Simultaneous Exoplanet Characterization and deep wide-field imaging with a diffractive pupil telescope

High-precision astrometry can identify exoplanets and measure their orbits and masses, while coronagraphic imaging enables detailed characterization of their physical properties and atmospheric compositions through spectroscopy. In a previous paper, we showed that a diffractive pupil telescope (DPT) in space can enable sub-microarcsecond accuracy astrometric measurements from wide-field images by creating faint but sharp diffraction spikes around the bright target star. The DPT allows simultaneous astrometric measurement and coronagraphic imaging, and we discuss and quantify in this paper the scientific benefits of this combination for exoplanet science investigations: identification of exoplanets with increased sensitivity and robustness, and ability to measure planetary masses to high accuracy. We show how using both measurements to identify planets and measure their masses offers greater sensitivity and provides more reliable measurements than possible with separate missions, and therefore results in a large gain in mission efficiency. The combined measurements reliably identify potentially habitable planets in multiple systems with a few observations, while astrometry or imaging alone would require many measurements over a long time baseline. In addition, the combined measurement allows direct determination of stellar masses to percent-level accuracy, using planets as test particles. We also show that the DPT maintains the full sensitivity of the telescope for deep wide-field imaging, and is therefore compatible with simultaneous scientific observations unrelated to exoplanets. We conclude that astrometry, coronagraphy, and deep wide-field imaging can be performed simultaneously on a single telescope without significant negative impact on the performance of any of the three techniques.Comment: 15 pages, 6 figures. This second paper, following the paper describing the diffractive pupil telescope (DPT) astrometric technique, shows how simultaneous astrometry and coronagraphy observations, enabled by the DPT concept, constrain the orbital parameters and mass of exoplanet

DESIGN AND CONSTRUCTION OF A MODULAR GAMMA CAMERA (NUCLEAR)

The Anger camera has been used for the last quarter century in many areas of science to image gamma radiation. Some typical applications include medicine, where functionality of organs are studied in vivo, and industrial inspection of fuel rods for nuclear reactors. The standard Anger geometry includes a large scintillation crystal, light guide, photomultiplier array, and analog processing electronics. Even the most modern gamma cameras built today still use the standard Anger design. The work presented here describes an alternative to the standard gamma-camera design that is flexible enough to be used in a wide variety of applications. Especially in single-photon emmission computed tomography (SPECT) applications, the new design has the potential to be more efficient than the standard design. The new design is modular, that is, several small, separate units comprise a system. Each unit consists of a small gamma camera that is optically and electronically independent from other units. The units, called "modular cameras," can be configured around the region of interest so as to provide the maximum amount of information for reconstruction algorithms or direct information to the operator. The theoretical and experimental investigation of this report focuses on the design and construction of the modular cameras. Each modular camera is, in esscence, a small Anger camera. Components of each module include a scintillation crystal, a light guide, and an array of four photomultiplier tubes. Instead of an analog processing network, each module utilizes fast digital circuitry which includes direct analog-to-digital conversion of the photomultiplier signals, a lookup table which maps detector responses to position estimates of the scintillation flashes in the crystal, and an image memory which accumulates the position estimates and forms an image of the radiation incident on the faceplate of the camera. The digital electronics are necessary because analog techniques fail to give satisfactory estimates of scintillation position when the flashes occur near the sides of the crystal. The contents of the lookup table are determined from the statistical properties of the detected signals as a function of scintillation position. Experiments are described in which "best" estimates of position are found by processing data collected from an array of point-source positions in contact with the crystal. Alternative methods for construction of the lookup table are also discussed, which involve computer generation of the estimates. Both maximum-likelihood and mimimum-mean-square-error estimation rules are used, and the results are compared. A mathematical bound on the performance of the estimators is calculated assuming Poisson statistics for the detection process. The bound, which is a Cramer-Rao lower bound, is used to compare module geometries before lookup tables are constructed. A one-dimensional module, which accumulates information along one axis of the faceplate, is designed first. The one-dimensional module provides proof-of-principle evidence for the estimation techniques and is used to determine critical parameters for modular-camera design. The results of the experiments with the one-dimensional camera are extended to two-dimensional designs, which yield position estimates along both axes of the camera faceplate. Several two-dimensional cameras are tested, and an optimum geometry is constructed and tested for spatial resolution and bias of the estimators

Practical measurement of cell-phone camera lens focal length

A practical instrumentation configuration for measuring focal length of cell-phone camera lenses is presented that uses a custom autocollimator, a grating, an autostigmatic microscope, and a precision stage. Uncertainty in LED wavelength is reduced by using a white LED and a set of narrow-band filters. The autocollimator is designed to allow for rapid focus adjustment at each test wavelength. Examples of the measurement technique and an error analysis are provided.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Optical design and system characterization of an imaging microscope at 121.6 nm

We present the optical design and system characterization of an imaging microscope prototype at 121.6 nm. System engineering processes are demonstrated through the construction of a Schwarzschild microscope objective, including tolerance analysis, fabrication, alignment, and testing. Further improvements on the as-built system with a correction phase plate are proposed and analyzed. Finally, the microscope assembly and the imaging properties of the prototype are demonstrated.National Science Foundation (NSF) [1306921]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Sparse wavefront control: A new approach to high-contrast imaging

Current high-contrast imaging systems implement wavefront control using traditional deformable mirrors developed for atmospheric turbulence correction, which require large strokes, high-speed, and continuous phase correction. However, high-contrast imaging has different requirements. Thus, developing a specialized deformable mirror for this application able to meet the demanding requirements of future exoplanet imaging flagship missions is valuable for the exoplanet scientific community. In this paper, we propose a novel wavefront control approach, called Sparse Wave-Front Control (SWFC), which enables high-contrast imaging using sparse phase changes on the active surface re-directing coherent starlight to null speckles. To validate SWFC, we simulated a telescope equipped with a Phase Induced Amplitude Apodization (PIAA) coronagraph and a 100 by 100 actuator sparse Deformable Mirror to null speckles caused by the optical system aberrations. We modeled the mirror as a flat surface where narrow gaussian influence functions represent actuators. We performed wavefront control utilizing Electric Field Conjugation achieving 6.7e-11 mean contrast between 3 to 35 lambda/D in monochromatic light and 7.4e-11 in 10% broadband light. In the second part of this paper, we propose an approach to manufacture Sparse Deformable Mirrors utilizing photosensitive polymers, which could be placed below the mirror coating and can be photonically actuated by back illumination through the mirror substrate.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Design, fabrication, and testing of stellar coronagraphs for exoplanet imaging

Complex-mask coronagraphs destructively interfere unwanted starlight with itself to enable direct imaging of exoplanets. This is accomplished using a focal plane mask (FPM); a FPM can be a simple occulter mask, or in the case of a complex-mask, is a multi-zoned device designed to phase-shift starlight over multiple wavelengths to create a deep achromatic null in the stellar point spread function. Creating these masks requires microfabrication techniques, yet many such methods remain largely unexplored in this context. We explore methods of fabrication of complex FPMs for a Phased-Induced Amplitude Apodization Complex-Mask Coronagraph (PIAACMC). Previous FPM fabrication efforts for PIAACMC have concentrated on mask manufacturability while modeling science yield, as well as assessing broadband wavelength operation. Moreover current fabrication efforts are concentrated on assessing coronagraph performance given a single approach. We present FPMs fabricated using several process paths, including deep reactive ion etching and focused ion beam etching using a silicon substrate. The characteristic size of the mask features is 5 mu m with depths ranging over 1 mu m. The masks are characterized for manufacturing quality using an optical interferometer and a scanning electron microscope. Initial testing is performed at the Subaru Extreme Adaptive Optics testbed, providing a baseline for future experiments to determine and improve coronagraph performance within fabrication tolerances.TRIF optics; NASA ExEP SCDA StudyThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]