Development Broadband Reflective Coatings for ATLAST and Other LUVOIR Space Telescopes

Development broadband reflective coatings for ATLAST & other LUVOIR space observatories for exoplanet direct imaging missions the search for other Earths, & for hot objectshttps://scholarsarchive.byu.edu/researchnetworking/1006/thumbnail.jp

What the Universe Means to People Like Me

When I picked up David\u27s paper to read it, I had a pencil in my hand. Years of reading my students\u27 and my own papers made it natural to edit as I read. However, I heard in my mind the voice of my mother advising me to put the pencil down. This wasn\u27t time to edit but to hear and understand. Still, I kept the pencil in my hand for the first few pages and made a few notes before I put it down and just read. I could hear David\u27s voice speaking the words I read. It was good to hear it. I have missed hearing his voice. We met David when we attended the Princeton Ward a little over thirty years ago. That was a powerful time. The ward was a mixture of local people and transplants from the West. Students were not the largest group, but there were enough to leaven the loaf. The Princeton Institute met Friday nights in a room in the Firestone Library on campus. It was still listed as the Deseret Club in the university\u27s publications, and the meetings were more like a graduate seminar than a seminary class. The students took turns presenting papers or thoughts on various themes. Most of us were graduate students and were comfortable with a seminar style

A Novel Technique for the Simultaneous Collection of Reflection and Transmission Data from Thin Films in the Extreme Ultraviolet

Studies of thin films in the Extreme Ultraviolet (EUV) are difficult given that most materials readily absorb photons of these energies. By depositing a thin film of the material of interest on a silicon photodiode, transmission measurements can be made throughout the EUV. If the measurements are made in a range of low absorption, the extinction coefficient, k, can be found with relative ease. However, if the material’s absorption is considerable, reflection measurements are needed to supplement the transmission data in order to find the optical constants n and k. The technique developed allows for reflection and transmission measurements to be taken simultaneously, which combined, account for all of the measurable photons from the original beam: (those which cannot be counted are photons absorbed into the thin film material). Also, the technique presented allows for data to be collected from practically all angles of incidence. This technique has been applied to a thin film of scandium oxide (d=65 nm), with measurements taken over wavelengths from 2.5-25 nm, and at angles of incidence 12 degrees from grazing to normal

The Effects of Oxidation on the Refractive Index of Uranium Thin Films in the Extreme Ultraviolet

We measured the transmittance and reflectance of two samples in the extreme ultraviolet (XUV) at the Advanced Light Source at Lawrence Berkeley National Laboratory. The samples were prepared with approximately 20 nm of UOx with one reactively sputtered onto a diode, and one allowed to oxidize naturally on an identical diode. Fitting the reflectance data to the Parratt model yielded a more precise thickness of the UOx film. This thickness combined with a simple analysis of the transmission measurements provides estimates for the imaginary part of the index of refraction for UOx at approximately every tenth of a nanometer from about 3 nm to 30 nm with emphasis in the 12- to 13-nm range. Using these values, a first approximation for the real part of the refractive index has also been calculated. These values provide researchers with information for modeling, design, and fabrication of optical systems in the extreme ultraviolet

The evolutionary dynamics of variant antigen genes in Babesia reveal a history of genomic innovation underlying host-parasite interaction

Babesia spp. are tick-borne, intraerythrocytic hemoparasites that use antigenic variation to resist host immunity, through sequential modification of the parasite-derived variant erythrocyte surface antigen (VESA) expressed on the infected red blood cell surface. We identified the genomic processes driving antigenic diversity in genes encoding VESA (ves1) through comparative analysis within and between three Babesia species, (B. bigemina, B. divergens and B. bovis). Ves1 structure diverges rapidly after speciation, notably through the evolution of shortened forms (ves2) from 5′ ends of canonical ves1 genes. Phylogenetic analyses show that ves1 genes are transposed between loci routinely, whereas ves2 genes are not. Similarly, analysis of sequence mosaicism shows that recombination drives variation in ves1 sequences, but less so for ves2, indicating the adoption of different mechanisms for variation of the two families. Proteomic analysis of the B. bigemina PR isolate shows that two dominant VESA1 proteins are expressed in the population, whereas numerous VESA2 proteins are co-expressed, consistent with differential transcriptional regulation of each family. Hence, VESA2 proteins are abundant and previously unrecognized elements of Babesia biology, with evolutionary dynamics consistently different to those of VESA1, suggesting that their functions are distinct

Comparison of Effective Medium Procedures for Optical Modeling of Laminar Structures

This study addresses the question, How can the optical properties of matter in ultrathin amorphous nonmetallic films in multilayers best be determined from reflectance (R) and transmission (T) measurements? A blue shift in the band gap of plasma CVD a-Si:H/a-SiNx:H multilayers was reported several years ago. It was suggested that the shift in the band gap, Eg, Relative to bulk a-Si:H as given by the Tauç plot was due to quantum confinement effects. The purpose of this study is to evaluate the usefulness of various effective media theories (EMT) for determining the optical constants of materials in a multilayer and to explore to what extent a shift in band gap to higher energy may be an artifact of the method of optical analysis. Incoherent approaches are the most common methods of determining band gap from R and T. These do not require iteration to obtain optical constants from the optical data. The band gap determined by such methods was, however, generally 8% higher than the actual band gap when a suitable hypothetical case was investigated. Coherent effective media theory provides a noteworthy alternative to both incoherent EMT and fully coherent multilayer modeling, (Which is accurate but is excessively complicated and poorly convergent). The accuracy of the band gap is at the limit, 2-3%, of what can be expected for graphical methods. A previously unappreciated source of optical artifacts was also identified . Dispersion, which is commonly ignored when Eg is determined graphically, is shown to distort, in certain cases, the anticipated straight line behavior of the √aE vs. E plot

Ungulate preference for burned patches reveals strength of fire–grazing interaction

The interactions between fire and grazing are widespread throughout fire-dependent landscapes. The utilization of burned areas by grazing animals establishes the fire–grazing interaction, but the preference for recently burned areas relative to other influences (water, topography, etc.) is unknown. In this study, we determine the strength of the fire–grazing interaction by quantifying the influence of fire on ungulate site selection. We compare the preference for recently burned patches relative to the influence of other environmental factors that contribute to site selection; compare that preference between native and introduced ungulates; test relationships between area burned and herbivore preference; and determine forage quality and quantity as mechanisms of site selection. We used two large ungulate species at two grassland locations within the southern Great Plains, USA. At each location, spatially distinct patches were burned within larger areas through time, allowing animals to select among burned and unburned areas. Using fine scale ungulate location data, we estimated resource selection functions to examine environmental factors in site selection. Ungulates preferred recently burned areas and avoided areas with greater time since fire, regardless of the size of landscape, herbivore species, or proportion of area burned. Forage quality was inversely related to time since fire, while forage quantity was positively related. We show that fire is an important component of large ungulate behavior with a strong influence on site selection that drives the fire–grazing interaction. This interaction is an ecosystem process that supersedes fire and grazing as separate factors, shaping grassland landscapes. Inclusion of the fire–grazing interaction into ecological studies and conservation practices of fire-prone systems will aid in better understanding and managing these systems

Photoconductive Characterization of ZnxCd1-xTe (0≤x≤0.25) Single Crystal Alloys

Large grain polycrystalline and single crystals of ZnxCd1-xTe grown by a modified Bridgman method were studied using the photoluminescence and photoconductivity techniques. The temperature dependence of the band gap, as determined by photoluminescence, follows the Varshni equation for measuring temperature in the range of 15-290 K. One of the fitted parameters, the Debye temperature, monotonically decreases with the increase of the atomic zinc concentration. A close correlation between the photoluminescence and photoconductivity measurements is also found. Samples in which the photoluminescence spectra exhibit emission bands associated to cadmium vacancies and other structural defects, show a photoresponse curve which includes, in addition to the intrinsic band, another broad band at lower energies. Using the ionization energies of the defect related bands in the photoluminescence spectra we have identified the second band in the photoresponse curve due to the photoexcitation of trapped carriers at levels related with the structural defects

Advanced Infrared Optically Black Baffle Materials

Infrared optically black baffle surfaces are an essential component of many advanced optical systems. All internal surfaces in advanced infrared optical sensors that require stray light management to achieve resolution are of primary concern in baffle design. Current industrial materials need improvements to meet advanced optical sensor systems requirements for optical, survivability, and endurability. Baffles are required to survive and operate in potentially severe environments. Robust diffuse-absorptive black surfaces, which are (1) thermally and mechanically stable to threats of x-ray, launch, and in-flight maneuver conditions, with specific densities to allow an acceptable weight load, (2) handleable during assembly, (3) cleanable, and (4) adaptive to affordable manufacturing, are required as optical baffle materials. In this paper an overview of recently developed advanced infrared optical baffle materials, requirements, manufacturing strategies, and the Optics MODIL (Manufacturing Operations Development and Integration Laboratory) Advanced Baffle Program will be discussed

Characterization of Metal/Carbon Multilayers by Raman Spectroscopy

Laser Raman spectroscopy has been found to be useful for characterizing amorphous semiconductor multilayers, especially the interfaces of multilayers. Recently, we have extended this technique to the characterization of magnetron sputtered multilayers commonly used as reflectors in soft x-ray optics. Unlike the multilayers previously studied which contained only semiconductors and dielectrics, these are generally semiconductor/metal multilayers. We report here on the Raman characterization of the most common class of multilayers used in soft x-ray optics, those that contain a high density metal like tungsten interspersed with layers of carbon. In all of the metal/carbon multilayers the dominate feature in the Raman spectra is due to a-C. The a-C spectra consists of a bread peak at about 1560 cm-1 (G-peak) and a shoulder at about 1400 cm-1 (D-peak). This can be deconvoluted with Gaussian line shapes to yield two peaks (one at about 1560 to 1570 cm-1 and the other at about 1380 to 1420 cm-1). Among the W/C multilayer samples peak positions and relative magnitudes changed little with carbon thickness over the range of 1 to 12 nm. Significant differences are, however, seen as the identity of the metal component is altered or, especially, as the preparations are varied. For example, the intensity ratio of the D-peak to G-peak was much larger for multilayer samples prepared under conditions of good plasma confinement