We describe a method for measuring the complex impedance of transition-edge-sensor ͑TES͒ calorimeters. Using this technique, we measured the impedance of a Mo/Au superconducting transition-edge-sensor calorimeter. The impedance data are in good agreement with our linear calorimeter model. From these measurements, we obtained measurements of unprecedented accuracy of the heat capacity and the gradient of resistance with respect to temperature and current of a TES calorimeter throughout the phase transition. The measurements probe the internal state of the superconductor in the phase transition and are useful for characterizing the calorimeter.
Micro Electromechanical System (MEMS) microshutter arrays are being developed at NASA Goddard Space Flight Center for use as a field selector of the Near Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST). The microshutter arrays are designed for the spontaneous selection of a large number of objects in the sky and the transmission of light to the NIRSpec detector with high contrast. The JWST environment requires cryogenic operation at 35K. Microshutter arrays are fabricated out of silicon-on-insulator (SOI) silicon wafers. Arrays are closepacked silicon nitride membranes with a pixel size of 100x200 m. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with a minimized mechanical stress concentration. Light shields are processed for blocking light from gaps between shutters and frames. The mechanical shutter arrays are fabricated using MEMS technologies. The processing includes multi-layer metal depositions, the patterning of magnetic stripes and shutter electrodes, a reactive ion etching (RIE) to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, followed by a deep RIE (DRIE) back-etch to form mechanical supporting grids and release shutters from the silicon substrate. An additional metal deposition is used to form back electrodes. Shutters are actuated by a magnetic force and latched using an electrostatic force. Optical tests, addressing tests, and life tests are conducted to evaluate the performance and the reliability of microshutter arrays.
We explore the design of a space mission, Project Lyman, which has the goal
of quantifying the ionization history of the universe from the present epoch to
a redshift of z ~ 3. Observations from WMAP and SDSS show that before a
redshift of z >~ 6 the first collapsed objects, possibly dwarf galaxies,
emitted Lyman continuum (LyC) radiation shortward of 912 A, reionizing most of
the universe. How LyC escapes from galactic environments, whether it induces
positive or negative feedback on the local and global collapse of structures,
and the role played by clumping, molecules, metallicity and dust are major
unanswered theoretical questions, requiring observational constraint. Numerous
intervening Lyman limit systems, which frustrate the detection of LyC from high
z objects, thin below z ~ 3 where there are a few objects with apparently very
high fesc. At low z there are only controversial detections and a handful of
upper limits. A wide-field multi-object spectroscopic survey with moderate
spectral and spatial resolution can quantify fesc within diverse spatially
resolved galactic environments over redshifts with significant evolution in
galaxy assemblage and quasar activity. It can also calibrate LyC escape against
Ly-alpha escape, providing an essential tool to JWST for probing the beginnings
of reionization. We present calculations showing the evolution of the
characteristic apparent magnitude of star-forming galaxy luminosity functions
at 900 A, as a function of redshift and assumed escape fraction to determine
the required aperture for detecting LyC. We review our efforts to build a
pathfinding dual order multi-object spectro/telescope with a (0.5deg)^2
field-of-view, using a GSFC microshutter array, and crossed delay-line
micro-channel plate detector.Comment: SPIE oral paper 7011-76 presented at Astronomical Telescopes 2008 -
23 -- 28 June Marseille, France, 12 page, 5 figure
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