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The traditional method for measuring CCD non-linearity using constant flux and variable exposure time is compared to a faster and potentially more accurate method that requires just two exposures at low intensity. Signal is varied by parallel-binning a successively greater number of lines. The binned image is compared to a conventional image with identical illumination, co-added digitally in the same pattern. This method requires no shutter calibration and is insensitive to illumination drift or charge transfer inefficiency. With some additional software effort, it can be arranged to tolerate illumination non-uniformity. We present data obtained by both methods for the 64 CD231-C6 outputs and discuss automated performance optimization. We find that the widely held assumption that non-linearity only affects high signals is incorrect when optimizing for minimum gain change over the full signal range, in which case slope increases with signal initially, then peaks in the mid-range before dropping again.

Zwicky Transient Facility is an integrated, multi-band astronomical survey system optimized for sensitivity, observing cadence, and efficiency. The key subsystem consists of a 600 megapixel CCD focal plane mounted in a flat-fielding vacuum cryostat, located at the prime focus of the 1.2-meter Samuel Oschin Telescope at Palomar Observatory. Supporting subsystems include a new 2.4-meter optical shutter assembly, a 1.35-meter diameter aspheric corrector plate, a cryostat stabilizing hexapod, a commercial robotic arm-based exchanger, three 440 millimeter width filters, four guide/focus CCDs, and dedicated optics compensating individual field curvature over each of sixteen 6k x 6k science CCDs.To optimize ZTF efficiency, all telescope and dome drives were upgraded for higher speed and acceleration, fast readout electronics were implemented, and a sophisticated robotic control system has been implemented. We present for the first time on-sky results from the recently completed ZTF including its realized optical image quality, CCD noise, and observing efficiency performance and discuss engineering challenges that have been overcome. Early scientific results from the ZTF survey are also included.

Pixelated Cadmium Zinc Telluride (CdZnTe) detectors are currently flying on the Nuclear Spectroscopic Telescope ARray (NuSTAR) NASA Astrophysics Small Explorer. While the pixel pitch of the detectors is ≈ 605 μm, we can leverage the detector readout architecture to determine the interaction location of an individual photon to much higher spatial accuracy. The sub-pixel spatial location allows us to finely oversample the point spread function of the optics and reduces imaging artifacts due to pixelation. In this paper we demonstrate how the sub-pixel information is obtained, how the detectors were calibrated, and provide ground verification of the quantum efficiency of our Monte Carlo model of the detector response.

The Cobra fiber positioner is being developed by the California Institute of Technology (CIT) and the Jet Propulsion Laboratory (JPL) for the Prime Focus Spectrograph (PFS) instrument that will be installed at the Subaru Telescope on Mauna Kea, Hawaii. PFS is a fiber fed multi-object spectrometer that uses an array of Cobra fiber positioners to rapidly reconfigure 2394 optical fibers at the prime focus of the Subaru Telescope that are capable of positioning a fiber to within 5um of a specified target location. A single Cobra fiber positioner measures 7.7mm in diameter and is 115mm tall. The Cobra fiber positioner uses two piezo-electric rotary motors to move a fiber optic anywhere in a 9.5mm diameter patrol area. In preparation for full-scale production of 2550 Cobra positioners an Engineering Model (EM) version was developed, built and tested to validate the design, reduce manufacturing costs, and improve system reliability. The EM leveraged the previously developed prototype versions of the Cobra fiber positioner. The requirements, design, assembly techniques, development testing, design qualification and performance evaluation of EM Cobra fiber positioners are described here. Also discussed is the use of the EM build and test campaign to validate the plans for full-scale production of 2550 Cobra fiber positioners scheduled to begin in late-2014.

The Prime Focus Spectrograph (PFS) is a new optical/near-infrared multi-fiber spectrograph design for the prime focus of the 8.2m Subaru telescope. PFS will cover 1.3 degree diameter field with 2394 fibers to complement the imaging capability of Hyper SuprimeCam (HSC). The prime focus unit of PFS called Prime Focus Instrument (PFI) provides the interface with the top structure of Subaru telescope and also accommodates the optical bench in which Cobra fiber positioners are located. In addition, the acquisition and guiding (A&G) cameras, the optical fiber positioner system, the cable wrapper, the fiducial fibers, illuminator, and viewer, the field element, and the telemetry system are located inside the PFI. The mechanical structure of the PFI was designed with special care such that its deflections sufficiently match those of the HSC Wide Field Corrector (WFC) so the fibers will stay on targets over the course of the observations within the required accuracy., 9 pages, 7 figures, SPIE Astronomical Telescopes and Instrumentation 2014

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing hard X-ray (5 -- 80 keV) telescope to orbit. NuSTAR will offer a factor 50 -- 100 sensitivity improvement compared to previous collimated or coded mask imagers that have operated in this energy band. In addition, NuSTAR provides sub-arcminute imaging with good spectral resolution over a 12-arcminute field of view. After launch, NuSTAR will carry out a two-year primary science mission that focuses on four key programs: studying the evolution of massive black holes through surveys carried out in fields with excellent multiwavelength coverage, understanding the population of compact objects and the nature of the massive black hole in the center of the Milky Way, constraining explosion dynamics and nucleosynthesis in supernovae, and probing the nature of particle acceleration in relativistic jets in active galactic nuclei. A number of additional observations will be included in the primary mission, and a guest observer program will be proposed for an extended mission to expand the range of scientific targets. The payload consists of two co-aligned depth-graded multilayer coated grazing incidence optics focused onto solid state CdZnTe pixel detectors. To be launched in early 2012 on a Pegasus rocket into a low-inclination Earth orbit. Data will be publicly available at GSFC's High Energy Astrophysics Science Archive Research Center (HEASARC) following validation at the science operations center located at Caltech.

The Nuclear Spectroscopic Telescope Array, NuSTAR, is a NASA funded Small Explorer Mission, SMEX, scheduled for launch in mid 2011. The spacecraft will fly two co-aligned conical approximation Wolter-I optics with a focal length of 10 meters. The mirrors will be deposited with Pt/SiC and W/Si multilayers to provide a broad band reflectivity from 6 keV up to 78.4 keV. To optimize the mirror coating we use a Figure of Merit procedure developed for gazing incidence optics, which averages the effective area over the energy range, and combines an energy weighting function with an angular weighting function to control the shape of the desired effective area. The NuSTAR multilayers are depth graded with a power-law, d_i = a/(b + i)^c, and we optimize over the total number of bi-layers, N, c, and the maximum bi-layer thickness, d_(max). The result is a 10 mirror group design optimized for a flat even energy response both on and off-axis.

We have developed large format CdZnTe pixel detectors optimized for astrophysical applications. The detectors, designed for the High Energy Focusing Telescope (HEFT) balloon experiment, each consists of an array of 24x44 pixels, on a 498 μm pitch. Each of the anode segments on a CdZnTe sensor is bonded to a custom, low-noise application-specific integrated circuit (ASIC)optimized to achieve low threshold and good energy resolution. We have studied detectors fabricated by two different bonding methods and corresponding anode plane designs---the first detector has a steering electrode grid, and is bonded to the ASIC with indium bumps; the second detector has no grid but a narrower gap between anode contacts, and is bonded to the ASIC with conductive epoxy bumps and gold stud bumps in series. In this paper, we present results from detailed X-ray testing of the HEFT pixel detectors. This includes measurements of the energy resolution for both single-pixel and split-pixel events, and characterization of the effects of charge trapping, electrode biases and temperature on the spectral performance. Detectors from the two bonding methods are contrasted.

The three most important quantities used to assess the performance of astronomical x-ray telescope optics are the on- axis collecting area, the field of view, and the half-power diameter. The first two quantities depend on the mirror packing arrangement and the multilayer coating design. In order to optimize the coating design, we have developed a figure-of-merit (FOM) that accounts for the coating response over a specified range of energies and off-axis angles. We present an example where we have used this FOM to optimize a specific coating design for the High Energy Focusing Telescope (HEFT) and to understand tradeoffs between performance and coating thickness.

We have measured the hard X-ray reflectivity and imaging performance from depth graded W/Si multilayer coated mirror segments mounted in a single reflection cylindrical prototype for the hard X-ray telescopes to be flown on the High Energy Focusing Telescope (HEFT) balloon mission. Data have been obtained in the energy range from 18 - 170 keV at the European Synchrotron Radiation Facility and at the Danish Space Research Institute at 8 keV. The modeling of the reflectivity data demonstrate that the multilayer structure can be well described by the intended power law distribution of the bilayer thicknesses optimized for the telescope performance and we find that all the data is consistent with an interfacial width of 4.5 angstroms. We have also demonstrated that the required 5% uniformity of the coatings is obtained over the mirror surface and we have shown that it is feasible to use similar W/Si coatings for much higher energies than the nominal energy range of HEFT leading the way for designing Gamma-ray telescopes for future astronomical applications. Finally we have demonstrate 35 arcsecond Half Power Diameter imaging performance of the one bounce prototype throughout the energy range of the HEFT telescopes.

Sensitive nuclear line spectroscopy for observations of prompt emission from supernovae, as well as mapping of remnants has been a primary goal of gamma-ray astrophysics since its inception. A number of key lines lie in the energy band from 10 - 600 keV. In this region of the spectrum, observations have to-date been limited by high background and poor angular resolution. In this paper, we present several designs capable of extending the sensitivity of grazing incidence optics into this energy range. In particular, we discuss a 15 m focal length design for NASA's High-Sensitivity Spectroscopic Imaging Mission concept, as well as a 50 m focal length design which can extend ESA's XEUS mission into this band. We demonstrate that an unprecedented line sensitivity of 10-7 cm-2s-1 can be achieved for the most important lines in this energy band.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The High Energy Focusing Telescope (HEFT) is a balloon-borne experiment employing focusing optics in the hard X-ray/soft gamma-ray band (20 - 100 keV) for sensitive observations of astrophysical sources. The primary scientific objectives include imaging and spectroscopy of 44Ti emission in young supernova remnants, sensitive hard X-ray observations of obscured Active Galactic Nuclei, and spectroscopic observations of accreting high-magnetic field pulsars. Over the last four years, we have developed grazing-incidence depth-graded multilayer optics and high spectral resolution solid stat Cadmium Zinc Telluride pixel detectors in order to assemble a balloon-borne experiment with sensitivity and imaging capability superior to previous satellite missions operating in this band. In this paper, we describe the instrument design, and present recent laboratory demonstrations of the optics and detector technologies.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We discuss the development of X-ray multilayer coatings for use as broad-band reflectors operating at energiesabove 100 keV. Such coatings can be used to produce hard X-ray telescopes that will make possible a variety of entirely newastronomical observations. We summarize our recent investigation into the growth, structure and hard X-ray performance ofdepth-graded W/Si multilayers, present follow-up information on Cu/Si multilayers, and discuss preliminary results obtainedwith Ni/Si, Ni8Cr2/Si, and Ni93V07/Si multilayers.Keywords: multilayer coatings, hard X-ray optics 1. INTRODUCTION Depth-graded multilayers are the enabling technology for a new generation of hard X-ray astronomical telescopes,including those being developed for the HEFT [1] and In-Focus [2] balloon instruments, and the Astro-G and Constellation-Xsatellite instruments [3]. These new telescopes, operating at photon energies in the range 20 — 100 keV, will provide animprovement in sensitivity by a factor of -4000 or more over previous (non-focusing) instruments, and will undoubtedly leadto a number of important astronomical discoveries.We describe here the development of depth-graded multilayer structures for use as hard X-ray reflectors operating atenergies greater than 100 keV. With a high-resolution, high-energy focusing mission based on such technology a variety ofnew observations will become possible, including: measuring the time-history of the emission from 5'Ni (158 keV) in Typela SNe; investigating the sites of particle acceleration in young SNR; measuring the nuclear continuum and cutoff in SeyfertI galaxies; and detection of Compton backscatter radiation (170 keV) in Galactic black hole candidates.Unlike periodic multilayers, which provide high reflectance only over a limited range of angles and X-ray energies,depth-graded multilayers are used for broadband reflectance: in a depth-graded multilayer structure the layer thicknessesvary with depth into the film stack, such that each bilayer is effectively tuned to a different X-ray wavelength. Depth-gradedmultilayer structures are particularly effective in the hard X-ray region (E > 20 keV) where hundreds or even thousands ofbilayers can be used, in principle, as a result of the low absorption and consequently high penetration depth in the film atthese energies. However, the performance of such structures depends critically on the achievable level of interfaceperfection: deviations from atomically smooth and chemically abrupt interfaces —

We have performed x-ray specular reflectivity and scattering measurements of thermally slumped glass substrates on x-ray diffractometers utilizing a rotating anode x-ray source at the Danish Space Research Institute (DSRI) and synchrotron radiation at the European Synchrotron Radiation Facility (ESRF) optics Bending Magnet beamline. In addition, we tested depth graded W/Si multilayer-coated slumped glass using x-ray specular reflectivity measurements at 8.048 keV and 28 keV and energy-dispersive measurements in the 20-50 keV rang at a double-axis diffractometer at the Orsted Laboratory, University of Copenhagen. The thermally slumped glass substrates will be used to fabricate the hard x-ray grazing incidence optics for the High-Energy Focusing Telescope. We compared the measurements to the SODART- mirrors from the SRG telescope mission program. The surface scatter measurement of the thermally slumped glass substrates yields Half Power Diameters (HPD's) of single- bounce mirrors of full-illuminated lengths of ~ 40 arcseconds for typical substrates and as low as ~ 10 arcseconds for the best substrates, whereas the SODART mirrors yields HPD's of ~ 80 arcseconds with very little variation. Both free-standing glass substrates and prototype mounted and multilayer-coated optics were tested. The result demonstrate that the surface scatter contribution, plus any contribution from the mounting procedure, to the Half Power Diameter from a telescope using the slumped glass optics will be in the subarcminute range.In addition we measured low surface microroughness, yielding high reflectivity, from the glass substrates, as well as from the depth graded W/Si multilayer-coated glass glass (interfacial width 4.2 A).

We report on the current status and performance of prototype hard x-ray optics we are producing for use on the high energy focusing telescope (HEFT) experiment. The baseline substrates are thermally formed glass mirrors that are overcoated with multilayers to provide good performance throughout the 20-80 keV bandpass. Progress made in the thermal forming process as well as in the multilayer performance has allowed production of optics that meet or exceed all HEFT requirements. We present metrology on the substrates and result from x-ray characterization. A novel mounting scheme for the individual telescope shells is currently being tested. If successful the mounting technique will produce a monolithic, extremely stiff and robust optic.

We are developing depth-graded, multilayer-coated mirrors for astrophysical hard X-ray focusing telescopes. In this paper, we discuss the primary technical challenges associated with the multilayer coatings, and report on progress to date. We have sputtered constant cl-spacing and depth-graded W / Si multilayers onto 0.3- 0.5 mm thick DURAN glass (AF45 and D263) and 0.4 mm thick epoxy replicated aluminum foils (ERAFs) , both of which are potential mirror substrates. We have characterized the interfacial roughness, uniformity, and stress of the coatings. The average interfacial roughness of each multilayer was measured from specular reflectivity scans (Bi = Br) using Cu K0 X-rays. The thin film stress was calculated from the change in curvature induced by the coating on flat glass substrates. Thickness and roughness uniformity were measured by taking specular reflectivity scans of a multilayer deposited on the inside surface of a quarter cylinder section. We found that interfacial roughness (a) in the multilayers was typically between 3.5 and 4.0 A on DESAG glass, and between 4.5 and 5.0 A on the ERAFs. Also, we found that coatings deposited on glass that has been thermally formed into a cylindrical shape performed as well as flat glass. The film stress, calculated from Stoney's equation, for a 200 layer graded multilayer was approximately 200 MPa. Our uniformity measurements show that with no baffles to alter the deposition profile on a curved optic, the layer thickness differs by "'203 between the center and the edge of the optic. Interfacial roughness, however, remained constant, around 3.6 A, throughout the curved piece, even as the layer spacing dropped off.

Reflectivity at (lambda) equals 0.154 nm and mechanical stress in the bulk thin films of tungsten and silicon and single d- spacing multilayers on their basis with d approximately equals 2.8 nm deposited by the magnetron sputtering technique on flat thin substrates of Si wafer (approximately 0.2 mm), glass (approximately 0.3 mm), and epoxy gold replicated aluminum foil (approximately 0.3 mm) have been studied. The interfacial roughness of the multilayers has been calculated from the x- ray reflectivity curves as the following: on Si wafer (sigma) approximately equals 0.31 nm, on glass (sigma) approximately equals 0.32 nm, and on foil (sigma) approximately equals 0.34 nm. There was not observed a significant dependence on the stress in the Si film with change in rf power, Ar gas pressure and biasing. For the W films an increase of dc power results in an increase of stress. A similar relationship is also evident for W films deposited by rf power, but this dependence is less pronounced. The influence of low temperature (up to 200 degrees Celsius) annealing on x-ray reflectivity and stress in the multilayers has been investigated. There was not found an appreciable changes in the absolute value of reflectivity or in d-spacing with annealing temperature. The stress in the coatings changes with annealing temperature from compressive to tensile. There was observed a temperature of annealing at which the stress is no longer present in the film. The absolute value of this temperature measured for W/Si multilayer is approximately 120 degrees Celsius.