Kevin Newman

Focal plane phase masks for PIAA: Design and manufacturing

The Phase Induced Amplitude Apodization Complex Mask Coronagraph (PIAACMC) is a coronagraph architecture for the direct detection of extrasolar planets, which can achieve close to the theoretical performance limit of any direct detection system. The primary components of a PIAACMC system are the Phase Induced Amplitude Apodization (PIAA) optics and the complex phase-shifting focal plane mask. PIAA optics have been produced and demonstrated with high coronagraph performance. In this paper, we describe the design process for the phase-shifting focal plane mask, and strategies for smoothing the mask profile. We describe the mask manufacturing process and show manufacturing results. Errors in the fabricated mask profile degrade the system performance, but we can recover performance by refining the manufacturing process and implementing wavefront control.

Development of PIAA Complex Mask Coronagraphs for large aperture ground-based telescopes

The Phase Induced Amplitude Apodization Complex Mask Coronagraph (PIAACMC) is an architecture for directly observing extra-solar planets, and can achieve performance near the theoretical limits for any direct-detection instrument. The PIAACMC architecture includes aspheric PIAA optics, and a complex phase-shifting focal plane mask that provides a pi phase shift to a portion of the on-axis starlight. The phase-shifted starlight is forced to interfere destructively with the un-shifted starlight, causing the starlight to be eliminated, and allowing a region for high-contrast imaging near the star. The PIAACMC architecture can be designed for segmented and obscured apertures, so it is particularly well suited for ground-based observing with the next generation of large telescopes. There will be unique scientific opportunities for directly observing Earth-like planets around nearby low-mass stars. We will discuss design strategies for adapting PIAACMC for the next generation of large ground-based telescopes, and present progress on the development of the focal plane mask technology. We also present simulations of wave-front control with PIAACMC, and suggest directions to apply the coronagraph architecture to future telescopes.

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.

An automated aircraft detection system to prevent illumination from the laser guide star beacons at the MMT and LBT

High powered guide star laser beams are a potential hazard for aircraft. Currently at the MMT telescope located on Mt. Hopkins in Southern Arizona, five Rayleigh guide stars create a total of 25 W of power at 532 nm wavelength. The ARGOS laser guide star for the Large Binocular Telescope (LBT) located on Mt. Graham in Southern Arizona will generate six Rayleigh guide stars with a total of 108 W at 532 nm. We present an automated system for use at the MMT and the LBT designed to detect aircraft and shutter the lasers when aircraft illumination is pending. The detection system at the MMT uses a single wide-angle CCD camera mounted to the optical support structure of the telescope. The LBT system employs two of the same CCD cameras, and an additional bore-sighted thermal infrared camera. The visible cameras integrate frames for 0.5 s to produce streaks from anti-collision beacons required for all aircraft. The IR camera serves as a backup and to protect unlighted aircraft. In each case, adjacent frames are compared using image processing software to detect streaks and movement in the field. If an aircraft is detected, the position and projected trajectory are calculated and compared to the position of the laser beams. If an aircraft illumination appears likely, the laser safety shutter is closed and a message is sent to the laser operator. As a safety precaution, a heartbeat signal from the control computer is required to keep the laser shutter open.

Status report on the Large Binocular Telescope's ARGOS ground-layer AO system

ARGOS, the laser-guided adaptive optics system for the Large Binocular Telescope (LBT), is now under construction at the telescope. By correcting atmospheric turbulence close to the telescope, the system is designed to deliver high resolution near infrared images over a field of 4 arc minute diameter. Each side of the LBT is being equipped with three Rayleigh laser guide stars derived from six 18 W pulsed green lasers and projected into two triangular constellations matching the size of the corrected field. The returning light is to be detected by wavefront sensors that are range gated within the seeing-limited depth of focus of the telescope. Wavefront correction will be introduced by the telescopes deformable secondary mirrors driven on the basis of the average wavefront errors computed from the respective guide star constellation. Measured atmospheric turbulence profiles from the site lead us to expect that by compensating the ground-layer turbulence, ARGOS will deliver median image quality of about 0.2 arc sec across the JHK bands. This will be exploited by a pair of multi-object near-IR spectrographs, LUCIFER1 and LUCIFER2, with 4 arc minute field already operating on the telescope. In future, ARGOS will also feed two interferometric imaging instruments, the LBT Interferometer operating in the thermal infrared, and LINC-NIRVANA, operating at visible and near infrared wavelengths. Together, these instruments will offer very broad spectral coverage at the diffraction limit of the LBTs combined aperture, 23 m in size.

AKITA: Application Knowledge Interface to Algorithms

We propose a methodology for using sensor metadata and targeted preprocessing to optimize which selection from a large suite of algorithms are most appropriate for a given data set. Rather than applying several general purpose algorithms or requiring a human operator to oversee the analysis of the data, our method allows the most effective algorithm to be automatically chosen, conserving both computational, network and human resources. For example, the amount of video data being produced daily is far greater than can ever be analyzed. Computer vision algorithms can help sift for the relevant data, but not every algorithm is suited to every data type nor is it efficient to run them all. A full body detector won’t work well when the camera is zoomed in or when it is raining and all the people are occluded by foul weather gear. However, leveraging metadata knowledge of the camera settings and the conditions under which the data was collected (generated by automatic preprocessing), face or umbrella detectors could be applied instead, increasing the likelihood of a correct reading. The Lockheed Martin AKITA™ system is a modular knowledge layer which uses knowledge of the system and environment to determine how to most efficiently and usefully process whatever data it is given.

Achromatic focal plane mask for exoplanet imaging coronagraphy

Recent advances in coronagraph technologies for exoplanet imaging have achieved contrasts close to 1e-10 at 4 λ/D and 1e-9 at 2 λ/D in monochromatic light. A remaining technological challenge is to achieve high contrast in broadband light; a challenge that is largely limited by chromaticity of the focal plane mask. The size of a star image scales linearly with wavelength. Focal plane masks are typically the same size at all wavelengths, and must be sized for the longest wavelength in the observational band to avoid starlight leakage. However, this oversized mask blocks useful discovery space from the shorter wavelengths. We present here the design, development, and testing of an achromatic focal plane mask based on the concept of optical filtering by a diffractive optical element (DOE). The mask consists of an array of DOE cells, the combination of which functions as a wavelength filter with any desired amplitude and phase transmission. The effective size of the mask scales nearly linearly with wavelength, and allows significant improvement in the inner working angle of the coronagraph at shorter wavelengths. The design is applicable to almost any coronagraph configuration, and enables operation in a wider band of wavelengths than would otherwise be possible. We include initial results from a laboratory demonstration of the mask with the Phase Induced Amplitude Apodization (PIAA) coronagraph.

Analysis of gravitational effects on liquid lenses (ANGEL)

Liquid lenses have been developed as a means for fast and reliable variable-focus optics by using an adjustable curvature in a liquid-liquid interface. The use of liquid lenses also provides the benefit of reducing the number of elements in a system, and providing a degree of freedom without any moving parts. Different methods for surface curvature actuation have been developed, including aperture adjustment, mechanical actuators, stimuli-responsive hydrogels, and mechanical-wetting. Current liquid lens designs are limited to small apertures (less than 4mm) and density-matching fluids to lessen the negative effects of gravity. By creating a lens intended for use in a microgravity environment, the aperture size can be increased by orders of magnitude, and optimal fluids can be used regardless of their density. Using a large-aperture (12mm) liquid lens, image and surface metrology was conducted using a fixed-focus configuration. The Software Configurable Optical Test System (SCOTS) method was utilized to test the effect of microgravity, standard gravity, and hypergravity on the liquid lens during parabolic flights. Under standard gravity, the RMS wavefront error (WFE) was 27 wavelengths, while microgravity conditions allowed an improvement to 17 wavelengths RMS WFE. Test performance can be improved by using lower viscosity fluids or longer duration microgravity flights. The experiment also served as an engineering demonstration for the SCOTS method in an environment where other methods of optical metrology would be impossible.

Lunar scintillometer to validate GLAO turbulence distribution measurements

A lunar scintillometer, LuSci, is an inexpensive and robust instrument which deploys a linear array of photodiodes pointed toward the moon to measure scintillation produced by atmospheric turbulence. Covariances between the signals from the photodiodes are analyzed to derive estimates of the turbulence profile within a few hundred meters above the ground. Instrument parameters and phase of the moon are taken into account. This method has been used for site testing and monitoring. We present the development of a new LuSci instrument used to validate the ground-layer turbulence distribution measured from the laser wavefront sensor signals of the Ground Layer Adaptive Optics system at the MMT. The near-simultaneous measurements are used to characterize the performance of the GLAO system. We describe the instrument, its operation, approaches to data reduction, and use in performance characterization of a GLAO system.

Performance characterization of a phase-induced amplitude apodization complex focal plane mask

The direct imaging of extrasolar planets is a prominent goal for modern astrophysics. Direct imaging is a technique which can detect some planets that are inherently not compatible with the transit or radial velocity techniques. Direct imaging can also make it possible to measure the spectrum of planet light, which can help to characterize the planet atmosphere. A coronagraph is a telescope instrument with the purpose of enabling direct detection of extrasolar planets and performing exoplanet science. A coronagraph operates by nulling the light from a single on-axis star so that the faint light of a nearby exoplanet can be observed. A typical coronagraph creates a focus of the starlight in the focal plane, and has an element known as a focal plane mask to block or manipulate the starlight. Another element in the pupil plane, known as the Lyot mask, is used to control diffraction from the blocked starlight.