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Kim W.,U.S. Navy | Baker C.,U.S. Navy | Villalobos G.,U.S. Navy | Frantz J.,U.S. Navy | And 7 more authors.
Journal of the American Ceramic Society | Year: 2011

We have synthesized high-purity Yb3+-doped Lu2O 3 powder by the coprecipitation method. We have demonstrated that the recrystallization of the metal nitrates greatly improve the chemical purity of the resulting oxides. From thermogravimetry and differential thermal analysis study, we have calculated the approximate formula of the oxinitrate precipitate precursor as Lu1.8Yb0.2(OH)5.44(NO 3)0.56·0.58H2O. Fine and soft agglomerate powders were obtained after calcinations. We have shown that the powder is mainly in the form of polycrystalline soft agglomerates composed with 15-20 nm size crystals. The resulting ceramic showed higher transparency (close to theoretical limit) compared with the ones fabricated with commercial powders. © 2011 The American Ceramic Society.


Rzasa J.,University of Maryland University College | Ertem M.C.,University Research Foundation | Davis C.C.,University of Maryland University College
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

High capacity directional wireless communications networks are an active research area because of their Gb/s or greater data rates over link lengths of many kilometers, providing fiber-like networks through the air. Their high data rates arise partly from their very high carrier frequencies (<60GHz for RF, and ∼1550nm for free-space optical (FSO)) and partly because of their very narrow beamwidths. This second characteristic requires that transceivers be pointed precisely to their counterparts. In almost all cases this means that the transceiver aperture is mechanically pointed by a rotation stage, commonly known as a gimbal. How these platforms initially point at a target, acquire the signal, and then stay locked on the signal is known as pointing, acquisition, and tracking (PAT). Approaches for PAT in both RF and FSO have some similarities, but require overall divergent solutions, especially if the platforms are moving. This paper elaborates on the various considerations required for designing and implementing a successful PAT system for both directional RF and FSO systems. Approaches for GPS or beacon based pointing, types of acquisition scans, and the effects of platform vibration are analyzed. The acquisition time for a spiral scan of a given radius with an initial pointing error has been measured experimentally for a gimbal pointing system. © 2013 SPIE.


Ertem G.,University of Maryland University College | Ertem M.C.,University Research Foundation | McKay C.P.,NASA | Hazen R.M.,Carnegie Institution for Science
International Journal of Astrobiology | Year: 2016

Organic compounds have been delivered over time to Mars via meteorites, comets and interplanetary dust particles. The fate of organic material on the surface of Mars must be affected by the Martian environment, in particular by ultraviolet (UV) and other ionizing radiation. Penetration depth of UV radiation into soils is in the sub-millimetre to millimetre range and depends on the properties of the soil. The aim of this research is to study the possible protective role of Martian analogue minerals and soils for survivability of biomolecules against UV radiation and to compare their decomposition rates within a 1 mm-thick portion of the surface. Results demonstrated that minerals offer significant protection to biomolecules purine, pyrimidine and uracil against UV photolysis. In the absence of these minerals, organic compounds are completely degraded when subjected directly to UV photolysis equivalent to only 5 Martian day's exposure. However, similar UV exposure of organics dried from solution onto powdered calcium carbonate (calcite; CaCO3), calcium sulphate (anhydrite; CaSO4), clay-bearing Atacama dessert soil and 7 Å clay mineral kaolinite [Al2Si2O5(OH)4] results in only 1–2% loss of organics. Mixtures of purine and uracil with calcium carbonate exposed to gamma radiation of 3 Gy (3 Gray), which corresponds to approximately 15 000 days on Mars, results in up to 10% loss of organics. By contrast, these organic compounds completely decomposed upon mixing with iron oxide (Fe2O3) before UV irradiation. As the search for extinct or extant life on Mars has been identified as a goal of top priority in NASA's Mars Exploration Program and continues with several missions planned to the red planet by both NASA and the European Space Agency (ESA) in the next few decades, our findings may play a useful role in identifying optimal target sites on the Martian surface for future missions. Copyright © Cambridge University Press 2016


Frantz J.A.,U.S. Navy | Myers J.D.,U.S. Navy | Bekele R.Y.,University Research Foundation | Busse L.E.,U.S. Navy | Sanghera J.S.,U.S. Navy
Progress in Photovoltaics: Research and Applications | Year: 2016

We describe microstructured ZnO coatings that improve photovoltaic (PV) device performance through their antireflective properties and their tendency to scatter incoming light at large angles. In many PV devices, reflection from the transparent conductive top contact significantly degrades performance. Traditional quarter-wave antireflective (AR) coatings reduce surface reflection but perform optimally for only a narrow spectral range and incident illumination angle. Furthermore, in some types of devices, absorption far from the junction increases the rate of recombination, and light management strategies are required to remedy this. The randomly patterned, microstructured ZnO coatings described in this paper, formed via a simple wet etch process, serve as both an AR layer with superior performance to that of a thin film AR coating alone as well as a large angle forward scatterer. We model formation of the coatings and evaluate their AR properties. When combined with a traditional quarter-wave MgF2 coating, these microstructured ZnO coatings increase short circuit currents of example Cu(In,Ga)Se2 (CIGS) devices by over 20% in comparison to those of uncoated devices at normal incidence. A similar improvement is observed for illumination angles of up to 60°. While demonstrated here for CIGS, these structures may prove useful for other PV technologies as well. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Progress in Photovoltaics: Research and Applications Published by John Wiley & Sons Ltd. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Progress in Photovoltaics: Research and Applications Published by John Wiley & Sons Ltd.


Gattass R.R.,U.S. Navy | Kung F.H.,University Research Foundation | Busse L.E.,U.S. Navy | Shaw L.B.,U.S. Navy | Sanghera J.S.,U.S. Navy
Optical Engineering | Year: 2014

The bending loss is a critical parameter for packaging, representing a limiting parameter in the minimization of fiber-based devices. For applications in the midinfrared spectral band, chalcogenide glass optical fibers are one of the few alternatives for high-power beam delivery. We present experimental results for the bending loss of a sulfide-based multimode chalcogenide fiber for a broad range of infrared wavelengths as well demonstrating 5.8 W power handling for a 6.25-mm radius bend. © The Authors.


Thapa R.,Sotera Defense Solutions | Gattass R.R.,U.S. Navy | Nguyen V.,U.S. Navy | Chin G.,University Research Foundation | And 4 more authors.
Optics Letters | Year: 2015

We demonstrate a low-loss, repeatable, and robust splice between single-mode silica fiber and single-mode chalcogenide (CHG) fiber. These splices are particularly difficult to create because of the significant difference in the two fibers' glass transition temperatures (∼1000°C) as well as the large difference in the coefficients of thermal expansion between the fibers (∼20 × 10-6 /°C). With 90% light coupled through the silica-CHG fiber splice, predominantly in the fundamental circular-symmetric mode, into the core of the CHG fiber and with 0.5 dB of splice loss measured around the wavelength of 2.5 μm, after correcting only for the Fresnel loss, the silica-CHG splice offers excellent beam quality and coupling efficiency. The tensile strength of the splice is greater than 12 kpsi, and the laser damage threshold is greater than 2 W (CW) and was limited by the available laser pump power. We also utilized this splicing technique to demonstrate 2 to 4.5 μm ultrabroadband supercontinuum generation in a monolithic all-fiber system comprising a CHG fiber and a high peak power 2 μm pulsed Raman-shifted thulium fiber laser. This is a major development toward compact form factor commercial applications of soft-glass mid-IR fibers. © 2015 Optical Society of America.


Tennyson E.M.,University of Maryland University College | Garrett J.L.,University of Maryland University College | Frantz J.A.,U.S. Navy | Myers J.D.,U.S. Navy | And 4 more authors.
Advanced Energy Materials | Year: 2015

A novel imaging platform to determine the open-circuit voltage of solar cells with nanoscale spatial resolution is presented. Here, a variant of illuminated Kelvin probe force microscopy can be implemented to quantify local variations in the voltage of different solar cells. The new metrology can be applied to any optoelectronic device, and works in ambient environments. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


MacK J.P.,University Research Foundation | Horton T.U.,University of Maryland University College | Astar W.,University of Maryland Baltimore County | Ritter K.J.,University of Maryland University College | Carter G.M.,University of Maryland Baltimore County
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2012

We demonstrate all-optical wavelength conversion of four channels of polarization scrambled 10 Gb/s dense wavelength division multiplexed signals consisting of both nonreturn-to-zero-ON-OFF-keyed and differential-phase-shift keyed signals using 20m of nonlinear birefringent photonic crystal fiber (PCF). Power penalties <0.5 dB were achieved for a conversion bandwidth of 22 nm with four-wave mixing efficiencies between 20 and 24 dB. A rack-mount wavelength converter prototype is presented that consists of a highly tunable sample grating distributed Bragg reflector pump laser, a high-power erbium-doped fiber amplifier, a tunable bandpass filter, and a polarization controller that are all controlled using a microcontroller. Automatic polarization control of the high-power pump is demonstrated for the first time using the polarization dependence of stimulated Brillouin scattering in the PCF as a feedback mechanism. © 2011 IEEE.


Bayya S.,U.S. Navy | Villalobos G.,U.S. Navy | Kim W.,U.S. Navy | Sanghera J.,U.S. Navy | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

There are several military or commercial systems operating in very harsh environments that require rugged windows. On some of these systems, windows become the single point of failure. These applications include sensor or imaging systems, high-energy laser weapons systems, submarine photonic masts, IR countermeasures and missiles. Based on the sea or land or air based platforms the window or dome on these systems must withstand wave slap, underwater or ground based explosions, or survive flight through heavy rain and sand storms while maintaining good optical transmission in the desired wavelength range. Some of these applications still use softer ZnS or fused silica windows because of lack of availability of rugged materials in shapes or sizes required. Sapphire, ALON and spinel are very rugged materials with significantly higher strengths compared to ZnS and fused silica. There have been recent developments in spinel, ALON and sapphire materials to fabricate in large sizes and conformal shapes. We have been developing spinel ceramics for several of these applications. We are also developing β-SiC as a transparent window material as it has higher hardness, strength, and toughness than sapphire, ALON and spinel. This paper gives a summary of our recent findings. © 2014 SPIE.


PubMed | University Research Foundation and U.S. Navy
Type: Journal Article | Journal: Chemical communications (Cambridge, England) | Year: 2016

A novel method combining elemental sulfur and selenium was developed, yielding crystalline sulfur-selenium compounds. The compounds were melted, and an organic comonomer added. Once the organic comonomer was consumed, the viscous compound was vitrified and allowed to cool yielding organic-inorganic hybrid polymers that are termed Organically Modified Chalcogenide (ORMOCHALC) polymers.

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