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Sökning: WFRF:(Ullom Joel N.)

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1.
  • Fullagar, Wilfred K., et al. (författare)
  • Beating Darwin-Bragg losses in lab-based ultrafast X-ray experiments
  • 2017
  • Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 4:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The use of low temperature thermal detectors for avoiding Darwin-Bragg losses in lab-based ultrafast experiments has begun. An outline of the background of this new development is offered, showing the relevant history and initiative taken by this work.
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2.
  • McCarrick, Heather, et al. (författare)
  • The Simons Observatory Microwave SQUID Multiplexing Detector Module Design
  • 2021
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 922:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Advances in cosmic microwave background (CMB) science depend on increasing the number of sensitive detectors observing the sky. New instruments deploy large arrays of superconducting transition-edge sensor (TES) bolometers tiled densely into ever larger focal planes. High multiplexing factors reduce the thermal loading on the cryogenic receivers and simplify their design. We present the design of focal-plane modules with an order of magnitude higher multiplexing factor than has previously been achieved with TES bolometers. We focus on the novel cold readout component, which employs microwave SQUID multiplexing (μmux). Simons Observatory will use 49 modules containing 70,000 bolometers to make exquisitely sensitive measurements of the CMB. We validate the focal-plane module design, presenting measurements of the readout component with and without a prototype detector array of 1728 polarization-sensitive bolometers coupled to feedhorns. The readout component achieves a 95% yield and a 910 multiplexing factor. The median white noise of each readout channel is 65 pA √Hz . This impacts the projected SO mapping speed by <8%, which is less than is assumed in the sensitivity projections. The results validate the full functionality of the module. We discuss the measured performance in the context of SO science requirements, which are exceeded.
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3.
  • O’Neil, Galen C., et al. (författare)
  • Ultrafast Time-Resolved X-ray Absorption Spectroscopy of Ferrioxalate Photolysis with a Laser Plasma X-ray Source and Microcalorimeter Array
  • 2017
  • Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:5, s. 1099-1104
  • Tidskriftsartikel (refereegranskat)abstract
    • The detailed pathways of photoactivity on ultrafast time scales are a topic of contemporary interest. Using a tabletop apparatus based on a laser plasma X-ray source and an array of cryogenic microcalorimeter X-ray detectors, we measured a transient X-ray absorption spectrum during the ferrioxalate photoreduction reaction. With these high-efficiency detectors, we observe the Fe K edge move to lower energies and the amplitude of the extended X-ray absorption fine structure reduce, consistent with a photoreduction mechanism in which electron transfer precedes disassociation. These results are compared to previously published transient X-ray absorption measurements on the same reaction and found to be consistent with the results from Ogi et al. and inconsistent with the results of Chen et al. (Ogi, Y.; et al. Struct. Dyn. 2015, 2, 034901; Chen, J.; Zhang, H.; Tomov, I. V.; Ding, X.; Rentzepis, P. M. Chem. Phys. Lett. 2007, 437, 50-55). We provide quantitative limits on the Fe-O bond length change. Finally, we review potential improvements to our measurement technique, highlighting the future potential of tabletop X-ray science using microcalorimeter sensors.
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