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NASA NTRS1980

Alignment of a two-beam interferometer

Two beam interferometers have been proposed for space applications such as sensing the shape of a large antenna. Since alignment and adjustment of interferometers have long been considered difficult laboratory tasks, the question of making their operation sufficiently automatic for space applications is a serious one. As a first step in addressing this question certain manual procedures, which may not be well known, have been collected from widely scattered sources. These techniques are illustrated by two examples: (1) the alignment of a Mach-Zehnder interferometer and the adjustment of fringe location. (2) The adjustment of a Michelson interferometer for zero path difference (white light fringes).

Tubbs, E. F.↗

NASA NTRS1988

Special relativity and interferometers

A new generation of gravitational wave detectors is expected to be based on interferometers. Yurke et al. (1986) introduced a class of interferometers characterized by SU(1,1) which can in principle achieve a phase sensitivity approaching 1/N, where N is thte total number of photons entering the interferometer. It is shown here that the SU(1,1) interferometer can serve as an analog computer for Wigner's little group of the Poincare\'| group.

Han, D.↗

NASA NTRS1990

Optical diameters of stars measured with the Mt. Wilson Mark III interferometer

Reliable stellar angular diameters can now be determined using the Mark III Optical Interferometer located on Mt. Wilson, California. The Mark III is a Michelson Interferometer capable of measuring the interferometric fringe visibility for stars using interferometer baselines varying from 3 to 31.5 meters in length. Angular diameters measured with the Mark III Optical Interferometer are presented for 12 stars at wavelengths of 450 and 800 nm.

Simon, R. S.↗

NASA NTRS1992

HARDI: A high angular resolution deployable interferometer for space

We describe here a proposed orbiting interferometer covering the UV, visible, and near-IR spectral ranges. With a 6-m baseline and a collecting area equivalent to about a 1.4 m diameter full aperture, this instrument will offer significant improvements in resolution over the Hubble Space Telescope, and complement the new generation of ground-based interferometers with much better limiting magnitude and spectral coverage. On the other hand, it has been designed as a considerably less ambitious project (one launch) than other current proposals. We believe that this concept is feasible given current technological capabilities, yet would serve to prove the concepts necessary for the much larger systems that must eventually be flown. The interferometer is of the Fizeau type. It therefore has a much larger field (for guiding) better UV throughout (only 4 surfaces) than phased arrays. Optimize aperture configurations and ideas for the cophasing and coalignment system are presented. The interferometer would be placed in a geosynchronous or sunsynchronous orbit to minimize thermal and mechanical disturbances and to maximize observing efficiency.

Bely, Pierre Y.↗

NASA NTRS1993

Measured optical performance of three Fabry-Perot interferometers for use in a tunable ultraviolet filter

A narrowband ultraviolet (UV) filter would allow the first monochromatic two-dimensional images of astrophysical plasmas to be obtained in UV emission lines. The high etendue and spectral resolving power of the Fabry-Perot (FP) interferometer make it an excellent candidate for use in a tunable UV filter, provided that adequate optical performance can be obtained. Laboratory measurements of three UV FP interferometers with progressively greater dielectric mirror reflectances are described. The measurements demonstrate the adequate reflectivity, absorption, and small-scale smoothness of currently available coatings and substrates for UV interferometry. The measurements are conducted at 228.8 nm utilizing a cadmium hollow cathode light source. The best performing interferometer has a finesse of 41 and maximum transmittance of 0.38 over a coating-performance-dominated 3-mm-diam subaperture and a finesse of 26 and maximum transmittance of 0.32 over a parabolic-defect-dominated 30-mm-diam aperture. This interferometer is well suited for use in a UV filter system.

Korendyke, Clarence M.↗

NASA NTRS1995

Stellar Interferometer Technology Experiment (SITE)

The MIT Space Engineering Research Center and the Jet Propulsion Laboratory stand ready to advance science sensor technology for discrete-aperture astronomical instruments such as space-based optical interferometers. The objective of the Stellar Interferometer Technology Experiment (SITE) is to demonstrate system-level functionality of a space-based stellar interferometer through the use of enabling and enhancing Controlled-Structures Technologies (CST). SITE mounts to the Mission Peculiar Experiment Support System inside the Shuttle payload bay. Starlight, entering through two apertures, is steered to a combining plate where it is interferred. Interference requires 27 nanometer pathlength (phasing) and 0.29 archsecond wavefront-tilt (pointing) control. The resulting 15 milli-archsecond angular resolution exceeds that of current earth-orbiting telescopes while maintaining low cost by exploiting active optics and structural control technologies. With these technologies, unforeseen and time-varying disturbances can be rejected while relaxing reliance on ground alignment and calibration. SITE will reduce the risk and cost of advanced optical space systems by validating critical technologies in their operational environment. Moreover, these technologies are directly applicable to commercially driven applications such as precision matching, optical scanning, and vibration and noise control systems for the aerospace, medical, and automotive sectors. The SITE team consists of experienced university, government, and industry researchers, scientists, and engineers with extensive expertise in optical interferometry, nano-precision opto-mechanical control and spaceflight experimentation. The experience exists and the technology is mature. SITE will validate these technologies on a functioning interferometer science sensor in order to confirm definitely their readiness to be baselined for future science missions.

Crawley, Edward F.↗

NASA NTRS1995

Liquid crystal point diffraction interferometer

A new instrument, the liquid crystal point diffraction-interferometer (LCPDI), has been developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point diffraction interferometer (PDI) and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with very high data density and with automated data reduction. This dissertation describes the theory of both the PDI and liquid crystal phase control. The design considerations for the LCPDI are presented, including manufacturing considerations. The operation and performance of the LCPDI are discussed, including sections regarding alignment, calibration, and amplitude modulation effects. The LCPDI is then demonstrated using two phase objects: defocus difference wavefront, and a temperature distribution across a heated chamber filled with silicone oil. The measured results are compared to theoretical or independently measured results and show excellent agreement. A computer simulation of the LCPDI was performed to verify the source of observed periodic phase measurement error. The error stems from intensity variations caused by dye molecules rotating within the liquid crystal layer. Methods are discussed for reducing this error. Algorithms are presented which reduce this error; they are also useful for any phase-stepping interferometer that has unwanted intensity fluctuations, such as those caused by unregulated lasers.

Mercer, Carolyn R.↗

NASA NTRS1996

First Results of the TOPSAR C-Band / L-Band Interferometer: Calibration and Differential Penetration

The NASA/JPL TOPSAR instrument recently was extended from a single wavelength C-band dual aperture synthetic aperture radar (SAR) interferometer to include a second wavelength at the L-band. Adding the second wavelength invites comparison of wavelength-diverse effects in topographic mapping of surfaces, with the principal goal of understanding the penetration of the radar signals in vegetation canopies, and determining the inferred topographic height. A first analysis of these data was conducted at two sites. Elkhorn Slough near Monterey, California presented flat, vegetation free terrain required for calibrating the radar interferometer parameters. A second site stretching from San Jose to Santa Cruz, California, which is heavily vegetated, provided the first test case for wavelength diverse penetration studies. Preliminary results show that: (a) the interferometer calibration determined at Elkhorn Slough is extenable to Laurel Quad and gives confidence in the C- and L-band height measurements; (b) Clear differences were observed between the C- and L-band heights associated with vegetation, with the C-band derived topographic heights generally higher than those from L-band. The noise level in the L-band interferometer is presently the limiting factor in penetration studies.

Rosen, Paul A.↗

NASA NTRS1998

Characterization of exozodiacal dust with the Keck interferometer, VLTI, and SIM

This overview discusses three interferometers for characterization of exozodiacal dust: Keck Interferometer, the Very Large Telescope Interferometer (VLTI), and the Space Interferometry Mission (SIM). The emphasis will be toward the Keck Interferometer, as exozodiacal dust characterization is one of its science requirements.

Colavita, Mark↗

NASA NTRS1998

Sensitivity of nulling interferometers to extra-solar zodiacal emission (EZE)

It should be possible to discover and to analyze the atmospheres of Earth-like planets of nearby stars, provided their thermal emission is not overwhelmed by a bright zodiacal cloud in the same system. Nulling interferometers in space, such as the Terrestrial Planet Finder, can efficiently suppress a stellar point source, but there is no way to suppress diffuse emission underlying the planet under study. A cloud much brighter than solar level would cause serious reduction in sensitivity, by its photon shot noise. Since some clouds have been detected that are orders of magnitude brighter, zodiacal measurements of TPF candidates to solar level are critically needed. These could be obtained relatively soon with the largest aperture ground-based interferometers observing in the 10 micron atmospheric window. A cloud would be detectable as an infrared excess, provided the stellar emission (some 10(exp 4) times brighter) is adequately suppressed by destructive interference. Ideally, the ground interferometer should have angular response similar to that of TPF, so as to measure directly the troublesome zodiacal component. The individual elements must be large, for even with approx. 8 m apertures, star cancellation and low thermal background, integration times of at least several hours will be needed to sense the clouds against shot noise from telescope thermal emission. In this paper we compare the sensitivity of TPF and ground based interferometers to a twin of the solar system at 10 pc, using Good's (1994) model of the zodiacal cloud.

Angel, Roger↗

NASA NTRS1999

[Build and Demonstrate a X-Ray Interferometer and Build and Fly a High Resolution Telescope on a Sounding Rocket}

This report is written with eight months still go on the 36 month period of the grant. This grant, as originally proposed three years ago, was two pronged - to build and demonstrate a practical x-ray interferometer, and to build and fly a high resolution telescope on a sounding rocket. As we started into these projects, we received community feedback that led to our giving priority to the interferometer., The rocket would achieve O.2-arcsecond resolution that, while better, than that of Chandra, would, because of the limited signal of a sub-orbital flight, not be of substantially greater scientific use. The interferometry, on the other hand, shows the potential for many orders of magnitude improvement. For this reason we gave priority to the lab interferometry, and the building of the telescope lagged behind. With our new understanding (and practical demonstration) of how to build an interferometer, we changed the telescope design from spherical surfaces in the Kirkpatrick-Baez configuration, to an interferometer with resolution between .005 and .05 arcseconds.

Source record↗

NASA NTRS1999

Overview of the Keck Interferometer

This is a presentation about the Keck Interferometer which is being constructed on top of Mauna Kea, Hawaii. This includes using the world's largest telescopes for optical and near-infrared astronomy, the twin 10 meter Keck telescopes. The two Keck telescopes, in conjunction with four proposed outrigger telescopes, will be used as an interferometer to conduct observations as part of NASA's Origins Program. These observations will address a variety of topics, including the origin and evolution of planetary systems. This presentation reviews the key features of the interferometer, and the specifications of the telescopes that will be used. It shows diagrams of the site, and the basement layout. It also reviews the science for which the interferometer will be used.

vanBelle, Gerard↗

NASA NTRS2001

Interferometers Characterization

Procedure and characterization result for two vibration insensitive phase shifting interferometers will be presented. Typical applications of the vibration insensitive interferometers include the testing of large astronomical primary mirrors with long radii of curvature in a severe vibration environment. The procedure list the steps for characterizing the two interferometers. The characterization compares the two interferometers and compares to its own specification.

Eng, Ron↗

NASA NTRS1999

The Palomar Testbed Interferometer

The Palomar Testbed Interferometer (PTI) is a long-baseline infrared interferometer located at Palomar Observatory, California. It was built as a testbed for interferometric techniques applicable to the Keck Interferometer. First fringes were obtained in 1995 July. PTI implements a dual-star architecture, tracking two stars simultaneously for phase referencing and narrow-angle astrometry. The three fixed 40 cm apertures can be combined pairwise to provide baselines to 110 m. The interferometer actively tracks the white-light fringe using an array detector at 2.2 microns and active delay lines with a range of +/-38 m. Laser metrology of the delay lines allows for servo control, and laser metrology of the complete optical path enables narrow-angle astrometric measurements. The instrument is highly automated, using a multiprocessing computer system for instrument control and sequencing.

Colavita, M. M.↗

NASA NTRS2006

CIV Vacuum Ultraviolet Fabry-Perot Interferometers for Transition-Region Magnetography

The vacuum ultraviolet region allows remote sensing of the upper levels of the solar atmosphere where the magnetic field dominates the physics. Obtaining an imaging interferometer that observes the transition region is the goal of this program. This paper gives a summary of our instrument development program (1998-2005) for a high-spectral-resolution, piezoelectric tunable Vacuum Ultraviolet Fabry-Perot Interferometer (VUV FPI) for obtaining narrow-passband images, magnetograms, and Dopplergrams of the transition region emission line of CN (155nm). A VUV interferometer will allow us to observe the magnetic field, flows, and heating events in the mid-transition region. The MSFC VUV FPI has measured values of FWHM approx. 9pm, FSR approx. 62pm, finesse approx. 5.3 and transmittance approx. 50% at 157nm. For the measurements, the University of Toronto's F2 eximer laser was used as an appropriate proxy for CIV 155nm. This has provided the first tunable interferometer with a FWHM compatible to VUV filter magnetograph.

Gary, G. Allen↗

NASA NTRS2009

Balloon Exoplanet Nulling Interferometer (BENI)

We evaluate the feasibility of using a balloon-borne nulling interferometer to detect and characterize exosolar planets and debris disks. The existing instrument consists of a 3-telescope Fizeau imaging interferometer with 3 fast steering mirrors and 3 delay lines operating at 800 Hz for closed-loop control of wavefront errors and fine pointing. A compact visible nulling interferometer is under development which when coupled to the imaging interferometer would in-principle allow deep suppression of starlight. We have conducted atmospheric simulations of the environment above 100,000 feet and believe balloons are a feasible path forward towards detection and characterization of a limited set of exoplanets and their debris disks. Herein we will discuss the BENI instrument, the balloon environment and the feasibility of such as mission.

Lyon, Richard G.↗

NASA NTRS2004

The StarLight Space Interferometer

Two papers describe the StarLight space interferometer a Michelson interferometer that would be implemented by two spacecraft flying in formation. The StarLight formation flying interferometer project has been testing and demonstrating engineering concepts for a new generation of space interferometers that would be employed in a search for extrasolar planets and in astrophysical investigations. As described in the papers, the original StarLight concept called for three spacecraft, and the main innovation embodied is a modification that makes it possible to reduce complexity by eliminating the third spacecraft. The main features of the modification are (1) introduction of an optical delay line on one spacecraft and (2) controlling the flying formation such that the two spacecraft are located at two points along a specified parabola so as to define the required baseline of specified length (which could be varied up to 125 m) perpendicular to the axis of the parabola. One of the papers presents a detailed description of the optical layout and discusses computational modeling of the performance; the other paper presents an overview of the requirements for operation and design, the overall architecture, and subsystems.

Folkner, William↗

NASA NTRS2004

White-Light Nulling Interferometers for Detecting Planets

A report proposes the development of a white-light nulling interferometer to be used in conjunction with a singleaperture astronomical telescope that would be operated in outer space. When such a telescope is aimed at a given star, the interferometer would suppress the light of that star while passing enough light from planets (if any) orbiting the star, to enable imaging or spectroscopic examination of the planets. In a nulling interferometer, according to the proposal, scattered light would be suppressed by spatial filtering in an array of single-mode optical fibers rather than by requiring optical surfaces to be accurate within 1/4,000 wavelength as in a coronagraph or an apodized telescope. As a result, angstrom-level precision would be needed in only the small nulling combiner, and not in large, meter-sized optics. The nulling interferometer could work as an independent instrument in space or in conjunction with a coronagraphic system to detect planets outside our solar system.

Mennesson, Bertrand↗