Remote sensing systems operating in the short-wave infrared (SWIR) wavelengths require high bandwidth (>1 GHz) and sensitive (fW/root Hz) photoreceivers that operate at room temperature or TE cooled temperatures. HgCdTe avalanche photodiode (APD) based receivers offer high sensitivity at low bandwidths (<100 MHz) due to low excess noise (k similar to 0.01), but they need to operate at 77K. On the other hand, InGaAs APD receivers offer high bandwidth (>1GHz), near room temperature operation but the sensitivity is limited by the high excess noise. Recently a group from University of Virginia, demonstrated InAlAsSb digital alloy APDs operating in the 1-2 mu m wavelengths with a very low excess noise, equivalent to silicon APDs. With a digital-alloy In0.3Al0.7AsSb multiplier, the excess noise is similar to that of Si APDs and the impact ionization parameter k is about 0.05 at gains >10. Using this digital alloy detector technology, our modeling calculations show that a noise equivalent power (NEP) comparable to HgCdTe APD receivers can be achieved at TE-cooled temperatures. We have designed and developed a 1 GHz receiver operating at -30 degrees C using the InAlAsSb digital alloy APD designed for 2 mu m wavelength operation. We measured an NEP of 600 fW/root Hz at 1.5 mu m wavelength. In this presentation, we will present the receiver design and characterization results and modeling data to show the potential to achieve high sensitivity comparable to HgCdTe and Si receivers.

Science communication and outreach are essential for training the next generation of scientists and raising public awareness for science. Providing effective science, technology, engineering, and mathematics (STEM) educational outreach to students in classrooms is challenging because of the need to form partnerships with teachers, the time commitment required for the presenting scientist, and the limited class time allotted for presentations. In our Present Your Ph.D. Thesis to a 12-Year Old outreach project, our novel solution to this problem is hosting a youth science workshop (YSW) on our university campus. The YSW is an interpersonal science communication and outreach experience in which graduate students from diverse scientific disciplines introduce middle and high school students to their cutting-edge research and mentor them to develop a white-board presentation to communicate the research to the workshop audience. Our assessment of the YSW indicated that participating young students expressed significantly more positive attitudes toward science and increased motivation to work in a STEM career after attending the workshop. Qualitative follow-up interviews with participating graduate students' show that even with minimal time commitment, an impactful science communication training experience can be achieved. The YSW is a low-cost, high-reward educational outreach event amenable to all disciplines of science. It enhances interest and support of basic science research while providing opportunities for graduate students to engage with the public, improve their science communication skills, and enhance public understanding of science. This YSW model can be easily implemented at other higher education institutions to globally enhance science outreach initiatives.

The unprecedented wide bandgap tunability (∼1 eV) of AlxIn1-xAsySb1-y lattice-matched to GaSb enables the fabrication of photodetectors over a wide range from near-infrared to mid-infrared. In this paper, the valence band-offsets in AlxIn1-xAsySb1-y with different Al compositions are analyzed by tight binding calculations and X-ray photoelectron spectroscopy measurements. The observed weak variation in valence band offsets is consistent with the lack of any minigaps in the valence band, compared to the conduction band.

In this letter, we report optical pump terahertz (THz) near-field probe (n-OPTP) and optical pump THz near-field emission (n-OPTE) experiments of graphene/InAs heterostructures. Near-field imaging contrasts between graphene and InAs using these newly developed techniques as well as spectrally integrated THz nano-imaging (THz s-SNOM) are systematically studied. We demonstrate that in the near-field regime (λ/6000), a single layer of graphene is transparent to near-IR (800 nm) optical excitation and completely "screens" the photo-induced far-infrared (THz) dynamics in its substrate (InAs). Our work reveals unique frequency-selective ultrafast dynamics probed at the near field. It also provides strong evidence that n-OPTE nanoscopy yields contrast that distinguishes single-layer graphene from its substrate.

We present a solution to the challenges of interfacing the ELT's METIS to the telescope using a steerable hexapod structure. To guide the architectural choices, lumped physical models were derived from inverse kinematics in order to address the load distribution in each arm. Complete FE Analysis is carried on the optimal solutions of these models. The hexapod arms, which are high precision heavy duty linear actuators enduring forces in the excess of 30 tons, are designed using standard components whenever possible. An overall fully functional support structure design, satisfying the ESO/ELT and METIS requirements, is described.

We present the design and measured performance of the Aperture Wheel and the Pupil and Filter Wheel mechanisms for the NIX camera of the VLT/ERIS instrument. Both mechanisms were developed for high opto-mechanical precision and stability while operating at 70 K. We summarise the design constraints and considerations. Further, we have developed a dedicated cryo-test facility to allow measuring the position repeatability under nominal operational conditions. We demonstrate that the wheel mechanisms perform as designed and provide the measurement methodology and results of the opto-mechanical tolerances.

We describe the molecular beam epitaxial growth, characterization, and device performance of conventional, staircase, and photoconductive avalanche photodetectors grown with AlInAsSb digital alloys. In particular, this is the first low-noise III-V avalanche photodiode alloy family and offers the band engineering flexibility necessary to achieve staircase avalanche photodiode operation.

We report the design and operation of a nonlinear intersubband polaritonic metasurface for mid-infrared second harmonic generation. The metasurface is made of plasmonic nanoresonators filled with a multiple-quantum-well semiconductor heterostructure. Unlike the previously reported nonlinear intersubband polaritonic metasurfaces that employ full-metal backplanes below the etched metal–semiconductor nanoresonators, the metasurface reported here employs an incomplete backplane that is complementary to the pattern of the top metallization of the etched semiconductor heterostructure nanoresonators. The new approach produces high-electric-field localization and enhancement in the nanoresonators, while requiring simplified fabrication and allowing the metasurface to operate in both transmission and reflection regimes.

A nonlinear intersubband polaritonic metasurface designed for difference-frequency generation that provides a practical level of nonlinear response under continuous wave illumination is reported. An effective nonlinear susceptibility of up to 340 nm V-1 is measured experimentally. Approximately 0.3% of = 5.4 mu m photons are downconverted to lambda = 12.9 mu m photons at the focal spot in the experiment. This work indicates that the ultrathin metasurface devices may provide a versatile nonlinear element for frequency down- and upconversion in a relatively broad spectral range and without phase-matching constrains of traditional bulk nonlinear crystals.

Within the VLT instrumentation program, the second generation instrument ERIS (Enhanced Resolution Imager and Spectrograph) combines two key scientifically successful elements of the VLT first generation instrumentation program: It consists of a full renovation of the integral field spectrograph SPIFFI and a new near-IR camera NIX, implementing the most scientifically important imaging modes offered so far by NACO (imaging in the J to M bands, astrometry, Sparse Aperture Masking and Apodizing Phase Plate (APP) coronagraphy).Both diffraction limited sub-systems of ERIS make use of the latest AO technologies with the newly installed AOF (AO Facility) Deformable Secondary Mirror with 1170 actuators and a new laser guide star system.We will describe the changes that will be implemented, give a summary of what SINFONI is currently achieving, and present what to expect from the performance upgrade.With instruments becoming more complex and therefore increasing development times, we describe the challenges to improve image quality, spectral and spatial resolution on the same focus of a VLT UT, which could become valuable lessons for the extension of the life of actual instruments and of future ones.We will address the impact of the aging of the instrument and what critical parts to consider in the design in view of future upgrades, to possibly extend the performances, capabilities and lifetime at lower development costs.

ERIS will be the next-generation AO facility on the VLT, combining the heritage of NACO imaging, with the spectroscopic capabilities of an upgraded SINFONI. Here we report on the all-new NIX imager that will deliver diffraction-limited imaging from the J to M band. The instrument will be equipped with both Apodizing Phase Plates and Sparse Aperture Masks to provide high-angular resolution imagery, especially suited for exoplanet imaging and characterization. This paper provides detail on the instrument’s design and how it is suited to address a broad range of science cases, from detailed studies of the galactic centre at the highest resolutions, to studying detailed resolved stellar populations.

The main coils of the new European DIPOle (EDIPO) test facility, which is able to provide a background magnetic field up to 12.35 T, were commissioned at the Center for Research in Plasma Physics in July 2013. A field homogeneity of +/-1% was achieved over a 900-mm length, as compared to SULTAN's 10.9 T over 425 mm. To complete the commissioning of the test facility, the new superconducting transformer has been operated in 2015, and a high-current NbTi sample, which was earlier tested in the SULTAN test facility, has been tested in EDIPO under the same conditions as in SULTAN to benchmark the results. During the initial commissioning of the 100-kA transformer in 2013, the primary coil was found to be insufficiently cooled due to the debonding of the primary winding from its former that also served as the liquid helium cryostat. The NbTi primary coil was therefore modified to be in direct contact with liquid helium. At the next attempt of commissioning, in March 2014, a mechanical failure due to the imperfect alignment of the primary and secondary windings caused major damage. A replacement primary coil, which was wound in Summer 2014, was used in the third commissioning campaign in November 2014, but it failed due to the poor impregnation of the NbTi winding. Eventually, the original primary winding was repaired and commissioned in April 2015. The commissioning included a calibration of the current meter for the secondary winding and the high-current test, i.e., up to 95 kA at various background fields, of the “Trasek” conductor sample, which is a rectangular cable-in-conduit conductor made of 324 SnAg-coated NbTi strands. An excellent agreement was found between the results obtained from the two facilities. The sample holder unit is also equipped with a high-temperature superconducting (HTS) adapter and a counterflow heat exchanger to allow testing in EDIPO of HTS high-current samples over a broad range of operating temperatures, from 4.5 up to 50 K.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTStabilization of a Metastable Fibrous Bi21.2(1)(Mn1–xCox)20 Phase with Pseudo-Pentagonal Symmetry Prepared Using a Bi Self-FluxSrinivasa Thimmaiah*†, Valentin Taufour†§, Scott Saunders§, Stephen March§, Yuemei Zhang‡, Matthew J. Kramer†∥, Paul C. Canfield†§, and Gordon J. Miller†‡View Author Information† The Ames Laboratory, U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, United States‡ Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States§ Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, United States∥ Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, United States*S. Thimmaiah. E-mail: [email protected]Cite this: Chem. Mater. 2016, 28, 23, 8484–8488Publication Date (Web):November 15, 2016Publication History Received21 October 2016Revised15 November 2016Published online17 November 2016Published inissue 13 December 2016https://pubs.acs.org/doi/10.1021/acs.chemmater.6b04505https://doi.org/10.1021/acs.chemmater.6b04505rapid-communicationACS PublicationsCopyright © 2016 American Chemical SocietyRequest reuse permissionsArticle Views454Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Crystal structure,Crystals,Energy,Group theory,Transition metals Get e-Alerts

The ITER Toroidal Field (TF) coil winding packs are designed to be wound in double-pancakes. The twin-box joint provides the electrical pancake-to-pancake connection between the two Nb3Sn 68 kA conductors and electrical coil-to-bus bar connection between the IF coil terminations and NbTi 68 kA bus bars conductors.The twin-box full size joint sample connecting two Nb3Sn conductors (pancake-to-pancake joint) was prepared in order to qualify the TF joint assembly in SULTAN Test Facility. The original goal of the test program was the measurement of joint resistance at different operating conditions. The accidental dump of the SULTAN background field caused a noticeable increase of resistance due to the induced electromagnetic transient load. The TF joint test was continued in order to investigate a change of joint resistance following electromagnetic transient loading which was triggered by intentional dump of the background field. Also, a dependence of the joint resistance on current was observed; in order to explore the origin of resistance change, additional experiments were performed with a modified (artificially degraded) TF twin-box joint.The test results of a TF twin-box joint after electromagnetic transient loading and performance of the joint after a modification are presented in this paper. The performance of Nb3Sn 68 kA conductor observed during those tests is highlighted as well. (C) 2015 Elsevier B.V. All rights reserved.

The Iter TF joints are of a twin-box design and the critical parameters of the overall resistance are 1) the contact between cable and termination, and 2) the resistance between two terminations. This paper describes applicability of non-destructive examination (NDE) to these joints. The TFEU joint was adapted to make the joint demountable and the contact area was artificially degraded. The TFEU Joint was measured in the range 30-70 kA, 0-6 T. With no artificial degradation, the resistance of the TFEU Joint was measured to be better than the inter-pancake criterion of 3 nΩ at 2 T, 68 kA. At high fields (6 T) the voltage-current (V I) characteristic of the joint is nonlinear and the resistance is higher than expected. The nonlinearity is worse when the joint is artificially degraded. An FEA model was used to demonstrate that the magneto-resistant copper's contribution to the overall joint resistance is low (<; ~1 nΩ) and does not explain the high field behavior. The nonlinear V I behavior is due to poor current redistribution within the joint, which is related to the resistance of the strand-bundle to copper interface. CRPP is developing a room temperature NDE technique based on resistance profiles to investigate this interface. Resistance measurements at low current and field, or high current and low field, do not guarantee performance at high field; joint tests under the operating conditions are required. Tests on the upper terminations of the TFEU Joint showed that large defects in the contact area between two terminations could be tolerated, when the joint has a good strand-bundle to copper contact resistance and effective current redistribution.

The article addresses the possibility of alloy elements in MnBi which may modify the thermodynamic stability of the NiAs-type structure without significantly degrading the magnetic properties. The addition of small amounts of Rh and Mn provides an improvement in the thermal stability with some degradation of the magnetic properties. The small amounts of Rh and Mn additions in MnBi stabilize an orthorhombic phase whose structural and magnetic properties are closely related to the ones of the previously reported high-temperature phase of MnBi (HT~MnBi). To date, the properties of the HT~MnBi, which is stable between $613$ and $719$~K, have not been studied in detail because of its transformation to the stable low-temperature MnBi (LT~MnBi), making measurements near and below its Curie temperature difficult. The Rh-stabilized MnBi with chemical formula Mn$_{1.0625-x}$Rh$_{x}$Bi [$x=0.02(1)$] adopts a new superstructure of the NiAs/Ni$_2$In structure family. It is ferromagnetic below a Curie temperature of $416$~K. The critical exponents of the ferromagnetic transition are not of the mean-field type but are closer to those associated with the Ising model in three dimensions. The magnetic anisotropy is uniaxial; the anisotropy energy is rather large, and it does not increase when raising the temperature, contrary to what happens in LT~MnBi. The saturation magnetization is approximately $3$~$\mu_B$/f.u. at low temperatures. While this exact composition may not be application ready, it does show that alloying is a viable route to modifying the stability of this class of rare-earth-free magnet alloys.

The EDIPO test facility is erected at CRPP Villigen with the aim of providing a flexible, high field test bed for high current force flow superconductors. The EDIPO main coil is a tilted-head race-track pair wound by a graded Nb3Sn cable-in-conduit conductor. The whole project, partly funded by the European Commission, started in 2004 and entered the commissioning phase in 2013. The final steps of instrumentation and installation of the main coil, delivered by industry in May 2011, lasted about 18 months. The first cool-down of the facility started in November 2012. The commissioning of the main coil, including the precise measurement of the generated magnetic field, was carried out in March 2013. At an operating current of 17.2 kA, a ± 1% homogenous field of 12.35 T was generated over a length of 900 mm in the center of the test well, 140 mm × 91 mm in cross section. Details about cool-down, flux jumps, forces and displacements, field map, and charging rate are presented in this paper.

In spring 2013, the Edipo facility of CRPP was commissioned. The dipole is powered via two 18 kA HTS current leads, designed and manufactured at CRPP. As part of the Edipo commissioning framework, the operational parameters of the leads were implemented in the control system. The in-situ tests were found to be in good agreement with the tests performed without a background field in 2011. The leads consist of a conduction cooled HTS module, made of AgMgAu/Bi-2223 stacks, and a wire bundle heat exchanger. The heat exchanger is cooled by forced flow helium gas, the inlet temperature of which was measured to vary between 65 K and 85 K. During operation with field, the mass flow rate is a function of current (2.05 g/s per lead at full field, 12.35 T, 17.2 kA). Reduced cooling investigations showed that 0.31 g/s per lead is suitable for overnight standby and 0.2 g/s per lead for longer periods. For detection of and protection against quench in the HTS module, a threshold of 10 mV was found to be appropriate. The heat exchanger has a voltage protection threshold of 120 mV. The temperatures of the heat exchanger, the HTS, and the helium inlet temperature were monitored in order to provide a further layer of protection.

In the framework of a collaboration, CRPP (Centre de Recherches en Physique des Plasmas) and WEKA AG have developed high-temperature superconductor (HTS) current leads for currents in the range of 3 to 30 kA, which are suitable for industrial fabrication. In the development project, two 10 kA HTS current leads, mainly distinguished by the design of the copper heat exchanger and the transition zone between the HTS module and the heat exchanger, have been manufactured by WEKA AG and tested at CRPP. The test of the current leads covered their behavior under normal operating conditions as well as in the case of a loss of flow. Furthermore, a quench of the current leads was initiated by increasing of the helium temperature by means of heaters immediately before the inlet. The measured quench temperatures provide an estimate of the operational limits of the 10 kA HTS current leads.