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NASA NTRS1997

High Resolution X-Ray Explorer (HIREX)

SAO is involved in a study to determine the feasibility of building an orbiting telescope capable of resolving 7 km structure on the Sun. In order to achieve the required imaging the telescope must have a resolution 0.01 arcsec. This fact challenges the state of the art of orbiting telescopes in several areas: Mirror Figuring; Optical Metrology; Optical Mounting; Mirror Figure Control; System Alignment; Optical Stability; Observatory Pointing; and Image Stability. The telescope design concept is based on a 0.6 m Gregorian-style telescope with a 240 meter effective focal length. This is achieved with 2 mirrors supported at opposite ends of a 35 m space-deployable boom. The telescope mirrors are coated with multilayers designed to reflect a broad XUV passband. A third, small mirror, near the focal plane performs the function of selecting the narrow band that is finally imaged. Image stabilization to the 0.005 arcsec level is achieved by active control of the secondary mirror. The primary mirror is held unadjustably to the spacecraft, its pointing set by the spacecraft orientation. The secondary mirror is mounted on a 6-axis stage that permits its position to be changed to align the telescope in space. The stage is intended for intermittent adjustment, both because of its speed of travel, and the TBD alignment procedure. The third mirror is called the TXI (Tuneable X-ray Imager). It is mounted on a gimbal that permits it to be tipped over a 60 degree range, selecting between the individual wavelengths in the initial bandpass. It can also rotated completely out of the way to allow the full, broadband EUV flux to strike the focal plane. Finally, the focal plane assembly is designed to rotate on the outer edge of a circle centered on the TXI mirror rotation axis. This permits the focal plane to move to the location that the TXI redirects the light once it has been set to a given wavelength response. The Engineering Study is divided into the following areas: Mirror Fabrication and Metrology; Optical Layout-Trade Study between On-axis and Off-axis; Overall System Design; and Pointing Control/Image Stabilization. The observational goals of the mission are described in the Mission Requirements document. The work is being performed to the requirements called out in the Science Requirements document.

Goulb, Leon↗

NASA NTRS1999

High Resolution X-Ray Explorer (HIREX)

SAO has carried out a study to determine the feasibility of building an orbiting telescope capable of resolving 7 km structure on the Sun. In order to achieve the required imaging the telescope must have a resolution 0.01 arcsec. This fact challenges the state of the art of orbiting telescopes in several areas: mirror figuring; optical metrology; optical mounting; mirror figure control; system alignment; optical stability; observatory pointing; and image stability image stability. The telescope design concept is based on a 0.6m Cassegrain-style telescope with a 240 meter effective focal length. This is achieved with 2 mirrors supported at opposite ends of a 27 m space-deployable boom. The telescope mirrors are coated with multilayers designed to reflect a broad XUV passband. A third, small mirror, near the focal plane performs the function of selecting the narrow band that is finally imaged. Image stabilization to the 0.005 a,rcsec level is achieved by active control of the secondary mirror. The primary mirror is held unadjustably to the spacecraft, its pointing set by the space- craft orientation. The secondary mirror is mounted on a 6-axis stage that permits its position to be changed to align the telescope in space. The stage is intended for intermittent adjustment, both because of its speed of travel, and the TBD alignment procedure. The third mirror is called the TXI (Tuneable X-ray Imager). It is mounted on a gimbal that permits it to be tipped over a 60 degree range, selecting between the individual wavelengths in the initial bandpass. It can also rotated completely out of the way to allow the full, broadband EUV flux to strike the focal plane.

Golub, Leon↗

NASA NTRS2004

Multilayer Dielectric Transmissive Optical Phase Modulator

A multilayer dielectric device has been fabricated as a prototype of a low-loss, low-distortion, transmissive optical phase modulator that would provide as much as a full cycle of phase change for all frequency components of a transmitted optical pulse over a frequency band as wide as 6.3 THz. Arrays of devices like this one could be an alternative to the arrays of mechanically actuated phase-control optics (adaptive optics) that have heretofore been used to correct for wave-front distortions in highly precise optical systems. Potential applications for these high-speed wave-front-control arrays of devices include agile beam steering, optical communications, optical metrology, optical tracking and targeting, directional optical ranging, and interferometric astronomy. The device concept is based on the same principle as that of band-pass interference filters made of multiple dielectric layers with fractional-wavelength thicknesses, except that here there is an additional focus on obtaining the desired spectral phase profile in addition to the device s spectral transmission profile. The device includes a GaAs substrate, on which there is deposited a stack of GaAs layers alternating with AlAs layers, amounting to a total of 91 layers. The design thicknesses of the layers range from 10 nm to greater than 1 micrometer. The number of layers and the thickness of each layer were chosen in a computational optimization process in which the wavelength dependences of the indices of refraction of GaAs and AlAs were taken into account as the design was iterated to maximize the transmission and minimize the group-velocity dispersion for a wavelength band wide enough to include all significant spectral components of the pulsed optical signal to be phase modulated.

Keys, Andrew Scott↗

NASA NTRS1992

Metrology of X-ray optics utilizing shearing interferometric techniques

This paper will discuss the optical testing of extreme grazing incidence mirror systems and normal incidence high-precision mirror systems during fabrication processing of the optical substrates. The optical metrology is closely coupled with an advanced material removal process which will be discussed in terms of the optical metrology. Interferometric data will be presented of the optical surfaces. Surface roughness data will be shown and discussed.

Baker, Phillip C.↗

NASA NTRS1988

Solid-State Single-Photon Counter

Avalanche photodiode used to detect single photons if cooled to optimum temperature and overbiased beyond breakdown voltage. Offers two to three times sensitvity of photomultiplier tubes commonly used for photon detection. When cooled to reduce number of thermal carriers, avalanche photodiode reverse-biased beyond normal breakdown voltage to give it extremely-high internal gain of 10 to seventh power to 10 to eigth power. Advantages of solid-state devices to applications requiring low-level light detection, optical communication, astronomy, remote sensing, optical metrology, and optical signal processing.

Robinson, D. L.↗

NASA NTRS2008

Improved Gas Filling and Sealing of an HC-PCF

An improved packaging approach has been devised for filling a hollow-core photonic-crystal fiber (HC-PCF) with a gas, sealing the HC-PCF to retain the gas, and providing for optical connections and, optionally, a plumbing fitting for changing or augmenting the gas filling. Gas-filled HC-PCFs can be many meters long and have been found to be attractive as relatively compact, lightweight, rugged alternatives to conventional gas-filled glass cells for use as molecular-resonance frequency references for stabilization of lasers in some optical-metrology, lidar, optical-communication, and other advanced applications. Prior approaches to gas filling and sealing of HC-PCFs have involved, variously, omission of any attempt to connectorize the PCF, connectorization inside a vacuum chamber (an awkward and expensive process), or temporary exposure of one end of an HC-PCF to the atmosphere, potentially resulting in contamination of the gas filling. Prior approaches have also involved, variously, fusion splicing of HC-PCFs with other optical fibers or other termination techniques that give rise to Fresnel reflections of about 4 percent, which results in output intensity noise.

Poberezhskiy, Ilya↗

NASA NTRSDate not supplied

Metrological and Spectral Characterization of the Aspera Flight Optics

Aspera is a NASA's Astrophysics Pioneers mission, led by the University of Arizona. The aim of this mission is to study the presence of hot gasses (T=10^5-10^6 K) in the circumgalactic medium (CGM) and how the flow of these gasses affects galactic formation. One key enabling technology in the Aspera optical system is the use of more efficient UV-reflective optical coatings particularly at around 103.2 nm where the O VI emission line is located . In order to meet radiometric effective area requirements, the Goddard Space Flight Center (GSFC) code 551 Optics Branch applied Al (aluminum) + eLiF (enhanced lithium fluoride) on these optics, where the Al+LiF is annealed at elevated temperature (~250˚C) after the deposition and thus providing an improved version of the Al+LiF used in FUSE . Furthermore, these optics are encapsulated with a thin film of atomic layer deposited MgF2 at the Jet Propulsion Laboratory for enhanced durability . The efficiency and durability of these coatings depends on the quality of the optical surface in terms of cleanliness and roughness. Roughness increases the scatter off the coating and reduces the specular reflectance, and surface contaminants can accommodate moisture and other contaminants, increase scattering, and are weak points in the coating that may affect adhesion and subsequently the longevity of these coatings. Extensive optical metrology is necessary to minimize and quantify the impact of surface roughness and contaminants on optical surfaces. In this proceeding we report the inspection procedure implemented for Aspera optics at GSFC, from initial receiving of the optics to post-coating. Inspection includes Atomic Force Microscopy (AFM), Scanning White Light Interferometry (SWILI), Dark Field Microscopy (DFM), Phase Shifting Interferometry (PSI), and Vacuum ultraviolet (VUV) spectroscopy. Combinations of these techniques are used to inspect flight optics at each of the following steps: i) as-received, pre-cleaning inspection, ii) pre-coating, post-cleaning inspection, and iii) post-coating inspection. The evolution of roughness and other surface inspections such as contaminants are compared between each step to quantify the effect each step has on the flight optics. The final far ultraviolet (FUV) spectral performance of witness samples coated with the flight optics are presented.

Far Ultraviolet (FUV)↗

NASA NTRS2011

Optimized Biasing of Pump Laser Diodes in a Highly Reliable Metrology Source for Long-Duration Space Missions

Optical metrology system reliability during a prolonged space mission is often limited by the reliability of pump laser diodes. We developed a metrology laser pump module architecture that meets NASA SIM Lite instrument optical power and reliability requirements by combining the outputs of multiple single-mode pump diodes in a low-loss, high port count fiber coupler. We describe Monte-Carlo simulations used to calculate the reliability of the laser pump module and introduce a combined laser farm aging parameter that serves as a load-sharing optimization metric. Employing these tools, we select pump module architecture, operating conditions, biasing approach and perform parameter sensitivity studies to investigate the robustness of the obtained solution.

808 mm diode pumps↗

NASA NTRSDate not supplied

Repurposing the James Webb Space Telescope’s center of curvature optical bench hexapod for future mirror calibration testing at NASA Marshall’s x-ray & cryogenic facility

The James Webb Space Telescope’s (JWST) center of curvature optical bench (CoCOB) hexapod was repurposed to enhance NASA Marshall Space Flight Center’s X-Ray & Cryogenic Facility (XRCF) optical metrology capabilities. This upgrade unlocked higher test article load capacity and extended the allowable ranges of motion of the CoCOB hexapod. The hexapod was also coupled to a new long-stroke, linear motion axis to form a 7 degrees of freedom system and allow for high precision testing of larger diameter test articles. A 9 degrees of freedom motion system, consisting of a three-axis linear mount in an X-Y-Z configuration and a commercially available hexapod, was also designed to allow high resolution positioning of the focal plane instrumentation over a large range of motion. A modern control architecture and graphical user interface was developed for the CoCOB hexapod and additional motion stages to permit streamlined commanding and operation. This paper discusses the justification for re-using the CoCOB hexapod by highlighting its unique precision motion control capabilities in a high vacuum and optically clean environment. The design, key component selection, and environmental compatibility for each of the additional motion stages is presented along with testing results for achieved range, repeatability, and minimum step size performance for all motion axes. Finally, a summary of the motion control system architecture and its flexibility to address tomorrow’s optical metrology needs are presented.

hexapod↗

NASA NTRS2000

Metrology of Optical Beam Expander for Space Readiness Coherent Lidar Experiment (SPARCLE)

Stringent requirements of the SPARCLE telescope demanded testing of its individual elements through each step of fabrication, and complete metrology of the integrated telescope both at Helium-Neon and the operational two micron wavelengths.

Kester, Thomas J.↗

NASA NTRS2018

Thermal Control of Boundaries for JWST Infrared Tests in Cryogenic Vacuum Configuration

In 2017, the combined Optical Telescope Element and Integrated Science Instrument Module (OTIS) of the James Webb Space Telescope (JWST) underwent functional testing and optical metrology verification under cryogenic vacuum conditions in Chamber A at the Johnson Space Center (JSC). Testing the infrared Science Instruments and OTIS optics below 50 degrees Kelvin required an environment architecture that comprehensively controlled the temperature and energy path of every seam and penetration in the over 1100 m2 of Chamber A helium shroud surfaces as well as the Ground Support Equipment (GSE) inside it. This paper outlines the design and implementation of thermal closeouts, thermal anchoring systems for electrical cables, and thermal control systems around room-temperature optical metrology equipment inside the helium shroud. It also details lessons learned from the repeated implementation and testing of these environmental control systems throughout the JWST Pathfinder test campaign.

Huguet, Jesse A.↗

NASA NTRS2018

Thermal Control of Boundaries for JWST Infrared Tests in Cryogenic Vacuum Configuration

In 2017, the combined Optical Telescope Element and Integrated Science Instrument Module (OTIS) of the James Webb Space Telescope (JWST) underwent functional testing and optical metrology verification under cryogenic vacuum conditions in Chamber A at the Johnson Space Center (JSC). Testing the infrared Science Instruments and OTIS optics below 50 K required an environment architecture that comprehensively controlled the temperature and energy path of every seam and penetration in the over 1100 sq m of Chamber A helium shroud surfaces as well as the Ground Support Equipment (GSE) inside it. This paper outlines the design and implementation of thermal closeouts, thermal anchoring systems for electrical cables, and thermal control systems around room-temperature optical metrology equipment inside the helium shroud. It also details lessons learned from the repeated implementation and testing of these environmental control systems throughout the JWST Pathfinder test campaign.

Huguet, Jesse A.↗

NASA NTRS1982

Holographic Twyman-Green interferometer

A dichromated gelatin off-axis Fresnel zone plate was designed, fabricated, and used in a new type of interferometer for optical metrology. This single hologram optical element combines the functions of a beam splitter, beam diverger, and aberrated null lens. Data presented show the successful application for an interferometric test of an f/6, 200-mm diam parabolic mirror.

Chen, C. W.↗

NASA NTRS2018

Thermal Management of JWST Cryo-Vacuum Test Support Equipment

Havey, Keith A., Jr.↗

NASA NTRS2012

Variable Sampling Mapping

The performance of an optical system (for example, a telescope) is limited by the misalignments and manufacturing imperfections of the optical elements in the system. The impact of these misalignments and imperfections can be quantified by the phase variations imparted on light traveling through the system. Phase retrieval is a methodology for determining these variations. Phase retrieval uses images taken with the optical system and using a light source of known shape and characteristics. Unlike interferometric methods, which require an optical reference for comparison, and unlike Shack-Hartmann wavefront sensors that require special optical hardware at the optical system's exit pupil, phase retrieval is an in situ, image-based method for determining the phase variations of light at the system s exit pupil. Phase retrieval can be used both as an optical metrology tool (during fabrication of optical surfaces and assembly of optical systems) and as a sensor used in active, closed-loop control of an optical system, to optimize performance. One class of phase-retrieval algorithms is the iterative transform algorithm (ITA). ITAs estimate the phase variations by iteratively enforcing known constraints in the exit pupil and at the detector, determined from modeled or measured data. The Variable Sampling Mapping (VSM) technique is a new method for enforcing these constraints in ITAs. VSM is an open framework for addressing a wide range of issues that have previously been considered detrimental to high-accuracy phase retrieval, including undersampled images, broadband illumination, images taken at or near best focus, chromatic aberrations, jitter or vibration of the optical system or detector, and dead or noisy detector pixels. The VSM is a model-to-data mapping procedure. In VSM, fully sampled electric fields at multiple wavelengths are modeled inside the phase-retrieval algorithm, and then these fields are mapped to intensities on the light detector, using the properties of the detector and optical system, for comparison with measured data. Ultimately, this model-to-data mapping procedure enables a more robust and accurate way of incorporating the exit-pupil and image detector constraints, which are fundamental to the general class of ITA phase retrieval algorithms.

Smith, Jeffrey, S.↗

NASA NTRS2018

Developing Controlled Conductive Boundaries for JWST Cryogenic Testing

In 2017, the James Webb Space Telescope (JWST) underwent functional testing and optical metrology verification of the combined Optical Telescope Element and Integrated Science Instrument Module (OTIS) under cryogenic vacuum conditions in Chamber A at the Johnson Space Center. Maintaining flight-like thermal boundary conditions was a critical requirement for optical testing and required unique and challenging Ground Support Equipment (GSE) design solutions. Two such GSE systems, the Integrated Science Instrument Module (ISIM) Precool Straps and the Hardpoint Struts were direct conduction interfaces to the flight hardware. Hardware safety during cooldown required detailed design of their conductivity, and thermal balance testing required "zero-Q" (0-Q) heater implementation to bring the heat flow to zero, thereby cutting off these non-flight conductive links after operating temperatures were achieved. This paper describes the design considerations and approach implemented to achieve the required flight hardware cool down and return to ambient conditions, ensure flight hardware safety, and minimize the non-flight-like heat flows to or from the observatory during cryo-stable testing.

Cooke, D.↗

NASA NTRS2018

Developing Controlled Conductive Boundaries for JWST Cryogenic Testing

In 2017, the James Webb Space Telescope (JWST) underwent functional testing and optical metrology verification of the combined Optical Telescope Element and Integrated Science Instrument Module (OTIS) under cryogenic vacuum conditions in Chamber A at the Johnson Space Center. Maintaining flight-like thermal boundary conditions was a critical requirement for optical testing and required unique and challenging Ground Support Equipment (GSE) design solutions. Two such GSE systems, the Integrated Science Instrument Module (ISIM) Precool Straps and the Hardpoint Struts were direct conduction interfaces to the flight hardware. Hardware safety during cooldown required detailed design of their conductivity, and thermal balance testing required zero-Q (0-Q) heater implementation to bring the heat flow to zero, thereby cutting off these non-flight conductive links after operating temperatures were achieved. This paper describes the design considerations and approach implemented to achieve the required flight hardware cool down and return to ambient conditions, ensure flight hardware safety, and minimize the non-flight-like heat flows to or from the observatory during cryo-stable testing.

Cooke, Dwight A.↗

NASA NTRS2017

Optics Alignment of a Balloon-Borne Far-Infrared Interferometer BETTII

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-m baseline far-infrared (FIR: 30 90 micrometer) interferometer providing spatially resolved spectroscopy. The initial scientific focus of BETTII is on clustered star formation, but this capability likely has a much broader scientific application.One critical step in developing an interferometer, such as BETTII, is the optical alignment of the system. We discuss how we determine alignment sensitivities of different optical elements on the interferogram outputs. Accordingly, an alignment plan is executed that makes use of a laser tracker and theodolites for precise optical metrology of both the large external optics and the small optics inside the cryostat. We test our alignment on the ground by pointing BETTII to bright near-infrared sources and obtaining their images in the tracking detectors.

Dhabal, Arnab↗