STScI Logo

Innovative Designs for the Next Large Aperture UV/Optical Telescope


Title: TPF Overview and Current Status
Abstract: TBD
Title: Silicon Lightweight Mirrors
Authors: David Content

Several forms of silicon lightweight mirrors are in development. As compared to SiC, silicon is much easier to polish with nearly equal mechanical & thermal properties allowing much more aggressive lightweighting than glass or metal materials. Recent developments are discussed.

Title: Spectral Interferometry for Broadband UV / Optical Missions
Authors: Jerry Edelstein and David J. Erskine

We describe a broadband high-resolution spectrograph using an externally dispersed interferometer ('EDI'), a hybrid of interferometry and classic grating-dispersion. In EDI, a grating spectrometer disperses the output of a fixed-delay white light interferometer. The interferometer provides a fiducial comb causing a spectral Moire┤ that effectively increases ('boosts') the conventional spectrograph resolution by factors of several-fold and diminishes deleterious effects such as focal blur or pupil shape change.

EDI may be applied to slit imaging, multi-object or echelle spectrometry because the inteferometer unit can accept a large field and preserves imaging. EDI works well for broad-band absorption spectroscopy because its spectral heterodyning technique overcomes detector resolution limitations and its classical dispersion tolerates the wide-band continuum noise penalty otherwise suffered by internally dispersed interferometers (e.g. SHS). EDI's sensitivity is comparable to a classical spectrograph?s and unlike purely interferometric Fourier Transform Spectrographs, EDI can operate over a wide simultaneous bandpass.

EDI spectroscopy offers important advantages for large aperture and high-resolution space-mission instrumentation because EDI boosting permits high-resolution results to be obtained with smaller low-resolution spectrograph units, large slit widths, or poor and unstable optical focus. We describe the EDI, show EDI-echelle and spectrograph results for astronomical objects, and explain how this method can be applied to space-missions for UV-Optical spectroscopy.

Title: Enabling Technologies for the Next Generation of UV-Optical Missions
Authors: James C. Green

New technological developments will provide significantly enhanced performance for the next generation of instruments. I will discuss the need for these capabilities from a scientific perspective, as well as show how they can be used to envision missions capable of achieving these science goals.

Title: NHST in Context: Future Steps to Large Optical Space Observatories 2010 - 2050
Authors: Steven Kilston

With several scenarios possible for developing large optical space astronomy missions over the next fifty years, and these missions requiring lengthy development times, it helps to understand how each mission might contribute to the technologies of subsequent missions, such as are described in NASA's long-term Structure and Evolution of the Universe and Origins programs. Scenarios we eventually choose to pursue should be driven by science goals and priorities, but also by the benefits of coordinating technology. Sketching out now a variety of possible integrated technology roadmaps helps put the potential paths in context, with the aim of maximizing the utility of our earlier missions, perhaps beginning with NHST.

Title: The Nulling Coronagraph-Using a Nulling Interferometer for Planet Detection in Visible Light with a Single Aperture Telescope
Authors: Michael Shao, B. Martin Levine, J. Kent Wallace, and Duncan Liu

This talk describes a space mission for direct detection of Earth-like extrasolar planets using a 'nulling coronagraph' instrument behind a 4m telescope in space. A 4 beam nulling interferometer is synthesized from the telescope pupil, to produce a null proportional to theta^4 which is then filtered by a coherent array of single mode fibers to suppress the residual scattered light. Starlight suppression of 1e-10 is achievable using diffraction limited telescope optics and similar quality components in the optical train (lambda/20). We show key features of the system design, present latest results of laboratory work in demonstrating deep and stable nulls, and discuss future key technical milestones.

Title: Deployable Telescope for the Next UV/Optical Telescope (NHST) Mission
Authors: Charles F. Lillie

The Hubble Space Telescope has demonstrated the ability of a large aperture telescope operating in the 0.1 to 1.0 micron spectral region for answering many outstanding scientific questions about planet detection/characterization, star/planet formation, dark matter and baryons, galaxy/black hole formation, and cosmology. This paper presents a design concept for a large aperture, deployable wide field telescope for UV/Optical imaging, spectroscopy and coronagraphy. The paper will also discuss the system trades, technology development efforts, and mirror manufacturing approaches leading to an affordable design for the next UV/Optical Telescope.

Title: Solid State UV Detectors
Authors: Shouleh Nikzad

Future NASA UV/Optical astrophysics missions are influenced by the objectives of the Origins and SEU themes of NASA. In order for missions beyond HST and GALEX to result in major new scientific impacts, they will require significant detector advances, particularly in quantum efficiency, resolution, and number of pixels.

The current UV detection technology can be classified into two major categories: 1. Solid-state devices based on silicon or wide bandgap semiconductors and 2. A combination of photoemissive device, i.e., photocathode, a gain component, and an electron detector. Electron bombarded CCDs (EBCCDs) and microchannel plates (MCPs) are in this category.

An immense investment has been made in silicon visible imagers in order to produce detectors with very low noise, low dark current, and very large imager formats. In addition, new techniques such as lateral gain CCDs and low noise CMOS sensors are being developed so that silicon sensors continue to improve and become viable for photon counting applications. High purity silicon detectors either in hybrid or monolithic format are also used for energy-resolved measurements. To achieve the highest UV/optical quantum efficiency in all of these silicon detectors, independent of their readout scheme, they must be back-illuminated and properly passivated.

Wide bandgap materials such as gallium nitride (GaN), silicon carbide and even diamond are intrinsically solar blind and are being formed into UV detector arrays as well as UV photocathodes. Usually an array of diodes is made and is hybridized to a CMOS readout. Additionally, monolithic imagers with transistors made from the host or substrate material exist at least in concept. These materials offer the promise of direct solar-blind UV imagers and research into their development is important. Further investment is necessary before imagers in these new materials can provide performance equivalent to silicon imagers.

In this talk, we will discuss silicon-based UV/optical detector technology, quantum efficiency enhancement, as well as wide bandgap material-based UV detector technology. In the wide bandgap category, we will focus on detectors based on GaN and its alloys as well as photocathodes based on this class of material.

Title: Deformable Mirror Technology
Authors: Mark Ealey

Deformable mirror technology has begun to change drastically in the last few years. In the past, deformable mirrors were a separate part of the optic train and consisted of discrete ceramic actuators bonded within a optical structure. The mirrors were usually some of the largest components in the system. Now we are seeing a revolution in mirror technology. Mirror are becoming substantially smaller as we integrate actuators and electrical connections within the ceramic structure. In addition, electronics are becoming smaller, lighter, with less power requirements. Xinetics will describe some of these advances and how they would apply to future space telescope systems.

Title: Large Format UV-Optical Hybrid Sensors: Si PIN Diodes and Related Technologies
Authors: B.J. Rauscher, D. Figer, & M. Regan

Silicone PIN diodes are emerging as an attractive alternative to CCDs for high-end space-based astronomy applications. Both Rockwell and Raytheon forecast 2Kx2K pixels formats on the near term and read noise per correlated double sample approaching that of a CCD. We review Si PIN diode technology and discuss their potential application to future UV-Optical space missions.

Title: High performance MCP detectors for UV-visible Astrophysics
Authors: Oswald Siegmund

Advances in photocathodes (GaN, Diamond, GaAs), microchannel plates (Silicon MCP's), and readouts (Cross strip) are poised to make a significant impact on the capabilities of future space instruments. Alkali halide cathode efficiencies have been improved and GaN photocathodes have achieved >40% DQE in the UV with a bandpass limit of ~400nm. In addition diamond photocathodes have been made with 40% DQE and bandpass up to 200nm, and GaAs photocathodes with ~50% DQE in the visible have been made. Silicon MCP's of 25mm format with ~7Ám pores, have been made, achieving gain of nearly 104 for a single Si MCP. The quantum detection efficiency for Si MCP's is the same as glass MCP's, but the background is as low as ~ 0.02 events sec-1 cm-2, the best for any MCP. Flat fields are free of any periodic modulation, and the gain uniformity is good. Silicon MCP's have low stopping power for X, gamma and cosmic rays, are stable at high temperatures (>800░C), and chemically compatible with many photocathodes. Cross strip anodes based on multi-layer metal and ceramic cross strip patterns encode event positions by direct sensing of the charge on each strip (cross strip) and determination of the charge cloud centroid for each event. The spatial resolution (<5um) achieved is sufficient to resolve 7um microchannel plate pores while using low MCP gain (≈2 x 10^6). Image linearity is good enough to see distortions in the microchannel plate pore alignment, and the low MCP gain will enhance the overall lifetime of MCP detector systems.

Title: Application of Precision Deformable Mirrors to Space Astronomy
Authors: John Trauger

Precision deformable mirrors are an enabling technology for active correction of large optical systems in space. Deformable mirrors, such as those developed by Xinetics specifically for application to space astronomy, bring together precision surface figure control, open-loop stability, high actuator count, and a compact format. The characteristics of these deformable mirrors, as measured in the laboratory at JPL, are combined with predictive models to illustrate their applications in high contrast space astronomy applications including TPF and pre-TPF planet-survey concepts.

Title: A JWST Derivative Design for the Next Large Aperture UV/Optical Telescope
Authors: William B. Whiddon

The James Webb Space Telescope (JWST) is designed for imaging and spectroscopy in the 0.6 to 28 micron spectral region with a ~6.5 meter diameter telescope that is diffraction limited at 2 microns and passively cooled to ~40 Kelvin. This paper will discuss the modifications to the JWST design that would be required to meet the astronomy community’s need for a large aperture (4-10m) telescope operating at UV/optical (UVO) wavelengths for wide-field, high spatial resolution imaging, multi-object spectroscopy, and coronagraphy after retirement of the Hubble Space Telescope. The paper will also discuss the design trades and technology development efforts needed to achieve these capabilities.

Title: Second-generation holographic grating technology
Authors: Erik Wilkinson

Diffraction gratings fabricated using holographic recording techniques are quickly becoming the gratings of choice for use in astronomical instrumentation due to their inherently low in-plane scatter and high efficiency. The aberration control available with holographic gratings has proven to be another advantage over their mechanically ruled counterparts. FUSE and HST/COS both capitalize on the performance enhancements provided by first-generation holographic gratings, aberration-corrected gratings recorded with spherical wave-fronts. Despite the gains in performance afforded by first-generation holographic grating technology, these gratings are inherently limited in their ability to correct aberrations higher than third order, e.g. coma or slit curvature.

In recent years the technology for recording second-generation holographic gratings has matured sufficiently to warrant serious consideration by the astronomical community. Second-generation holographic gratings are recorded with aberrated wave-fronts. This effectively increases the number of aberrations in the light path that can be controlled and opens up the potential for non-conventional instrument designs that could meet the needs of future UCV/optical space-based missions.

I will present first generation holographic design theory and methodology and compare to second-generation holographic grating technology. I will discuss the potential for performance gains using second-generation holographic gratings and discuss areas where these gratings could support spectrometers for the next generation of UV/optical instrumentation.

Title: Design concepts for future large aperture wide field of view UVIS optical systems
Authors: Robert A. Woodruff

The Hubble Space Telescope (HST) has provided superb imaging and spectroscopic capability for studying galaxies, stars, and nebulae in the ultraviolet and visible (UVIS) wavelength regions, as well as in the near infrared. The HST is a 2.4-meter telescope with imaging, spectroscopic, and limited coronagraphic instrumentation. NASA plans to discontinue its operations in 2010. Next generation ultraviolet and visible telescope capability to replace HST is currently under discussion. The new facility would include a very large aperture collector, ultra wide field of view (WFOV) imagery, precise wavefront control, and high UVIS efficiency. Such a facility would combine ultra wide FOV imagery that is diffraction-limited at Lyman-a (l=122 nm) with efficient broad spectral coverage. The design must also provide spectroscopic, and possibly coronagraphic, capability in addition to imagery. This paper will discuss design trades for such capabilities and present design configurations. The paper will also identify key technologies needed to support the implementation of the new facility.