAA mirror set built by Tinsley and designed for broadband; and finally, discuss our most important past limiting factors as well as expected future ones.

First results on a new PIAA coronagraph testbed at NASA Ames

Direct imaging of extrasolar planets, and Earth-like planets in particular, is an exciting but difficult problem requiring a telescope imaging system with 1010 contrast at separations of 100mas and less. Furthermore, the current NASA science budget may only allow for a small 1-2m space telescope for this task, which puts strong demands on the performance of the imaging instrument. Fortunately, an efficient coronagraph called the Phase Induced Amplitude Apodization (PIAA) coronagraph has been maturing and may enable Earth-like planet imaging for such small telescopes. In this paper, we report on the latest results from a new testbed at NASA Ames focused on testing the PIAA coronagraph. This laboratory facility was built in 2008 and is designed to be flexible, operated in a highly stabilized air environment, and to complement existing efforts at NASA JPL. For our wavefront control we are focusing on using small Micro-Electro- Mechanical-System deformable mirrors (MEMS DMs), which promises to reduce the size of the beam and overall instrument, a consideration that becomes very important for small telescopes. At time of this writing, we are operating a refractive PIAA system and have achieved contrasts of about 1.2x10-7 in a dark zone from 2.0 to 4.8 λ/D (with 6.6x10-8 in selected regions). In this paper, we present these results, describe our methods, present an analysis of current limiting factors, and solutions to overcome them.

Laboratory demonstration of high-contrast imaging at 2 λ/D on a temperature-stabilized testbed in air

Direct imaging of extrasolar planets in visible light, and Earth-like planets in particular, is an exciting but difficult problem requiring a telescope imaging system with 10-10 contrast at separations of 100mas and less. Furthermore, only a small 1-2m space telescope may be realistic for a mission in the foreseeable future, which puts strong demands on the performance of the imaging instrument. Fortunately, an efficient coronagraph called the Phase Induced Amplitude Apodization (PIAA) coronagraph may enable Earth-like planet imaging for such small telescopes if any exist around the nearest stars. In this paper, we report on the latest results from a testbed at the NASA Ames Research Center focused on testing the PIAA coronagraph. This laboratory facility was built in 2008 and is designed to be flexible, operated in a highly stabilized air environment, and to complement efforts at NASA JPLs High Contrast Imaging Testbed. For our wavefront control we are focusing on using small Micro-Electro-Mechanical-System deformable mirrors (MEMS DMs), which promises to reduce the size of the beam and overall instrument, a consideration that becomes very important for small telescopes. In this paper, we briefly describe our lab and methods, including the new active thermal control system, and report the demonstration of 5.4×10-8 average raw contrast in a dark zone from 2.0 - 5.2 λ/D. In addition, we present an analysis of our current limits and solutions to overcome them.

Demonstration of broadband contrast at 1.2λ/D and greater for the EXCEDE starlight suppression system

Abstract. The EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) science mission concept uses a visible-wavelength phase-induced amplitude apodization (PIAA) coronagraph to enable high-contrast imaging of circumstellar debris systems and some giant planets at angular separations reaching into the habitable zones of some of the nearest stars. We report on the experimental results obtained in the vacuum chamber at the Lockheed Martin Advanced Technology Center in 10% broadband light centered about 650 nm, with a median contrast of 1×10−5 between 1.2 and 2.0λ/D simultaneously with 3×10−7 contrast between 2 and 11λ/D for a single-sided dark hole using a deformable mirror (DM) upstream of the PIAA coronagraph. These results are stable and repeatable as demonstrated by three measurement runs with DM settings set from scratch and maintained on the best 90% out of the 1000 collected frames. We compare the reduced experimental data with simulation results from modeling observed experimental limits. The observed performance is consistent with uncorrected low-order modes not estimated by the low-order wavefront sensor. Modeled sensitivity to bandwidth and residual tip/tilt modes is well matched to the experiment.

EXCEDE technology development I: First demonstrations of high contrast at 1.2 λ/D for an explorer space telescope mission

Coronagraph technology is advancing and promises to enable space telescopes capable of seeing debris disks as well as seeing and spectrally characterizing exo-Earths. Recently, NASAs explorer program has selected the EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer) mission concept for technology development. EXCEDE is a 0.7m space telescope concept designed to achieve raw contrasts of 1e-6 at an inner working angle of 1.2 λ/D and 1e- 7 at 2 λ/D. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the Phase Induced Amplitude Apodization (PIAA) coronagraph to provide high throughput and high contrast close to the diffraction limit, enabling aggressive performance on small telescopes. We report on the latest progress in developing the SSS and present coronagraphic performance results from our air testbed at NASA Ames. Our results include a lab demonstration of 1e-5 contrast at 1.2 λ/D, 1.3e-6 contrast at 1.4 λ/D and 2e-8 at 2 λ/D in monochromatic light. In addition, we discuss tip-tilt instabilities, which are believed to be our main limiting factor at present, and ways of characterizing them.

Development of a miniaturized deformable mirror controller

High-Performance Adaptive Optics systems are rapidly spreading as useful applications in the fields of astronomy, ophthalmology, and telecommunications. This technology is critical to enable coronagraphic direct imaging of exoplanets utilized in ground-based telescopes and future space missions such as WFIRST, EXO-C, HabEx, and LUVOIR. We have developed a miniaturized Deformable Mirror controller to enable active optics on small space imaging mission. The system is based on the Boston Micromachines Corporation Kilo-DM, which is one of the most widespread DMs on the market. The system has three main components: The Deformable Mirror, the Driving Electronics, and the Mechanical and Heat management. The system is designed to be extremely compact and have lowpower consumption to enable its use not only on exoplanet missions, but also in a wide-range of applications that require precision optical systems, such as direct line-of-sight laser communications, and guidance systems. The controller is capable of handling 1,024 actuators with 220V maximum dynamic range, 16bit resolution, and 14bit accuracy, and operating at up to 1kHz frequency. The system fits in a 10x10x5cm volume, weighs less than 0.5kg, and consumes less than 8W. We have developed a turnkey solution reducing the risk for currently planned as well as future missions, lowering their cost by significantly reducing volume, weight and power consumption of the wavefront control hardware.

Optomechanical design of the vacuum compatible EXCEDE's mission testbed

In this paper we describe the opto-mechanical design, tolerance error budget an alignment strategies used to build the Starlight Suppression System (SSS) for the Exoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) NASA’s mission. EXCEDE is a highly efficient 0.7m space telescope concept designed to directly image and spatially resolve circumstellar disks with as little as 10 zodis of circumstellar dust, as well as large planets. The main focus of this work was the design of a vacuum compatible opto-mechanical system that allows remote alignment and operation of the main components of the EXCEDE. SSS, which are: a Phase Induced Amplitude Apodization (PIAA) coronagraph to provide high throughput and high contrast at an inner working angle (IWA) equal to the diffraction limit (IWA = 1.2 l/D), a wavefront (WF) control system based on a Micro-Electro-Mechanical-System deformable mirror (MEMS DM), and low order wavefront sensor (LOWFS) for fine pointing and centering. We describe in strategy and tolerance error budget for this system, which is especially relevant to achieve the theoretical performance that PIAA coronagraph can offer. We also discuss the vacuum cabling design for the actuators, cameras and the Deformable Mirror. This design has been implemented at the vacuum chamber facility at Lockheed Martin (LM), which is based on successful technology development at the Ames Coronagraph Experiment (ACE) facility.

EXCEDE Technology Development II: Demonstration of High Contrast at 1.2 λ/D and Preliminary Broadband Results.

Coronagraph technology is advancing and promises to enable space telescopes capable of directly detecting low surface brightness circumstellar debris disks as well as giant planets as close as in the habitable zones of their host stars. One mission capable of doing this is called EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), which in 2011 was selected by NASAs Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept designed to achieve raw contrasts of 10-6 at an inner working angle of 1.2 λ/D and 10-7 at 2 λ/D and beyond. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the Phase Induced Amplitude Apodization (PIAA) coronagraph to provide high throughput and high contrast close to the diffraction limit, enabling aggressive performance. We report on our continuing progress of developing the SSS for EXCEDE, including (a) high contrast performance demonstrations at 1.2 λD, which includes a lab demonstration of 2x10-7 median contrast between 1.2 and 2.0 λ/D simultaneously with 6.5x10-8 median contrast between 2 and 4 λ/D in monochromatic light at 655nm, meeting a major milestone in our technology development program; (b) the installation of a new Low Order Wavefront Sensor (LOWFS) which enabled achieving deep contrasts at aggressive inner working angles; (c) implementation of more efficient model-based wavefront control algorithms; and (d) a preliminary broadband contrast result of 6x10-6 contrast at 1.2 λ/D in a 10% band.

EXCEDE technology development III: first vacuum tests

This paper is the third in the series on the technology development for the EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer) mission concept, which in 2011 was selected by NASAs Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept designed to achieve raw contrasts of 1e6 at an inner working angle of 1.2 l/D and 1e7 at 2 l/D and beyond. This will allow it to directly detect and spatially resolve low surface brightness circumstellar debris disks as well as image giant planets as close as in the habitable zones of their host stars. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for any future exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the PIAA coronagraph, enabling aggressive performance. Previously, we reported on the achievement of our first milestone (demonstration of EXCEDE IWA and contrast in monochromatic light) in air. In this presentation, we report on our continuing progress of developing the SSS for EXCEDE, and in particular (a) the reconfiguration of our system into a more flight-like layout, with an upstream deformable mirror and an inverse PIAA system, and (b) testing this system in a vacuum chamber, including IWA, contrast, and stability performance. Even though this technology development is primarily targeted towards EXCEDE, it is also germane to any exoplanet direct imaging space-based telescopes because of the many challenges common to different coronagraph architectures and mission requirements. This work was supported in part by the NASA Explorer program and Ames Research Center, University of Arizona, and Lockheed Martin SSC.

Preflight performance of the Echelon-Cross-Echelle Spectrograph for SOFIA

The Echelon-Cross-Echelle Spectrograph (EXES) is one of the first generation instruments for the Stratospheric Observatory for Infrared Astronomy (SOFIA). The primary goal of EXES is to provide high-resolution, cross-dispersed spectroscopy, with resolutions of 50,000-100,000 and wavelength coverage of 0.5-1.5% between 4.5 μm and 28.3 μm. EXES will also have medium (R=5000-25000) and low (R=1500-4000) modes available, as well as a target acquisition imaging mode and a pupil-imaging mode for alignment testing. EXES is scheduled for commissioning flights in February 2014. It will be available to the public for shared-risk observations in SOFIA’s Cycle 2. Here we give an overview of the design and capabilities of EXES as well as its laboratory performance to date.