Clocking Femtosecond Collisional Dynamics via Resonant X-Ray Spectroscopy

NASA Astrophysics Data System (ADS)

van den Berg, Q. Y.; Fernandez-Tello, E. V.; Burian, T.; Chalupský, J.; Chung, H.-K.; Ciricosta, O.; Dakovski, G. L.; Hájková, V.; Hollebon, P.; Juha, L.; Krzywinski, J.; Lee, R. W.; Minitti, M. P.; Preston, T. R.; de la Varga, A. G.; Vozda, V.; Zastrau, U.; Wark, J. S.; Velarde, P.; Vinko, S. M.

2018-02-01

Electron-ion collisional dynamics is of fundamental importance in determining plasma transport properties, nonequilibrium plasma evolution, and electron damage in diffraction imaging applications using bright x-ray free-electron lasers (FELs). Here we describe the first experimental measurements of ultrafast electron impact collisional ionization dynamics using resonant core-hole spectroscopy in a solid-density magnesium plasma, created and diagnosed with the Linac Coherent Light Source x-ray FEL. By resonantly pumping the 1 s →2 p transition in highly charged ions within an optically thin plasma, we have measured how off-resonance charge states are populated via collisional processes on femtosecond time scales. We present a collisional cross section model that matches our results and demonstrates how the cross sections are enhanced by dense-plasma effects including continuum lowering. Nonlocal thermodynamic equilibrium collisional radiative simulations show excellent agreement with the experimental results and provide new insight on collisional ionization and three-body-recombination processes in the dense-plasma regime.

Phonon spectroscopy with sub-meV resolution by femtosecond x-ray diffuse scattering

DOE PAGES

Zhu, Diling; Robert, Aymeric; Henighan, Tom; ...

2015-08-10

We present a reconstruction of the transverse acoustic phonon dispersion of germanium from femtosecond time-resolved x-ray diffuse scattering measurements at the Linac Coherent Light Source. We demonstrate an energy resolution of 0.3 meV with a momentum resolution of 0.01 nm -1 using 10-keV x rays with a bandwidth of ~ 1 eV. This high resolution was achieved simultaneously for a large section of reciprocal space including regions closely following three of the principal symmetry directions. The phonon dispersion was reconstructed with less than 3 h of measurement time, during which neither the x-ray energy, the sample orientation, nor the detectormore » position were scanned. In conclusion, these results demonstrate how time-domain measurements can complement conventional frequency domain inelastic-scattering techniques.« less

Liquid sample delivery techniques for serial femtosecond crystallography

PubMed Central

Weierstall, Uwe

2014-01-01

X-ray free-electron lasers overcome the problem of radiation damage in protein crystallography and allow structure determination from micro- and nanocrystals at room temperature. To ensure that consecutive X-ray pulses do not probe previously exposed crystals, the sample needs to be replaced with the X-ray repetition rate, which ranges from 120 Hz at warm linac-based free-electron lasers to 1 MHz at superconducting linacs. Liquid injectors are therefore an essential part of a serial femtosecond crystallography experiment at an X-ray free-electron laser. Here, we compare different techniques of injecting microcrystals in solution into the pulsed X-ray beam in vacuum. Sample waste due to mismatch of the liquid flow rate to the X-ray repetition rate can be addressed through various techniques. PMID:24914163

Simultaneous Femtosecond X-ray Spectroscopy and Diffraction of Photosystem II at Room Temperature

PubMed Central

Kern, Jan; Alonso-Mori, Roberto; Tran, Rosalie; Hattne, Johan; Gildea, Richard J.; Echols, Nathaniel; Glöckner, Carina; Hellmich, Julia; Laksmono, Hartawan; Sierra, Raymond G.; Lassalle-Kaiser, Benedikt; Koroidov, Sergey; Lampe, Alyssa; Han, Guangye; Gul, Sheraz; DiFiore, Dörte; Milathianaki, Despina; Fry, Alan R.; Miahnahri, Alan; Schafer, Donald W.; Messerschmidt, Marc; Seibert, M. Marvin; Koglin, Jason E.; Sokaras, Dimosthenis; Weng, Tsu-Chien; Sellberg, Jonas; Latimer, Matthew J.; Grosse-Kunstleve, Ralf W.; Zwart, Petrus H.; White, William E.; Glatzel, Pieter; Adams, Paul D.; Bogan, Michael J.; Williams, Garth J.; Boutet, Sébastien; Messinger, Johannes; Zouni, Athina; Sauter, Nicholas K.; Yachandra, Vittal K.; Bergmann, Uwe; Yano, Junko

2013-01-01

Intense femtosecond X-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous X-ray diffraction (XRD) and X-ray emission spectroscopy (XES) of microcrystals of Photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S1) and the first illuminated state (S2) of PS II. Our simultaneous XRD/XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies. PMID:23413188

Simultaneous femtosecond X-ray spectroscopy and diffraction of photosystem II at room temperature.

PubMed

Kern, Jan; Alonso-Mori, Roberto; Tran, Rosalie; Hattne, Johan; Gildea, Richard J; Echols, Nathaniel; Glöckner, Carina; Hellmich, Julia; Laksmono, Hartawan; Sierra, Raymond G; Lassalle-Kaiser, Benedikt; Koroidov, Sergey; Lampe, Alyssa; Han, Guangye; Gul, Sheraz; Difiore, Dörte; Milathianaki, Despina; Fry, Alan R; Miahnahri, Alan; Schafer, Donald W; Messerschmidt, Marc; Seibert, M Marvin; Koglin, Jason E; Sokaras, Dimosthenis; Weng, Tsu-Chien; Sellberg, Jonas; Latimer, Matthew J; Grosse-Kunstleve, Ralf W; Zwart, Petrus H; White, William E; Glatzel, Pieter; Adams, Paul D; Bogan, Michael J; Williams, Garth J; Boutet, Sébastien; Messinger, Johannes; Zouni, Athina; Sauter, Nicholas K; Yachandra, Vittal K; Bergmann, Uwe; Yano, Junko

2013-04-26

Intense femtosecond x-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous x-ray diffraction (XRD) and x-ray emission spectroscopy (XES) of microcrystals of photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S1) and the first illuminated state (S2) of PS II. Our simultaneous XRD-XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.

Performance of a first generation X-band photoelectron rf gun

DOE PAGES

Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.; ...

2016-05-04

Building more compact accelerators to deliver high brightness electron beams for the generation of high flux, highly coherent radiation is a priority for the photon science community. A relatively straightforward reduction in footprint can be achieved by using high-gradient X-band (11.4 GHz) rf technology. To this end, an X-band injector consisting of a 5.5 cell rf gun and a 1-m long linac has been commissioned at SLAC. It delivers an 85 MeV electron beam with peak brightness somewhat better than that achieved in S-band photoinjectors, such as the one developed for the Linac Coherent Light Source (LCLS). The X-band rfmore » gun operates with up to a 200 MV/m peak field on the cathode, and has been used to produce bunches of a few pC to 1.2 nC in charge. Notably, bunch lengths as short as 120 fs rms have been measured for charges of 5 pC (~3×10 7 electrons), and normalized transverse emittances as small as 0.22 mm-mrad have been measured for this same charge level. Bunch lengths as short as 400 (250) fs rms have been achieved for electron bunches of 100 (20) pC with transverse normalized emittances of 0.7 (0.35) mm-mrad. As a result, we report on the performance and the lessons learned from the operation and optimization of this first generation X-band gun.« less

Performance of a first generation X-band photoelectron rf gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.

Building more compact accelerators to deliver high brightness electron beams for the generation of high flux, highly coherent radiation is a priority for the photon science community. A relatively straightforward reduction in footprint can be achieved by using high-gradient X-band (11.4 GHz) rf technology. To this end, an X-band injector consisting of a 5.5 cell rf gun and a 1-m long linac has been commissioned at SLAC. It delivers an 85 MeV electron beam with peak brightness somewhat better than that achieved in S-band photoinjectors, such as the one developed for the Linac Coherent Light Source (LCLS). The X-band rfmore » gun operates with up to a 200 MV/m peak field on the cathode, and has been used to produce bunches of a few pC to 1.2 nC in charge. Notably, bunch lengths as short as 120 fs rms have been measured for charges of 5 pC (~3×10 7 electrons), and normalized transverse emittances as small as 0.22 mm-mrad have been measured for this same charge level. Bunch lengths as short as 400 (250) fs rms have been achieved for electron bunches of 100 (20) pC with transverse normalized emittances of 0.7 (0.35) mm-mrad. As a result, we report on the performance and the lessons learned from the operation and optimization of this first generation X-band gun.« less

Modulators for the S-band test linac at DESY

NASA Astrophysics Data System (ADS)

Bieler, M.; Choroba, S.; Hameister, J.; Lewin, H.-Ch.

1995-07-01

The development of adequate modulators for high peak power klystrons is one of the focus points for linear collider R&D programs. For the DESY/THD S-band linear collider study 150 MW rf-pulse power at 50 Hz repetition rate and 3 μs pulse duration is required [1]. Two different modulator schemes are under investigation. One is the conventional line type pulser, using a pulse forming network and a step up transformer, the other one is a hard tube pulser, using a dc power source at the full klystron voltage and a switch tube. This paper is focused on the modulator development for the S-band Test Linac at DESY. After a short overview over the test linac and a brief description of the 150 MW S-band klystron the circuitry of the line type pulse (LTP) is given. A hard tube pulser (HTP), which switches the high voltage directly from a storage capacitor to the klystron, has been built up at DESY. Circuitry and the results of the commissioning of the switch tube are reported.

Clocking Femtosecond Collisional Dynamics via Resonant X-Ray Spectroscopy

DOE PAGES

van den Berg, Q. Y.; Fernandez-Tello, E. V.; Burian, T.; ...

2018-02-01

Electron-ion collisional dynamics is of fundamental importance in determining plasma transport properties, nonequilibrium plasma evolution, and electron damage in diffraction imaging applications using bright x-ray free-electron lasers (FELs). Here in this paper, we describe the first experimental measurements of ultrafast electron impact collisional ionization dynamics using resonant core-hole spectroscopy in a solid-density magnesium plasma, created and diagnosed with the Linac Coherent Light Source x-ray FEL. By resonantly pumping the 1s → 2p transition in highly charged ions within an optically thin plasma, we have measured how off-resonance charge states are populated via collisional processes on femtosecond time scales. We presentmore » a collisional cross section model that matches our results and demonstrates how the cross sections are enhanced by dense-plasma effects including continuum lowering. Nonlocal thermodynamic equilibrium collisional radiative simulations show excellent agreement with the experimental results and provide new insight on collisional ionization and three-body-recombination processes in the dense-plasma regime.« less

Solid-State Powered X-band Accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Othman, Mohamed A.K.; Nann, Emilio A.; Dolgashev, Valery A.

2017-03-06

In this report we disseminate the hot test results of an X-band 100-W solid state amplifier chain for linear accelerator (linac) applications. Solid state power amplifiers have become increasingly attractive solutions for achieving high power in radar and maritime applications. Here the performance of solid state amplifiers when driving an RF cavity is investigated. Commercially available, matched and fully-packaged GaN on SiC HEMTs are utilized, comprising a wideband driver stage and two power stages. The amplifier chain has a high poweradded- efficiency and is able to supply up to ~1.2 MV/m field gradient at 9.2 GHz in a simple testmore » cavity, with a peak power exceeding 100 W. These findings set forth the enabling technology for solid-state powered linacs.« less

Femtosecond time-resolved X-ray absorption spectroscopy of anatase TiO2 nanoparticles using XFEL

PubMed Central

Obara, Yuki; Ito, Hironori; Ito, Terumasa; Kurahashi, Naoya; Thürmer, Stephan; Tanaka, Hiroki; Katayama, Tetsuo; Togashi, Tadashi; Owada, Shigeki; Yamamoto, Yo-ichi; Karashima, Shutaro; Nishitani, Junichi; Yabashi, Makina; Suzuki, Toshinori; Misawa, Kazuhiko

2017-01-01

The charge-carrier dynamics of anatase TiO2 nanoparticles in an aqueous solution were studied by femtosecond time-resolved X-ray absorption spectroscopy using an X-ray free electron laser in combination with a synchronized ultraviolet femtosecond laser (268 nm). Using an arrival time monitor for the X-ray pulses, we obtained a temporal resolution of 170 fs. The transient X-ray absorption spectra revealed an ultrafast Ti K-edge shift and a subsequent growth of a pre-edge structure. The edge shift occurred in ca. 100 fs and is ascribed to reduction of Ti by localization of generated conduction band electrons into shallow traps of self-trapped polarons or deep traps at penta-coordinate Ti sites. Growth of the pre-edge feature and reduction of the above-edge peak intensity occur with similar time constants of 300–400 fs, which we assign to the structural distortion dynamics near the surface. PMID:28713842

Femtosecond Structural Dynamics Drives the Trans/Cis Isomerization in Photoactive Yellow Protein

PubMed Central

Pande, Kanupriya; Hutchison, Christopher D. M.; Groenhof, Gerrit; Aquila, Andy; Robinson, Josef S.; Tenboer, Jason; Basu, Shibom; Boutet, Sébastien; DePonte, Daniel P.; Liang, Mengning; White, Thomas A.; Zatsepin, Nadia A.; Yefanov, Oleksandr; Morozov, Dmitry; Oberthuer, Dominik; Gati, Cornelius; Subramanian, Ganesh; James, Daniel; Zhao, Yun; Koralek, Jake; Brayshaw, Jennifer; Kupitz, Christopher; Conrad, Chelsie; Roy-Chowdhury, Shatabdi; Coe, Jesse D.; Metz, Markus; Xavier, Paulraj Lourdu; Grant, Thomas D.; Koglin, Jason E.; Ketawala, Gihan; Fromme, Raimund; Šrajer, Vukica; Henning, Robert; Spence, John C. H.; Ourmazd, Abbas; Schwander, Peter; Weierstall, Uwe; Frank, Matthias; Fromme, Petra; Barty, Anton; Chapman, Henry N.; Moffat, Keith; van Thor, Jasper J.; Schmidt, Marius

2017-01-01

A variety of organisms have evolved mechanisms to detect and respond to light, in which the response is mediated by protein structural changes following photon absorption. The initial step is often the photo-isomerization of a conjugated chromophore. Isomerization occurs on ultrafast timescales, and is substantially influenced by the chromophore environment. Here we identify structural changes associated with the earliest steps in the trans to cis isomerization of the chromophore in photoactive yellow protein. Femtosecond, hard X-ray pulses emitted by the Linac Coherent Light Source were used to conduct time-resolved serial femtosecond crystallography on PYP microcrystals over the time range from 100 femtoseconds to 3 picoseconds to determine the structural dynamics of the photoisomerization reaction. PMID:27151871

Two mirror X-ray pulse split and delay instrument for femtosecond time resolved investigations at the LCLS free electron laser facility

DOE PAGES

Berrah, Nora; Fang, Li; Murphy, Brendan F.; ...

2016-05-20

We built a two-mirror based X-ray split and delay (XRSD) device for soft X-rays at the Linac Coherent Light Source free electron laser facility. The instrument is based on an edge-polished mirror design covering an energy range of 250 eV-1800 eV and producing a delay between the two split pulses variable up to 400 femtoseconds with a sub-100 attosecond resolution. We present experimental and simulation results regarding molecular dissociation dynamics in CH3I and CO probed by the XRSD device. In conclusion, we observed ion kinetic energy and branching ratio dependence on the delay times which were reliably produced by themore » XRSD instrument.« less

The LLRF System for the S-Band RF Plants of the FERMI Linac

NASA Astrophysics Data System (ADS)

Fabris, A.; Byrd, J.; D'Auria, G.; Doolittle, L.; Gelmetti, F.; Huang, G.; Jones, J.; Milloch, M.; Predonzani, M.; Ratti, A.; Rohlev, T.; Salom, A.; Serrano, C.; Stettler, M.

2016-04-01

Specifications on electron beam quality for the operation of a linac-based free-electron laser (FEL), as FERMI in Trieste (Italy), impose stringent requirements on the stability of the electromagnetic fields of the accelerating sections. These specifications can be met only with state-of-the-art low-level RF (LLRF) systems based on advanced digital technologies. Design considerations, construction, and performance results of the FERMI digital LLRF are presented in this paper. The stability requirements derived by simulations are better than 0.1% in amplitude and 0.1° S-band in phase. The system installed in the FERMI Linac S-band RF plants has met these specifications and is in operation on a 24-h basis as a user facility. Capabilities of the system allow planning for new developments that are also described here.

Goniometer-based femtosecond X-ray diffraction of mutant 30S ribosomal subunit crystals

DOE PAGES

Dao, E. Han; Sierra, Raymond G.; Laksmono, Hartawan; ...

2015-04-30

In this work, we collected radiation-damage-free data from a set of cryo-cooled crystals for a novel 30S ribosomal subunit mutant using goniometer-based femtosecond crystallography. Crystal quality assessment for these samples was conducted at the X-ray Pump Probe end-station of the Linac Coherent Light Source (LCLS) using recently introduced goniometer-based instrumentation. These 30S subunit crystals were genetically engineered to omit a 26-residue protein, Thx, which is present in the wild-type Thermus thermophilus 30S ribosomal subunit. We are primarily interested in elucidating the contribution of this ribosomal protein to the overall 30S subunit structure. To assess the viability of this study, femtosecondmore » X-ray diffraction patterns from these crystals were recorded at the LCLS during a protein crystal screening beam time. During our data collection, we successfully observed diffraction from these difficult-to-grow 30S ribosomal subunit crystals. Most of our crystals were found to diffract to low resolution, while one crystal diffracted to 3.2 Å resolution. These data suggest the feasibility of pursuing high-resolution data collection as well as the need to improve sample preparation and handling in order to collect a complete radiation-damage-free data set using an X-ray Free Electron Laser.« less

Design and experiments of RF transverse focusing in S-Band, 1 MeV standing wave linac

NASA Astrophysics Data System (ADS)

Mondal, J.; Chandan, Shiv; Parashar, S.; Bhattacharjee, D.; Tillu, A. R.; Tiwari, R.; Jayapraksh, D.; Yadav, V.; Banerjee, S.; Choudhury, N.; Ghodke, S. R.; Dixit, K. P.; Nimje, V. T.

2015-09-01

S-Band standing wave (SW) linacs in the range of 1-10 MeV have many potential industrial applications world wide. In order to mitigate the industrial requirement it is required to reduce the overall size and weight of the system. On this context a 2856 M Hz, 1 Me V, bi-periodic on axis coupled self transverse focused SW linac has been designed and tested. The RF phase focusing is achieved by introducing an asymmetric field distribution in the first cell of the 1 MeV linac. The pulsed electron beam of 40 keV, 650 mA and 5 μs duration is injected from a LaB6 thermionic gun. This paper presents the structure design, beam dynamics simulation, fabrication and experimental results of the 1 MeV auto-focusing SW linac.

Demonstration of simultaneous experiments using thin crystal multiplexing at the Linac Coherent Light Source

DOE PAGES

Feng, Y.; Alonso-Mori, R.; Barends, T. R. M.; ...

2015-04-10

Multiplexing of the Linac Coherent Light Source beam was demonstrated for hard X-rays by spectral division using a near-perfect diamond thin-crystal monochromator operating in the Bragg geometry. The wavefront and coherence properties of both the reflected and transmitted beams were well preserved, thus allowing simultaneous measurements at two separate instruments. In this report, the structure determination of a prototypical protein was performed using serial femtosecond crystallography simultaneously with a femtosecond time-resolved XANES studies of photoexcited spin transition dynamics in an iron spin-crossover system. The results of both experiments using the multiplexed beams are similar to those obtained separately, using amore » dedicated beam, with no significant differences in quality.« less

An Overview of the MaRIE X-FEL and Electron Radiography LINAC RF Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bradley, Joseph Thomas III; Rees, Daniel Earl; Scheinker, Alexander

The purpose of the Matter-Radiation Interactions in Extremes (MaRIE) facility at Los Alamos National Laboratory is to investigate the performance limits of materials in extreme environments. The MaRIE facility will utilize a 12 GeV linac to drive an X-ray Free-Electron Laser (FEL). Most of the same linac will also be used to perform electron radiography. The main linac is driven by two shorter linacs; one short linac optimized for X-FEL pulses and one for electron radiography. The RF systems have historically been the one of the largest single component costs of a linac. We will describe the details of themore » different types of RF systems required by each part of the linacs. Starting with the High Power RF system, we will present our methodology for the choice of RF system peak power and pulselength with respect to klystron parameters, modulator parameters, performance requirements and relative costs. We will also present an overview of the Low Level RF systems that are proposed for MaRIE and briefly describe their use with some proposed control schemes.« less

Band alignment at the Cu2ZnSn(SxSe1-x)4/CdS interface

NASA Astrophysics Data System (ADS)

Haight, Richard; Barkhouse, Aaron; Gunawan, Oki; Shin, Byungha; Copel, Matt; Hopstaken, Marinus; Mitzi, David B.

2011-06-01

Energy band alignments between CdS and Cu2ZnSn(SxSe1-x)4 (CZTSSe) grown via solution-based and vacuum-based deposition routes were studied as a function of the [S]/[S+Se] ratio with femtosecond laser ultraviolet photoelectron spectroscopy, photoluminescence, medium energy ion scattering, and secondary ion mass spectrometry. Band bending in the underlying CZTSSe layer was measured via pump/probe photovoltage shifts of the photoelectron spectra and offsets were determined with photoemission under flat band conditions. Increasing the S content of the CZTSSe films produces a valence edge shift to higher binding energy and increases the CZTSSe band gap. In all cases, the CdS conduction band offsets were spikes.

The X-ray Pump-Probe instrument at the Linac Coherent Light Source.

PubMed

Chollet, Matthieu; Alonso-Mori, Roberto; Cammarata, Marco; Damiani, Daniel; Defever, Jim; Delor, James T; Feng, Yiping; Glownia, James M; Langton, J Brian; Nelson, Silke; Ramsey, Kelley; Robert, Aymeric; Sikorski, Marcin; Song, Sanghoon; Stefanescu, Daniel; Srinivasan, Venkat; Zhu, Diling; Lemke, Henrik T; Fritz, David M

2015-05-01

The X-ray Pump-Probe instrument achieves femtosecond time-resolution with hard X-ray methods using a free-electron laser source. It covers a photon energy range of 4-24 keV. A femtosecond optical laser system is available across a broad spectrum of wavelengths for generating transient states of matter. The instrument is designed to emphasize versatility and the scientific goals encompass ultrafast physical, chemical and biological processes involved in the transformation of matter and transfer of energy at the atomic scale.

Femtosecond Broad-Band Sum Frequency Generation Spectroscopy: Measurements of Ethanol Fuel Cell Catalysis

DTIC Science & Technology

2012-12-03

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing...Washington Headquarters Services, Directorate for Information Operations and Reports , 1215 Jefferson Davis Highway, Suite 1204, Arlington VA, 22202-4302... REPORT Femtosecond Broad-Band Sum Frequency Generation Spectroscopy: Measurements of Ethanol Fuel Cell Catalysis 14. ABSTRACT 16. SECURITY

Simulation studies of a XUV/soft X-ray harmonic-cascade FEL for the proposed LBNL recirculating linac*

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fawley, W.M.; Barletta, W.A.; Corlett, J.N.

Presently there is significant interest at LBNL in designing and building a facility for ultrafast (i.e. femtosecond time scale) x-ray science based upon a superconducting, recirculating RF linac (see Corlett et al. for more details). In addition to producing synchrotron radiation pulses in the 1-15 keV energy range, we are also considering adding one or more free-electron laser (FEL) beamlines using a harmonic cascade approach to produce coherent XUV soft X-ray emission beginning with a strong input seed at {approx}200 nm wavelength obtained from a ''conventional'' laser. Each cascade is composed of a radiator together with a modulator section, separatedmore » by a magnetic chicane. The chicane temporally delays the electron beam pulse in order that a ''virgin'' pulse region (with undegraded energy spread) be brought into synchronism with the radiation pulse, which together then undergo FEL action in the modulator. We present various results obtained with the GINGER simulation code examining final output sensitivity to initial electron beam parameters. We also discuss the effects of spontaneous emission and shot noise upon this particular cascade approach which can limit the final output coherence.« less

Development of new S-band SLED for PAL-XFEL Linac

NASA Astrophysics Data System (ADS)

Joo, Youngdo; Park, Yongjung; Heo, Hoon; Heo, Jinyul; Park, Sung-Soo; Kim, Sang-Hee; Kim, Kwang-Hoon; Kang, Heung-Sik; Lee, Heung-Soo; Noh, Sungju; Oh, Kyoungmin

2017-01-01

In order to achieve beam acceleration to the beam energy of 10 GeV at the end of its 716 m-long linear accelerator (Linac), the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) is going to operate the Stanford Linear Accelerator Energy Doubler (SLED) at the maximum klystron output peak power of 80 MW, with a pulse length of 4 μs, and at a repetition rate of 60 Hz. The original SLED that had been used in Pohang Light Source-II (PLS-II) can no longer sustain such a high-power operation because excessive radiation caused by RF breakdown has been frequently detected even at the lower klystron peak power during the PLS-II operation. Therefore, a new SLED is designed by modifying both the 3-dB power hybrid and the waveguide-cavity coupling structure of the original SLED where the excessive radiation has been mainly detected. The finite-difference time-domain (FDTD) simulation in the CST Microwave Studio shows that the new SLED has a peak electric field and a surface current lower than those of the original SLED at the same level of the RF input peak power, which would secure stable high-power operation. All of the 42 SLEDs in the PAL-XFEL Linac are newly fabricated and installed. During the RF conditioning of the PAL-XFEL Linac, no significant vacuum and radiation issue was found in the new SLEDs. Finally, the accelerated electron beam energy of 10 GeV obtained at the end of the PAL-XFEL Linac verified that the RF performance of the new SLED is stable.

Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics

PubMed Central

Picón, A.; Lehmann, C. S.; Bostedt, C.; Rudenko, A.; Marinelli, A.; Osipov, T.; Rolles, D.; Berrah, N.; Bomme, C.; Bucher, M.; Doumy, G.; Erk, B.; Ferguson, K. R.; Gorkhover, T.; Ho, P. J.; Kanter, E. P.; Krässig, B.; Krzywinski, J.; Lutman, A. A.; March, A. M.; Moonshiram, D.; Ray, D.; Young, L.; Pratt, S. T.; Southworth, S. H.

2016-01-01

New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site. PMID:27212390

Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics

DOE PAGES

Picón, A.; Lehmann, C. S.; Bostedt, C.; ...

2016-05-23

New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Specifically, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. In this paper, we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ionsmore » during the fragmentation of XeF 2 molecules following X-ray absorption at the Xe site.« less

Hetero-site-specific X-ray pump-probe spectroscopy for femtosecond intramolecular dynamics.

PubMed

Picón, A; Lehmann, C S; Bostedt, C; Rudenko, A; Marinelli, A; Osipov, T; Rolles, D; Berrah, N; Bomme, C; Bucher, M; Doumy, G; Erk, B; Ferguson, K R; Gorkhover, T; Ho, P J; Kanter, E P; Krässig, B; Krzywinski, J; Lutman, A A; March, A M; Moonshiram, D; Ray, D; Young, L; Pratt, S T; Southworth, S H

2016-05-23

New capabilities at X-ray free-electron laser facilities allow the generation of two-colour femtosecond X-ray pulses, opening the possibility of performing ultrafast studies of X-ray-induced phenomena. Particularly, the experimental realization of hetero-site-specific X-ray-pump/X-ray-probe spectroscopy is of special interest, in which an X-ray pump pulse is absorbed at one site within a molecule and an X-ray probe pulse follows the X-ray-induced dynamics at another site within the same molecule. Here we show experimental evidence of a hetero-site pump-probe signal. By using two-colour 10-fs X-ray pulses, we are able to observe the femtosecond time dependence for the formation of F ions during the fragmentation of XeF2 molecules following X-ray absorption at the Xe site.

Linac Coherent Light Source Undulator RF BPM System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lill, R.M.; Morrison, L.H.; Waldschmidt, G.J.

2007-04-17

The Linac Coherent Light Source (LCLS) will be the world's first x-ray free-electron laser (FEL) when it becomes operational in 2009. The LCLS is currently in the construction phase. The beam position monitor (BPM) system planned for the LCLS undulator will incorporate a high-resolution X-band cavity BPM system described in this paper. The BPM system will provide high-resolution measurements of the electron beam trajectory on a pulse-to-pulse basis and over many shots. The X-band cavity BPM size, simple fabrication, and high resolution make it an ideal choice for LCLS beam position detection. We will discuss the system specifications, design, andmore » prototype test results.« less

The X-ray Pump–Probe instrument at the Linac Coherent Light Source

DOE PAGES

Chollet, Matthieu; Alonso-Mori, Roberto; Cammarata, Marco; ...

2015-04-21

The X-ray Pump–Probe instrument achieves femtosecond time-resolution with hard X-ray methods using a free-electron laser source. It covers a photon energy range of 4–24 keV. A femtosecond optical laser system is available across a broad spectrum of wavelengths for generating transient states of matter. The instrument is designed to emphasize versatility and the scientific goals encompass ultrafast physical, chemical and biological processes involved in the transformation of matter and transfer of energy at the atomic scale.

Femtosecond all-optical synchronization of an X-ray free-electron laser

DOE PAGES

Schulz, S.; Grguraš, I.; Behrens, C.; ...

2015-01-20

Many advanced applications of X-ray free-electron lasers require pulse durations and time resolutions of only a few femtoseconds. To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed. Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses. Crucially, our analysis indicates that the performance of this optical synchronization is limited primarilymore » by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses.« less

Femtosecond all-optical synchronization of an X-ray free-electron laser

PubMed Central

Schulz, S.; Grguraš, I.; Behrens, C.; Bromberger, H.; Costello, J. T.; Czwalinna, M. K.; Felber, M.; Hoffmann, M. C.; Ilchen, M.; Liu, H. Y.; Mazza, T.; Meyer, M.; Pfeiffer, S.; Prędki, P.; Schefer, S.; Schmidt, C.; Wegner, U.; Schlarb, H.; Cavalieri, A. L.

2015-01-01

Many advanced applications of X-ray free-electron lasers require pulse durations and time resolutions of only a few femtoseconds. To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed. Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses. Crucially, our analysis indicates that the performance of this optical synchronization is limited primarily by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses. PMID:25600823

Linac coherent light source (LCLS) undulator RF BPM system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lill, R.; Waldschmidt, G.; Morrison, L.

2006-01-01

The Linac Coherent Light Source (LCLS) will be the world's first x-ray free-electron laser (FEL) when it becomes operational in 2009. The LCLS is currently in the construction phase. The beam position monitor (BPM) system planned for the LCLS undulator will incorporate a high-resolution X-band cavity BPM system described in this paper. The BPM system will provide high-resolution measurements of the electron beam trajectory on a pulse-to-pulse basis and over many shots. The X-band cavity BPM size, simple fabrication, and high resolution make it an ideal choice for LCLS beam position detection. We will discuss the system specifications, design, andmore » prototype test results.« less

The linac coherent light source single particle imaging road map

PubMed Central

Aquila, A.; Barty, A.; Bostedt, C.; Boutet, S.; Carini, G.; dePonte, D.; Drell, P.; Doniach, S.; Downing, K. H.; Earnest, T.; Elmlund, H.; Elser, V.; Gühr, M.; Hajdu, J.; Hastings, J.; Hau-Riege, S. P.; Huang, Z.; Lattman, E. E.; Maia, F. R. N. C.; Marchesini, S.; Ourmazd, A.; Pellegrini, C.; Santra, R.; Schlichting, I.; Schroer, C.; Spence, J. C. H.; Vartanyants, I. A.; Wakatsuki, S.; Weis, W. I.; Williams, G. J.

2015-01-01

Intense femtosecond x-ray pulses from free-electron laser sources allow the imaging of individual particles in a single shot. Early experiments at the Linac Coherent Light Source (LCLS) have led to rapid progress in the field and, so far, coherent diffractive images have been recorded from biological specimens, aerosols, and quantum systems with a few-tens-of-nanometers resolution. In March 2014, LCLS held a workshop to discuss the scientific and technical challenges for reaching the ultimate goal of atomic resolution with single-shot coherent diffractive imaging. This paper summarizes the workshop findings and presents the roadmap toward reaching atomic resolution, 3D imaging at free-electron laser sources. PMID:26798801

The linac coherent light source single particle imaging road map

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aquila, A.; Barty, A.; Bostedt, C.

Intense femtosecond x-ray pulses from free-electron laser sources allow the imaging of individual particles in a single shot. Early experiments at the Linac Coherent Light Source (LCLS) have led to rapid progress in the field and, so far, coherent diffractive images have been recorded from biological specimens, aerosols, and quantum systems with a few-tens-of-nanometers resolution. In March 2014, LCLS held a workshop to discuss the scientific and technical challenges for reaching the ultimate goal of atomic resolution with single-shot coherent diffractive imaging. This paper summarizes the workshop findings and presents the roadmap toward reaching atomic resolution, 3D imaging at free-electronmore » laser sources.« less

Compact Short-Pulsed Electron Linac Based Neutron Sources for Precise Nuclear Material Analysis

NASA Astrophysics Data System (ADS)

Uesaka, M.; Tagi, K.; Matsuyama, D.; Fujiwara, T.; Dobashi, K.; Yamamoto, M.; Harada, H.

2015-10-01

An X-band (11.424GHz) electron linac as a neutron source for nuclear data study for the melted fuel debris analysis and nuclear security in Fukushima is under development. Originally we developed the linac for Compton scattering X-ray source. Quantitative material analysis and forensics for nuclear security will start several years later after the safe settlement of the accident is established. For the purpose, we should now accumulate more precise nuclear data of U, Pu, etc., especially in epithermal (0.1-10 eV) neutrons. Therefore, we have decided to modify and install the linac in the core space of the experimental nuclear reactor "Yayoi" which is now under the decommission procedure. Due to the compactness of the X-band linac, an electron gun, accelerating tube and other components can be installed in a small space in the core. First we plan to perform the time-of-flight (TOF) transmission measurement for study of total cross sections of the nuclei for 0.1-10 eV energy neutrons. Therefore, if we adopt a TOF line of less than 10m, the o-pulse length of generated neutrons should be shorter than 100 ns. Electronenergy, o-pulse length, power, and neutron yield are ~30 MeV, 100 ns - 1 micros, ~0.4 kW, and ~1011 n/s (~103 n/cm2/s at samples), respectively. Optimization of the design of a neutron target (Ta, W, 238U), TOF line and neutron detector (Ce:LiCAF) of high sensitivity and fast response is underway. We are upgrading the electron gun and a buncher to realize higher current and beam power with a reasonable beam size in order to avoid damage of the neutron target. Although the neutron flux is limited in case of the X-band electron linac based source, we take advantage of its short pulse aspect and availability for nuclear data measurement with a short TOF system. First, we form a tentative configuration in the current experimental room for Compton scattering in 2014. Then, after the decommissioning has been finished, we move it to the "Yayoi" room and perform

All-optical switching of magnetoresistive devices using telecom-band femtosecond laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Li; Chen, Jun-Yang; Wang, Jian-Ping, E-mail: jpwang@umn.edu, E-mail: moli@umn.edu

Ultrafast all-optical switching of the magnetization of various magnetic systems is an intriguing phenomenon that can have tremendous impact on information storage and processing. Here, we demonstrate all-optical switching of GdFeCo alloy films using a telecom-band femtosecond fiber laser. We further fabricate Hall cross devices and electrically readout all-optical switching by measuring anomalous Hall voltage changes. The use of a telecom laser and the demonstrated all-optical switching of magnetoresistive devices represent the first step toward integration of opto-magnetic devices with mainstream photonic devices to enable novel optical and spintronic functionalities.

FEM design and simulation of a short, 10 MV, S-band Linac with Monte Carlo dose simulations.

PubMed

Baillie, Devin; St Aubin, J; Fallone, B G; Steciw, S

2015-04-01

Current commercial 10 MV Linac waveguides are 1.5 m. The authors' current 6 MV linear accelerator-magnetic resonance imager (Linac-MR) system fits in typical radiotherapy vaults. To allow 10 MV treatments with the Linac-MR and still fit within typical vaults, the authors design a 10 MV Linac with an accelerator waveguide of the same length (27.5 cm) as current 6 MV Linacs. The first design stage is to design a cavity such that a specific experimental measurement for breakdown is applicable to the cavity. This is accomplished through the use of finite element method (FEM) simulations to match published shunt impedance, Q factor, and ratio of peak to mean-axial electric field strength from an electric breakdown study. A full waveguide is then designed and tuned in FEM simulations based on this cavity design. Electron trajectories are computed through the resulting radio frequency fields, and the waveguide geometry is modified by shifting the first coupling cavity in order to optimize the electron beam properties until the energy spread and mean energy closely match values published for an emulated 10 MV Linac. Finally, Monte Carlo dose simulations are used to compare the resulting photon beam depth dose profile and penumbra with that produced by the emulated 10 MV Linac. The shunt impedance, Q factor, and ratio of peak to mean-axial electric field strength are all matched to within 0.1%. A first coupling cavity shift of 1.45 mm produces an energy spectrum width of 0.347 MeV, very close to the published value for the emulated 10 MV of 0.315 MeV, and a mean energy of 10.53 MeV, nearly identical to the published 10.5 MeV for the emulated 10 MV Linac. The depth dose profile produced by their new Linac is within 1% of that produced by the emulated 10 MV spectrum for all depths greater than 1.5 cm. The penumbra produced is 11% narrower, as measured from 80% to 20% of the central axis dose. The authors have successfully designed and simulated an S-band waveguide of length

X-ray two-photon absorption with high fluence XFEL pulses

DOE PAGES

Hoszowska, Joanna; Szlachetko, J.; Dousse, J. -Cl.; ...

2015-09-07

Here, we report on nonlinear interaction of solid Fe with intense femtosecond hard x-ray free-electron laser (XFEL) pulses. The experiment was performed at the CXI end-station of the Linac Coherent Light Source (LCLS) by means of high- resolution x-ray emission spectroscopy. The focused x-ray beam provided extreme fluence of ~10 5 photons/Å 2. Two-photon absorption leading to K-shell hollow atom formation and to single K-shell ionization of solid Fe was investigated.

Band structure of cavity-type hypersonic phononic crystals fabricated by femtosecond laser-induced two-photon polymerization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rakhymzhanov, A. M.; Utegulov, Z. N., E-mail: zhutegulov@nu.edu.kz, E-mail: fytas@mpip-mainz.mpg.de; Optics Laboratory, National Laboratory Astana, Nazarbayev University, Astana 10000

2016-05-16

The phononic band diagram of a periodic square structure fabricated by femtosecond laser pulse-induced two photon polymerization is recorded by Brillouin light scattering (BLS) at hypersonic (GHz) frequencies and computed by finite element method. The theoretical calculations along the two main symmetry directions quantitatively capture the band diagrams of the air- and liquid-filled structure and moreover represent the BLS intensities. The theory helps identify the observed modes, reveals the origin of the observed bandgaps at the Brillouin zone boundaries, and unravels direction dependent effective medium behavior.

Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction

NASA Astrophysics Data System (ADS)

Minitti, M. P.; Budarz, J. M.; Kirrander, A.; Robinson, J. S.; Ratner, D.; Lane, T. J.; Zhu, D.; Glownia, J. M.; Kozina, M.; Lemke, H. T.; Sikorski, M.; Feng, Y.; Nelson, S.; Saita, K.; Stankus, B.; Northey, T.; Hastings, J. B.; Weber, P. M.

2015-06-01

Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction.

PubMed

Minitti, M P; Budarz, J M; Kirrander, A; Robinson, J S; Ratner, D; Lane, T J; Zhu, D; Glownia, J M; Kozina, M; Lemke, H T; Sikorski, M; Feng, Y; Nelson, S; Saita, K; Stankus, B; Northey, T; Hastings, J B; Weber, P M

2015-06-26

Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

Observation of femtosecond X-ray interactions with matter using an X-ray–X-ray pump–probe scheme

PubMed Central

Inoue, Ichiro; Inubushi, Yuichi; Sato, Takahiro; Tono, Kensuke; Katayama, Tetsuo; Kameshima, Takashi; Ogawa, Kanade; Togashi, Tadashi; Owada, Shigeki; Amemiya, Yoshiyuki; Tanaka, Takashi; Hara, Toru

2016-01-01

Resolution in the X-ray structure determination of noncrystalline samples has been limited to several tens of nanometers, because deep X-ray irradiation required for enhanced resolution causes radiation damage to samples. However, theoretical studies predict that the femtosecond (fs) durations of X-ray free-electron laser (XFEL) pulses make it possible to record scattering signals before the initiation of X-ray damage processes; thus, an ultraintense X-ray beam can be used beyond the conventional limit of radiation dose. Here, we verify this scenario by directly observing femtosecond X-ray damage processes in diamond irradiated with extraordinarily intense (∼1019 W/cm2) XFEL pulses. An X-ray pump–probe diffraction scheme was developed in this study; tightly focused double–5-fs XFEL pulses with time separations ranging from sub-fs to 80 fs were used to excite (i.e., pump) the diamond and characterize (i.e., probe) the temporal changes of the crystalline structures through Bragg reflection. It was found that the pump and probe diffraction intensities remain almost constant for shorter time separations of the double pulse, whereas the probe diffraction intensities decreased after 20 fs following pump pulse irradiation due to the X-ray–induced atomic displacement. This result indicates that sub-10-fs XFEL pulses enable conductions of damageless structural determinations and supports the validity of the theoretical predictions of ultraintense X-ray–matter interactions. The X-ray pump–probe scheme demonstrated here would be effective for understanding ultraintense X-ray–matter interactions, which will greatly stimulate advanced XFEL applications, such as atomic structure determination of a single molecule and generation of exotic matters with high energy densities. PMID:26811449

X-ray laser–induced electron dynamics observed by femtosecond diffraction from nanocrystals of Buckminsterfullerene

PubMed Central

Abbey, Brian; Dilanian, Ruben A.; Darmanin, Connie; Ryan, Rebecca A.; Putkunz, Corey T.; Martin, Andrew V.; Wood, David; Streltsov, Victor; Jones, Michael W. M.; Gaffney, Naylyn; Hofmann, Felix; Williams, Garth J.; Boutet, Sébastien; Messerschmidt, Marc; Seibert, M. Marvin; Williams, Sophie; Curwood, Evan; Balaur, Eugeniu; Peele, Andrew G.; Nugent, Keith A.; Quiney, Harry M.

2016-01-01

X-ray free-electron lasers (XFELs) deliver x-ray pulses with a coherent flux that is approximately eight orders of magnitude greater than that available from a modern third-generation synchrotron source. The power density of an XFEL pulse may be so high that it can modify the electronic properties of a sample on a femtosecond time scale. Exploration of the interaction of intense coherent x-ray pulses and matter is both of intrinsic scientific interest and of critical importance to the interpretation of experiments that probe the structures of materials using high-brightness femtosecond XFEL pulses. We report observations of the diffraction of extremely intense 32-fs nanofocused x-ray pulses by a powder sample of crystalline C60. We find that the diffraction pattern at the highest available incident power significantly differs from the one obtained using either third-generation synchrotron sources or XFEL sources operating at low output power and does not correspond to the diffraction pattern expected from any known phase of crystalline C60. We interpret these data as evidence of a long-range, coherent dynamic electronic distortion that is driven by the interaction of the periodic array of C60 molecular targets with intense x-ray pulses of femtosecond duration. PMID:27626076

Solenoid Fringe Field Effects for the Neutrino Factory Linac - MAD-X Investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

M. Aslaninejad,C. Bontoiu,J. Pasternak,J. Pozimski,Alex Bogacz

2010-05-01

International Design Study for the Neutrino Factory (IDS-NF) assumes the first stage of muon acceleration (up to 900 MeV) to be implemented with a solenoid based Linac. The Linac consists of three styles of cryo-modules, containing focusing solenoids and varying number of SRF cavities for acceleration. Fringe fields of the solenoids and the focusing effects in the SRF cavities have significant impact on the transverse beam dynamics. Using an analytical formula, the effects of fringe fields are studied in MAD-X. The resulting betatron functions are compared with the results of beam dynamics simulations using OptiM code.

Investigating radiation induced damage processes with femtosecond x-ray pulses (Conference Presentation)

NASA Astrophysics Data System (ADS)

Song, Changyong

2017-05-01

Interest in high-resolution structure investigation has been zealous, especially with the advent of X-ray free electron lasers (XFELs). The intense and ultra-short X-ray laser pulses ( 10 GW) pave new routes to explore structures and dynamics of single macromolecules, functional nanomaterials and complex electronic materials. In the last several years, we have developed XFEL single-shot diffraction imaging by probing ultrafast phase changes directly. Pump-probe single-shot imaging was realized by synchronizing femtosecond (<10 fs in FWHM) X-ray laser (probe) with femtosecond (50 fs) IR laser (pump) at better than 1 ps resolution. Nanoparticles under intense fs-laser pulses were investigated with fs XFEL pulses to provide insight into the irreversible particle damage processes with nanoscale resolution. Research effort, introduced, aims to extend the current spatio-temporal resolution beyond the present limit. We expect this single-shot dynamic imaging to open new science opportunity with XFELs.

Optical synchronization system for femtosecond X-ray sources

DOEpatents

Wilcox, Russell B [El Cerrito, CA; Holzwarth, Ronald [Munich, DE

2011-12-13

Femtosecond pump/probe experiments using short X-Ray and optical pulses require precise synchronization between 100 meter-10 km separated lasers in a various experiments. For stabilization in the hundred femtosecond range a CW laser is amplitude modulated at 1-10 GHz, the signal retroreflected from the far end, and the relative phase used to correct the transit time with various implementations. For the sub-10 fsec range the laser frequency itself is upshifted 55 MHz with an acousto-optical modulator, retroreflected, upshifted again and phase compared at the sending end to a 110 MHz reference. Initial experiments indicate less than 1 fsec timing jitter. To lock lasers in the sub-10 fs range two single-frequency lasers separated by several teraHertz will be lock to a master modelocked fiber laser, transmit the two frequencies over fiber, and lock two comb lines of a slave laser to these frequencies, thus synchronizing the two modelocked laser envelopes.

Goniometer-based femtosecond crystallography with X-ray free electron lasers

PubMed Central

Cohen, Aina E.; Soltis, S. Michael; González, Ana; Aguila, Laura; Alonso-Mori, Roberto; Barnes, Christopher O.; Baxter, Elizabeth L.; Brehmer, Winnie; Brewster, Aaron S.; Brunger, Axel T.; Calero, Guillermo; Chang, Joseph F.; Chollet, Matthieu; Ehrensberger, Paul; Eriksson, Thomas L.; Feng, Yiping; Hattne, Johan; Hedman, Britt; Hollenbeck, Michael; Holton, James M.; Keable, Stephen; Kobilka, Brian K.; Kovaleva, Elena G.; Kruse, Andrew C.; Lemke, Henrik T.; Lin, Guowu; Lyubimov, Artem Y.; Manglik, Aashish; Mathews, Irimpan I.; McPhillips, Scott E.; Nelson, Silke; Peters, John W.; Sauter, Nicholas K.; Smith, Clyde A.; Song, Jinhu; Stevenson, Hilary P.; Tsai, Yingssu; Uervirojnangkoorn, Monarin; Vinetsky, Vladimir; Wakatsuki, Soichi; Weis, William I.; Zadvornyy, Oleg A.; Zeldin, Oliver B.; Zhu, Diling; Hodgson, Keith O.

2014-01-01

The emerging method of femtosecond crystallography (FX) may extend the diffraction resolution accessible from small radiation-sensitive crystals and provides a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzymes. Automated goniometer-based instrumentation developed for use at the Linac Coherent Light Source enabled efficient and flexible FX experiments to be performed on a variety of sample types. In the case of rod-shaped Cpl hydrogenase crystals, only five crystals and about 30 min of beam time were used to obtain the 125 still diffraction patterns used to produce a 1.6-Å resolution electron density map. For smaller crystals, high-density grids were used to increase sample throughput; 930 myoglobin crystals mounted at random orientation inside 32 grids were exposed, demonstrating the utility of this approach. Screening results from cryocooled crystals of β2-adrenoreceptor and an RNA polymerase II complex indicate the potential to extend the diffraction resolution obtainable from very radiation-sensitive samples beyond that possible with undulator-based synchrotron sources. PMID:25362050

Goniometer-based femtosecond crystallography with X-ray free electron lasers

DOE PAGES

Cohen, Aina E.; Soltis, S. Michael; González, Ana; ...

2014-10-31

The emerging method of femtosecond crystallography (FX) may extend the diffraction resolution accessible from small radiation-sensitive crystals and provides a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzymes. Automated goniometer-based instrumentation developed for use at the Linac Coherent Light Source enabled efficient and flexible FX experiments to be performed on a variety of sample types. In the case of rod-shaped Cpl hydrogenase crystals, only five crystals and about 30 min of beam time were used to obtain the 125 still diffraction patterns used to produce a 1.6-Å resolution electron density map. With smaller crystals, high-density grids were usedmore » to increase sample throughput; 930 myoglobin crystals mounted at random orientation inside 32 grids were exposed, demonstrating the utility of this approach. Screening results from cryocooled crystals of β 2-adrenoreceptor and an RNA polymerase II complex indicate the potential to extend the diffraction resolution obtainable from very radiation-sensitive samples beyond that possible with undulator-based synchrotron sources.« less

Design study of an S-band RF cavity of a dual-energy electron LINAC for the CIS

NASA Astrophysics Data System (ADS)

Lee, Byeong-No; Park, Hyungdal; Song, Ki-baek; Li, Yonggui; Lee, Byung Cheol; Cha, Sung-su; Lee, Jong-Chul; Shin, Seung-Wook; Chai, Jong-seo

2014-01-01

The design of a resonance frequency (RF) cavity for the dual-energy S-band electron linear accelerator (LINAC) has been carried out for the cargo inspection system (CIS). This Standing-wave-type RF cavity is operated at a frequency under the 2856-MHz resonance frequency and generates electron beams of 9 MeV (high mode) and 6 MeV (low mode). The electrons are accelerated from the initial energy of the electron gun to the target energy (9 or 6 MeV) inside the RF cavity by using the RF power transmitted from a 5.5-MW-class klystron. Then, electron beams with a 1-kW average power (both high mode and low mode) bombard an X-ray target a 2-mm spot size. The proposed accelerating gradient was 13 MV/m, and the designed Q value was about 7100. On going research on 15-MeV non-destructive inspections for military or other applications is presented.

Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses

DOE Data Explorer

Daurer, Benedikt, J.

2016-12-09

Facilitating the very short and intense pulses from an X-ray laser for the purpose of imaging small bioparticles carries the potential for structure determination at atomic resolution without the need for crystallization. In this study, we explore experimental strategies for this idea based on data collected at the Linac Coherent Light Source from 40 nm virus particles injected into a hard X-ray beam.

FEM design and simulation of a short, 10 MV, S-band Linac with Monte Carlo dose simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baillie, Devin; Aubin, J. St.; Steciw, S., E-mail: ssteciw@ualberta.ca

2015-04-15

successfully designed and simulated an S-band waveguide of length of 27.5 cm capable of producing a 10 MV photon beam. This waveguide operates well within the breakdown threshold determined for the cavity geometry used. The designed Linac produces depth dose profiles similar to those of the emulated 10 MV Linac (waveguide-length of 1.5 m) but yields a narrower penumbra.« less

Serial femtosecond X-ray diffraction of enveloped virus microcrystals

DOE PAGES

Lawrence, Robert M.; Conrad, Chelsie E.; Zatsepin, Nadia A.; ...

2015-08-20

Serial femtosecond crystallography (SFX) using X-ray free-electron lasers has produced high-resolution, room temperature, time-resolved protein structures. We report preliminary SFX of Sindbis virus, an enveloped icosahedral RNA virus with ~700 Å diameter. Microcrystals delivered in viscous agarose medium diffracted to ~40 Å resolution. Small-angle diffuse X-ray scattering overlaid Bragg peaks and analysis suggests this results from molecular transforms of individual particles. Viral proteins undergo structural changes during entry and infection, which could, in principle, be studied with SFX. This is a pertinent step toward determining room temperature structures from virus microcrystals that may enable time-resolved studies of enveloped viruses.

C (G)-Band & X (I) - Band Noncoherent Radar Transponder Performance Specification Standard

DTIC Science & Technology

2002-04-01

TRAINING RANGE NEVADA TEST SITE STANDARD 262-02 ELECTRONIC TRAJECTORY MEASUREMENTS GROUP C (G) – BAND & X (I) – BAND NONCOHERENT RADAR...Date 00 Apr 2002 Report Type N/A Dates Covered (from... to) - Title and Subtitle C (G)-Band & X (I) - Band Noncoherent Radar Transponder...Number of Pages 157 i STANDARD 262-02 C (G) – BAND & X (I) – BAND NONCOHERENT RADAR TRANSPONDER PERFORMANCE SPECIFICATION STANDARD APRIL 2002 Prepared by

Block 3 X-band receiver-exciter

NASA Technical Reports Server (NTRS)

Johns, C. E.

1987-01-01

The development of an X-band exciter, for use in the X-Band Uplink Subsystem, was completed. The exciter generates the drive signal for the X-band transmitter and also generates coherent test signals for the S- and X-band Block 3 translator and a Doppler reference signal for the Doppler extractor system. In addition to the above, the exciter generates other reference signals that are described. Also presented is an overview of the exciter design and some test data taken on the prototype. A brief discussion of the Block 3 Doppler extractor is presented.

Ultrafast molecular processes mapped by femtosecond x-ray diffraction

NASA Astrophysics Data System (ADS)

Elsaesser, Thomas

2012-02-01

X-ray diffraction with a femtosecond time resolution allows for mapping photoinduced structural dynamics on the length scale of a chemical bond and in the time domain of atomic and molecular motion. In a pump-probe approach, a femtosecond excitation pulse induces structural changes which are probed by diffracting a femtosecond hard x-ray pulse from the excited sample. The transient angular positions and intensities of diffraction peaks give insight into the momentary atomic or molecular positions and into the distribution of electronic charge density. The simultaneous measurement of changes on different diffraction peaks is essential for determining atom positions and charge density maps with high accuracy. Recent progress in the generation of ultrashort hard x-ray pulses (Cu Kα, wavelength λ=0.154 nm) in laser-driven plasma sources has led to the implementation of the powder diffraction and the rotating crystal method with a time resolution of 100 fs. In this contribution, we report new results from powder diffraction studies of molecular materials. A first series of experiments gives evidence of a so far unknown concerted transfer of electrons and protons in ammonium sulfate [(NH4)2SO4], a centrosymmetric structure. Charge transfer from the sulfate groups results in the sub-100 fs generation of a confined electron channel along the c-axis of the unit cell which is stabilized by transferring protons from the adjacent ammonium groups into the channel. Time-dependent charge density maps display a periodic modulation of the channel's charge density by low-frequency lattice motions with a concerted electron and proton motion between the channel and the initial proton binding site. A second study addresses atomic rearrangements and charge dislocations in the non-centrosymmetric potassium dihydrogen phosphate [KH2PO4, KDP]. Photoexcitation generates coherent low-frequency motions along the LO and TO phonon coordinates, leaving the average atomic positions unchanged

An 'X-banded' Tidbinbilla interferometer

NASA Technical Reports Server (NTRS)

Batty, Michael J.; Gardyne, R. G.; Gay, G. J.; Jauncy, David L.; Gulkis, S.; Kirk, A.

1986-01-01

The recent upgrading of the Tidbinbilla two-element interferometer to simultaneous S-band (2.3 GHz) and X-band (8.4 GHz) operation has provided a powerful new astronomical facility for weak radio source measurement in the Southern Hemisphere. The new X-band system has a minimum fringe spacing of 38 arcsec, and about the same positional measurement capability (approximately 2 arcsec) and sensitivity (1 s rms noise of 10 mJy) as the previous S-band system. However, the far lower confusion limit will allow detection and accurate positional measurements for sources as weak as a few millijanskys. This capability will be invaluable for observations of radio stars, X-ray sources and other weak, compact radio sources.

AN OSCILLATOR CONFIGURATION FOR FULL REALIZATION OF HARD X-RAY FREE ELECTRON LASER*

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, K.-J.; Kolodziej, T.; Lindberg, R. R.

2017-06-01

An x-ray free electron laser oscillator (XFELO) is feasible by employing an X-ray cavity with Bragg mirrors such as diamond crystals. An XFELO at the 5th harmonic frequency may be implemented at the LCLS II using its 4 GeV superconducting linac, producing stable, fully coherent, high-spectral-purity hard x-rays. In addition, its output can be a coherent seed to the LCLS amplifier for stable, high-power, femto-second x-ray pulses. We summarize the recent progress in various R&D efforts addressing critical issues for realizing an XFELO at LCLS II.

Spectral and spatial resolving of photoelectric property of femtosecond laser drilled holes of GaSb(1-x)Bi(x).

PubMed

Pan, C B; Zha, F X; Song, Y X; Shao, J; Dai, Y; Chen, X R; Ye, J Y; Wang, S M

2015-07-15

Femtosecond laser drilled holes of GaSbBi were characterized by the joint measurements of photoconductivity (PC) spectroscopy and laser-beam-induced current (LBIC) mapping. The excitation light in PC was focused down to 60 μm presenting the spectral information of local electronic property of individual holes. A redshift of energy band edge of about 6-8 meV was observed by the PC measurement when the excitation light irradiated on the laser drilled holes. The spatial resolving of photoelectric property was achieved by the LBIC mapping which shows "pseudo-holes" with much larger dimensions than the geometric sizes of the holes. The reduced LBIC current with the pseudo-holes is associated with the redshift effect indicating that the electronic property of the rim areas of the holes is modified by the femtosecond laser drilling.

Implications of the focal beam profile in serial femtosecond crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galli, Lorenzo; Chapman, Henry N.; Metcalf, Peter

The photon density profile of an X-ray free-electron laser (XFEL) beam at the focal position is a critical parameter for serial femtosecond crystallography (SFX), but is difficult to measure because of the destructive power of the beam. A novel high intensity radiation induced phasing method (HIRIP) has been proposed as a general experimental approach for protein structure determination, but has proved to be sensitive to variations of the X-ray intensity, with uniform incident fluence desired for best performance. Here we show that experimental SFX data collected at the nano-focus chamber of the Coherent X-ray Imaging end-station at the Linac Coherentmore » Light Source using crystals with a limited size distribution suggests an average profile of the X-ray beam that has a large variation of intensity. We propose a new method to improve the quality of high fluence data for HI-RIP, by identifying and removing diffraction patterns from crystals exposed to the low intensity region of the beam. The method requires crystals of average size comparable to the width of the focal spot.« less

Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

PubMed Central

Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; van Driel, Tim B.; Adachi, Shin-ichi; Bordage, Amélie; Bressler, Christian; Chabera, Pavel; Christensen, Morten; Dohn, Asmus O.; Galler, Andreas; Gawelda, Wojciech; Gosztola, David; Haldrup, Kristoffer; Harlang, Tobias; Liu, Yizhu; Møller, Klaus B.; Németh, Zoltán; Nozawa, Shunsuke; Pápai, Mátyás; Sato, Tokushi; Sato, Takahiro; Suarez-Alcantara, Karina; Togashi, Tadashi; Tono, Kensuke; Uhlig, Jens; Vithanage, Dimali A.; Wärnmark, Kenneth; Yabashi, Makina; Zhang, Jianxin; Sundström, Villy; Nielsen, Martin M.

2015-01-01

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined. PMID:25727920

Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

DOE PAGES

Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; ...

2015-03-02

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances.more » Thus experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined.« less

X-Band CubeSat Communication System Demonstration

NASA Technical Reports Server (NTRS)

Altunc, Serhat; Kegege, Obadiah; Bundick, Steve; Shaw, Harry; Schaire, Scott; Bussey, George; Crum, Gary; Burke, Jacob C.; Palo, Scott; O'Conor, Darren

2015-01-01

Today's CubeSats mostly operate their communications at UHF- and S-band frequencies. UHF band is presently crowded, thus downlink communications are at lower data rates due to bandwidth limitations and are unreliable due to interference. This research presents an end-to-end robust, innovative, compact, efficient and low cost S-band uplink and X-band downlink CubeSat communication system demonstration between a balloon and a Near Earth Network (NEN) ground system. Since communication systems serve as umbilical cords for space missions, demonstration of this X-band communication system is critical for successfully supporting current and future CubeSat communication needs. This research has three main objectives. The first objective is to design, simulate, and test a CubeSat S- and X-band communication system. Satellite Tool Kit (STK) dynamic link budget calculations and HFSS Simulations and modeling results have been used to trade the merit of various designs for small satellite applications. S- and X-band antennas have been tested in the compact antenna test range at Goddard Space Flight Center (GSFC) to gather radiation pattern data. The second objective is simulate and test a CubeSat compatible X-band communication system at 12.5Mbps including S-band antennas, X-band antennas, Laboratory for Atmospheric and Space Physics (LASP) /GSFC transmitter and an S-band receiver from TRL-5 to TRL-8 by the end of this effort. Different X-band communication system components (antennas, diplexers, etc.) from GSFC, other NASA centers, universities, and private companies have been investigated and traded, and a complete component list for the communication system baseline has been developed by performing analytical and numerical analysis. This objective also includes running simulations and performing trades between different X-band antenna systems to optimize communication system performance. The final objective is to perform an end-to-end X-band CubeSat communication system

Fixed target matrix for femtosecond time-resolved and in situ serial micro-crystallography.

PubMed

Mueller, C; Marx, A; Epp, S W; Zhong, Y; Kuo, A; Balo, A R; Soman, J; Schotte, F; Lemke, H T; Owen, R L; Pai, E F; Pearson, A R; Olson, J S; Anfinrud, P A; Ernst, O P; Dwayne Miller, R J

2015-09-01

We present a crystallography chip enabling in situ room temperature crystallography at microfocus synchrotron beamlines and X-ray free-electron laser (X-FEL) sources. Compared to other in situ approaches, we observe extremely low background and high diffraction data quality. The chip design is robust and allows fast and efficient loading of thousands of small crystals. The ability to load a large number of protein crystals, at room temperature and with high efficiency, into prescribed positions enables high throughput automated serial crystallography with microfocus synchrotron beamlines. In addition, we demonstrate the application of this chip for femtosecond time-resolved serial crystallography at the Linac Coherent Light Source (LCLS, Menlo Park, California, USA). The chip concept enables multiple images to be acquired from each crystal, allowing differential detection of changes in diffraction intensities in order to obtain high signal-to-noise and fully exploit the time resolution capabilities of XFELs.

Fixed target matrix for femtosecond time-resolved and in situ serial micro-crystallography

PubMed Central

Mueller, C.; Marx, A.; Epp, S. W.; Zhong, Y.; Kuo, A.; Balo, A. R.; Soman, J.; Schotte, F.; Lemke, H. T.; Owen, R. L.; Pai, E. F.; Pearson, A. R.; Olson, J. S.; Anfinrud, P. A.; Ernst, O. P.; Dwayne Miller, R. J.

2015-01-01

We present a crystallography chip enabling in situ room temperature crystallography at microfocus synchrotron beamlines and X-ray free-electron laser (X-FEL) sources. Compared to other in situ approaches, we observe extremely low background and high diffraction data quality. The chip design is robust and allows fast and efficient loading of thousands of small crystals. The ability to load a large number of protein crystals, at room temperature and with high efficiency, into prescribed positions enables high throughput automated serial crystallography with microfocus synchrotron beamlines. In addition, we demonstrate the application of this chip for femtosecond time-resolved serial crystallography at the Linac Coherent Light Source (LCLS, Menlo Park, California, USA). The chip concept enables multiple images to be acquired from each crystal, allowing differential detection of changes in diffraction intensities in order to obtain high signal-to-noise and fully exploit the time resolution capabilities of XFELs. PMID:26798825

Ultrafast myoglobin structural dynamics observed with an X-ray free-electron laser

DOE PAGES

Levantino, Matteo; Schirò, Giorgio; Lemke, Henrik Till; ...

2015-04-02

Light absorption can trigger biologically relevant protein conformational changes. The light induced structural rearrangement at the level of a photoexcited chromophore is known to occur in the femtosecond timescale and is expected to propagate through the protein as a quake-like intramolecular motion. Here we report direct experimental evidence of such ‘proteinquake’ observed in myoglobin through femtosecond X-ray solution scattering measurements performed at the Linac Coherent Light Source X-ray free-electron laser. An ultrafast increase of myoglobin radius of gyration occurs within 1 picosecond and is followed by a delayed protein expansion. As the system approaches equilibrium it undergoes damped oscillations withmore » a ~3.6-picosecond time period. Our results unambiguously show how initially localized chemical changes can propagate at the level of the global protein conformation in the picosecond timescale.« less

Serial femtosecond crystallography datasets from G protein-coupled receptors.

PubMed

White, Thomas A; Barty, Anton; Liu, Wei; Ishchenko, Andrii; Zhang, Haitao; Gati, Cornelius; Zatsepin, Nadia A; Basu, Shibom; Oberthür, Dominik; Metz, Markus; Beyerlein, Kenneth R; Yoon, Chun Hong; Yefanov, Oleksandr M; James, Daniel; Wang, Dingjie; Messerschmidt, Marc; Koglin, Jason E; Boutet, Sébastien; Weierstall, Uwe; Cherezov, Vadim

2016-08-01

We describe the deposition of four datasets consisting of X-ray diffraction images acquired using serial femtosecond crystallography experiments on microcrystals of human G protein-coupled receptors, grown and delivered in lipidic cubic phase, at the Linac Coherent Light Source. The receptors are: the human serotonin receptor 2B in complex with an agonist ergotamine, the human δ-opioid receptor in complex with a bi-functional peptide ligand DIPP-NH2, the human smoothened receptor in complex with an antagonist cyclopamine, and finally the human angiotensin II type 1 receptor in complex with the selective antagonist ZD7155. All four datasets have been deposited, with minimal processing, in an HDF5-based file format, which can be used directly for crystallographic processing with CrystFEL or other software. We have provided processing scripts and supporting files for recent versions of CrystFEL, which can be used to validate the data.

X-band Uplink Ground Systems Development

NASA Technical Reports Server (NTRS)

Johns, C. E.

1984-01-01

The development of the X-band exciter and Doppler extractor equipment for the X-band uplink was completed. Stability measurements were made on the exciter and Doppler reference signals and the results are presented.

Hit detection in serial femtosecond crystallography using X-ray spectroscopy of plasma emission.

PubMed

Jönsson, H Olof; Caleman, Carl; Andreasson, Jakob; Tîmneanu, Nicuşor

2017-11-01

Serial femtosecond crystallography is an emerging and promising method for determining protein structures, making use of the ultrafast and bright X-ray pulses from X-ray free-electron lasers. The upcoming X-ray laser sources will produce well above 1000 pulses per second and will pose a new challenge: how to quickly determine successful crystal hits and avoid a high-rate data deluge. Proposed here is a hit-finding scheme based on detecting photons from plasma emission after the sample has been intercepted by the X-ray laser. Plasma emission spectra are simulated for systems exposed to high-intensity femtosecond pulses, for both protein crystals and the liquid carrier systems that are used for sample delivery. The thermal radiation from the glowing plasma gives a strong background in the XUV region that depends on the intensity of the pulse, around the emission lines from light elements (carbon, nitrogen, oxygen). Sample hits can be reliably distinguished from the carrier liquid based on the characteristic emission lines from heavier elements present only in the sample, such as sulfur. For buffer systems with sulfur present, selenomethionine substitution is suggested, where the selenium emission lines could be used both as an indication of a hit and as an aid in phasing and structural reconstruction of the protein.

Exciter For X-Band Transmitter And Receiver

NASA Technical Reports Server (NTRS)

Johns, Carl E.

1989-01-01

Report describes developmental X-band exciter for X-band uplink subsystem of Deep Space Network. X-band transmitter-exciting signal expected to have fractional frequency stability of 5.2 X 10 to negative 15th power during 1,000-second integration period. Generates coherent test signals for S- and X-band Block III translator of Deep Space Network, Doppler-reference signal for associated Doppler-extractor system, first-local-oscillator signal for associated receiver, and reference signal for associated ranging subsystem. Tests of prototype exciter show controlling and monitoring and internal phase-correcting loops perform according to applicable design criteria. Measurements of stability of frequency and of single-sideband noise spectral density of transmitter-exciting signal made subsequently.

Self-referenced coherent diffraction x-ray movie of Ångstrom- and femtosecond-scale atomic motion

DOE PAGES

Glownia, J. M.; Natan, A.; Cryan, J. P.; ...

2016-10-03

Time-resolved femtosecond x-ray diffraction patterns from laser-excited molecular iodine are used to create a movie of intramolecular motion with a temporal and spatial resolution of 30 fs and 0.3 Å. This high fidelity is due to interference between the nonstationary excitation and the stationary initial charge distribution. The initial state is used as the local oscillator for heterodyne amplification of the excited charge distribution to retrieve real-space movies of atomic motion on ångstrom and femtosecond scales. This x-ray interference has not been employed to image internal motion in molecules before. In conclusion, coherent vibrational motion and dispersion, dissociation, and rotationalmore » dephasing are all clearly visible in the data, thereby demonstrating the stunning sensitivity of heterodyne methods.« less

Coherent Soft X-ray Diffraction Imaging of Coliphage PR772 at the Linac Coherent Light Source

DOE Data Explorer

Reddy, Hemanth, K.N.

2017-01-05

A dataset of coherent soft X-ray diffraction images of Coliphage PR772 virus, collected at the Atomic Molecular Optics (AMO) beamline with pnCCD detectors in the LAMP instrument at the Linac Coherent Light Source.

Energy-dispersive X-ray emission spectroscopy using an X-ray free-electron laser in a shot-by-shot mode

DOE PAGES

Alonso-Mori, Roberto; Kern, Jan; Gildea, Richard J.; ...

2012-11-05

The ultrabright femtosecond X-ray pulses provided by X-ray free-electron lasers open capabilities for studying the structure and dynamics of a wide variety of systems beyond what is possible with synchrotron sources. Recently, this “probe-before-destroy” approach has been demonstrated for atomic structure determination by serial X-ray diffraction of microcrystals. There has been the question whether a similar approach can be extended to probe the local electronic structure by X-ray spectroscopy. To address this, we have carried out femtosecond X-ray emission spectroscopy (XES) at the Linac Coherent Light Source using redox-active Mn complexes. XES probes the charge and spin states as wellmore » as the ligand environment, critical for understanding the functional role of redox-active metal sites. Kβ 1,3 XES spectra of Mn II and Mn 2 III,IV complexes at room temperature were collected using a wavelength dispersive spectrometer and femtosecond X-ray pulses with an individual dose of up to >100 MGy. The spectra were found in agreement with undamaged spectra collected at low dose using synchrotron radiation. Our results demonstrate that the intact electronic structure of redox active transition metal compounds in different oxidation states can be characterized with this shot-by-shot method. This opens the door for studying the chemical dynamics of metal catalytic sites by following reactions under functional conditions. Furthermore, the technique can be combined with X-ray diffraction to simultaneously obtain the geometric structure of the overall protein and the local chemistry of active metal sites and is expected to prove valuable for understanding the mechanism of important metalloproteins, such as photosystem II.« less

Energy-dispersive X-ray emission spectroscopy using an X-ray free-electron laser in a shot-by-shot mode

PubMed Central

Alonso-Mori, Roberto; Kern, Jan; Gildea, Richard J.; Sokaras, Dimosthenis; Weng, Tsu-Chien; Lassalle-Kaiser, Benedikt; Tran, Rosalie; Hattne, Johan; Laksmono, Hartawan; Hellmich, Julia; Glöckner, Carina; Echols, Nathaniel; Sierra, Raymond G.; Schafer, Donald W.; Sellberg, Jonas; Kenney, Christopher; Herbst, Ryan; Pines, Jack; Hart, Philip; Herrmann, Sven; Grosse-Kunstleve, Ralf W.; Latimer, Matthew J.; Fry, Alan R.; Messerschmidt, Marc M.; Miahnahri, Alan; Seibert, M. Marvin; Zwart, Petrus H.; White, William E.; Adams, Paul D.; Bogan, Michael J.; Boutet, Sébastien; Williams, Garth J.; Zouni, Athina; Messinger, Johannes; Glatzel, Pieter; Sauter, Nicholas K.; Yachandra, Vittal K.; Yano, Junko; Bergmann, Uwe

2012-01-01

The ultrabright femtosecond X-ray pulses provided by X-ray free-electron lasers open capabilities for studying the structure and dynamics of a wide variety of systems beyond what is possible with synchrotron sources. Recently, this “probe-before-destroy” approach has been demonstrated for atomic structure determination by serial X-ray diffraction of microcrystals. There has been the question whether a similar approach can be extended to probe the local electronic structure by X-ray spectroscopy. To address this, we have carried out femtosecond X-ray emission spectroscopy (XES) at the Linac Coherent Light Source using redox-active Mn complexes. XES probes the charge and spin states as well as the ligand environment, critical for understanding the functional role of redox-active metal sites. Kβ1,3 XES spectra of MnII and Mn2III,IV complexes at room temperature were collected using a wavelength dispersive spectrometer and femtosecond X-ray pulses with an individual dose of up to >100 MGy. The spectra were found in agreement with undamaged spectra collected at low dose using synchrotron radiation. Our results demonstrate that the intact electronic structure of redox active transition metal compounds in different oxidation states can be characterized with this shot-by-shot method. This opens the door for studying the chemical dynamics of metal catalytic sites by following reactions under functional conditions. The technique can be combined with X-ray diffraction to simultaneously obtain the geometric structure of the overall protein and the local chemistry of active metal sites and is expected to prove valuable for understanding the mechanism of important metalloproteins, such as photosystem II. PMID:23129631

Serial femtosecond crystallography datasets from G protein-coupled receptors

PubMed Central

White, Thomas A.; Barty, Anton; Liu, Wei; Ishchenko, Andrii; Zhang, Haitao; Gati, Cornelius; Zatsepin, Nadia A.; Basu, Shibom; Oberthür, Dominik; Metz, Markus; Beyerlein, Kenneth R.; Yoon, Chun Hong; Yefanov, Oleksandr M.; James, Daniel; Wang, Dingjie; Messerschmidt, Marc; Koglin, Jason E.; Boutet, Sébastien; Weierstall, Uwe; Cherezov, Vadim

2016-01-01

We describe the deposition of four datasets consisting of X-ray diffraction images acquired using serial femtosecond crystallography experiments on microcrystals of human G protein-coupled receptors, grown and delivered in lipidic cubic phase, at the Linac Coherent Light Source. The receptors are: the human serotonin receptor 2B in complex with an agonist ergotamine, the human δ-opioid receptor in complex with a bi-functional peptide ligand DIPP-NH2, the human smoothened receptor in complex with an antagonist cyclopamine, and finally the human angiotensin II type 1 receptor in complex with the selective antagonist ZD7155. All four datasets have been deposited, with minimal processing, in an HDF5-based file format, which can be used directly for crystallographic processing with CrystFEL or other software. We have provided processing scripts and supporting files for recent versions of CrystFEL, which can be used to validate the data. PMID:27479354

X-ray detectors at the Linac Coherent Light Source.

PubMed

Blaj, Gabriel; Caragiulo, Pietro; Carini, Gabriella; Carron, Sebastian; Dragone, Angelo; Freytag, Dietrich; Haller, Gunther; Hart, Philip; Hasi, Jasmine; Herbst, Ryan; Herrmann, Sven; Kenney, Chris; Markovic, Bojan; Nishimura, Kurtis; Osier, Shawn; Pines, Jack; Reese, Benjamin; Segal, Julie; Tomada, Astrid; Weaver, Matt

2015-05-01

Free-electron lasers (FELs) present new challenges for camera development compared with conventional light sources. At SLAC a variety of technologies are being used to match the demands of the Linac Coherent Light Source (LCLS) and to support a wide range of scientific applications. In this paper an overview of X-ray detector design requirements at FELs is presented and the various cameras in use at SLAC are described for the benefit of users planning experiments or analysts looking at data. Features and operation of the CSPAD camera, which is currently deployed at LCLS, are discussed, and the ePix family, a new generation of cameras under development at SLAC, is introduced.

X-ray detectors at the Linac Coherent Light Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blaj, Gabriel; Caragiulo, Pietro; Carini, Gabriella

Free-electron lasers (FELs) present new challenges for camera development compared with conventional light sources. At SLAC a variety of technologies are being used to match the demands of the Linac Coherent Light Source (LCLS) and to support a wide range of scientific applications. In this paper an overview of X-ray detector design requirements at FELs is presented and the various cameras in use at SLAC are described for the benefit of users planning experiments or analysts looking at data. Features and operation of the CSPAD camera, which is currently deployed at LCLS, are discussed, and the ePix family, a newmore » generation of cameras under development at SLAC, is introduced.« less

X-ray detectors at the Linac Coherent Light Source

DOE PAGES

Blaj, Gabriel; Caragiulo, Pietro; Carini, Gabriella; ...

2015-04-21

Free-electron lasers (FELs) present new challenges for camera development compared with conventional light sources. At SLAC a variety of technologies are being used to match the demands of the Linac Coherent Light Source (LCLS) and to support a wide range of scientific applications. In this paper an overview of X-ray detector design requirements at FELs is presented and the various cameras in use at SLAC are described for the benefit of users planning experiments or analysts looking at data. Features and operation of the CSPAD camera, which is currently deployed at LCLS, are discussed, and the ePix family, a newmore » generation of cameras under development at SLAC, is introduced.« less

X-ray detectors at the Linac Coherent Light Source

PubMed Central

Blaj, Gabriel; Caragiulo, Pietro; Carini, Gabriella; Carron, Sebastian; Dragone, Angelo; Freytag, Dietrich; Haller, Gunther; Hart, Philip; Hasi, Jasmine; Herbst, Ryan; Herrmann, Sven; Kenney, Chris; Markovic, Bojan; Nishimura, Kurtis; Osier, Shawn; Pines, Jack; Reese, Benjamin; Segal, Julie; Tomada, Astrid; Weaver, Matt

2015-01-01

Free-electron lasers (FELs) present new challenges for camera development compared with conventional light sources. At SLAC a variety of technologies are being used to match the demands of the Linac Coherent Light Source (LCLS) and to support a wide range of scientific applications. In this paper an overview of X-ray detector design requirements at FELs is presented and the various cameras in use at SLAC are described for the benefit of users planning experiments or analysts looking at data. Features and operation of the CSPAD camera, which is currently deployed at LCLS, are discussed, and the ePix family, a new generation of cameras under development at SLAC, is introduced. PMID:25931071

The fluid dynamics of microjet explosions caused by extremely intense X-ray pulses

NASA Astrophysics Data System (ADS)

Stan, Claudiu; Laksmono, Hartawan; Sierra, Raymond; Milathianaki, Despina; Koglin, Jason; Messerschmidt, Marc; Williams, Garth; Demirci, Hasan; Botha, Sabine; Nass, Karol; Stone, Howard; Schlichting, Ilme; Shoeman, Robert; Boutet, Sebastien

2014-11-01

Femtosecond X-ray scattering experiments at free-electron laser facilities typically requires liquid jet delivery methods to bring samples to the region of interaction with X-rays. We have imaged optically the damage process in water microjets due to intense hard X-ray pulses at the Linac Coherent Light Source (LCLS), using time-resolved imaging techniques to record movies at rates up to half a billion frames per second. For pulse energies larger than a few percent of the maximum pulse energy available at LCLS, the X-rays deposit energies much larger than the latent heat of vaporization in water, and induce a phase explosion that opens a gap in the jet. The LCLS pulses last a few tens of femtoseconds, but the full evolution of the broken jet is orders of magnitude slower - typically in the microsecond range - due to complex fluid dynamics processes triggered by the phase explosion. Although the explosion results in a complex sequence of phenomena, they lead to an approximately self-similar flow of the liquid in the jet.

X -band rf driven free electron laser driver with optics linearization

DOE PAGES

Sun, Yipeng; Emma, Paul; Raubenheimer, Tor; ...

2014-11-13

In this paper, a compact hard X-ray free electron lasers (FEL) design is proposed with all X-band rf acceleration and two stage bunch compression. It eliminates the need of a harmonic rf linearization section by employing optics linearization in its first stage bunch compression. Quadrupoles and sextupoles are employed in a bunch compressor one (BC1) design, in such a way that second order longitudinal dispersion of BC1 cancels the second order energy correlation in the electron beam. Start-to-end 6-D simulations are performed with all the collective effects included. Emittance growth in the horizontal plane due to coherent synchrotron radiation ismore » investigated and minimized, to be on a similar level with the successfully operating Linac coherent light source (LCLS). At a FEL radiation wavelength of 0.15 nm, a saturation length of 40 meters can be achieved by employing an undulator with a period of 1.5 cm. Without tapering, a FEL radiation power above 10 GW is achieved with a photon pulse length of 50 fs, which is LCLS-like performance. The overall length of the accelerator plus undulator is around 250 meters which is much shorter than the LCLS length of 1230 meters. That makes it possible to build hard X-ray FEL in a laboratory with limited size.« less

Dutch X-band SLAR calibration

NASA Technical Reports Server (NTRS)

Groot, J. S.

1990-01-01

In August 1989 the NASA/JPL airborne P/L/C-band DC-8 SAR participated in several remote sensing campaigns in Europe. Amongst other test sites, data were obtained of the Flevopolder test site in the Netherlands on August the 16th. The Dutch X-band SLAR was flown on the same date and imaged parts of the same area as the SAR. To calibrate the two imaging radars a set of 33 calibration devices was deployed. 16 trihedrals were used to calibrate a part of the SLAR data. This short paper outlines the X-band SLAR characteristics, the experimental set-up and the calibration method used to calibrate the SLAR data. Finally some preliminary results are given.

Time-Resolved IR-Absorption Spectroscopy of Hot-Electron Dynamics in Satellite and Upper Conduction Bands in GaP

NASA Technical Reports Server (NTRS)

Cavicchia, M. A.; Alfano, R. R.

1995-01-01

The relaxation dynamics of hot electrons in the X6 and X7 satellite and upper conduction bands in GaP was directly measured by femtosecond UV-pump-IR-probe absorption spectroscopy. From a fit to the induced IR-absorption spectra the dominant scattering mechanism giving rise to the absorption at early delay times was determined to be intervalley scattering of electrons out of the X7 upper conduction-band valley. For long delay times the dominant scattering mechanism is electron-hole scattering. Electron transport dynamics of the upper conduction band of GaP has been time resolved.

Cd-free buffer layer materials on Cu2ZnSn(SxSe1-x)4: Band alignments with ZnO, ZnS, and In2S3

NASA Astrophysics Data System (ADS)

Barkhouse, D. Aaron R.; Haight, Richard; Sakai, Noriyuki; Hiroi, Homare; Sugimoto, Hiroki; Mitzi, David B.

2012-05-01

The heterojunctions formed between Cu2ZnSn(SxSe1-x)4 (CZTSSe) and three Cd-free n-type buffers, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission and photovoltage spectroscopy. The electronic properties including the Fermi level location at the interface, band bending in the CZTSSe substrate, and valence and conduction band offsets were determined and correlated with device properties. We also describe a method for determining the band bending in the buffer layer and demonstrate this for the In2S3/CZTSSe system. The chemical bath deposited In2S3 buffer is found to have near optimal conduction band offset (0.15 eV), enabling the demonstration of Cd-free In2S3/CZTSSe solar cells with 7.6% power conversion efficiency.

Magnetic field effects on ultrafast lattice compression dynamics of Si(111) crystal when excited by linearly-polarized femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Hatanaka, Koji; Odaka, Hideho; Ono, Kimitoshi; Fukumura, Hiroshi

2007-03-01

Time-resolved X-ray diffraction measurements of Si (111) single crystal are performed when excited by linearly-polarized femtosecond laser pulses (780 nm, 260 fs, negatively-chirped, 1 kHz) under a magnetic field (0.47 T). Laser fluence on the sample surface is 40 mJ/cm^2, which is enough lower than the ablation threshold at 200 mJ/cm^2. Probing X-ray pulses of iron characteristic X-ray lines at 0.193604 and 0.193998 nm are generated by focusing femtosecond laser pulses onto audio-cassette tapes in air. Linearly-polarized femtosecond laser pulse irradiation onto Si(111) crystal surface induces transient lattice compression in the picosecond time range, which is confirmed by transient angle shift of X-ray diffraction to higher angles. Little difference of compression dynamics is observed when the laser polarization is changed from p to s-pol. without a magnetic field. On the other hand, under a magnetic field, the lattice compression dynamics changes when the laser is p-polarized which is vertical to the magnetic field vector. These results may be assigned to photo-carrier formation and energy-band distortion.

Mariner Venus Mercury 1973 S/X-band experiment

NASA Technical Reports Server (NTRS)

Levy, G. S.

1977-01-01

The S/X-band experiment on the Mariner Venus/Mercury 1973 spacecraft constituted a unique opportunity to demonstrate the capability of an X-band downlink coherent with the normal S-band downlink. This was both a technological and scientific experiment, and the results indicated that it was successful in both cases. Analysis of the tracking data shows that the new S/X data type was capable of reducing the miss distance at the planet Mercury by 80% (post-processed data). The use of S/X electron content was demonstrated by comparison with Faraday rotation data. An X-band turnaround telemetry experiment showed the feasibility of a planetary X-band link. In the science area, the model atmospheric environment of Venus was refined. The ionosphere of the planet was measured to a higher accuracy than before, and the value of the dual-frequency link for measuring the scale size of turbulence was demonstrated. The estimate of the scale size was increased from 100 m to above 5 km.

Automated x-ray/light field congruence using the LINAC EPID panel.

PubMed

Polak, Wojciech; O'Doherty, Jim; Jones, Matt

2013-03-01

X-ray/light field alignment is a test described in many guidelines for the routine quality control of clinical linear accelerators (LINAC). Currently, the gold standard method for measuring alignment is through utilization of radiographic film. However, many modern LINACs are equipped with an electronic portal imaging device (EPID) that may be used to perform this test and thus subsequently reducing overall cost, processing, and analysis time, removing operator dependency and the requirement to sustain the departmental film processor. This work describes a novel method of utilizing the EPID together with a custom inhouse designed jig and automatic image processing software allowing measurement of the light field size, x-ray field size, and congruence between them. The authors present results of testing the method for aS1000 and aS500 Varian EPID detectors for six LINACs at a range of energies (6, 10, and 15 MV) in comparison with the results obtained from the use of radiographic film. Reproducibility of the software in fully automatic operation under a range of operating conditions for a single image showed a congruence of 0.01 cm with a coefficient of variation of 0. Slight variation in congruence repeatability was noted through semiautomatic processing by four independent operators due to manual marking of positions on the jig. Testing of the methodology using the automatic method shows a high precision of 0.02 mm compared to a maximum of 0.06 mm determined by film processing. Intraindividual examination of operator measurements of congruence was shown to vary as much as 0.75 mm. Similar congruence measurements of 0.02 mm were also determined for a lower resolution EPID (aS500 model), after rescaling of the image to the aS1000 image size. The designed methodology was proven to be time efficient, cost effective, and at least as accurate as using the gold standard radiographic film. Additionally, congruence testing can be easily performed for all four cardinal

The X-ray correlation spectroscopy instrument at the Linac Coherent Light Source

DOE PAGES

Alonso-Mori, Roberto; Caronna, Chiara; Chollet, Matthieu; ...

2015-03-03

The X-ray Correlation Spectroscopy instrument is dedicated to the study of dynamics in condensed matter systems using the unique coherence properties of free-electron lasers. It covers a photon energy range of 4–25 keV. The intrinsic temporal characteristics of the Linac Coherent Light Source, in particular the 120 Hz repetition rate, allow for the investigation of slow dynamics (milliseconds) by means of X-ray photon correlation spectroscopy. Double-pulse schemes could probe dynamics on the picosecond timescale. In addition, a description of the instrument capabilities and recent achievements is presented.

A programmable ultra-low noise X-band exciter.

PubMed

MacMullen, A; Hoover, L R; Justice, R D; Callahan, B S

2001-07-01

A programmable ultra-low noise X-band exciter has been developed using commercial off-the-shelf components. Its phase noise is more than 10 dB below the best available microwave synthesizers. It covers a 7% frequency band with 0.1-Hz resolution. The X-band output at +23 dBm is a combination of signals from an X-band sapphire-loaded cavity oscillator (SLCO), a low noise UHF frequency synthesizer, and special-purpose frequency translation and up-conversion circuitry.

X-band uplink ground systems development: Part 2

NASA Technical Reports Server (NTRS)

Johns, C. E.

1987-01-01

The prototype X-band exciter testing has been completed. Stability and single-sideband phase noise measurements have been made on the X-band exciter signal (7.145-7.235 GHz) and on the coherent X- and S-band receiver test signals (8.4-8.5 GHz and 2.29-2.3 GHz) generated within the exciter equipment. Outputs are well within error budgets.

180 MW/180 KW pulse modulator for S-band klystron of LUE-200 linac of IREN installation of JINR

NASA Astrophysics Data System (ADS)

Su, Kim Dong; Sumbaev, A. P.; Shvetsov, V. N.

2014-09-01

The offer on working out of the pulse modulator with 180 MW pulse power and 180 kW average power for pulse S-band klystrons of LUE-200 linac of IREN installation at the Laboratory of neutron physics (FLNP) at JINR is formulated. Main requirements, key parameters and element base of the modulator are presented. The variant of the basic scheme on the basis of 14 (or 11) stage 2 parallel PFN with the thyratron switchboard (TGI2-10K/50) and six parallel high voltage power supplies (CCPS Power Supply) is considered.

Simulation of radar backscattering from snowpack at X-band and Ku-band

NASA Astrophysics Data System (ADS)

Gay, Michel; Phan, Xuan-Vu; Ferro-Famil, Laurent

2016-04-01

This paper presents a multilayer snowpack electromagnetic backscattering model, based on Dense Media Radiative Transfer (DMRT). This model is capable of simulating the interaction of electromagnetic wave (EMW) at X-band and Ku-band frequencies with multilayer snowpack. The air-snow interface and snow-ground backscattering components are calculated using the Integral Equation Model (IEM) by [1], whereas the volume backscattering component is calculated based on the solution of Vector Radiative Transfer (VRT) equation at order 1. Case study has been carried out using measurement data from NoSREx project [2], which include SnowScat data in X-band and Ku-band, TerraSAR-X acquisitions and snowpack stratigraphic in-situ measurements. The results of model simulations show good agreement with the radar observations, and therefore allow the DMRT model to be used in various applications, such as data assimilation [3]. [1] A.K. Fung and K.S. Chen, "An update on the iem surface backscattering model," Geoscience and Remote Sensing Letters, IEEE, vol. 1, no. 2, pp. 75 - 77, april 2004. [2] J. Lemmetyinen, A. Kontu, J. Pulliainen, A. Wiesmann, C. Werner, T. Nagler, H. Rott, and M. Heidinger, "Technical assistance for the deployment of an x- to ku-band scatterometer during the nosrex ii experiment," Final Report, ESA ESTEC Contract No. 22671/09/NL/JA., 2011. [3] X. V. Phan, L. Ferro-Famil, M. Gay, Y. Durand, M. Dumont, S. Morin, S. Allain, G. D'Urso, and A. Girard, "3d-var multilayer assimilation of x-band sar data into a detailed snowpack model," The Cryosphere Discussions, vol. 7, no. 5, pp. 4881-4912, 2013.

Femtosecond response of polyatomic molecules to ultra-intense hard X-rays.

PubMed

Rudenko, A; Inhester, L; Hanasaki, K; Li, X; Robatjazi, S J; Erk, B; Boll, R; Toyota, K; Hao, Y; Vendrell, O; Bomme, C; Savelyev, E; Rudek, B; Foucar, L; Southworth, S H; Lehmann, C S; Kraessig, B; Marchenko, T; Simon, M; Ueda, K; Ferguson, K R; Bucher, M; Gorkhover, T; Carron, S; Alonso-Mori, R; Koglin, J E; Correa, J; Williams, G J; Boutet, S; Young, L; Bostedt, C; Son, S-K; Santra, R; Rolles, D

2017-06-01

X-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions. Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 10 20 watts per square centimetre). However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities. Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption, which in a heteronuclear molecular system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge. In serial femtosecond crystallography of biological objects-an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure-the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects and has been suggested as a way of phasing the diffraction data. On the basis of experiments using either soft or less-intense hard X-rays, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions. Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 10 20 watts per square centimetre), hard (with photon energies of 8.3 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization of a molecule is

Femtosecond response of polyatomic molecules to ultra-intense hard X-rays

DOE PAGES

Rudenko, A.; Inhester, L.; Hanasaki, K.; ...

2017-05-31

We report x-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions. Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 10 20 watts per square centimetre). However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities. Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption, which in a heteronuclear molecularmore » system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge. In serial femtosecond crystallography of biological objects—an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure—the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects and has been suggested as a way of phasing the diffraction data. On the basis of experiments using either soft or less-intense hard X-rays, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions. Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 10 20 watts per square centimetre), hard (with photon energies of 8.3 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization

Femtosecond response of polyatomic molecules to ultra-intense hard X-rays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudenko, A.; Inhester, L.; Hanasaki, K.

We report x-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions. Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 10 20 watts per square centimetre). However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities. Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption, which in a heteronuclear molecularmore » system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge. In serial femtosecond crystallography of biological objects—an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure—the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects and has been suggested as a way of phasing the diffraction data. On the basis of experiments using either soft or less-intense hard X-rays, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions. Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 10 20 watts per square centimetre), hard (with photon energies of 8.3 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization

Modeling Multi-Bunch X-band Photoinjector Challenges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marsh, R A; Anderson, S G; Gibson, D J

An X-band test station is being developed at LLNL to investigate accelerator optimization for future upgrades to mono-energetic gamma-ray technology at LLNL. The test station will consist of a 5.5 cell X-band rf photoinjector, single accelerator section, and beam diagnostics. Of critical import to the functioning of the LLNL X-band system with multiple electron bunches is the performance of the photoinjector. In depth modeling of the Mark 1 LLNL/SLAC X-band rf photoinjector performance will be presented addressing important challenges that must be addressed in order to fabricate a multi-bunch Mark 2 photoinjector. Emittance performance is evaluated under different nominal electronmore » bunch parameters using electrostatic codes such as PARMELA. Wake potential is analyzed using electromagnetic time domain simulations using the ACE3P code T3P. Plans for multi-bunch experiments and implementation of photoinjector advances for the Mark 2 design will also be discussed.« less

The X-ray Correlation Spectroscopy instrument at the Linac Coherent Light Source

PubMed Central

Alonso-Mori, Roberto; Caronna, Chiara; Chollet, Matthieu; Curtis, Robin; Damiani, Daniel S.; Defever, Jim; Feng, Yiping; Flath, Daniel L.; Glownia, James M.; Lee, Sooheyong; Lemke, Henrik T.; Nelson, Silke; Bong, Eric; Sikorski, Marcin; Song, Sanghoon; Srinivasan, Venkat; Stefanescu, Daniel; Zhu, Diling; Robert, Aymeric

2015-01-01

The X-ray Correlation Spectroscopy instrument is dedicated to the study of dynamics in condensed matter systems using the unique coherence properties of free-electron lasers. It covers a photon energy range of 4–25 keV. The intrinsic temporal characteristics of the Linac Coherent Light Source, in particular the 120 Hz repetition rate, allow for the investigation of slow dynamics (milli­seconds) by means of X-ray photon correlation spectroscopy. Double-pulse schemes could probe dynamics on the picosecond timescale. A description of the instrument capabilities and recent achievements is presented. PMID:25931061

Apparatus and method for nanoflow liquid jet and serial femtosecond x-ray protein crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bogan, Michael J.; Laksmono, Hartawan; Sierra, Raymond G.

Techniques for nanoflow serial femtosecond x-ray protein crystallography include providing a sample fluid by mixing a plurality of a first target of interest with a carrier fluid and injecting the sample fluid into a vacuum chamber at a rate less than about 4 microliters per minute. In some embodiments, the carrier fluid has a viscosity greater than about 3 centipoise.

Analysis of copper contamination in transformer insulating material with nanosecond- and femtosecond-laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Aparna, N.; Vasa, N. J.; Sarathi, R.

2018-06-01

This work examines the oil-impregnated pressboard insulation of high-voltage power transformers, for the determination of copper contamination. Nanosecond- and femtosecond-laser-induced breakdown spectroscopy revealed atomic copper lines and molecular copper monoxide bands due to copper sulphide diffusion. X-ray diffraction studies also indicated the presence of CuO emission. Elemental and molecular mapping compared transformer insulating material ageing in different media—air, N2, He and vacuum.

X-Band RF Gun Development

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlieks, Arnold; Dolgashev, Valery; Tantawi, Sami

In support of the MEGa-ray program at LLNL and the High Gradient research program at SLAC, a new X-band multi-cell RF gun is being developed. This gun, similar to earlier guns developed at SLAC for Compton X-ray source program, will be a standing wave structure made of 5.5 cells operating in the pi mode with copper cathode. This gun was designed following criteria used to build SLAC X-band high gradient accelerating structures. It is anticipated that this gun will operate with surface electric fields on the cathode of 200 MeV/m with low breakdown rate. RF will be coupled into themore » structure through a final cell with symmetric duel feeds and with a shape optimized to minimize quadrupole field components. In addition, geometry changes to the original gun, operated with Compton X-ray source, will include a wider RF mode separation, reduced surface electric and magnetic fields.« less

Nonlinear increase of X-ray intensities from thin foils irradiated with a 200 TW femtosecond laser

PubMed Central

Faenov, A. Ya.; Colgan, J.; Hansen, S. B.; Zhidkov, A.; Pikuz, T. A.; Nishiuchi, M.; Pikuz, S. A.; Skobelev, I. Yu.; Abdallah, J.; Sakaki, H.; Sagisaka, A.; Pirozhkov, A. S.; Ogura, K.; Fukuda, Y.; Kanasaki, M.; Hasegawa, N.; Nishikino, M.; Kando, M.; Watanabe, Y.; Kawachi, T.; Masuda, S.; Hosokai, T.; Kodama, R.; Kondo, K.

2015-01-01

We report, for the first time, that the energy of femtosecond optical laser pulses, E, with relativistic intensities I > 1021  W/cm2 is efficiently converted to X-ray radiation, which is emitted by “hot” electron component in collision-less processes and heats the solid density plasma periphery. As shown by direct high-resolution spectroscopic measurements X-ray radiation from plasma periphery exhibits unusual non-linear growth ~E4–5 of its power. The non-linear power growth occurs far earlier than the known regime when the radiation reaction dominates particle motion (RDR). Nevertheless, the radiation is shown to dominate the kinetics of the plasma periphery, changing in this regime (now labeled RDKR) the physical picture of the laser plasma interaction. Although in the experiments reported here we demonstrated by observation of KK hollow ions that X-ray intensities in the keV range exceeds ~1017  W/cm2, there is no theoretical limit of the radiation power. Therefore, such powerful X-ray sources can produce and probe exotic material states with high densities and multiple inner-shell electron excitations even for higher Z elements. Femtosecond laser-produced plasmas may thus provide unique ultra-bright X-ray sources, for future studies of matter in extreme conditions, material science studies, and radiography of biological systems. PMID:26330230

Nonlinear increase of X-ray intensities from thin foils irradiated with a 200 TW femtosecond laser

DOE PAGES

Faenov, A. Ya.; Colgan, J.; Hansen, S. B.; ...

2015-09-02

We report, for the first time, that the energy of femtosecond optical laser pulses, E, with relativistic intensities I > 10 21 W/cm 2 is efficiently converted to X-ray radiation, which is emitted by “hot” electron component in collision-less processes and heats the solid density plasma periphery. As shown by direct high-resolution spectroscopic measurements X-ray radiation from plasma periphery exhibits unusual non-linear growth ~E 4–5 of its power. The non-linear power growth occurs far earlier than the known regime when the radiation reaction dominates particle motion (RDR). Nevertheless, the radiation is shown to dominate the kinetics of the plasma periphery,more » changing in this regime (now labeled RDKR) the physical picture of the laser plasma interaction. Although in the experiments reported here we demonstrated by observation of KK hollow ions that X-ray intensities in the keV range exceeds ~10 17 W/cm 2, there is no theoretical limit of the radiation power. Therefore, such powerful X-ray sources can produce and probe exotic material states with high densities and multiple inner-shell electron excitations even for higher Z elements. As a result, femtosecond laser-produced plasmas may thus provide unique ultra-bright X-ray sources, for future studies of matter in extreme conditions, material science studies, and radiography of biological systems.« less

Towards band structure and band offset engineering of monolayer Mo(1-x)W(x)S2 via Strain

NASA Astrophysics Data System (ADS)

Kim, Joon-Seok; Ahmad, Rafia; Pandey, Tribhuwan; Rai, Amritesh; Feng, Simin; Yang, Jing; Lin, Zhong; Terrones, Mauricio; Banerjee, Sanjay K.; Singh, Abhishek K.; Akinwande, Deji; Lin, Jung-Fu

2018-01-01

Semiconducting transition metal dichalcogenides (TMDs) demonstrate a wide range of optoelectronic properties due to their diverse elemental compositions, and are promising candidates for next-generation optoelectronics and energy harvesting devices. However, effective band offset engineering is required to implement practical structures with desirable functionalities. Here, we explore the pressure-induced band structure evolution of monolayer WS2 and Mo0.5W0.5S2 using hydrostatic compressive strain applied in a diamond anvil cell (DAC) apparatus and theoretical calculations, in order to study the modulation of band structure and explore the possibility of band alignment engineering through different compositions. Higher W composition in Mo(1-x)W(x)S2 contributes to a greater pressure-sensitivity of direct band gap opening, with a maximum value of 54 meV GPa-1 in WS2. Interestingly, while the conduction band minima (CBMs) remains largely unchanged after the rapid gap increase, valence band maxima (VBMs) significantly rise above the initial values. It is suggested that the pressure- and composition-engineering could introduce a wide variety of band alignments including type I, type II, and type III heterojunctions, and allow to construct precise structures with desirable functionalities. No structural transition is observed during the pressure experiments, implying the pressure could provide selective modulation of band offset.

Generation of stable subfemtosecond hard x-ray pulses with optimized nonlinear bunch compression

DOE PAGES

Huang, Senlin; Ding, Yuantao; Huang, Zhirong; ...

2014-12-15

In this paper, we propose a simple scheme that leverages existing x-ray free-electron laser hardware to produce stable single-spike, subfemtosecond x-ray pulses. By optimizing a high-harmonic radio-frequency linearizer to achieve nonlinear compression of a low-charge (20 pC) electron beam, we obtain a sharp current profile possessing a few-femtosecond full width at half maximum temporal duration. A reverse undulator taper is applied to enable lasing only within the current spike, where longitudinal space charge forces induce an electron beam time-energy chirp. Simulations based on the Linac Coherent Light Source parameters show that stable single-spike x-ray pulses with a duration less thanmore » 200 attoseconds can be obtained.« less

A split-beam probe-pump-probe scheme for femtosecond time resolved protein X-ray crystallography

PubMed Central

van Thor, Jasper J.; Madsen, Anders

2015-01-01

In order to exploit the femtosecond pulse duration of X-ray Free-Electron Lasers (XFEL) operating in the hard X-ray regime for ultrafast time-resolved protein crystallography experiments, critical parameters that determine the crystallographic signal-to-noise (I/σI) must be addressed. For single-crystal studies under low absorbed dose conditions, it has been shown that the intrinsic pulse intensity stability as well as mode structure and jitter of this structure, significantly affect the crystallographic signal-to-noise. Here, geometrical parameters are theoretically explored for a three-beam scheme: X-ray probe, optical pump, X-ray probe (or “probe-pump-probe”) which will allow experimental determination of the photo-induced structure factor amplitude differences, ΔF, in a ratiometric manner, thereby internally referencing the intensity noise of the XFEL source. In addition to a non-collinear split-beam geometry which separates un-pumped and pumped diffraction patterns on an area detector, applying an additional convergence angle to both beams by focusing leads to integration over mosaic blocks in the case of well-ordered stationary protein crystals. Ray-tracing X-ray diffraction simulations are performed for an example using photoactive yellow protein crystals in order to explore the geometrical design parameters which would be needed. The specifications for an X-ray split and delay instrument that implements both an offset angle and focused beams are discussed, for implementation of a probe-pump-probe scheme at the European XFEL. We discuss possible extension of single crystal studies to serial femtosecond crystallography, particularly in view of the expected X-ray damage and ablation due to the first probe pulse. PMID:26798786

A split-beam probe-pump-probe scheme for femtosecond time resolved protein X-ray crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

van Thor, Jasper J.; Madsen, Anders

In order to exploit the femtosecond pulse duration of X-ray Free-Electron Lasers (XFEL) operating in the hard X-ray regime for ultrafast time-resolved protein crystallography experiments, critical parameters that determine the crystallographic signal-to-noise (I/σI) must be addressed. For single-crystal studies under low absorbed dose conditions, it has been shown that the intrinsic pulse intensity stability as well as mode structure and jitter of this structure, significantly affect the crystallographic signal-to-noise. Here, geometrical parameters are theoretically explored for a three-beam scheme: X-ray probe, optical pump, X-ray probe (or “probe-pump-probe”) which will allow experimental determination of the photo-induced structure factor amplitude differences, ΔF,more » in a ratiometric manner, thereby internally referencing the intensity noise of the XFEL source. In addition to a non-collinear split-beam geometry which separates un-pumped and pumped diffraction patterns on an area detector, applying an additional convergence angle to both beams by focusing leads to integration over mosaic blocks in the case of well-ordered stationary protein crystals. Ray-tracing X-ray diffraction simulations are performed for an example using photoactive yellow protein crystals in order to explore the geometrical design parameters which would be needed. The specifications for an X-ray split and delay instrument that implements both an offset angle and focused beams are discussed, for implementation of a probe-pump-probe scheme at the European XFEL. We discuss possible extension of single crystal studies to serial femtosecond crystallography, particularly in view of the expected X-ray damage and ablation due to the first probe pulse.« less

A split-beam probe-pump-probe scheme for femtosecond time resolved protein X-ray crystallography

DOE PAGES

van Thor, Jasper J.; Madsen, Anders

2015-01-01

In order to exploit the femtosecond pulse duration of X-ray Free-Electron Lasers (XFEL) operating in the hard X-ray regime for ultrafast time-resolved protein crystallography experiments, critical parameters that determine the crystallographic signal-to-noise (I/σI) must be addressed. For single-crystal studies under low absorbed dose conditions, it has been shown that the intrinsic pulse intensity stability as well as mode structure and jitter of this structure, significantly affect the crystallographic signal-to-noise. Here, geometrical parameters are theoretically explored for a three-beam scheme: X-ray probe, optical pump, X-ray probe (or “probe-pump-probe”) which will allow experimental determination of the photo-induced structure factor amplitude differences, ΔF,more » in a ratiometric manner, thereby internally referencing the intensity noise of the XFEL source. In addition to a non-collinear split-beam geometry which separates un-pumped and pumped diffraction patterns on an area detector, applying an additional convergence angle to both beams by focusing leads to integration over mosaic blocks in the case of well-ordered stationary protein crystals. Ray-tracing X-ray diffraction simulations are performed for an example using photoactive yellow protein crystals in order to explore the geometrical design parameters which would be needed. The specifications for an X-ray split and delay instrument that implements both an offset angle and focused beams are discussed, for implementation of a probe-pump-probe scheme at the European XFEL. We discuss possible extension of single crystal studies to serial femtosecond crystallography, particularly in view of the expected X-ray damage and ablation due to the first probe pulse.« less

Emerging opportunities in structural biology with X-ray free-electron lasers

PubMed Central

Schlichting, Ilme; Miao, Jianwei

2012-01-01

X-ray free-electron lasers (X-FELs) produce X-ray pulses with extremely brilliant peak intensity and ultrashort pulse duration. It has been proposed that radiation damage can be “outrun” by using an ultra intense and short X-FEL pulse that passes a biological sample before the onset of significant radiation damage. The concept of “diffraction-before-destruction” has been demonstrated recently at the Linac Coherent Light Source, the first operational hard X-ray FEL, for protein nanocrystals and giant virus particles. The continuous diffraction patterns from single particles allow solving the classical “phase problem” by the oversampling method with iterative algorithms. If enough data are collected from many identical copies of a (biological) particle, its three-dimensional structure can be reconstructed. We review the current status and future prospects of serial femtosecond crystallography (SFX) and single-particle coherent diffraction imaging (CDI) with X-FELs. PMID:22922042

Femtosecond crystallography with ultrabright electrons and x-rays: capturing chemistry in action.

PubMed

Miller, R J Dwayne

2014-03-07

With the recent advances in ultrabright electron and x-ray sources, it is now possible to extend crystallography to the femtosecond time domain to literally light up atomic motions involved in the primary processes governing structural transitions. This review chronicles the development of brighter and brighter electron and x-ray sources that have enabled atomic resolution to structural dynamics for increasingly complex systems. The primary focus is on achieving sufficient brightness using pump-probe protocols to resolve the far-from-equilibrium motions directing chemical processes that in general lead to irreversible changes in samples. Given the central importance of structural transitions to conceptualizing chemistry, this emerging field has the potential to significantly improve our understanding of chemistry and its connection to driving biological processes.

An X-Band Gun Test Area at SLAC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Limborg-Deprey, C.; Adolphsen, C.; Chu, T.S.

The X-Band Test Area (XTA) is being assembled in the NLCTA tunnel at SLAC to serve as a test facility for new RF guns. The first gun to be tested will be an upgraded version of the 5.6 cell, 200 MV/m peak field X-band gun designed at SLAC in 2003 for the Compton Scattering experiment run in ASTA. This new version includes some features implemented in 2006 on the LCLS gun such as racetrack couplers, increased mode separation and elliptical irises. These upgrades were developed in collaboration with LLNL since the same gun will be used in an injector formore » a LLNL Gamma-ray Source. Our beamline includes an X-band acceleration section which takes the electron beam up to 100 MeV and an electron beam measurement station. Other X-Band guns such as the UCLA Hybrid gun will be characterized at our facility.« less

X-SAR: The X-band synthetic aperture radar on board the Space Shuttle

NASA Technical Reports Server (NTRS)

Werner, Marian U.

1993-01-01

The X-band synthetic aperture radar (X-SAR) is the German/Italian contribution to the NASA/JPL Shuttle Radar Lab missions as part of the preparation for the Earth Observation System (EOS) program. The Shuttle Radar Lab is a combination of several radars: an L-band (1.2 GHz) and a C-band (5.3 GHz) multipolarization SAR known as SIR-C (Shuttle Imaging Radar); and an X-band (9.6 GHz) vertically polarized SAR which will be operated synchronously over the same target areas to deliver calibrated multifrequency and multipolarization SAR data at multiple incidence angles from space. A joint German/Italian project office at DARA (German Space Agency) is responsible for the management of the X-SAR project. The space hardware has been developed and manufactured under industrial contract by Dornier and Alenia Spazio. Besides supporting all the technical and scientific tasks, DLR, in cooperation with ASI (Agencia Spaziale Italiano) is responsible for mission operation, calibration, and high precision SAR processing. In addition, DLR developed an airborne X-band SAR to support the experimenters with campaigns to prepare for the missions. The main advantage of adding a shorter wavelength (3 cm) radar to the SIR-C radars is the X-band radar's weaker penetration into vegetation and soil and its high sensitivity to surface roughness and associated phenomena. The performance of each of the three radars is comparable with respect to radiometric and geometric resolution.

Photon-in photon-out hard X-ray spectroscopy at the Linac Coherent Light Source

DOE PAGES

Alonso-Mori, Roberto; Sokaras, Dimosthenis; Zhu, Diling; ...

2015-04-15

X-ray free-electron lasers (FELs) have opened unprecedented possibilities to study the structure and dynamics of matter at an atomic level and ultra-fast timescale. Many of the techniques routinely used at storage ring facilities are being adapted for experiments conducted at FELs. In order to take full advantage of these new sources several challenges have to be overcome. They are related to the very different source characteristics and its resulting impact on sample delivery, X-ray optics, X-ray detection and data acquisition. Here it is described how photon-in photon-out hard X-ray spectroscopy techniques can be applied to study the electronic structure andmore » its dynamics of transition metal systems with ultra-bright and ultra-short FEL X-ray pulses. In particular, some of the experimental details that are different compared with synchrotron-based setups are discussed and illustrated by recent measurements performed at the Linac Coherent Light Source.« less

Impurity-Band Model for GaP1-xNx

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fluegel, B.; Zhang, Y.; Geisz, J. F.

2005-11-01

Low-temperature absorption studies on free-standing GaP1-xNx films provide direct experimental evidence that the host conduction-band minimum (CBM) near X1C does not plunge downward with increased nitrogen doping, contrary to what has been suggested recently; rather, it remains stationary for x up to 0.1%. This fact, combined with the results of earlier studies of the CBM at ..GAMMA.. and conduction-band edge near L, confirms that the giant bandgap lowering observed in GaP1-xNx results from a CBM that evolves purely from nitrogen impurity bands.

600 eV falcon-linac thomson x-ray source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crane, J K; LeSage, G P; Ditmire, T

2000-12-15

The advent of 3rd generation light sources such as the Advanced Light Source (ALS) at LBL, and the Advanced Photon Source at Argonne, have produced a revolution in x-ray probing of dense matter during the past decade. These machines use electron-synchrotrons in conjunction with undulator stages to produce 100 psec x-ray pulses with photon energies of several kiloelectronvolts (keV). The applications for x-ray probing of matter are numerous and diverse with experiments in medicine and biology, semiconductors and materials science, and plasma and solid state physics. In spite of the success of the 3rd generation light sources there is strongmore » motivation to push the capabilities of x-ray probing into new realms, requiring shorter pulses, higher brightness and harder x-rays. A 4th generation light source, the Linac Coherent Light Source (LCLS), is being considered at the Stanford Linear Accelerator [1]. The LCLS will produce multi-kilovolt x-rays of subpicosecond duration that are 10 orders of magnitude brighter than today's 3rd generation light sources.[1] Although the LCLS will provide unprecedented capability for performing time-resolved x-ray probing of ultrafast phenomena at solid densities, this machine will not be completed for many years. In the meantime there is a serious need for an ultrashort-pulse, high-brightness, hard x-ray source that is capable of probing deep into high-Z solid materials to measure dynamic effects that occur on picosecond time scales. Such an instrument would be ideal for probing the effects of shock propagation in solids using Bragg and Laue diffraction. These techniques can be used to look at phase transitions, melting and recrystallization, and the propagation of defects and dislocations well below the surface in solid materials. [2] These types of dynamic phenomena undermine the mechanical properties of metals and are of general interest in solid state physics, materials science, metallurgy, and have specific relevance to

Understanding of sub-band gap absorption of femtosecond-laser sulfur hyperdoped silicon using synchrotron-based techniques

PubMed Central

Limaye, Mukta V.; Chen, S. C.; Lee, C. Y.; Chen, L. Y.; Singh, Shashi B.; Shao, Y. C.; Wang, Y. F.; Hsieh, S. H.; Hsueh, H. C.; Chiou, J. W.; Chen, C. H.; Jang, L. Y.; Cheng, C. L.; Pong, W. F.; Hu, Y. F.

2015-01-01

The correlation between sub-band gap absorption and the chemical states and electronic and atomic structures of S-hyperdoped Si have been extensively studied, using synchrotron-based x-ray photoelectron spectroscopy (XPS), x-ray absorption near-edge spectroscopy (XANES), extended x-ray absorption fine structure (EXAFS), valence-band photoemission spectroscopy (VB-PES) and first-principles calculation. S 2p XPS spectra reveal that the S-hyperdoped Si with the greatest (~87%) sub-band gap absorption contains the highest concentration of S2− (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S2− species, but significantly increases the concentration of larger S clusters [polysulfides (Sn2−, n > 2)]. The Si K-edge XANES spectra show that S hyperdoping in Si increases (decreased) the occupied (unoccupied) electronic density of states at/above the conduction-band-minimum. VB-PES spectra evidently reveal that the S-dopants not only form an impurity band deep within the band gap, giving rise to the sub-band gap absorption, but also cause the insulator-to-metal transition in S-hyperdoped Si samples. Based on the experimental results and the calculations by density functional theory, the chemical state of the S species and the formation of the S-dopant states in the band gap of Si are critical in determining the sub-band gap absorptance of hyperdoped Si samples. PMID:26098075

Combining THz laser excitation with resonant soft X-ray scattering at the Linac Coherent Light Source

DOE PAGES

Turner, Joshua J.; Dakovski, Georgi L.; Hoffmann, Matthias C.; ...

2015-04-11

This paper describes the development of new instrumentation at the Linac Coherent Light Source for conducting THz excitation experiments in an ultra high vacuum environment probed by soft X-ray diffraction. This consists of a cantilevered, fully motorized mirror system which can provide 600 kV cm⁻¹ electric field strengths across the sample and an X-ray detector that can span the full Ewald sphere with in-vacuum motion. The scientific applications motivated by this development, the details of the instrument, and spectra demonstrating the field strengths achieved using this newly developed system are discussed.

Structure determination of molecules in an alignment laser field by femtosecond photoelectron diffraction using an X-ray free-electron laser

PubMed Central

Minemoto, Shinichirou; Teramoto, Takahiro; Akagi, Hiroshi; Fujikawa, Takashi; Majima, Takuya; Nakajima, Kyo; Niki, Kaori; Owada, Shigeki; Sakai, Hirofumi; Togashi, Tadashi; Tono, Kensuke; Tsuru, Shota; Wada, Ken; Yabashi, Makina; Yoshida, Shintaro; Yagishita, Akira

2016-01-01

We have successfully determined the internuclear distance of I2 molecules in an alignment laser field by applying our molecular structure determination methodology to an I 2p X-ray photoelectron diffraction profile observed with femtosecond X-ray free electron laser pulses. Using this methodology, we have found that the internuclear distance of the sample I2 molecules in an alignment Nd:YAG laser field of 6 × 1011 W/cm2 is elongated by from 0.18 to 0.30 Å “in average” relatively to the equilibrium internuclear distance of 2.666 Å. Thus, the present experiment constitutes a critical step towards the goal of femtosecond imaging of chemical reactions and opens a new direction for the study of ultrafast chemical reaction in the gas phase. PMID:27934891

X/X/Ka-band prime focus feed antenna for the Mars Observer beacon spacecraft

NASA Technical Reports Server (NTRS)

Stanton, P.; Reilly, H.; Esquivel, M.

1988-01-01

The results of an X/X/Ka-band feed design concept demonstration are presented. The purpose is to show the feasibility of adding a Ka-band beacon to the Mars Observer spacecraft. Scale model radiation patterns were made and analyzed.

Femtosecond Laser Eyewear Protection: Measurements and Precautions

PubMed Central

Stromberg, Christopher J.; Hadler, Joshua A.; Alberding, Brian G.; Heilweil, Edwin J.

2018-01-01

Ultrafast laser systems are becoming more widespread throughout the research and industrial communities yet eye protection for these high power, bright pulsed sources still require scrupulous characterization and testing before use. Femtosecond lasers, with pulses naturally possessing broad-bandwidth and high average power with variable repetition rate, can exhibit spectral side-bands and subtly changing center wavelengths, which may unknowingly affect eyewear safety protection. Pulse spectral characterization and power diagnostics are presented for a 80 MHz, Ti+3:Sapphire, ≈ 800 nm, ≈40 femtosecond oscillator system. Power and spectral transmission for 22 test samples are measured to determine whether they fall within manufacturer specifications. PMID:29353984

Femtosecond Laser Eyewear Protection: Measurements and Precautions.

PubMed

Stromberg, Christopher J; Hadler, Joshua A; Alberding, Brian G; Heilweil, Edwin J

2017-11-01

Ultrafast laser systems are becoming more widespread throughout the research and industrial communities yet eye protection for these high power, bright pulsed sources still require scrupulous characterization and testing before use. Femtosecond lasers, with pulses naturally possessing broad-bandwidth and high average power with variable repetition rate, can exhibit spectral side-bands and subtly changing center wavelengths, which may unknowingly affect eyewear safety protection. Pulse spectral characterization and power diagnostics are presented for a 80 MHz, Ti +3 :Sapphire, ≈ 800 nm, ≈40 femtosecond oscillator system. Power and spectral transmission for 22 test samples are measured to determine whether they fall within manufacturer specifications.

Diffraction data of core-shell nanoparticles from an X-ray free electron laser

DOE PAGES

Li, Xuanxuan; Chiu, Chun -Ya; Wang, Hsiang -Ju; ...

2017-04-11

X-ray free-electron lasers provide novel opportunities to conduct single particle analysis on nanoscale particles. Coherent diffractive imaging experiments were performed at the Linac Coherent Light Source (LCLS), SLAC National Laboratory, exposing single inorganic core-shell nanoparticles to femtosecond hard-X-ray pulses. Each facetted nanoparticle consisted of a crystalline gold core and a differently shaped palladium shell. Scattered intensities were observed up to about 7 nm resolution. Analysis of the scattering patterns revealed the size distribution of the samples, which is consistent with that obtained from direct real-space imaging by electron microscopy. Furthermore, scattering patterns resulting from single particles were selected and compiledmore » into a dataset which can be valuable for algorithm developments in single particle scattering research.« less

Femtosecond X-ray Diffraction: Applications for Laser-Irradiated Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wark, Justin S.

2009-09-10

Over the past few years short pulse x-ray diffraction at the nanosecond and picosecond level has become an established technique in many high-power laser laboratories for interrogating the lattice response of laser-perturbed and shocked matter, and is now finding applications in diagnosing the state of crystalline materials subject to quasi-isentropic compression. We review some of the previous results obtained in this area, for example the direct observation of coherent phonons, the first direct confirmation of the alpha-epsilon transition in shocked iron, and recent measurements indicating that the strength of matter can be measured at shock pressures exceeding a Mbar. Themore » majority of sources used to date have been laser-plasma based, with some work being performed using 3{sup rd} generation synchrotron sources. However, the development of 4{sup th} generation x-ray free-electron lasers, such as LCLS, afford many new opportunities, with pulse lengths in the femtosecond regime. The extremely low divergence and monochromatic nature of the LCLS beam make it well suited to study compressed polycrystalline matter, especially samples with small grain sizes. At extremely short pulse lengths, such that the pulse is shorter than an x-ray extinction depth traversal time, the diffraction process itself becomes time-dependent, and in certain cases the full wave-field solution will be required, particularly if the matter itself is being rapidly perturbed, as will occur if the intense x-ray radiation is used to create warm dense matter, as in recent experiments on FLASH at DESY.« less

Standard Observing Bands: Is Now the Time to Replace S/X with X/Ka?

NASA Technical Reports Server (NTRS)

Jacobs, C. S.; Lanyi, G. E.; Naudet, C. J.

2004-01-01

In this paper we will argue that the VLBI community should be developing a road map to transition from S/X to simultaneous X and Ka-band (32 GHz) observations. There are both negative and positive reasons for planning such a transition. On the negative side, we will outline concerns that S-band observations may be headed toward obsolescence. On the positive side, we will refer to evidence that X/Ka has potential for providing a more stable reference frame than S/X. We will propose timetables for a transition to X/Ka observing starting from the current status of X/Ka and plans that are now taking shape. First X/Ka fringes were obtained in 2001 with the Deep Space Network. Future plans will be discussed including a proposed X/Ka-band upgrade to the VLBA. Lastly, we will consider the need for a period of overlap between S/X and X/Ka so that the long and rich history of astrometric and geodetic VLBI is not compromised.

X-band preamplifier filter

NASA Technical Reports Server (NTRS)

Manshadi, F.

1986-01-01

A low-loss bandstop filter designed and developed for the Deep Space Network's 34-meter high-efficiency antennas is described. The filter is used for protection of the X-band traveling wave masers from the 20-kW transmitter signal. A combination of empirical and theoretical techniques was employed as well as computer simulation to verify the design before fabrication.

BEAM DYNAMICS STUDIES FOR A COMPACT CARBON ION LINAC FOR THERAPY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plastun, A.; Mustapha, B.; Nassiri, A.

2016-05-01

Feasibility of an Advanced Compact Carbon Ion Linac (ACCIL) for hadron therapy is being studied at Argonne National Laboratory in collaboration with RadiaBeam Technologies. The 45-meter long linac is designed to deliver 109 carbon ions per second with variable energy from 45 MeV/u to 450 MeV/u. S-band structure provides the acceleration in this range. The carbon beam energy can be adjusted from pulse to pulse, making 3D tumor scanning straightforward and fast. Front end accelerating structures such as RFQ, DTL and coupled DTL are designed to operate at lower frequencies. The design of the linac was accompanied with extensive end-to-endmore » beam dynamics studies which are presented in this paper.« less

A new RF window designed for high-power operation in an S-band LINAC RF system

NASA Astrophysics Data System (ADS)

Joo, Youngdo; Kim, Seung-Hwan; Hwang, Woonha; Ryu, Jiwan; Roh, Sungjoo

2016-09-01

A new RF window is designed for high-power operation at the Pohang Light Source-II (PLSII) S-band linear accelerator (LINAC) RF system. In order to reduce the strength of the electric field component perpendicular to the ceramic disk, which is commonly known as the main cause of most discharge breakdowns in ceramic disk, we replace the pill-box type cavity in the conventional RF window with an overmoded cavity. The overmoded cavity is coupled with input and output waveguides through dual side-wall coupling irises to reduce the electric field strength at the iris and the number of possible mode competitions. The finite-difference time-domain (FDTD) simulation, CST MWS, was used in the design process. The simulated maximum electric field component perpendicular to the ceramic for the new RF window is reduced by an order of magnitude compared with taht for the conventional RF window, which holds promise for stable high-power operation.

Band gap bowing in NixMg1−xO

PubMed Central

Niedermeier, Christian A.; Råsander, Mikael; Rhode, Sneha; Kachkanov, Vyacheslav; Zou, Bin; Alford, Neil; Moram, Michelle A.

2016-01-01

Epitaxial transparent oxide NixMg1−xO (0 ≤ x ≤ 1) thin films were grown on MgO(100) substrates by pulsed laser deposition. High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1−xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1−xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1−xO solid solution system. PMID:27503808

High-intensity double-pulse X-ray free-electron laser

DOE PAGES

Marinelli, A.; Ratner, D.; Lutman, A. A.; ...

2015-03-06

The X-ray free-electron laser has opened a new era for photon science, improving the X-ray brightness by ten orders of magnitude over previously available sources. Similar to an optical laser, the spectral and temporal structure of the radiation pulses can be tailored to the specific needs of many experiments by accurately manipulating the lasing medium, that is, the electron beam. Here we report the generation of mJ-level two-colour hard X-ray pulses of few femtoseconds duration with an XFEL driven by twin electron bunches at the Linac Coherent Light Source. This performance represents an improvement of over an order of magnitudemore » in peak power over state-of-the-art two-colour XFELs. The unprecedented intensity and temporal coherence of this new two-colour X-ray free-electron laser enable an entirely new set of scientific applications, ranging from X-ray pump/X-ray probe experiments to the imaging of complex biological samples with multiple wavelength anomalous dispersion.« less

Short-arc orbit determination using coherent X-band ranging data

NASA Technical Reports Server (NTRS)

Thurman, S. W.; Mcelrath, T. P.; Pollmeier, V. M.

1992-01-01

The use of X-band frequencies in ground-spacecraft and spacecraft-ground telecommunication links for current and future robotic interplanetary missions makes it possible to perform ranging measurements of greater accuracy than previously obtained. It is shown that ranging data of sufficient accuracy, when acquired from multiple stations, can sense the geocentric angular position of a distant spacecraft. The application of high-accuracy S/X-band and X-band ranging to orbit determination with relatively short data arcs is investigated in planetary approach and encounter scenarios. Actual trajectory solutions for the Ulysses spacecraft constructed from S/X-band ranging and Doppler data are presented; error covariance calculations are used to predict the performance of X-band ranging and Doppler data. The Ulysses trajectory solutions indicate that the aim point for the spacecraft's February 1992 Jupiter encounter was predicted to a geocentric accuracy of 0.20 to 0.23/microrad. Explicit modeling of range bias parameters for each station pass is shown to largely remove systematic ground system calibration errors and transmission media effects from the Ulysses range measurements, which would otherwise corrupt the angle finding capabilities of the data. The Ulysses solutions were found to be reasonably consistent with the theoretical results, which suggest that angular accuracies of 0.08 to 0.1/microrad are achievable with X-band ranging.

A doubly curved reflector X-band antenna with integrated IFF array

NASA Astrophysics Data System (ADS)

Alia, F.; Barbati, S.

Primary radar antennas and Identification Friend or Foe (IFF) antennas must rotate with the same speed and synchronism, so that the target echo and IFF transponder mark will appear to the operator at the same time and at the same angular direction. A doubly-curved reflector antenna with a six-element microstrip array integrated in the reflector surface is presented to meet this requirement. The main antenna operates at X-band for low angle search radar, while the secondary antenna operates at L-band for IFF functions. The new configuration minimizes masking of the X-band radiated energy as a result of the IFF L-band elements. In fact, the only effect of the microstrip array on the X-band radiation pattern is the presence of several sidelobes in the + or - 90 deg angular region. The proposed new solution is compared to three other L-band/X-band integrated antenna configurations, and is found to be more advantageous with respect to masking, mechanical aspects, and production costs.

Inflatable Antenna for CubeSat: Extension of the Previously Developed S-Band Design to the X-Band

NASA Technical Reports Server (NTRS)

Babuscia, Alessandra; Choi, Thomas; Cheung, Kar-Ming; Thangavelautham, Jekan; Ravichandran, Mithun; Chandra, Aman

2015-01-01

The inflatable antenna for CubeSat is a 1 meter antenna reflector designed with one side reflective Mylar, another side clear Mylar with a patch antenna at the focus. The development of this technology responds to the increasing need for more capable communication systems to allow CubeSats to operate autonomously in interplanetary missions. An initial version of the antenna for the S-Band was developed and tested in both anechoic chamber and vacuum chamber. Recent developments in transceivers and amplifiers for CubeSat at X-band motivated the extension from the S-Band to the X-Band. This paper describes the process of extending the design of the antenna to the X-Band focusing on patch antenna redesign, new manufacturing challenges and initial results of experimental tests.

Conceptual Design for the New RPI 2020 Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adolphsen, C.; Bane, K.; Dolgashev, V.

2014-10-29

The Rensselaer Polytechnic Institute (RPI) spectrometer is an installation based on an L-band linear accelerator designed and installed many decades ago. While this installation has served many important experiments over the decades, a new more powerful and more flexible linac to serve a wider range of experiments is envisioned as an upgrade to the existing installation by 2020.

Chemical trends of the luminescence in wide band gap II 1-xMn xVI semimagnetic semiconductors

NASA Astrophysics Data System (ADS)

Benecke, C.; Busse, W.; Gumlich, H.-E.

1990-04-01

Time resolved emission and excitation spectroscopy is used to investigate the Mn correlated luminescence in wide band gap II-VI compounds, i.e. Zn 1-xMn xS, Cd 1-xMn xSe, Zn 1-xMn xTe and Cd 1-xMn xTe. Additional Information has been obtained with CdxZnyMnzTe( x+ y+ z=1) in checking the luminescence by variation of the ratio of the cations Cd and Zn. Generally speaking, at least two distinct emissions bands can be observed for each II 1- xMn xVI compound. One emissions band is attributed to the internal transition 4T 1(G)→ 6A 1(S) of the 3d 5 electron of the Mn 2+ on regular metal sites with energies of about ≈2 eV. The other emission band is found to occur in the near infrared range of about ≈1.3 eV. This emission band is tentatively interpreted as a transition of Mn 2+ ions on interstitial sites or in small Mn chalcogenide clusters, both interpretations assuming cubic symmetry. This model is supported by the existence of low energy excitation bands and by the great similarity of the shape of the two emission bands which lead to comparable Huang-Rhys factors and effective phonon energies. Also the established trend in the experimental data of the II-VI compounds under consideration confirm this interpretation. For both the IR and the yellow Mn 2+ center, the Racah parameters B and C and the crystal field parameter Dq are determined on the basis of experimental data. As a result, the energy of both the emission and the excitation bands is predominantly determined by the sorrounding anions. These bands shift to higher energies when the anions are changed in the fixed order: Te→Se→S. Regularly, there is also a spectral shift when Zn is replaced by Cd, which is smaller than the shift due to the variation of onions.

Technical Note: A Feasibility Study of Using the Flat Panel Detector on Linac for the kV X-ray Generator Test.

PubMed

Cai, Bin; Dolly, Steven; Kamal, Gregory; Yaddanapudi, Sridhar; Sun, Baozhou; Goddu, S Murty; Mutic, Sasa; Li, Hua

2018-04-28

To investigate the feasibility of using kV flat panel detector on linac for consistency evaluations of kV X-ray generator performance. An in-house designed aluminum (Al) array phantom with six 9×9 cm 2 square regions having various thickness was proposed and used in this study. Through XML script-driven image acquisition, kV images with various acquisition settings were obtained using the kV flat panel detector. Utilizing pre-established baseline curves, the consistency of X-ray tube output characteristics including tube voltage accuracy, exposure accuracy and exposure linearity were assessed through image quality assessment metrics including ROI mean intensity, ROI standard deviation (SD) and noise power spectrums (NPS). The robustness of this method was tested on two linacs for a three-month period. With the proposed method, tube voltage accuracy can be verified through conscience check with a 2% tolerance and 2 kVp intervals for forty different kVp settings. The exposure accuracy can be tested with a 4% consistency tolerance for three mAs settings over forty kVp settings. The exposure linearity tested with three mAs settings achieved a coefficient of variation (CV) of 0.1. We proposed a novel approach that uses the kV flat panel detector available on linac for X-ray generator test. This approach eliminates the inefficiencies and variability associated with using third party QA detectors while enabling an automated process. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

PubMed Central

Ryan, Rebecca A.; Williams, Sophie; Martin, Andrew V.; Dilanian, Ruben A.; Darmanin, Connie; Putkunz, Corey T.; Wood, David; Streltsov, Victor A.; Jones, Michael W.M.; Gaffney, Naylyn; Hofmann, Felix; Williams, Garth J.; Boutet, Sebastien; Messerschmidt, Marc; Seibert, M. Marvin; Curwood, Evan K.; Balaur, Eugeniu; Peele, Andrew G.; Nugent, Keith A.; Quiney, Harry M.; Abbey, Brian

2017-01-01

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered 'random'. This would then allow the supposedly incoherent contribution from the electronic motion to be treated as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. This paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data. PMID:28872125

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryan, Rebecca A.; Williams, Sophie; Martin, Andrew V.

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered 'random'. This would then allow the supposedly incoherent contribution from the electronic motion to be treatedmore » as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C 60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C 60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. Our paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.« less

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

DOE PAGES

Ryan, Rebecca A.; Williams, Sophie; Martin, Andrew V.; ...

2017-08-22

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered 'random'. This would then allow the supposedly incoherent contribution from the electronic motion to be treatedmore » as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C 60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C 60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. Our paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.« less

Femtosecond Pulse Characterization as Applied to One-Dimensional Photonic Band Edge Structures

NASA Technical Reports Server (NTRS)

Fork, Richard L.; Gamble, Lisa J.; Diffey, William M.

1999-01-01

The ability to control the group velocity and phase of an optical pulse is important to many current active areas of research. Electronically addressable one-dimensional photonic crystals are an attractive candidate to achieve this control. This report details work done toward the characterization of photonic crystals and improvement of the characterization technique. As part of the work, the spectral dependence of the group delay imparted by a GaAs/AlAs photonic crystal was characterized. Also, a first generation an electrically addressable photonic crystal was tested for the ability to electronically control the group delay. The measurement technique, using 100 femtosecond continuum pulses was improved to yield high spectral resolution (1.7 nanometers) and concurrently with high temporal resolution (tens of femtoseconds). Conclusions and recommendations based upon the work done are also presented.

Polarization control in an X-ray free-electron laser

DOE PAGES

Lutman, Alberto A.; MacArthur, James P.; Ilchen, Markus; ...

2016-05-09

X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500–1,200 eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98 –0.04 +0.02 at 707 eV and may be scanned inmore » energy. We also present a new two-colour X-ray pump–X-ray probe operating mode for the LCLS. As a result, energy differences of ΔE/E = 2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified.« less

Hybrid density functional study of band alignment in ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures.

PubMed

Wang, Zhenhai; Zhao, Mingwen; Wang, Xiaopeng; Xi, Yan; He, Xiujie; Liu, Xiangdong; Yan, Shishen

2012-12-05

The band alignment in ZnO-GaN and related heterostructures is crucial for uses in solar harvesting technology. Here, we report our density functional calculations of the band alignment and optical properties of ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures using a Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. We found that the conventional GGA functionals underestimate not only the band gap but also the band offset of these heterostructures. Using the hybrid functional calculations, we show that the (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution has a direct band gap of about 2.608 eV, in good agreement with the experimental data. More importantly, this solid solution forms type-II band alignment with the host materials. A GaN-(Ga(1-x)Zn(x))(N(1-x)O(x))-ZnO core-shell solar cell model is presented to improve the visible light absorption ability and carrier collection efficiency.

Ballistic-electron-emission spectroscopy of Al{sub x}Ga{sub 1{minus}x}As/GaAs heterostructures: Conduction-band offsets, transport mechanisms, and band-structure effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

OShea, J.J.; Brazel, E.G.; Rubin, M.E.

1997-07-01

We report an extensive investigation of semiconductor band-structure effects in single-barrier Al{sub x}Ga{sub 1{minus}x}As/GaAs heterostructures using ballistic-electron-emission spectroscopy (BEES). The transport mechanisms in these single-barrier structures were studied systematically as a function of temperature and Al composition over the full compositional range (0{le}x{le}1). The initial ({Gamma}) BEES thresholds for Al{sub x}Ga{sub 1{minus}x}As single barriers with 0{le}x{le}0.42 were extracted using a model which includes the complete transmission probability of the metal-semiconductor interface and the semiconductor heterostructure. Band offsets measured by BEES are in good agreement with previous measurements by other techniques which demonstrates the accuracy of this technique. BEES measurements atmore » 77 K give the same band-offset values as at room temperature. When a reverse bias is applied to the heterostructures, the BEES thresholds shift to lower voltages in good agreement with the expected bias-induced band-bending. In the indirect band-gap regime ({ital x}{gt}0.45), spectra show a weak ballistic-electron-emission microscopy current contribution due to intervalley scattering through Al{sub x}Ga{sub 1{minus}x}As {ital X} valley states. Low-temperature spectra show a marked reduction in this intervalley current component, indicating that intervalley phonon scattering at the GaAs/Al{sub x}Ga{sub 1{minus}x}As interface produces a significant fraction of this{ital X} valley current. A comparison of the BEES thresholds with the expected composition dependence of the Al{sub x}Ga{sub 1{minus}x}As {Gamma}, {ital L}, and {ital X} points yields good agreement over the entire composition range. {copyright} {ital 1997} {ital The American Physical Society}« less

THz-pump and X-ray-probe sources based on an electron linac

NASA Astrophysics Data System (ADS)

Setiniyaz, Sadiq; Park, Seong Hee; Kim, Hyun Woo; Vinokurov, Nikolay A.; Jang, Kyu-Ha; Lee, Kitae; Baek, In Hyung; Jeong, Young Uk

2017-11-01

We describe a compact THz-pump and X-ray-probe beamline, based on an electron linac, for ultrafast time-resolved diffraction applications. Two high-energy electron (γ > 50) bunches, 5 ns apart, impinge upon a single-foil or multifoil radiator and generate THz radiation and X-rays simultaneously. The THz pulse from the first bunch is synchronized to the X-ray beam of the second bunch by using an adjustable optical delay of a THz pulse. The peak power of THz radiation from the multifoil radiator is estimated to be 0.14 GW for a 200 pC well-optimized electron bunch. GEANT4 simulations show that a carbon foil with a thickness of 0.5-1.0 mm has the highest yield of 10-20 keV hard X-rays for a 25 MeV beam, which is approximately 103 photons/(keV pC-electrons) within a few degrees of the polar angle. A carbon multifoil radiator with 35 foils (25 μm thick each) can generate close to 103 hard X-rays/(keV pC-electrons) within a 2° acceptance angle. With 200 pC charge and a 100 Hz repetition rate, we can generate 107 X-rays per 1 keV energy bin per second or 105 X-rays per 1 keV energy bin per pulse. The longitudinal time profile of an X-ray pulse ranges from 400 to 600 fs depending on the acceptance angle. The broadening of the time duration of an X-ray pulse is observed owing to its diverging effect. A double-crystal monochromator will be used to select and transport the desired X-rays to the sample. The heating of the radiators by an electron beam is negligible because of the low beam current.

THz-pump and X-ray-probe sources based on an electron linac.

PubMed

Setiniyaz, Sadiq; Park, Seong Hee; Kim, Hyun Woo; Vinokurov, Nikolay A; Jang, Kyu-Ha; Lee, Kitae; Baek, In Hyung; Jeong, Young Uk

2017-11-01

We describe a compact THz-pump and X-ray-probe beamline, based on an electron linac, for ultrafast time-resolved diffraction applications. Two high-energy electron (γ > 50) bunches, 5 ns apart, impinge upon a single-foil or multifoil radiator and generate THz radiation and X-rays simultaneously. The THz pulse from the first bunch is synchronized to the X-ray beam of the second bunch by using an adjustable optical delay of a THz pulse. The peak power of THz radiation from the multifoil radiator is estimated to be 0.14 GW for a 200 pC well-optimized electron bunch. GEANT4 simulations show that a carbon foil with a thickness of 0.5-1.0 mm has the highest yield of 10-20 keV hard X-rays for a 25 MeV beam, which is approximately 10 3 photons/(keV pC-electrons) within a few degrees of the polar angle. A carbon multifoil radiator with 35 foils (25 μm thick each) can generate close to 10 3 hard X-rays/(keV pC-electrons) within a 2° acceptance angle. With 200 pC charge and a 100 Hz repetition rate, we can generate 10 7 X-rays per 1 keV energy bin per second or 10 5 X-rays per 1 keV energy bin per pulse. The longitudinal time profile of an X-ray pulse ranges from 400 to 600 fs depending on the acceptance angle. The broadening of the time duration of an X-ray pulse is observed owing to its diverging effect. A double-crystal monochromator will be used to select and transport the desired X-rays to the sample. The heating of the radiators by an electron beam is negligible because of the low beam current.

Carrier-Specific Femtosecond XUV Transient Absorption of PbI 2 Reveals Ultrafast Nonradiative Recombination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Ming-Fu; Verkamp, Max A.; Leveillee, Joshua

Femtosecond carrier recombination in PbI 2 is measured using tabletop high-harmonic extreme ultraviolet (XUV) transient absorption spectroscopy and ultrafast electron diffraction. XUV absorption from 45 eV to 62 eV measures transitions from the iodine 4d core level to the conduction band density of states. Photoexcitation at 400 nm creates separate and distinct transient absorption signals for holes and electrons, separated in energy by the 2.4 eV band gap of the semiconductor. The shape of the conduction band and therefore the XUV absorption spectrum is temperature dependent, and nonradiative recombination converts the initial electronic excitation to thermal excitation within picoseconds. Ultrafastmore » electron diffraction (UED) is used to measure the lattice temperature and confirm the recombination mechanism. Lastly, the XUV and UED results support a 2nd-order recombination model with a rate constant of 2.5x10 -9 cm 3/s.« less

Carrier-Specific Femtosecond XUV Transient Absorption of PbI 2 Reveals Ultrafast Nonradiative Recombination

DOE PAGES

Lin, Ming-Fu; Verkamp, Max A.; Leveillee, Joshua; ...

2017-11-30

Femtosecond carrier recombination in PbI 2 is measured using tabletop high-harmonic extreme ultraviolet (XUV) transient absorption spectroscopy and ultrafast electron diffraction. XUV absorption from 45 eV to 62 eV measures transitions from the iodine 4d core level to the conduction band density of states. Photoexcitation at 400 nm creates separate and distinct transient absorption signals for holes and electrons, separated in energy by the 2.4 eV band gap of the semiconductor. The shape of the conduction band and therefore the XUV absorption spectrum is temperature dependent, and nonradiative recombination converts the initial electronic excitation to thermal excitation within picoseconds. Ultrafastmore » electron diffraction (UED) is used to measure the lattice temperature and confirm the recombination mechanism. Lastly, the XUV and UED results support a 2nd-order recombination model with a rate constant of 2.5x10 -9 cm 3/s.« less

Crystal structure of rhodopsin bound to arrestin by femtosecond X-ray laser

PubMed Central

Kang, Yanyong; Zhou, X. Edward; Gao, Xiang; He, Yuanzheng; Liu, Wei; Ishchenko, Andrii; Barty, Anton; White, Thomas A.; Yefanov, Oleksandr; Han, Gye Won; Xu, Qingping; de Waal, Parker W.; Ke, Jiyuan; Eileen Tan, M. H.; Zhang, Chenghai; Moeller, Arne; West, Graham M.; Pascal, Bruce; Van Eps, Ned; Caro, Lydia N.; Vishnivetskiy, Sergey A.; Lee, Regina J.; Suino-Powell, Kelly M.; Gu, Xin; Pal, Kuntal; Ma, Jinming; Zhi, Xiaoyong; Boutet, Sébastien; Williams, Garth J.; Messerschmidt, Marc; Gati, Cornelius; Zatsepin, Nadia A.; Wang, Dingjie; James, Daniel; Basu, Shibom; Roy-Chowdhury, Shatabdi; Conrad, Chelsie; Coe, Jesse; Liu, Haiguang; Lisova, Stella; Kupitz, Christopher; Grotjohann, Ingo; Fromme, Raimund; Jiang, Yi; Tan, Minjia; Yang, Huaiyu; Li, Jun; Wang, Meitian; Zheng, Zhong; Li, Dianfan; Howe, Nicole; Zhao, Yingming; Standfuss, Jörg; Diederichs, Kay; Dong, Yuhui; Potter, Clinton S; Carragher, Bridget; Caffrey, Martin; Jiang, Hualiang; Chapman, Henry N.; Spence, John C. H.; Fromme, Petra; Weierstall, Uwe; Ernst, Oliver P.; Katritch, Vsevolod; Gurevich, Vsevolod V.; Griffin, Patrick R.; Hubbell, Wayne L.; Stevens, Raymond C.; Cherezov, Vadim; Melcher, Karsten; Xu, H. Eric

2015-01-01

G protein-coupled receptors (GPCRs) signal primarily through G proteins or arrestins. Arrestin binding to GPCRs blocks G protein interaction and redirects signaling to numerous G protein-independent pathways. Here we report the crystal structure of a constitutively active form of human rhodopsin bound to a pre-activated form of the mouse visual arrestin, determined by serial femtosecond X-ray laser crystallography. Together with extensive biochemical and mutagenesis data, the structure reveals an overall architecture of the rhodopsin-arrestin assembly, in which rhodopsin uses distinct structural elements, including TM7 and Helix 8 to recruit arrestin. Correspondingly, arrestin adopts the pre-activated conformation, with a ~20° rotation between the N- and C- domains, which opens up a cleft in arrestin to accommodate a short helix formed by the second intracellular loop of rhodopsin. This structure provides a basis for understanding GPCR-mediated arrestin-biased signaling and demonstrates the power of X-ray lasers for advancing the frontiers of structural biology. PMID:26200343

Crystal structure of rhodopsin bound to arrestin by femtosecond X-ray laser.

PubMed

Kang, Yanyong; Zhou, X Edward; Gao, Xiang; He, Yuanzheng; Liu, Wei; Ishchenko, Andrii; Barty, Anton; White, Thomas A; Yefanov, Oleksandr; Han, Gye Won; Xu, Qingping; de Waal, Parker W; Ke, Jiyuan; Tan, M H Eileen; Zhang, Chenghai; Moeller, Arne; West, Graham M; Pascal, Bruce D; Van Eps, Ned; Caro, Lydia N; Vishnivetskiy, Sergey A; Lee, Regina J; Suino-Powell, Kelly M; Gu, Xin; Pal, Kuntal; Ma, Jinming; Zhi, Xiaoyong; Boutet, Sébastien; Williams, Garth J; Messerschmidt, Marc; Gati, Cornelius; Zatsepin, Nadia A; Wang, Dingjie; James, Daniel; Basu, Shibom; Roy-Chowdhury, Shatabdi; Conrad, Chelsie E; Coe, Jesse; Liu, Haiguang; Lisova, Stella; Kupitz, Christopher; Grotjohann, Ingo; Fromme, Raimund; Jiang, Yi; Tan, Minjia; Yang, Huaiyu; Li, Jun; Wang, Meitian; Zheng, Zhong; Li, Dianfan; Howe, Nicole; Zhao, Yingming; Standfuss, Jörg; Diederichs, Kay; Dong, Yuhui; Potter, Clinton S; Carragher, Bridget; Caffrey, Martin; Jiang, Hualiang; Chapman, Henry N; Spence, John C H; Fromme, Petra; Weierstall, Uwe; Ernst, Oliver P; Katritch, Vsevolod; Gurevich, Vsevolod V; Griffin, Patrick R; Hubbell, Wayne L; Stevens, Raymond C; Cherezov, Vadim; Melcher, Karsten; Xu, H Eric

2015-07-30

G-protein-coupled receptors (GPCRs) signal primarily through G proteins or arrestins. Arrestin binding to GPCRs blocks G protein interaction and redirects signalling to numerous G-protein-independent pathways. Here we report the crystal structure of a constitutively active form of human rhodopsin bound to a pre-activated form of the mouse visual arrestin, determined by serial femtosecond X-ray laser crystallography. Together with extensive biochemical and mutagenesis data, the structure reveals an overall architecture of the rhodopsin-arrestin assembly in which rhodopsin uses distinct structural elements, including transmembrane helix 7 and helix 8, to recruit arrestin. Correspondingly, arrestin adopts the pre-activated conformation, with a ∼20° rotation between the amino and carboxy domains, which opens up a cleft in arrestin to accommodate a short helix formed by the second intracellular loop of rhodopsin. This structure provides a basis for understanding GPCR-mediated arrestin-biased signalling and demonstrates the power of X-ray lasers for advancing the frontiers of structural biology.

Retinal isomerization in bacteriorhodopsin captured by a femtosecond x-ray laser.

PubMed

Nogly, Przemyslaw; Weinert, Tobias; James, Daniel; Carbajo, Sergio; Ozerov, Dmitry; Furrer, Antonia; Gashi, Dardan; Borin, Veniamin; Skopintsev, Petr; Jaeger, Kathrin; Nass, Karol; Båth, Petra; Bosman, Robert; Koglin, Jason; Seaberg, Matthew; Lane, Thomas; Kekilli, Demet; Brünle, Steffen; Tanaka, Tomoyuki; Wu, Wenting; Milne, Christopher; White, Thomas; Barty, Anton; Weierstall, Uwe; Panneels, Valerie; Nango, Eriko; Iwata, So; Hunter, Mark; Schapiro, Igor; Schertler, Gebhard; Neutze, Richard; Standfuss, Jörg

2018-06-14

Ultrafast isomerization of retinal is the primary step in photoresponsive biological functions including vision in humans and ion-transport across bacterial membranes. We studied the sub-picosecond structural dynamics of retinal isomerization in the light-driven proton pump bacteriorhodopsin using an x-ray laser. A series of structural snapshots with near-atomic spatial and temporal resolution in the femtosecond regime show how the excited all- trans retinal samples conformational states within the protein binding pocket prior to passing through a twisted geometry and emerging in the 13 -cis conformation. Our findings suggest ultrafast collective motions of aspartic acid residues and functional water molecules in the proximity of the retinal Schiff base as a key ingredient for this stereo-selective and efficient photochemical reaction. Copyright © 2018, American Association for the Advancement of Science.

Small X-Band Oscillator Antennas

NASA Technical Reports Server (NTRS)

Lee, Richard Q.; Miranda, Felix A.; Clark, Eric B.; Wilt, David M.; Mueller, Carl H.; Kory, Carol L.; Lambert, Kevin M.

2009-01-01

A small, segmented microstrip patch antenna integrated with an X-band feedback oscillator on a high-permittivity substrate has been built and tested. This oscillator antenna is a prototype for demonstrating the feasibility of such devices as compact, low-power-consumption building blocks of advanced, lightweight, phased antenna arrays that would generate steerable beams for communication and remotesensing applications.

The Linac Coherent Light Source

DOE PAGES

White, William E.; Robert, Aymeric; Dunne, Mike

2015-05-01

The Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory was the first hard X-ray free-electron laser (FEL) to operate as a user facility. After five years of operation, LCLS is now a mature FEL user facility. Our personal views about opportunities and challenges inherent to these unique light sources are discussed.

Electron linac for medical isotope production with improved energy efficiency and isotope recovery

DOEpatents

Noonan, John; Walters, Dean; Virgo, Matt; Lewellen, John

2015-09-08

A method and isotope linac system are provided for producing radio-isotopes and for recovering isotopes. The isotope linac is an energy recovery linac (ERL) with an electron beam being transmitted through an isotope-producing target. The electron beam energy is recollected and re-injected into an accelerating structure. The ERL provides improved efficiency with reduced power requirements and provides improved thermal management of an isotope target and an electron-to-x-ray converter.

Native sulfur/chlorine SAD phasing for serial femtosecond crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakane, Takanori; Song, Changyong; POSTECH, Pohang 790-784

Sulfur SAD phasing facilitates the structure determination of diverse native proteins using femtosecond X-rays from free-electron lasers via serial femtosecond crystallography. Serial femtosecond crystallography (SFX) allows structures to be determined with minimal radiation damage. However, phasing native crystals in SFX is not very common. Here, the structure determination of native lysozyme from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of sulfur and chlorine at a wavelength of 1.77 Å is successfully demonstrated. This sulfur SAD method can be applied to a wide range of proteins, which will improve the determination of native crystal structures.

Femtosecond X-ray coherent diffraction of aligned amyloid fibrils on low background graphene.

PubMed

Seuring, Carolin; Ayyer, Kartik; Filippaki, Eleftheria; Barthelmess, Miriam; Longchamp, Jean-Nicolas; Ringler, Philippe; Pardini, Tommaso; Wojtas, David H; Coleman, Matthew A; Dörner, Katerina; Fuglerud, Silje; Hammarin, Greger; Habenstein, Birgit; Langkilde, Annette E; Loquet, Antoine; Meents, Alke; Riek, Roland; Stahlberg, Henning; Boutet, Sébastien; Hunter, Mark S; Koglin, Jason; Liang, Mengning; Ginn, Helen M; Millane, Rick P; Frank, Matthias; Barty, Anton; Chapman, Henry N

2018-05-09

Here we present a new approach to diffraction imaging of amyloid fibrils, combining a free-standing graphene support and single nanofocused X-ray pulses of femtosecond duration from an X-ray free-electron laser. Due to the very low background scattering from the graphene support and mutual alignment of filaments, diffraction from tobacco mosaic virus (TMV) filaments and amyloid protofibrils is obtained to 2.7 Å and 2.4 Å resolution in single diffraction patterns, respectively. Some TMV diffraction patterns exhibit asymmetry that indicates the presence of a limited number of axial rotations in the XFEL focus. Signal-to-noise levels from individual diffraction patterns are enhanced using computational alignment and merging, giving patterns that are superior to those obtainable from synchrotron radiation sources. We anticipate that our approach will be a starting point for further investigations into unsolved structures of filaments and other weakly scattering objects.

Valence band offsets of Sc x Ga1-x N/AlN and Sc x Ga1-x N/GaN heterojunctions

NASA Astrophysics Data System (ADS)

Tsui, H. C. L.; Goff, L. E.; Palgrave, R. G.; Beere, H. E.; Farrer, I.; Ritchie, D. A.; Moram, M. A.

2016-07-01

The valence band offsets of Sc x Ga1-x N/AlN heterojunctions were measured by x-ray photoelectron spectroscopy (XPS) and were found to increase from 0.42 eV to 0.95 eV as the Sc content x increased from 0 to 0.15. The increase in valence band offset with increasing x is attributed to the corresponding increase in spontaneous polarization of the wurtzite structure. The Sc x Ga1-x N/AlN heterojunction is type I, similar to other III-nitride-based heterojunctions. The data also indicate that a type II staggered heterojunction, which can enhance spatial charge separation, could be formed if Sc x Ga1-x N is grown on GaN.

Development and performance test of a new high power RF window in S-band PLS-II LINAC

NASA Astrophysics Data System (ADS)

Hwang, Woon-Ha; Joo, Young-Do; Kim, Seung-Hwan; Choi, Jae-Young; Noh, Sung-Ju; Ryu, Ji-Wan; Cho, Young-Ki

2017-12-01

A prototype of RF window was developed in collaboration with the Pohang Accelerator Laboratory (PAL) and domestic companies. High power performance tests of the single RF window were conducted at PAL to verify the operational characteristics for its application in the Pohang Light Source-II (PLS-II) linear accelerator (Linac). The tests were performed in the in-situ facility consisting of a modulator, klystron, waveguide network, vacuum system, cooling system, and RF analyzing equipment. The test results with Stanford linear accelerator energy doubler (SLED) have shown no breakdown up to 75 MW peak power with 4.5 μs RF pulse width at a repetition rate of 10 Hz. The test results with the current operation level of PLS-II Linac confirm that the RF window well satisfies the criteria for PLS-II Linac operation.

W-Band Transmission MeasurementS and X-Band Dielectric Properties Measurements for a Radome Material Sample

NASA Technical Reports Server (NTRS)

Cravey, Robin L.; Tiemsin, Pacita I.

1997-01-01

This paper describes measurements which were performed on a sample of radome material in the Electromagnetic Properties Measurements Laboratory (EPML). The purpose of the measurements described in this paper was to determine the one-way transmission loss through the flat panel of radome material for a frequency range of 84 to 94 GHz, for varying incidence angles. The panel, which was manufactured by Norton Performance Plastics Corporation, was provided to the EPML by TRW. The size of the panel is 40 in x 36 in x 0.422 in and consists of a foam material with one side coated with a smooth white coating (this side will be referred to as the front side). The dielectric properties of the foam material from the inside of the panel were also determined at X-band (8.2-12.4 GHz). The W-band free space measurements are presented first, followed by the X-band dielectric properties measurements.

Nanosurgery with near-infrared 12-femtosecond and picosecond laser pulses

NASA Astrophysics Data System (ADS)

Uchugonova, Aisada; Zhang, Huijing; Lemke, Cornelius; König, Karsten

2011-03-01

Laser-assisted surgery based on multiphoton absorption of NIR laser light has great potential for high precision surgery at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact laser method also supports contamination-free cell nanosurgery. Here we apply femtosecond laser scanning microscopes for sub-100 nm surgery of human cells and metaphase chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770 nm/830 nm) with an in situ pulse duration at the target ranging from 12 femtoseconds up to 3 picoseconds was employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force microscopy (AFM) and electron microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond laser pulses at low mean milliwatt powers for sub-100 nm surgery.

Nitrogen-related intermediate band in P-rich GaN xP yAs 1-x-y alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zelazna, K.; Gladysiewicz, M.; Polak, M. P.

The electronic band structure of phosphorus-rich GaN xP yAs 1-x-y alloys (x ~ 0.025 and y ≥ 0.6) is studied experimentally using optical absorption, photomodulated transmission, contactless electroreflectance, and photoluminescence. Here, it is shown that incorporation of a few percent of N atoms has a drastic effect on the electronic structure of the alloys. The change of the electronic band structure is very well described by the band anticrossing (BAC) model in which localized nitrogen states interact with the extended states of the conduction band of GaAsP host. The BAC interaction results in the formation of a narrow intermediate bandmore » (E - band in BAC model) with the minimum at the Γ point of the Brillouin zone resulting in a change of the nature of the fundamental band gap from indirect to direct. The splitting of the conduction band by the BAC interaction is further confirmed by a direct observation of the optical transitions to the E + band using contactless electroreflectance spectroscopy.« less

Nitrogen-related intermediate band in P-rich GaN xP yAs 1-x-y alloys

DOE PAGES

Zelazna, K.; Gladysiewicz, M.; Polak, M. P.; ...

2017-11-16

The electronic band structure of phosphorus-rich GaN xP yAs 1-x-y alloys (x ~ 0.025 and y ≥ 0.6) is studied experimentally using optical absorption, photomodulated transmission, contactless electroreflectance, and photoluminescence. Here, it is shown that incorporation of a few percent of N atoms has a drastic effect on the electronic structure of the alloys. The change of the electronic band structure is very well described by the band anticrossing (BAC) model in which localized nitrogen states interact with the extended states of the conduction band of GaAsP host. The BAC interaction results in the formation of a narrow intermediate bandmore » (E - band in BAC model) with the minimum at the Γ point of the Brillouin zone resulting in a change of the nature of the fundamental band gap from indirect to direct. The splitting of the conduction band by the BAC interaction is further confirmed by a direct observation of the optical transitions to the E + band using contactless electroreflectance spectroscopy.« less

Coherent diffraction of single Rice Dwarf virus particles using hard X-rays at the Linac Coherent Light Source.

PubMed

Munke, Anna; Andreasson, Jakob; Aquila, Andrew; Awel, Salah; Ayyer, Kartik; Barty, Anton; Bean, Richard J; Berntsen, Peter; Bielecki, Johan; Boutet, Sébastien; Bucher, Maximilian; Chapman, Henry N; Daurer, Benedikt J; DeMirci, Hasan; Elser, Veit; Fromme, Petra; Hajdu, Janos; Hantke, Max F; Higashiura, Akifumi; Hogue, Brenda G; Hosseinizadeh, Ahmad; Kim, Yoonhee; Kirian, Richard A; Reddy, Hemanth K N; Lan, Ti-Yen; Larsson, Daniel S D; Liu, Haiguang; Loh, N Duane; Maia, Filipe R N C; Mancuso, Adrian P; Mühlig, Kerstin; Nakagawa, Atsushi; Nam, Daewoong; Nelson, Garrett; Nettelblad, Carl; Okamoto, Kenta; Ourmazd, Abbas; Rose, Max; van der Schot, Gijs; Schwander, Peter; Seibert, M Marvin; Sellberg, Jonas A; Sierra, Raymond G; Song, Changyong; Svenda, Martin; Timneanu, Nicusor; Vartanyants, Ivan A; Westphal, Daniel; Wiedorn, Max O; Williams, Garth J; Xavier, Paulraj Lourdu; Yoon, Chun Hong; Zook, James

2016-08-01

Single particle diffractive imaging data from Rice Dwarf Virus (RDV) were recorded using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). RDV was chosen as it is a well-characterized model system, useful for proof-of-principle experiments, system optimization and algorithm development. RDV, an icosahedral virus of about 70 nm in diameter, was aerosolized and injected into the approximately 0.1 μm diameter focused hard X-ray beam at the CXI instrument of LCLS. Diffraction patterns from RDV with signal to 5.9 Ångström were recorded. The diffraction data are available through the Coherent X-ray Imaging Data Bank (CXIDB) as a resource for algorithm development, the contents of which are described here.

Band alignment of SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) determined by X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Feng, Zhaoqing; Feng, Qian; Zhang, Jincheng; Li, Xiang; Li, Fuguo; Huang, Lu; Chen, Hong-Yan; Lu, Hong-Liang; Hao, Yue

2018-03-01

In this work, we report the investigation of the band alignment of SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) utilizing the high resolution X-ray photoelectron spectroscopy (XPS) measurements. The single crystallinity and orientation of β-(AlxGa1-x)2O3 films grown on sapphire by pulsed laser deposition were studied with the high resolution X-ray diffraction. The Ga 2p3/2 and Si 2p core-level spectra as well as valence band spectra were used in the analysis of band alignment. As the mole fraction x of Al increases from 0 to 0.49, the bandgap and conduction band offset values of SiO2/(AlxGa1-x)2O3 increases from 4.9 to 5.6 eV and from 1.5 to 2.1 eV, respectively, while that of valence band offset decreases from 2.2 to 0.9 eV. From the results obtained, the energy band diagram of the studied SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) interfaces is found to be of type I. Energy band lineups of SiO2/(AlxGa1-x)2O3 were thus determined which can be used as for Ga2O3 based power device technology.

Crystal structure of rhodopsin bound to arrestin by femtosecond X-ray laser

DOE PAGES

Kang, Yanyong; Zhou, X. Edward; Gao, Xiang; ...

2015-07-22

G-protein-coupled receptors (GPCRs) signal primarily through G proteins or arrestins. Arrestin binding to GPCRs blocks G protein interaction and redirects signalling to numerous G-protein-independent pathways. Here we report the crystal structure of a constitutively active form of human rhodopsin bound to a pre-activated form of the mouse visual arrestin, determined by serial femtosecond X-ray laser crystallography. Together with extensive biochemical and mutagenesis data, the structure reveals an overall architecture of the rhodopsin-arrestin assembly in which rhodopsin uses distinct structural elements, including transmembrane helix 7 and helix 8, to recruit arrestin. Correspondingly, arrestin adopts the pre-activated conformation, with a ~20° rotationmore » between the amino and carboxy domains, which opens up a cleft in arrestin to accommodate a short helix formed by the second intracellular loop of rhodopsin. In conclusion, this structure provides a basis for understanding GPCR-mediated arrestin-biased signalling and demonstrates the power of X-ray lasers for advancing the frontiers of structural biology.« less

Crystal structure of rhodopsin bound to arrestin by femtosecond X-ray laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Yanyong; Zhou, X. Edward; Gao, Xiang

G-protein-coupled receptors (GPCRs) signal primarily through G proteins or arrestins. Arrestin binding to GPCRs blocks G protein interaction and redirects signalling to numerous G-protein-independent pathways. Here we report the crystal structure of a constitutively active form of human rhodopsin bound to a pre-activated form of the mouse visual arrestin, determined by serial femtosecond X-ray laser crystallography. Together with extensive biochemical and mutagenesis data, the structure reveals an overall architecture of the rhodopsin-arrestin assembly in which rhodopsin uses distinct structural elements, including transmembrane helix 7 and helix 8, to recruit arrestin. Correspondingly, arrestin adopts the pre-activated conformation, with a ~20° rotationmore » between the amino and carboxy domains, which opens up a cleft in arrestin to accommodate a short helix formed by the second intracellular loop of rhodopsin. In conclusion, this structure provides a basis for understanding GPCR-mediated arrestin-biased signalling and demonstrates the power of X-ray lasers for advancing the frontiers of structural biology.« less

The electronic band structure of Ge1-x Sn x in the full composition range: indirect, direct, and inverted gaps regimes, band offsets, and the Burstein-Moss effect

NASA Astrophysics Data System (ADS)

Polak, M. P.; Scharoch, P.; Kudrawiec, R.

2017-05-01

A comprehensive and detailed study of the composition dependence of lattice constants, band gaps and band offsets has been performed for bulk Ge1-x Sn x alloy in the full composition range using state-of-the-art density functional theory methods. A spectral weight approach to band unfolding has been applied as a means of distinguishing the indirect and direct band gaps from folded supercell band structures. In this way, four characteristic regions of the band gap character have been identified for Ge1-x Sn x alloy: an indirect band gap (x  <  6.5%), a direct band gap (6.5%  <  x  <  25%) and an inverse band gap (x  >  25%) with inverse spin-orbit split-off for 45%  <  x  <  85%. In general, it has been observed that the bowing parameters of band edges (Γ and L-point in conduction band (CBΓ and CB L ), valence band (VB), and spin-orbit (SO) band) are rather large ({{b}\\text{C{{\\text{B}} Γ }}}   =  2.43  ±  0.06 eV, {{b}\\text{C{{\\text{B}}L}}}   =  0.64  ±  0.04 eV, {{b}\\text{VB}}   =  -0.59  ±  0.04 eV, and {{b}\\text{SO}}   =  -0.49  ±  0.05 eV). This indicates that Ge1-x Sn x behaves like a highly mismatched group IV alloy. The composition dependence of lattice constant shows negligible bowing (b a   =  -0.083 Å). Obtained results have been compared with available experimental data. The origin of band gap reduction and large bowing has been analyzed and conclusions have been drawn regarding the relationship between experimental and theoretical results. It is shown that due to the low DOS at the Γ-point, a significant filling of CB by electrons in the direct gap regime may easily take place. Therefore, the Burstein-Moss effect should be considered when comparing experimental data with theoretical predictions as has already been shown for other intrinsic n-type narrow gap semiconductors (e.g. InN).

Evaluation of band alignment of α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterostructures by X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Uchida, Takayuki; Jinno, Riena; Takemoto, Shu; Kaneko, Kentaro; Fujita, Shizuo

2018-04-01

The band alignment at an α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterointerface, with different Al compositions (x), grown on a c-plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy. The experimental results show that the heterointerface has the type-I band discontinuity with the valence band offsets of 0.090, 0.12, and 0.14 eV, and the conduction band offsets of 0.34, 0.79, and 1.87 eV, for x values of 0.1, 0.4, and 0.8, respectively. The small band offset for the valence band is attributed to the fact that the valence band of oxides is constituted by the localized O 2p level, which is dominated by the nature of oxygen atoms. The type-I band discontinuity is desirable for a variety of heterostructure devices.

Numerical simulations of the hard X-ray pulse intensity distribution at the Linac Coherent Light Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pardini, Tom; Aquila, Andrew; Boutet, Sebastien

Numerical simulations of the current and future pulse intensity distributions at selected locations along the Far Experimental Hall, the hard X-ray section of the Linac Coherent Light Source (LCLS), are provided. Estimates are given for the pulse fluence, energy and size in and out of focus, taking into account effects due to the experimentally measured divergence of the X-ray beam, and measured figure errors of all X-ray optics in the beam path. Out-of-focus results are validated by comparison with experimental data. Previous work is expanded on, providing quantitatively correct predictions of the pulse intensity distribution. Numerical estimates in focus aremore » particularly important given that the latter cannot be measured with direct imaging techniques due to detector damage. Finally, novel numerical estimates of improvements to the pulse intensity distribution expected as part of the on-going upgrade of the LCLS X-ray transport system are provided. As a result, we suggest how the new generation of X-ray optics to be installed would outperform the old one, satisfying the tight requirements imposed by X-ray free-electron laser facilities.« less

Numerical simulations of the hard X-ray pulse intensity distribution at the Linac Coherent Light Source

DOE PAGES

Pardini, Tom; Aquila, Andrew; Boutet, Sebastien; ...

2017-06-15

Numerical simulations of the current and future pulse intensity distributions at selected locations along the Far Experimental Hall, the hard X-ray section of the Linac Coherent Light Source (LCLS), are provided. Estimates are given for the pulse fluence, energy and size in and out of focus, taking into account effects due to the experimentally measured divergence of the X-ray beam, and measured figure errors of all X-ray optics in the beam path. Out-of-focus results are validated by comparison with experimental data. Previous work is expanded on, providing quantitatively correct predictions of the pulse intensity distribution. Numerical estimates in focus aremore » particularly important given that the latter cannot be measured with direct imaging techniques due to detector damage. Finally, novel numerical estimates of improvements to the pulse intensity distribution expected as part of the on-going upgrade of the LCLS X-ray transport system are provided. As a result, we suggest how the new generation of X-ray optics to be installed would outperform the old one, satisfying the tight requirements imposed by X-ray free-electron laser facilities.« less

Generation of plasma X-ray sources via high repetition rate femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Baguckis, Artūras; Plukis, Artūras; Reklaitis, Jonas; Remeikis, Vidmantas; Giniūnas, Linas; Vengris, Mikas

2017-12-01

In this study, we present the development and characterization of Cu plasma X-ray source driven by 20 W average power high repetition rate femtosecond laser in ambient atmosphere environment. The peak Cu- Kα photon flux of 2.3 × 109 photons/s into full solid angle is demonstrated (with a process conversion efficiency of 10-7), using pulses with peak intensity of 4.65 × 1014 W/cm2. Such Cu- Kα flux is significantly larger than others found in comparable experiments, performed in air environment. The effects of resonance plasma absorption process, when optimized, are shown to increase measured flux by the factor of 2-3. The relationship between X-ray photon flux and plasma-driving pulse repetition rate is quasi-linear, suggesting that fluxes could further be increased to 1010 photons/s using even higher average powers of driving radiation. These results suggest that to fully utilize the potential of high repetition rate laser sources, novel target material delivery systems (for example, jet-based ones) are required. On the other hand, this study demonstrates that high energy lasers currently used for plasma X-ray sources can be conveniently and efficiently replaced by high average power and repetition rate laser radiation, as a way to increase the brightness of the generated X-rays.

Hybrid functional study of band structures of GaAs1-xNx and GaSb1-xNx alloys

NASA Astrophysics Data System (ADS)

Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.

2012-02-01

Band structures of GaAs1-xNx and GaSb1-xNx alloys are studied in the framework of the density functional theory within the hybrid functional scheme (HSE06). We find that the scheme gives a clear improvement over the traditional (semi)local functionals in describing, in a qualitative agreement with experiments, the bowing of electron energy band gap in GaAs1-xNx alloys. In the case of GaSb1-xNx alloys, the hybrid functional used makes the study of band structures possible ab initio without any empirical parameter fitting. We explain the trends in the band gap reductions in the two materials that result mainly from the positions of the nitrogen-induced states with respect to the bottoms of the bulk conduction bands.

The accumulation of femtosecond laser radiation energy in crystals of lithium fluoride

NASA Astrophysics Data System (ADS)

Dresvyanskiy, V. P.; Glazunov, D. S.; Alekseev, S. V.; Losev, V. F.; Chadraa, B.; Bukhtsooj, O.; Baasankhuu, N.; Zandan, B.; Martynovich, E. F.

2015-12-01

We present the results of studies of energy accumulation during the non-destructive interaction of extremely intense near infrared laser radiation with model wide band gap dielectric crystals of lithium fluoride, when the intensity of pulses is sufficient for effective highly nonlinear absorption of light and for the excitation of the electron subsystem of matter and the energy of pulses is still not sufficient for significant heating, evaporation, laser breakdown or other destruction to occur. We studied the emission of energy in the form of light sum of thermally stimulated luminescence accumulated under conditions of self-focusing and multiple filamentation of femtosecond laser radiation. It was established that it's the F2 and F3+ color centers and supplementary to them centers of interstitial type which accumulate energy under the action of a single femtosecond laser pulses. When irradiated by series of pulses the F3, F3- and F4 centers additionally appear. F2 centers are the main centers of emission in the process of thermally stimulated luminescence of accumulated energy. The interstitial fluoride ions (I-centers) are the kinetic particles. They split off from the X3- centers in the result of thermal decomposition of latter on the I-centers and molecules X20. I-centers recombine with F3+ centers and form F2 centers in excited state. The latter produce the characteristic emission spectrum emitted in the form of thermally stimulated luminescence.

Coherent diffraction of single Rice Dwarf virus particles using hard X-rays at the Linac Coherent Light Source

PubMed Central

Munke, Anna; Andreasson, Jakob; Aquila, Andrew; Awel, Salah; Ayyer, Kartik; Barty, Anton; Bean, Richard J.; Berntsen, Peter; Bielecki, Johan; Boutet, Sébastien; Bucher, Maximilian; Chapman, Henry N.; Daurer, Benedikt J.; DeMirci, Hasan; Elser, Veit; Fromme, Petra; Hajdu, Janos; Hantke, Max F.; Higashiura, Akifumi; Hogue, Brenda G.; Hosseinizadeh, Ahmad; Kim, Yoonhee; Kirian, Richard A.; Reddy, Hemanth K.N.; Lan, Ti-Yen; Larsson, Daniel S.D.; Liu, Haiguang; Loh, N. Duane; Maia, Filipe R.N.C.; Mancuso, Adrian P.; Mühlig, Kerstin; Nakagawa, Atsushi; Nam, Daewoong; Nelson, Garrett; Nettelblad, Carl; Okamoto, Kenta; Ourmazd, Abbas; Rose, Max; van der Schot, Gijs; Schwander, Peter; Seibert, M. Marvin; Sellberg, Jonas A.; Sierra, Raymond G.; Song, Changyong; Svenda, Martin; Timneanu, Nicusor; Vartanyants, Ivan A.; Westphal, Daniel; Wiedorn, Max O.; Williams, Garth J.; Xavier, Paulraj Lourdu; Yoon, Chun Hong; Zook, James

2016-01-01

Single particle diffractive imaging data from Rice Dwarf Virus (RDV) were recorded using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). RDV was chosen as it is a well-characterized model system, useful for proof-of-principle experiments, system optimization and algorithm development. RDV, an icosahedral virus of about 70 nm in diameter, was aerosolized and injected into the approximately 0.1 μm diameter focused hard X-ray beam at the CXI instrument of LCLS. Diffraction patterns from RDV with signal to 5.9 Ångström were recorded. The diffraction data are available through the Coherent X-ray Imaging Data Bank (CXIDB) as a resource for algorithm development, the contents of which are described here. PMID:27478984

Coherent diffraction of single Rice Dwarf virus particles using hard X-rays at the Linac Coherent Light Source

DOE PAGES

Munke, Anna; Andreasson, Jakob; Aquila, Andrew; ...

2016-08-01

Single particle diffractive imaging data from Rice Dwarf Virus (RDV) were recorded using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). RDV was chosen as it is a well-characterized model system, useful for proof-of-principle experiments, system optimization and algorithm development. RDV, an icosahedral virus of about 70 nm in diameter, was aerosolized and injected into the approximately 0.1 μm diameter focused hard X-ray beam at the CXI instrument of LCLS. Diffraction patterns from RDV with signal to 5.9 Ångström were recorded. Here, the diffraction data are available through the Coherent X-ray Imaging Data Bank (CXIDB)more » as a resource for algorithm development, the contents of which are described here.« less

Following the dynamics of matter with femtosecond precision using the X-ray streaking method

DOE PAGES

David, C.; Karvinen, P.; Sikorski, M.; ...

2015-01-06

X-ray Free Electron Lasers (FELs) can produce extremely intense and very short pulses, down to below 10 femtoseconds (fs). Among the key applications are ultrafast time-resolved studies of dynamics of matter by observing responses to fast excitation pulses in a pump-probe manner. Detectors with sufficient time resolution for observing these processes are not available. Therefore, such experiments typically measure a sample's full dynamics by repeating multiple pump-probe cycles at different delay times. This conventional method assumes that the sample returns to an identical or very similar state after each cycle. Here we describe a novel approach that can provide amore » time trace of responses following a single excitation pulse, jitter-free, with fs timing precision. We demonstrate, in an X-ray diffraction experiment, how it can be applied to the investigation of ultrafast irreversible processes.« less

First-principle study of effect of variation of `x' on the band alignment in CZTS1-xSex

NASA Astrophysics Data System (ADS)

Ghemud, Vipul; Kshirsagar, Anjali

2018-04-01

The present work concentrates on the electronic structure study of CZTS1-xSex alloy with x ranging from 0 to 1. For the alloy study, we have carried out first-principles calculations employing generalized gradient approximation for structural optimization and further hybrid functional approach to compare the optical band gap with that obtained from the experiments. A systematic increase in the lattice parameters with lowering of band gap from 1.52eV to 1.04eV is seen with increasing Se concentration from 0 to 100%, however the lowering of valence band edge and conduction band edge is not linear with the concentration variation. Our results indicate that the lowering of band gap is a result increased Cu:d and Se:p hybridization with increasing `x'.

All-diamond optical assemblies for a beam-multiplexing X-ray monochromator at the Linac Coherent Light Source

PubMed Central

Stoupin, S.; Terentyev, S. A.; Blank, V. D.; Shvyd’ko, Yu. V.; Goetze, K.; Assoufid, L.; Polyakov, S. N.; Kuznetsov, M. S.; Kornilov, N. V.; Katsoudas, J.; Alonso-Mori, R.; Chollet, M.; Feng, Y.; Glownia, J. M.; Lemke, H.; Robert, A.; Sikorski, M.; Song, S.; Zhu, D.

2014-01-01

A double-crystal diamond (111) monochromator recently implemented at the Linac Coherent Light Source (LCLS) enables splitting of the primary X-ray beam into a pink (transmitted) and a monochromatic (reflected) branch. The first monochromator crystal, with a thickness of ∼100 µm, provides sufficient X-ray transmittance to enable simultaneous operation of two beamlines. This article reports the design, fabrication and X-ray characterization of the first and second (300 µm-thick) crystals utilized in the monochromator and the optical assemblies holding these crystals. Each crystal plate has a region of about 5 × 2 mm with low defect concentration, sufficient for use in X-ray optics at the LCLS. The optical assemblies holding the crystals were designed to provide mounting on a rigid substrate and to minimize mounting-induced crystal strain. The induced strain was evaluated using double-crystal X-ray topography and was found to be small over the 5 × 2 mm working regions of the crystals. PMID:25242912

Design study of high gradient, low impedance accelerating structures for the FERMI free electron laser linac upgrade

NASA Astrophysics Data System (ADS)

Shafqat, N.; Di Mitri, S.; Serpico, C.; Nicastro, S.

2017-09-01

The FERMI free-electron laser (FEL) of Elettra Sincrotrone Trieste, Italy, is a user facility driven by a 1.5 GeV 10-50 Hz S-band radiofrequency linear accelerator (linac), and it is based on an external laser seeding scheme that allows lasing at the shortest fundamental wavelength of 4 nm. An increase of the beam energy to 1.8 GeV at a tolerable breakdown rate, and an improvement of the final beam quality is desired in order to allow either lasing at 4 nm with a higher flux, or lasing at shorter wavelengths. This article presents the impedance analysis of newly designed S-band accelerating structures, for replacement of the existing backward travelling wave structures (BTWS) in the last portion of the FERMI linac. The new structure design promises higher accelerating gradient and lower impedance than those of the existing BTWS. Particle tracking simulations show that, with the linac upgrade, the beam relative energy spread, its linear and nonlinear z-correlation internal to the bunch, and the beam transverse emittances can be made smaller than the ones in the present configuration, with expected advantage to the FEL performance. The repercussion of the upgrade on the linac quadrupole magnets setting, for a pre-determined electron beam optics, is also considered.

V x In (2–x) S 3 Intermediate Band Absorbers Deposited by Atomic Layer Deposition

DOE PAGES

McCarthy, Robert F.; Weimer, Matthew S.; Haasch, Richard T.; ...

2016-03-21

Substitutional alloys of several thin film semiconductors have been proposed as intermediate band (IB) materials for use in next-generation photovoltaics, which aim to utilize a larger fraction of the solar spectrum without sacrificing significant photovoltage. Here, we demonstrate a novel approach to IB material growth, namely atomic layer deposition (ALD), to enable unique control over substitutional-dopant location and density. Two new ALD processes for vanadium sulfide incorporation are introduced, one of which incorporates a vanadium (III) amidinate previously untested for ALD. We synthesize the first thin film V xIn (2-x)S 3 intermediate band semiconductors, using this process, and further demonstratemore » that the V:In ratio, and therefore intraband gap density of states, can be finely tuned according to the ALD dosing schedule. Deposition on a crystalline In 2S 3 underlayer promotes the growth of a tetragonal β-In 2S 3-like phase V xIn (2-x)S 3, which exhibits a distinct sub-band gap absorption peak with onset near 1.1 eV in agreement with computational predictions. But, the V xIn (2-x)S 3 films lack the lower energy transition predicted for a partially filled IB, and photoelectrochemical devices reveal a photocurrent response only from illumination with energy sufficient to span the parent band-gap.« less

Coherent soft X-ray diffraction imaging of coliphage PR772 at the Linac coherent light source

PubMed Central

Reddy, Hemanth K.N.; Yoon, Chun Hong; Aquila, Andrew; Awel, Salah; Ayyer, Kartik; Barty, Anton; Berntsen, Peter; Bielecki, Johan; Bobkov, Sergey; Bucher, Maximilian; Carini, Gabriella A.; Carron, Sebastian; Chapman, Henry; Daurer, Benedikt; DeMirci, Hasan; Ekeberg, Tomas; Fromme, Petra; Hajdu, Janos; Hanke, Max Felix; Hart, Philip; Hogue, Brenda G.; Hosseinizadeh, Ahmad; Kim, Yoonhee; Kirian, Richard A.; Kurta, Ruslan P.; Larsson, Daniel S.D.; Duane Loh, N.; Maia, Filipe R.N.C.; Mancuso, Adrian P.; Mühlig, Kerstin; Munke, Anna; Nam, Daewoong; Nettelblad, Carl; Ourmazd, Abbas; Rose, Max; Schwander, Peter; Seibert, Marvin; Sellberg, Jonas A.; Song, Changyong; Spence, John C.H.; Svenda, Martin; Van der Schot, Gijs; Vartanyants, Ivan A.; Williams, Garth J.; Xavier, P. Lourdu

2017-01-01

Single-particle diffraction from X-ray Free Electron Lasers offers the potential for molecular structure determination without the need for crystallization. In an effort to further develop the technique, we present a dataset of coherent soft X-ray diffraction images of Coliphage PR772 virus, collected at the Atomic Molecular Optics (AMO) beamline with pnCCD detectors in the LAMP instrument at the Linac Coherent Light Source. The diameter of PR772 ranges from 65–70 nm, which is considerably smaller than the previously reported ~600 nm diameter Mimivirus. This reflects continued progress in XFEL-based single-particle imaging towards the single molecular imaging regime. The data set contains significantly more single particle hits than collected in previous experiments, enabling the development of improved statistical analysis, reconstruction algorithms, and quantitative metrics to determine resolution and self-consistency. PMID:28654088

Coherent soft X-ray diffraction imaging of coliphage PR772 at the Linac coherent light source.

PubMed

Reddy, Hemanth K N; Yoon, Chun Hong; Aquila, Andrew; Awel, Salah; Ayyer, Kartik; Barty, Anton; Berntsen, Peter; Bielecki, Johan; Bobkov, Sergey; Bucher, Maximilian; Carini, Gabriella A; Carron, Sebastian; Chapman, Henry; Daurer, Benedikt; DeMirci, Hasan; Ekeberg, Tomas; Fromme, Petra; Hajdu, Janos; Hanke, Max Felix; Hart, Philip; Hogue, Brenda G; Hosseinizadeh, Ahmad; Kim, Yoonhee; Kirian, Richard A; Kurta, Ruslan P; Larsson, Daniel S D; Duane Loh, N; Maia, Filipe R N C; Mancuso, Adrian P; Mühlig, Kerstin; Munke, Anna; Nam, Daewoong; Nettelblad, Carl; Ourmazd, Abbas; Rose, Max; Schwander, Peter; Seibert, Marvin; Sellberg, Jonas A; Song, Changyong; Spence, John C H; Svenda, Martin; Van der Schot, Gijs; Vartanyants, Ivan A; Williams, Garth J; Xavier, P Lourdu

2017-06-27

Single-particle diffraction from X-ray Free Electron Lasers offers the potential for molecular structure determination without the need for crystallization. In an effort to further develop the technique, we present a dataset of coherent soft X-ray diffraction images of Coliphage PR772 virus, collected at the Atomic Molecular Optics (AMO) beamline with pnCCD detectors in the LAMP instrument at the Linac Coherent Light Source. The diameter of PR772 ranges from 65-70 nm, which is considerably smaller than the previously reported ~600 nm diameter Mimivirus. This reflects continued progress in XFEL-based single-particle imaging towards the single molecular imaging regime. The data set contains significantly more single particle hits than collected in previous experiments, enabling the development of improved statistical analysis, reconstruction algorithms, and quantitative metrics to determine resolution and self-consistency.

Tropical-forest biomass estimation at X-Band from the spaceborne TanDEM-X interferometer

Treesearch

R. Treuhaft; F. Goncalves; J.R. dos Santos; M. Keller; M. Palace; S.N. Madsen; F. Sullivan; P.M.L.A. Graca

2014-01-01

This letter reports the sensitivity of X-band interferometric synthetic aperture radar (InSAR) data from the first dual-spacecraft radar interferometer, TanDEM-X, to variations in tropical-forest aboveground biomass (AGB). It also reports the first tropical-forest AGB estimates fromTanDEM-X data. Tropical forests account for...

Femtosecond laser ablation of bovine cortical bone

NASA Astrophysics Data System (ADS)

Cangueiro, Liliana T.; Vilar, Rui; Botelho do Rego, Ana M.; Muralha, Vania S. F.

2012-12-01

We study the surface topographical, structural, and compositional modifications induced in bovine cortical bone by femtosecond laser ablation. The tests are performed in air, with a Yb:KYW chirped-pulse-regenerative amplification laser system (500 fs, 1030 nm) at fluences ranging from 0.55 to 2.24 J/cm2. The ablation process is monitored by acoustic emission measurements. The topography of the laser-treated surfaces is studied by scanning electron microscopy, and their constitution is characterized by glancing incidence x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and micro-Raman spectroscopy. The results show that femtosecond laser ablation allows removing bone without melting, carbonization, or cracking. The structure and composition of the remaining tissue are essentially preserved, the only constitutional changes observed being a reduction of the organic material content and a partial recrystallization of hydroxyapatite in the most superficial region of samples. The results suggest that, within this fluence range, ablation occurs by a combination of thermal and electrostatic mechanisms, with the first type of mechanism predominating at lower fluences. The associated thermal effects explain the constitutional changes observed. We show that femtosecond lasers are a promising tool for delicate orthopaedic surgeries, where small amounts of bone must be cut with negligible damage, thus minimizing surgical trauma.

Electron Beam Focusing in the Linear Accelerator (linac)

NASA Astrophysics Data System (ADS)

Jauregui, Luis

2015-10-01

To produce consistent data with an electron accelerator, it is critical to have a well-focused beam. To keep the beam focused, quadrupoles (quads) are employed. Quads are magnets, which focus the beam in one direction (x or y) and defocus in the other. When two or more quads are used in series, a net focusing effect is achieved in both vertical and horizontal directions. At start up there is a 5% calibration error in the linac at Thomas Jefferson National Accelerator Facility. This means that the momentum of particles passing through the quads isn't always what is expected, which affects the focusing of the beam. The objective is to find exactly how sensitive the focusing in the linac is to this 5% error. A linac was simulated, which contained 290 RF Cavities with random electric fields (to simulate the 5% calibration error), and a total momentum kick of 1090 MeV. National Science Foundation, Department of Energy, Jefferson Lab, Old Dominion University.

The excitonic photoluminescence mechanism and lasing action in band-gap-tunable CdS(1-x)Se(x) nanostructures.

PubMed

Dai, Jun; Zhou, Pengxia; Lu, Junfeng; Zheng, Hongge; Guo, Jiyuan; Wang, Fang; Gu, Ning; Xu, Chunxiang

2016-01-14

Bandgap tunable semiconductor materials have wide application in integrated-optoelectronic and communication devices. The CdS1-xSex ternary semiconductor materials covering green-red bands have been reported previously, but their basic band-gap and optical properties crucial to the performance of the CdS1-xSex-based optoelectronic devices have not been deeply understood. In this paper, we theoretically simulated and discussed the feasibility of bandgap-tunable CdS1-xSex nanomaterials for designing wavelength tunable microlasers. Then we fabricated the CdS1-xSex nanobelts with their band gap ranging from 2.4 to 1.74 eV by adjusting the composition ratio x in the vapor-phase-transport growth process. The temperature-dependent photoluminescence and exciton-related optical constants of the CdS1-xSex nanobelts were carefully demonstrated. Finally, the wavelength-tunable Fabry-Perot lasing in CdS1-xSex nanobelts was obtained, and the Fabry-Perot lasing mechanism was numerically simulated by the FDTD method. The systematic results on the mechanism of the tunable band gap, exciton properties and lasing of the CdS1-xSex nanostructure help us deeply understand the intrinsic optical properties of this material, and will build a strong foundation for future application of green-red wavelength-tunable CdS1-xSex microlasers.

Inverted S-Shaped Compact Antenna for X-Band Applications

PubMed Central

Samsuzzaman, M.; Islam, M. T.

2014-01-01

A novel probe-fed compact inverted S-shaped multifrequency patch antenna is designed. By employing two rectangular slots that change the conventional rectangular patch into an inverted S-shaped patch, the antenna is able to operate in triple frequency in the X-band. The performance criteria of the proposed design have been experimentally verified by fabricating a printed prototype. The measured results show that the −10 dB impedance bandwidth of the proposed antenna at lower band is 5.02% (8.69–9.14 GHz), at middle band is 9.13% (10.47–11.48 GHz), and at upper band is 3.79% (11.53–11.98 GHz). Two elliptical slots are introduced in the ground plane to increase the peak gain. The antenna is excited by a simple probe feeding mechanism. The overall antenna dimension is  0.52λ × 0.60λ × 0.046λ at a lower resonance frequency of 9.08 GHz. The antenna configuration and parametric investigation are conducted with the help of the high frequency structural simulator, and a good agreement is achieved between the simulated and measured data. The stable gain, omnidirectional radiation pattern, and consistent radiation efficiency in the achieved operating band make the proposed antenna a suitable candidate for X-band applications. PMID:24895656

Flow-aligned, single-shot fiber diffraction using a femtosecond X-ray free-electron laser

DOE PAGES

Popp, David; Loh, N. Duane; Zorgati, Habiba; ...

2017-06-02

A major goal for X-ray free-electron laser (XFEL) based science is to elucidate structures of biological molecules without the need for crystals. Filament systems may provide some of the first single macromolecular structures elucidated by XFEL radiation, since they contain one-dimensional translational symmetry and thereby occupy the diffraction intensity region between the extremes of crystals and single molecules. Here, we demonstrate flow alignment of as few as 100 filaments ( Escherichia coli pili, F-actin, and amyloid fibrils), which when intersected by femtosecond X-ray pulses result in diffraction patterns similar to those obtained from classical fiber diffraction studies. We also determinemore » that F-actin can be flow-aligned to a disorientation of approximately 5 degrees. Using this XFEL-based technique, we determine that gelsolin amyloids are comprised of stacked β-strands running perpendicular to the filament axis, and that a range of order from fibrillar to crystalline is discernable for individual α-synuclein amyloids.« less

Flow-aligned, single-shot fiber diffraction using a femtosecond X-ray free-electron laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popp, David; Loh, N. Duane; Zorgati, Habiba

A major goal for X-ray free-electron laser (XFEL) based science is to elucidate structures of biological molecules without the need for crystals. Filament systems may provide some of the first single macromolecular structures elucidated by XFEL radiation, since they contain one-dimensional translational symmetry and thereby occupy the diffraction intensity region between the extremes of crystals and single molecules. Here, we demonstrate flow alignment of as few as 100 filaments ( Escherichia coli pili, F-actin, and amyloid fibrils), which when intersected by femtosecond X-ray pulses result in diffraction patterns similar to those obtained from classical fiber diffraction studies. We also determinemore » that F-actin can be flow-aligned to a disorientation of approximately 5 degrees. Using this XFEL-based technique, we determine that gelsolin amyloids are comprised of stacked β-strands running perpendicular to the filament axis, and that a range of order from fibrillar to crystalline is discernable for individual α-synuclein amyloids.« less

Open data set of live cyanobacterial cells imaged using an X-ray laser

NASA Astrophysics Data System (ADS)

van der Schot, Gijs; Svenda, Martin; Maia, Filipe R. N. C.; Hantke, Max F.; Deponte, Daniel P.; Seibert, M. Marvin; Aquila, Andrew; Schulz, Joachim; Kirian, Richard A.; Liang, Mengning; Stellato, Francesco; Bari, Sadia; Iwan, Bianca; Andreasson, Jakob; Timneanu, Nicusor; Bielecki, Johan; Westphal, Daniel; Nunes de Almeida, Francisca; Odić, Duško; Hasse, Dirk; Carlsson, Gunilla H.; Larsson, Daniel S. D.; Barty, Anton; Martin, Andrew V.; Schorb, Sebastian; Bostedt, Christoph; Bozek, John D.; Carron, Sebastian; Ferguson, Ken; Rolles, Daniel; Rudenko, Artem; Epp, Sascha W.; Foucar, Lutz; Rudek, Benedikt; Erk, Benjamin; Hartmann, Robert; Kimmel, Nils; Holl, Peter; Englert, Lars; Loh, N. Duane; Chapman, Henry N.; Andersson, Inger; Hajdu, Janos; Ekeberg, Tomas

2016-08-01

Structural studies on living cells by conventional methods are limited to low resolution because radiation damage kills cells long before the necessary dose for high resolution can be delivered. X-ray free-electron lasers circumvent this problem by outrunning key damage processes with an ultra-short and extremely bright coherent X-ray pulse. Diffraction-before-destruction experiments provide high-resolution data from cells that are alive when the femtosecond X-ray pulse traverses the sample. This paper presents two data sets from micron-sized cyanobacteria obtained at the Linac Coherent Light Source, containing a total of 199,000 diffraction patterns. Utilizing this type of diffraction data will require the development of new analysis methods and algorithms for studying structure and structural variability in large populations of cells and to create abstract models. Such studies will allow us to understand living cells and populations of cells in new ways. New X-ray lasers, like the European XFEL, will produce billions of pulses per day, and could open new areas in structural sciences.

Open data set of live cyanobacterial cells imaged using an X-ray laser.

PubMed

van der Schot, Gijs; Svenda, Martin; Maia, Filipe R N C; Hantke, Max F; DePonte, Daniel P; Seibert, M Marvin; Aquila, Andrew; Schulz, Joachim; Kirian, Richard A; Liang, Mengning; Stellato, Francesco; Bari, Sadia; Iwan, Bianca; Andreasson, Jakob; Timneanu, Nicusor; Bielecki, Johan; Westphal, Daniel; Nunes de Almeida, Francisca; Odić, Duško; Hasse, Dirk; Carlsson, Gunilla H; Larsson, Daniel S D; Barty, Anton; Martin, Andrew V; Schorb, Sebastian; Bostedt, Christoph; Bozek, John D; Carron, Sebastian; Ferguson, Ken; Rolles, Daniel; Rudenko, Artem; Epp, Sascha W; Foucar, Lutz; Rudek, Benedikt; Erk, Benjamin; Hartmann, Robert; Kimmel, Nils; Holl, Peter; Englert, Lars; Loh, N Duane; Chapman, Henry N; Andersson, Inger; Hajdu, Janos; Ekeberg, Tomas

2016-08-01

Structural studies on living cells by conventional methods are limited to low resolution because radiation damage kills cells long before the necessary dose for high resolution can be delivered. X-ray free-electron lasers circumvent this problem by outrunning key damage processes with an ultra-short and extremely bright coherent X-ray pulse. Diffraction-before-destruction experiments provide high-resolution data from cells that are alive when the femtosecond X-ray pulse traverses the sample. This paper presents two data sets from micron-sized cyanobacteria obtained at the Linac Coherent Light Source, containing a total of 199,000 diffraction patterns. Utilizing this type of diffraction data will require the development of new analysis methods and algorithms for studying structure and structural variability in large populations of cells and to create abstract models. Such studies will allow us to understand living cells and populations of cells in new ways. New X-ray lasers, like the European XFEL, will produce billions of pulses per day, and could open new areas in structural sciences.

Open data set of live cyanobacterial cells imaged using an X-ray laser

PubMed Central

van der Schot, Gijs; Svenda, Martin; Maia, Filipe R.N.C.; Hantke, Max F.; DePonte, Daniel P.; Seibert, M. Marvin; Aquila, Andrew; Schulz, Joachim; Kirian, Richard A.; Liang, Mengning; Stellato, Francesco; Bari, Sadia; Iwan, Bianca; Andreasson, Jakob; Timneanu, Nicusor; Bielecki, Johan; Westphal, Daniel; Nunes de Almeida, Francisca; Odić, Duško; Hasse, Dirk; Carlsson, Gunilla H.; Larsson, Daniel S.D.; Barty, Anton; Martin, Andrew V.; Schorb, Sebastian; Bostedt, Christoph; Bozek, John D.; Carron, Sebastian; Ferguson, Ken; Rolles, Daniel; Rudenko, Artem; Epp, Sascha W.; Foucar, Lutz; Rudek, Benedikt; Erk, Benjamin; Hartmann, Robert; Kimmel, Nils; Holl, Peter; Englert, Lars; Loh, N. Duane; Chapman, Henry N.; Andersson, Inger; Hajdu, Janos; Ekeberg, Tomas

2016-01-01

Structural studies on living cells by conventional methods are limited to low resolution because radiation damage kills cells long before the necessary dose for high resolution can be delivered. X-ray free-electron lasers circumvent this problem by outrunning key damage processes with an ultra-short and extremely bright coherent X-ray pulse. Diffraction-before-destruction experiments provide high-resolution data from cells that are alive when the femtosecond X-ray pulse traverses the sample. This paper presents two data sets from micron-sized cyanobacteria obtained at the Linac Coherent Light Source, containing a total of 199,000 diffraction patterns. Utilizing this type of diffraction data will require the development of new analysis methods and algorithms for studying structure and structural variability in large populations of cells and to create abstract models. Such studies will allow us to understand living cells and populations of cells in new ways. New X-ray lasers, like the European XFEL, will produce billions of pulses per day, and could open new areas in structural sciences. PMID:27479514

Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses

PubMed Central

Okamoto, Kenta; Bielecki, Johan; Maia, Filipe R. N. C.; Mühlig, Kerstin; Seibert, M. Marvin; Hantke, Max F.; Benner, W. Henry; Svenda, Martin; Ekeberg, Tomas; Loh, N. Duane; Pietrini, Alberto; Zani, Alessandro; Rath, Asawari D.; Westphal, Daniel; Kirian, Richard A.; Awel, Salah; Wiedorn, Max O.; van der Schot, Gijs; Carlsson, Gunilla H.; Hasse, Dirk; Sellberg, Jonas A.; Barty, Anton; Andreasson, Jakob; Boutet, Sébastien; Williams, Garth; Koglin, Jason; Hajdu, Janos; Larsson, Daniel S. D.

2017-01-01

This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of ∼40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from ∼35 to ∼300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 × 1012 photons per µm2 per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers. PMID:28512572

Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses

DOE PAGES

Daurer, Benedikt J.; Okamoto, Kenta; Bielecki, Johan; ...

2017-04-07

This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. AerosolizedOmono River virusparticles of ~40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to amore » wider than expected size distribution (from ~35 to ~300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 × 10 12photons per µm 2per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. Finally, the results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.« less

Band structure engineering for solar energy applications: Zinc oxide(1-x) selenium(x) films and devices

NASA Astrophysics Data System (ADS)

Mayer, Marie Annette

New technologies motivate the development of new semiconducting materials, for which structural, electrical and chemical properties are not well understood. In addition to new materials systems, there are huge opportunities for new applications, especially in solar energy conversion. In this dissertation I explore the role of band structure engineering of semiconducting oxides for solar energy. Due to the abundance and electrochemical stability of oxides, the appropriate modification could make them appealing for applications in both photovoltaics and photoelectrochemical hydrogen production. This dissertation describes the design, synthesis and evaluation of the alloy ZnO1-xSe x for these purposes. I review several methods of band structure engineering including strain, quantum confinement and alloying. A detailed description of the band anticrossing (BAC) model for highly mismatched alloys is provided, including the derivation of the BAC model as well as recent work and potential applications. Thin film ZnOxSe1-x samples are grown by pulsed laser deposition (PLD). I describe in detail the effect of growth conditions (temperature, pressure and laser fluence) on the chemistry, structure and optoelectronic properties of ZnOxSe1-x. The films are grown using different combinations of PLD conditions and characterized with a variety of techniques. Phase pure films with low roughness and high crystallinity were obtained at temperatures below 450¢ªC, pressures less than 10-4 Torr and laser fluences on the order of 1.5 J/cm 2. Electrical conduction was still observed despite heavy concentrations of grain boundaries. The band structure of ZnO1-xSex is then examined in detail. The bulk electron affinity of a ZnO thin film was measured to be 4.5 eV by pinning the Fermi level with native defects. This is explained in the framework of the amphoteric defect model. A shift in the ZnO1-xSe x valence band edge with x is observed using synchrotron x-ray absorption and emission

Transient lattice contraction in the solid to plasma transition of x-ray heated xenon clusters

NASA Astrophysics Data System (ADS)

Bostedt, C.; Ferguson, K.; Gorkhover, T.; Bucksbaum, P. H.; Boutet, S.; Koglin, J. E.; Lutman, A.; Marinelli, A.; Turner, J.; Bucher, M.; Ho, P.; Knight, C.; Young, L.; Fukuzawa, H.; Kumagai, Y.; Ueda, K.; Nagaya, K.; Messerschmidt, M.; Williams, G.

2016-05-01

Any sample in the focus of intense x-ray pulses will be transformed into a nanoplasma within femtoseconds. We have employed the novel two-color two-pulse mode available at the Linac Coherent Light Source free-electron laser to investigate the structural dynamics in nanoparticles upon x-ray exposure. We find that the nanoparticle transiently contracts within the first 80 fs following x-ray irradiation before ultimately disintegrating in a rapid hydrodynamic expansion. The contraction can be attributed to the massive x-ray induced electronic excitation that induces a collective change in the bond character of the nanoparticles. Alternative explanations for the contraction include a compression wave stemming from a rapid surface explosion of the nanoparticle. Computer simulations under way can elucidate the dominant contraction mechanism and yield further insight into the complex x-ray induced dynamics in nanoscale samples. This work is funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, under Contract No. DE-AC02-06CH11357.

Coherent soft X-ray diffraction imaging of coliphage PR772 at the Linac coherent light source

DOE PAGES

Reddy, Hemanth K. N.; Yoon, Chun Hong; Aquila, Andrew; ...

2017-06-27

Single-particle diffraction from X-ray Free Electron Lasers offers the potential for molecular structure determination without the need for crystallization. In an effort to further develop the technique, we present a dataset of coherent soft X-ray diffraction images of Coliphage PR772 virus, collected at the Atomic Molecular Optics (AMO) beamline with pnCCD detectors in the LAMP instrument at the Linac Coherent Light Source. The diameter of PR772 ranges from 65–70 nm, which is considerably smaller than the previously reported ~600 nm diameter Mimivirus. This reflects continued progress in XFEL-based single-particle imaging towards the single molecular imaging regime. As a result, themore » data set contains significantly more single particle hits than collected in previous experiments, enabling the development of improved statistical analysis, reconstruction algorithms, and quantitative metrics to determine resolution and self-consistency.« less

Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses

PubMed Central

Boll, Rebecca; Erk, Benjamin; Coffee, Ryan; Trippel, Sebastian; Kierspel, Thomas; Bomme, Cédric; Bozek, John D.; Burkett, Mitchell; Carron, Sebastian; Ferguson, Ken R.; Foucar, Lutz; Küpper, Jochen; Marchenko, Tatiana; Miron, Catalin; Patanen, Minna; Osipov, Timur; Schorb, Sebastian; Simon, Marc; Swiggers, Michelle; Techert, Simone; Ueda, Kiyoshi; Bostedt, Christoph; Rolles, Daniel; Rudenko, Artem

2016-01-01

Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse. PMID:27051675

Simultaneous S- and X-band uplink-downlink performance at DSS 13

NASA Technical Reports Server (NTRS)

Freiley, A. J.

1988-01-01

The Deep Space Station 13 26-meter antenna with the second generation S/X feedcone was tested to determine the dual S- and X-band (2.1 to 2.3 GHz and 7.1 to 8.5 GHz) transmit and receive performance. Measurements were conducted using the 20 kW transmitters at S- and X-band while simultaneously receiving S- and X-band. This system proved to be very quiet compared with the other DSN antennas. Under normal tracking configurations, no noise burst or intermodulation product (IMP) activity was detectable to the -175 dBm level. To prove the instrumentation's ability to detect such phenomena, an IMP generator was introduced onto the system with positive, verifiable results. The IMP occurred at the -162 dBm level, accompanied by moderate noise burst activity, and was readily repeatable. The measurement also showed the possible need for additional fourth channel filtering in the system to reduce the effect of the transmitter power on the low noise amplifiers.

Intercomparison of attenuation correction algorithms for single-polarized X-band radars

NASA Astrophysics Data System (ADS)

Lengfeld, K.; Berenguer, M.; Sempere Torres, D.

2018-03-01

Attenuation due to liquid water is one of the largest uncertainties in radar observations. The effects of attenuation are generally inversely proportional to the wavelength, i.e. observations from X-band radars are more affected by attenuation than those from C- or S-band systems. On the other hand, X-band radars can measure precipitation fields in higher temporal and spatial resolution and are more mobile and easier to install due to smaller antennas. A first algorithm for attenuation correction in single-polarized systems was proposed by Hitschfeld and Bordan (1954) (HB), but it gets unstable in case of small errors (e.g. in the radar calibration) and strong attenuation. Therefore, methods have been developed that restrict attenuation correction to keep the algorithm stable, using e.g. surface echoes (for space-borne radars) and mountain returns (for ground radars) as a final value (FV), or adjustment of the radar constant (C) or the coefficient α. In the absence of mountain returns, measurements from C- or S-band radars can be used to constrain the correction. All these methods are based on the statistical relation between reflectivity and specific attenuation. Another way to correct for attenuation in X-band radar observations is to use additional information from less attenuated radar systems, e.g. the ratio between X-band and C- or S-band radar measurements. Lengfeld et al. (2016) proposed such a method based isotonic regression of the ratio between X- and C-band radar observations along the radar beam. This study presents a comparison of the original HB algorithm and three algorithms based on the statistical relation between reflectivity and specific attenuation as well as two methods implementing additional information of C-band radar measurements. Their performance in two precipitation events (one mainly convective and the other one stratiform) shows that a restriction of the HB is necessary to avoid instabilities. A comparison with vertically pointing

Development of an automatic frequency control system for an X-band (=9300 MHz) RF electron linear accelerator

NASA Astrophysics Data System (ADS)

Cha, Sungsu; Kim, Yujong; Lee, Byung Cheol; Park, Hyung Dal; Lee, Seung Hyun; Buaphad, Pikad

2017-05-01

turn). The developed system is a more compact new resonance frequency control system. In addition, a frequency measuring part is included and it can measure the real-time resonance frequency from the magnetron. We have succeeded in the stable provisioning of RF power by recording the results of a 0.01% frequency deviation in the AFC during an RF test. Accordingly, in this paper, the detailed design, fabrication, and a high power test of the AFC system for the X-band linac are presented.

Monitoring deformation at the Geysers Geothermal Field, California using C-band and X-band interferometric synthetic aperture radar

DOE PAGES

Vasco, D. W.; Rutqvist, Jonny; Ferretti, Alessandro; ...

2013-06-07

In this study, we resolve deformation at The Geysers Geothermal Field using two distinct sets of interferometric synthetic aperture radar (InSAR) data. The first set of observations utilize archived European Space Agency C-band synthetic aperture radar data from 1992 through 1999 to image the long-term and large-scale subsidence at The Geysers. The peak range velocity of approximately 50 mm/year agrees with previous estimates from leveling and global positioning system observations. Data from a second set of measurements, acquired by TerraSAR-X satellites, extend from May 2011 until April 2012 and overlap the C-band data spatially but not temporally. These X-band data,more » analyzed using a combined permanent and distributed scatterer algorithm, provide a higher density of scatterers (1122 per square kilometer) than do the C-band data (12 per square kilometer). The TerraSAR-X observations resolve 1 to 2 cm of deformation due to water injection into a Northwest Geysers enhanced geothermal system well, initiated on October 2011. Lastly, the temporal variation of the deformation is compatible with estimates from coupled numerical modeling.« less

The Celestial Reference Frame at X/Ka-band (8.4/32 GHz)

NASA Technical Reports Server (NTRS)

Jacobs, C. S.; Clark, J. E.; Heflin, M. B.; Skjerve, L. J.; Sovers, O. J.; Garcia-Miro, C.; Moll, V. E.; Horiuchi, S.

2011-01-01

A celestial reference frame at X/Ka-band (8.4/32 GHz) has been constructed using fifty-one 24-hour sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 hours of right ascension and declinations down to -45 deg. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec in a cos delta and 290 micro-arcsec in delta. There is evidence for zonal errors at the 100 micro-arcsec level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.

Two-dimensional wide-band-gap nitride semiconductors: Single-layer 1 T -X N2 (X =S ,Se , and Te )

NASA Astrophysics Data System (ADS)

Lin, Jia-He; Zhang, Hong; Cheng, Xin-Lu; Miyamoto, Yoshiyuki

2016-11-01

Recently, the two-dimensional (2D) semiconductors arsenene and antimonene, with band gaps larger than 2.0 eV, have attracted tremendous interest, especially for potential applications in optoelectronic devices with a photoresponse in the blue and UV range. Motivated by this exciting discovery, types of highly stable wide-band-gap 2D nitride semiconductors were theoretically designed. We propose single-layer 1 T -X N2 (X =S , Se, and Te) via first-principles simulations. We compute 1 T -X N2 (X =S , Se, and Te) with indirect band gaps of 2.825, 2.351, and 2.336 eV, respectively. By applying biaxial strain, they are able to induce the transition from a wide-band-gap semiconductor to a metal, and the range of absorption spectra of 1 T -X N2 (X =S , Se, and Te) obviously extend from the ultraviolet region to the blue-purple light region. With an underlying graphene, we find that 1 T -X N2 can completely shield the light absorption of graphene in the range of 1-1.6 eV. Our research paves the way for optoelectronic devices working under blue or UV light, and mechanical sensors based on these 2D crystals.

Electron beam energy chirp control with a rectangular corrugated structure at the Linac Coherent Light Source

DOE PAGES

Zhang, Zhen; Bane, Karl; Ding, Yuantao; ...

2015-01-30

In this study, electron beam energy chirp is an important parameter that affects the bandwidth and performance of a linac-based, free-electron laser. In this paper we study the wakefields generated by a beam passing between at metallic plates with small corrugations, and then apply such a device as a passive dechirper for the Linac Coherent Light Source (LCLS) energy chirp control with a multi-GeV and femtosecond electron beam. Similar devices have been tested in several places at relatively low energies (~100 MeV) and with relatively long bunches (> 1ps). In the parameter regime of the LCLS dechirper, with the corrugationmore » size similar to the gap between the plates, the analytical solutions of the wakefields are no longer applicable, and we resort to a field matching program to obtain the wakes. Based on the numerical calculations, we fit the short-range, longitudinal wakes to simple formulas, valid over a large, useful parameter range. Finally, since the transverse wakefields - both dipole and quadrupole-are strong, we compute and include them in beam dynamics simulations to investigate the error tolerances when this device is introduced in the LCLS.« less

Performance and applications of the 14 MEV electron radiation linac at CIAE

NASA Astrophysics Data System (ADS)

Zhai, X. L.; Chen, G. C.; Qi, B. M.; Xu, F. J.; Pan, L. H.; Zhang, Z. M.; Shi, X. Z.; Chen, J. K.; Wang, F. Y.

1993-07-01

A 14 MeV electron linear accelerator which was designed and manufactured by the China Institute of Atomic Energy (CIAE) has been modified into an radiation processing accelerator in 1987. It consists of an electron gun, two prebunchers, one buncher, a three meter long accelerating section, and a 90 degree bending magnet. The linac is S-band (2856 MHz), travelling wave accelerator driven by a Chinese-made klystron. The energy of electrons can be adjusted from 8 MeV to 18 MeV and the average beam power is about 2 kW. The beam width is 600 mm and the uniformity of scanning beam is better than 10%. The linac is used to irradiate power semiconductor devices for controlling the minority carrier lifetime (MCL). More than twenty factories and scientific institutions use this linac to irradiate silicon controlled rectifiers (SCR) and the fast recovery diodes (FRD), and more than 0.2 million pieces of SCR have been irradiated. Tests have also been carried out for colour-change of topaz.

X-band inverse class-F GaN internally-matched power amplifier

NASA Astrophysics Data System (ADS)

Zhao, Bo-Chao; Lu, Yang; Han, Wen-Zhe; Zheng, Jia-Xin; Zhang, Heng-Shuang; Ma, Pei-jun; Ma, Xiao-Hua; Hao, Yue

2016-09-01

An X-band inverse class-F power amplifier is realized by a 1-mm AlGaN/GaN high electron mobility transistor (HEMT). The intrinsic and parasitic components inside the transistor, especially output capacitor Cds, influence the harmonic impedance heavily at the X-band, so compensation design is used for meeting the harmonic condition of inverse class-F on the current source plane. Experiment results show that, in the continuous-wave mode, the power amplifier achieves 61.7% power added efficiency (PAE), which is 16.3% higher than the class-AB power amplifier realized by the same kind of HEMT. To the best of our knowledge, this is the first inverse class-F GaN internally-matched power amplifier, and the PAE is quite high at the X-band. Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA016801).

Microjet formation and hard x-ray production from a liquid metal target irradiated by intense femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Lar'kin, A.; Uryupina, D.; Ivanov, K.; Savel'ev, A.; Bonnet, T.; Gobet, F.; Hannachi, F.; Tarisien, M.; Versteegen, M.; Spohr, K.; Breil, J.; Chimier, B.; Dorchies, F.; Fourment, C.; Leguay, P.-M.; Tikhonchuk, V. T.

2014-09-01

By using a liquid metal as a target one may significantly enhance the yield of hard x-rays with a sequence of two intense femtosecond laser pulses. The influence of the time delay between the two pulses is studied experimentally and interpreted with numerical simulations. It was suggested that the first arbitrary weak pulse produces microjets from the target surface, while the second intense pulse provides an efficient electron heating and acceleration along the jet surface. These energetic electrons are the source of x-ray emission while striking the target surface. The microjet formation is explained based on the results given by both optical diagnostics and hydrodynamic modeling by a collision of shocks originated from two distinct zones of laser energy deposition.

Control of Ge1-x-ySixSny layer lattice constant for energy band alignment in Ge1-xSnx/Ge1-x-ySixSny heterostructures

NASA Astrophysics Data System (ADS)

Fukuda, Masahiro; Watanabe, Kazuhiro; Sakashita, Mitsuo; Kurosawa, Masashi; Nakatsuka, Osamu; Zaima, Shigeaki

2017-10-01

The energy band alignment of Ge1-xSnx/Ge1-x-ySixSny heterostructures was investigated, and control of the valence band offset at the Ge1-xSnx/Ge1-x-ySixSny heterointerface was achieved by controlling the Si and Sn contents in the Ge1-x-ySixSny layer. The valence band offset in the Ge0.902Sn0.098/Ge0.41Si0.50Sn0.09 heterostructure was evaluated to be as high as 330 meV, and its conduction band offset was estimated to be 150 meV by considering the energy bandgap calculated from the theoretical prediction. In addition, the formation of the strain-relaxed Ge1-x-ySixSny layer was examined and the crystalline structure was characterized. The epitaxial growth of a strain-relaxed Ge0.64Si0.21Sn0.15 layer with the degree of strain relaxation of 55% was examined using a virtual Ge substrate. Moreover, enhancement of the strain relaxation was demonstrated by post-deposition annealing, where a degree of strain relaxation of 70% was achieved after annealing at 400 °C. These results indicate the possibility for enhancing the indirect-direct crossover with a strained and high-Sn-content Ge1-xSnx layer on a strain-relaxed Ge1-x-ySixSny layer, realizing preferable carrier confinement by type-I energy band alignment with high conduction and valence band offsets.

Visible-light absorption and large band-gap bowing of GaN 1-xSb x from first principles

DOE PAGES

Sheetz, R. Michael; Richter, Ernst; Andriotis, Antonis N.; ...

2011-08-01

Applicability of the Ga(Sb x)N 1-x alloys for practical realization of photoelectrochemical water splitting is investigated using first-principles density functional theory incorporating the local density approximation and generalized gradient approximation plus the Hubbard U parameter formalism. Our calculations reveal that a relatively small concentration of Sb impurities is sufficient to achieve a significant narrowing of the band gap, enabling absorption of visible light. Theoretical results predict that Ga(Sb x)N 1-x alloys with 2-eV band gaps straddle the potential window at moderate to low pH values, thus indicating that dilute Ga(Sb x)N 1-x alloys could be potential candidates for splitting watermore » under visible light irradiation.« less

Batch crystallization of rhodopsin for structural dynamics using an X-ray free-electron laser

DOE PAGES

Wu, Wenting; Nogly, Przemyslaw; Rheinberger, Jan; ...

2015-06-27

Rhodopsin is a membrane protein from the G protein-coupled receptor family. Together with its ligand retinal, it forms the visual pigment responsible for night vision. In order to perform ultrafast dynamics studies, a time-resolved serial femtosecond crystallography method is required owing to the nonreversible activation of rhodopsin. In such an approach, microcrystals in suspension are delivered into the X-ray pulses of an X-ray free-electron laser (XFEL) after a precise photoactivation delay. Here in this study, a millilitre batch production of high-density microcrystals was developed by four methodical conversion steps starting from known vapour-diffusion crystallization protocols: (i) screening the low-salt crystallizationmore » conditions preferred for serial crystallography by vapour diffusion, (ii) optimization of batch crystallization, (iii) testing the crystal size and quality using second-harmonic generation (SHG) imaging and X-ray powder diffraction and (iv) production of millilitres of rhodopsin crystal suspension in batches for serial crystallography tests; these crystals diffracted at an XFEL at the Linac Coherent Light Source using a liquid-jet setup.« less

Coherence Conversion for Optimized Resolution in Optical Measurements - Example of Femtosecond Time Resolution Using the Transverse Coherence of 100-Picosecond X-Rays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Bernhard W.

2015-01-01

A way is proposed to obtain a femtosecond time resolution over a picosecond range in x-ray spectroscopic measurements where the light source and the detector are much slower than that. It is based on the invariance of the modulus of the Fourier transform to object translations. The method geometrically correlates time in the sample with x-ray amplitudes over a spatial coordinate, and then takes the optical Fourier transform through far-field diffraction. Thus, explicitly time-invariant intensities that encode the time evolution of the sample can be measured with a slow detector. This corresponds to a phase-space transformation that converts the transversemore » coherence to become effective in the longitudinal direction. Because synchrotron-radiation sources have highly anisotropic coherence properties with about $10^5$ longitudinal electromagnetic-field modes at 1 eV bandwidth, but only tens to hundreds transverse modes, coherence conversion can drastically improve the time resolution. Reconstruction of the femtosecond time evolution in the sample from the Fourier intensities is subject to a phase ambiguity that is well-known in crystallography. However, a way is presented to resolve it that is not available in that discipline. Finally, data from a demonstration experiment are presented. The same concept can be used to obtain attosecond time resolution with an x-ray free-electron laser.« less

X-ray Laser Animated Fly-Through

ScienceCinema

None

2018-01-16

Take a tour with an electron's-eye-view through SLAC's revolutionary new X-ray laser facility with this 5 1/2 minute animation. See how the X-ray pulses are generated using the world's longest linear accelerator along with unique arrays of machinery specially designed for this one-of-a-kind tool. For more than 40 years, SLAC's two-mile-long linear accelerator (or linac) linac has produced high-energy electrons for cutting-edge physics experiments. Now, SLAC's linac has entered a new phase of its career with the creation of the Linac Coherent Light Source (LCLS).

DSN 70-meter antenna X- and S-band calibration. Part 1: Gain measurements

NASA Technical Reports Server (NTRS)

Richter, P. H.; Slobin, S. D.

1989-01-01

Aperture efficiency measurements made during 1988 on the three 70-m stations (DSS-14, DSS-43, and DSS-63) at X-band (8420 MHz) and S-band (2295 MHz) have been analyzed and reduced to yield best estimates of antenna gain versus elevation. The analysis has been carried out by fitting the gain data to a theoretical expression based on the Ruze formula. Newly derived flux density and source-size correction factors for the natural radio calibration sources used in the measurements have been used in the reduction of the data. Peak gains measured at the three stations were 74.18 (plus or minus 0.10) dBi at X-band, and 63.34 (plus or minus 0.03) dBi at S-band, with corresponding peak aperture efficiencies of 0.687 (plus or minus 0.015) and 0.762 (plus or minus 0.006), respectively. The values quoted assume no atmosphere is present, and the estimated absolute accuracy of the gain measurements is approximately plus or minus 0.2 dB at X-band and plus or minus 0.1 dB at S-band (1-sigma values).

An X-Band SOS Resistive Gate-Insulator-Semiconductor /RIS/ switch

NASA Astrophysics Data System (ADS)

Kwok, S. P.

1980-02-01

The new X-Band Resistive Gate-Insulator-Semiconductor (RIS) switch has been fabricated on silicon-on-sapphire, and its equivalent circuit model characterized. An RIS SPST switch with 20-dB on/off isolation, 1.2-dB insertion loss, and power handling capacity in excess of 20-W peak has been achieved at X band. The device switching time is on the order of 600 ns, and it requires negligible control holding current in both on and off states. The device is compatible with monolithic integrated-circuit technology and thus is suitable for integration into low-cost monolithic phase shifters or other microwave integrated circuits.

Playback system designed for X-Band SAR

NASA Astrophysics Data System (ADS)

Yuquan, Liu; Changyong, Dou

2014-03-01

SAR(Synthetic Aperture Radar) has extensive application because it is daylight and weather independent. In particular, X-Band SAR strip map, designed by Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, provides high ground resolution images, at the same time it has a large spatial coverage and a short acquisition time, so it is promising in multi-applications. When sudden disaster comes, the emergency situation acquires radar signal data and image as soon as possible, in order to take action to reduce loss and save lives in the first time. This paper summarizes a type of X-Band SAR playback processing system designed for disaster response and scientific needs. It describes SAR data workflow includes the payload data transmission and reception process. Playback processing system completes signal analysis on the original data, providing SAR level 0 products and quick image. Gigabit network promises radar signal transmission efficiency from recorder to calculation unit. Multi-thread parallel computing and ping pong operation can ensure computation speed. Through gigabit network, multi-thread parallel computing and ping pong operation, high speed data transmission and processing meet the SAR radar data playback real time requirement.

Development of new S-band RF window for stable high-power operation in linear accelerator RF system

NASA Astrophysics Data System (ADS)

Joo, Youngdo; Lee, Byung-Joon; Kim, Seung-Hwan; Kong, Hyung-Sup; Hwang, Woonha; Roh, Sungjoo; Ryu, Jiwan

2017-09-01

For stable high-power operation, a new RF window is developed in the S-band linear accelerator (Linac) RF systems of the Pohang Light Source-II (PLS-II) and the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL). The new RF window is designed to mitigate the strength of the electric field at the ceramic disk and also at the waveguide-cavity coupling structure of the conventional RF window. By replacing the pill-box type cavity in the conventional RF window with an overmoded cavity, the electric field component perpendicular to the ceramic disk that caused most of the multipacting breakdowns in the ceramic disk was reduced by an order of magnitude. The reduced electric field at the ceramic disk eliminated the Ti-N coating process on the ceramic surface in the fabrication procedure of the new RF window, preventing the incomplete coating from spoiling the RF transmission and lowering the fabrication cost. The overmoded cavity was coupled with input and output waveguides through dual side-wall coupling irises to reduce the electric field strength at the waveguide-cavity coupling structure and the possibility of mode competitions in the overmoded cavity. A prototype of the new RF window was fabricated and fully tested with the Klystron peak input power, pulse duration and pulse repetition rate of 75 MW, 4.5 μs and 10 Hz, respectively, at the high-power test stand. The first mass-produced new RF window installed in the PLS-II Linac is running in normal operation mode. No fault is reported to date. Plans are being made to install the new RF window to all S-band accelerator RF modules of the PLS-II and PAL-XFEL Linacs. This new RF window may be applied to the output windows of S-band power sources like Klystron as wells as the waveguide windows of accelerator facilities which operate in S-band.

Testing Omega P’s 650 KW, 1.3 GHZ Low-Voltage Multi-Beam Klystron for the Project X Pulsed LINAC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fermi Research Alliance; Omega-P Inc.

Omega-P Inc. had developed a multi beam 1.3 GHz klystron (MBK) for the Project X pulsed linac application. Testing of the klystron require a special hardware such as a modulator, RF components, control system, power supplies, etc, as well as associated infrastructure( electricity, water, safety). This is an expensive part of klystron development for which Omega-P does not have the required equipment. Fermilab will test the MBK at Fermilab site providing contribution to the project all the necessary facilities, infrastructure and manpower for MBK test performance and analysis.

Conduction- and Valence-Band Energies in Bulk InAs(1-x)Sb(x) and Type II InAs(1-x) Sb(x)/InAs Strained-Layer Superlattices

DTIC Science & Technology

2013-03-08

tions in the studied SLS structures . The fit of the dependence of the valence- band energy of unstrained InAs1!xSbx on the composition x with a... band . STRUCTURES Bulk InAsSb epilayers on metamorphic buffers and InAsSb/InAs strained-layer superlattices (SLS) were grown on GaSb substrates by solid...meV in InAs and Ev = 0 meV in InSb. For InAsSb with 22.5% Sb grown on GaSb , an unstrained valence- band energy of Ev = !457 meV was obtained. For the

A model for the energy band gap of GaSbxAs1-x and InSbxAs1-x in the whole composition range

NASA Astrophysics Data System (ADS)

Zhao, Chuan-Zhen; Ren, He-Yu; Wei, Tong; Wang, Sha-Sha; Wang, Jun

2018-04-01

The band gap evolutions of GaSbxAs1-x and InSbxAs1-x in the whole composition range are investigated. It is found that the band gap evolutions of GaSbxAs1-x and InSbxAs1-x are determined by two factors. One is the impurity-host interaction in the As-rich and Sb-rich composition ranges. The other is the intraband coupling within the conduction band and separately within the valence band in the moderate composition range. Based on the band gap evolutions of GaSbxAs1-x and InSbxAs1-x, a model is established. In addition, it is found that the impurity-host interaction is determined by not only the mismatches in size and electronegativity between the introduced atoms in the host material and the anions of the host material, but also the difference in electronegativity between the introduced atoms in the host material and the cations of the host material.

Magnetic decoupling of the linac in a low field biplanar linac-MR system.

PubMed

St Aubin, J; Steciw, S; Fallone, B G

2010-09-01

The integration of a low field biplanar magnetic resonance (MR) imager and linear accelerator (linac) causes magnetic interference at the linac due to the MR fringe fields. In order to eliminate this interference, passive and active magnetic shielding designs are investigated. The optimized design of passive magnetic shielding was performed using the finite element method. The design was required to achieve no greater than a 20% electron beam loss within the linac waveguide and electron gun, no greater than 0.06 T at the multileaf collimator (MLC) motors, and generate a distortion of the main MR imaging volume of no greater than 300 ppm. Through the superposition of the analytical solution for a single current carrying wire loop, active shielding designs in the form of three and four sets of coil pairs surrounding the linac waveguide and electron gun were also investigated. The optimized current and coil center locations that yielded the best cancellation of the MR fringe fields at the linac were determined using sequential quadratic programming. Optimized passive shielding in the form of two steel cylinders was designed to meet the required constraints. When shielding the MLC motors along with the waveguide and electron gun, the thickness of the cylinders was less than 1 mm. If magnetically insensitive MLC motors are used, no MLC shielding would be required and the waveguide shield (shielding the waveguide and electron gun) became 1.58 mm thick. In addition, the optimized current and coil spacing for active shielding was determined for both three and four coil pair configurations. The results of the active shielding optimization produced no beam loss within the waveguide and electron gun and a maximum MR field distortion of 91 ppm over a 30 cm diameter spherical volume. Very simple passive and active shielding designs have been shown to magnetically decouple the linac from the MR imager in a low field biplanar linac-MR system. The MLC passive shielding produced

UV waveguides light fabricated in fluoropolymer CYTOP by femtosecond laser direct writing.

PubMed

Hanada, Yasutaka; Sugioka, Koji; Midorikawa, Katsumi

2010-01-18

We have fabricated optical waveguides inside the UV-transparent polymer, CYTOP, by femtosecond laser direct writing for propagating UV light in biochip applications. Femtosecond laser irradiation is estimated to increase the refractive index of CYTOP by 1.7 x 10(-3) due to partial bond breaking in CYTOP. The waveguide in CYTOP has propagation losses of 0.49, 0.77, and 0.91 dB/cm at wavelengths of 632.8, 355, and 266 nm, respectively.

Science Results from the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR): Progress Report

NASA Technical Reports Server (NTRS)

Evans, Diane L. (Editor); Plaut, Jeffrey (Editor)

1996-01-01

The Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) is the most advanced imaging radar system to fly in Earth orbit. Carried in the cargo bay of the Space Shuttle Endeavour in April and October of 1994, SIR-C/X-SAR simultaneously recorded SAR data at three wavelengths (L-, C-, and X-bands; 23.5, 5.8, and 3.1 cm, respectively). The SIR-C/X-SAR Science Team consists of 53 investigator teams from more than a dozen countries. Science investigations were undertaken in the fields of ecology, hydrology, ecology, and oceanography. This report contains 44 investigator team reports and several additional reports from coinvestigators and other researchers.

Femtosecond laser fluorescence and propagation in very dense potassium vapor.

PubMed

Makdisi, Y; Kokaj, J; Afrousheh, K; Nair, R; Mathew, J; Pichler, G

2013-12-16

Femtosecond (fs) laser propagation and fluorescence of dense potassium vapor was studied, and the spectral region around the first and the second doublets of the principal series lines of potassium atoms was investigated. In our search we did not observe the conical emission in the far field, although it was previously observed in the case of rubidium. We discuss the possible reason of this unexpected result. The fluorescence spectrum revealed Rb impurity resonance lines in emission due to the collisional redistribution from the K(4p) levels into the Rb(5p) levels. In the forward propagation of 400 nm femtosecond light we observed the molecular band red shifted from potassium second doublet. However, no molecular spectrum was observed when the mode-locked fs laser light was discretely tuned within the wings of the first resonance lines, at 770 nm.

The Celestial Reference Frame at X/Ka-band (8.4/32 GHz)

NASA Technical Reports Server (NTRS)

Jacobs, C. S.; Clark, J. E.; Heflin, M. B.; Skjerve, L. J.; Sovers, O. J.; Garcia-Miro, C.; Moll, V. E.; Horiuchi, S.

2010-01-01

A celestial reference frame at X/Kaband (8.4/32 GHz) has been constructed using fiftyone 24-hour sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 hours of right ascension and declinations down to -45 deg. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec ( mu as) in alpha cos delta and 290 mu as in delta. There is evidence for zonal errors at the 100 mu as level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.

Control of the kerf size and microstructure in Inconel 738 superalloy by femtosecond laser beam cutting

NASA Astrophysics Data System (ADS)

Wei, J.; Ye, Y.; Sun, Z.; Liu, L.; Zou, G.

2016-05-01

Femtosecond laser beam cutting is becoming widely used to meet demands for increasing accuracy in micro-machining. In this paper, the effects of processing parameters in femtosecond laser beam cutting on the kerf size and microstructure in Inconel 738 have been investigated. The defocus, pulse width and scanning speed were selected to study the controllability of the cutting process. Adjusting and matching the processing parameters was a basic enhancement method to acquire well defined kerf size and the high-quality ablation of microstructures, which has contributed to the intensity clamping effect. The morphology and chemical compositions of these microstructures on the cut surface have been characterized by a scanning electron microscopy equipped with an energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Additionally, the material removal mechanism and oxidation mechanism on the Inconel 738 cut surface have also been discussed on the basis of the femtosecond laser induced normal vaporization or phase explosion, and trapping effect of the dangling bonds.

X-band noise temperature effects of rain on DSN antenna feedhorns

NASA Technical Reports Server (NTRS)

Slobin, S. D.; Franco, M. M.; Clauss, R. C.

1982-01-01

Simulated rain tests were carried out to determine the noise temperature contribution of liquid water adhering to the aperture cover material on both a standard DSN X-band feedhorn and on an S/X-band common aperture feedhorn. It was found that for the particular common aperture feedhorn tested, system noise temperature increases were much greater when the plastic horn cover material was old and weathered than when it was new. The age and condition of the aperture cover material is believed to be a major factor in the amount of degradation experienced by a telecommunications system during rain events.

Sleuthing the MSL EDL performance from an X band carrier perspective

NASA Astrophysics Data System (ADS)

Oudrhiri, Kamal; Asmar, Sami; Estabrook, Polly; Kahan, Daniel; Mukai, Ryan; Ilott, Peter; Schratz, Brian; Soriano, Melissa; Finley, Susan; Shidner, Jeremy

During the Entry, Descent, and Landing (EDL) of NASA's Mars Science Laboratory (MSL), or Curiosity, rover to Gale Crater on Mars on August 6, 2012 UTC, the rover transmitted an X-band signal composed of carrier and tone frequencies and a UHF signal modulated with an 8kbps data stream. During EDL, the spacecraft's orientation is determined by its guidance and mechanical subsystems to ensure that the vehicle land safely at its destination. Although orientation to maximize telecom performance is not possible, antennas are especially designed and mounted to provide the best possible line of sight to Earth and to the Mars orbiters supporting MSL's landing. The tones and data transmitted over these links are selected carefully to reflect the most essential parameters of the vehicle's state and the performance of the EDL subsystems for post-EDL reconstruction should no further data transmission from the vehicle be possible. This paper addresses the configuration of the X band receive system used at NASA / JPL's Deep Space Network (DSN) to capture the signal spectrum of MSL's X band carrier and tone signal, examines the MSL vehicle state information obtained from the X band carrier signal only and contrasts the Doppler-derived information against the post-EDL known vehicle state. The paper begins with a description of the MSL EDL sequence of events and discusses the impact of the EDL maneuvers such as guided entry, parachute deploy, and powered descent on the frequency observables expected at the DSN. The range of Doppler dynamics possible is derived from extensive 6 Degrees-Of-Freedom (6 DOF) vehicle state calculations performed by MSL's EDL simulation team. The configuration of the DSN's receive system, using the Radio Science Receivers (RSR) to perform open-loop recording for both for nominal and off-nominal EDL scenarios, is detailed. Expected signal carrier power-to-noise levels during EDL are shown and their impact on signal detection is considered. Particula

Sleuthing the MSL EDL Performance from an X Band Carrier Perspective

NASA Technical Reports Server (NTRS)

Oudrhiri, Kamal; Asmar, Sami; Estabrook, Polly; Kahan, Daniel; Mukai, Ryan; Ilott, Peter; Schratz, Brian; Soriano, Melissa; Finley, Susan; Shidner, Jeremy

2013-01-01

During the Entry, Descent, and Landing (EDL) of NASA's Mars Science Laboratory (MSL), or Curiosity, rover to Gale Crater on Mars on August 6, 2012 UTC, the rover transmitted an X-band signal composed of carrier and tone frequencies and a UHF signal modulated with an 8kbps data stream. During EDL, the spacecraft's orientation is determined by its guidance and mechanical subsystems to ensure that the vehicle land safely at its destination. Although orientation to maximize telecom performance is not possible, antennas are especially designed and mounted to provide the best possible line of sight to Earth and to the Mars orbiters supporting MSL's landing. The tones and data transmitted over these links are selected carefully to reflect the most essential parameters of the vehicle's state and the performance of the EDL subsystems for post-EDL reconstruction should no further data transmission from the vehicle be possible. This paper addresses the configuration of the X band receive system used at NASA / JPL's Deep Space Network (DSN) to capture the signal spectrum of MSL's X band carrier and tone signal, examines the MSL vehicle state information obtained from the X band carrier signal only and contrasts the Doppler-derived information against the post-EDL known vehicle state. The paper begins with a description of the MSL EDL sequence of events and discusses the impact of the EDL maneuvers such as guided entry, parachute deploy, and powered descent on the frequency observables expected at the DSN. The range of Doppler dynamics possible is derived from extensive 6 Degrees-Of-Freedom (6 DOF) vehicle state calculations performed by MSL's EDL simulation team. The configuration of the DSN's receive system, using the Radio Science Receivers (RSR) to perform open-loop recording for both for nominal and off-nominal EDL scenarios, is detailed. Expected signal carrier power-to-noise levels during EDL are shown and their impact on signal detection is considered. Particular

High Peak Power Test and Evaluation of S-band Waveguide Switches

NASA Astrophysics Data System (ADS)

Nassiri, A.; Grelick, A.; Kustom, R. L.; White, M.

1997-05-01

The injector and source of particles for the Advanced Photon Source is a 2856-MHz S-band electron-positron linear accelerator (linac) which produces electrons with energies up to 650 MeV or positrons with energies up to 450 MeV. To improve the linac rf system availability, an additional modulator-klystron subsystem is being constructed to provide a switchable hot spare unit for each of the five exsisting S-band transmitters. The switching of the transmitters will require the use of SF6-pressurized S-band waveguide switches at a peak operating power of 35 MW. Such rf switches have been successfully operated at other accelerator facilities but at lower peak powers. A test stand has been set up at the Stanford Linear Accelerator Center (SLAC) Klystron Factory to conduct tests comparing the power handling characteristics of two WR-284 and one WR-340 switches. Test results are presented and their implications for the design of the switching system are discussed.

Superconducting heavy ion injector linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shepard, K.W.

1985-01-01

A conceptual design for a very low velocity (.007 < v/c < .07) superconducting heavy-ion linac is reviewed. This type of linac may have significant cost and performance advantages over room-temperature linacs, at least for applications requiring modest beam currents. Some general features of the design of very-low velocity superconducting accelerating structures are discussed and a design for a 48.5 MHz, v/c = .009 structure, together with the status of a niobium prototype, is discussed in detail. Preliminary results of a beam dynamics study indicate that the low velocity linac may be able to produce heavy-ion beams with time-energy spreadsmore » of a few keV-nsec. 11 refs, 4 figs.« less

Optical laser systems at the Linac Coherent Light Source

DOE PAGES

Minitti, Michael P.; Robinson, Joseph S.; Coffee, Ryan N.; ...

2015-04-22

Ultrafast optical lasers play an essential role in exploiting the unique capabilities of recently commissioned X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS). Pump–probe experimental techniques reveal ultrafast dynamics in atomic and molecular processes and reveal new insights in chemistry, biology, material science and high-energy-density physics. This manuscript describes the laser systems and experimental methods that enable cutting-edge optical laser/X-ray pump–probe experiments to be performed at LCLS.

Femtosecond timing distribution and control for next generation accelerators and light sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Li -Jin

Femtosecond Timing Distribution At LCLS Free-electron-lasers (FEL) have the capability of producing high photon flux from the IR to the hard x-ray wavelength range and to emit femtosecond and eventually even attosecond pulses. This makes them an ideal tool for fundamental as well as applied re-search. Timing precision at the Stanford Linear Coherent Light Source (LCLS) between the x-ray FEL (XFEL) and ultrafast optical lasers is currently no better than 100 fs RMS. Ideally this precision should be much better and could be limited only by the x-ray pulse duration, which can be as short as a few femtoseconds. Anmore » increasing variety of science problems involving electron and nuclear dynamics in chemical and material systems will become accessible as the timing improves to a few femtoseconds. Advanced methods of electron beam conditioning or pulse injection could allow the FEL to achieve pulse durations less than one femtosecond. The objective of the work described in this proposal is to set up an optical timing distribution system based on mode locked Erbium doped fiber lasers at LCLS facility to improve the timing precision in the facility and allow time stamping with a 10 fs precision. The primary commercial applications for optical timing distributions systems are seen in the worldwide accelerator facilities and next generation light sources community. It is reasonable to expect that at least three major XFELs will be built in the next decade. In addition there will be up to 10 smaller machines, such as FERMI in Italy and Maxlab in Sweden, plus the market for upgrading already existing facilities like Jefferson Lab. The total market is estimated to be on the order of a 100 Million US Dollars. The company owns the exclusive rights to the IP covering the technology enabling sub-10 fs synchronization systems. Testing this technology, which has set records in a lab environment, at LCLS, hence in a real world scenario, is an important corner stone of bringing the

High gradient linac for proton therapy

NASA Astrophysics Data System (ADS)

Benedetti, S.; Grudiev, A.; Latina, A.

2017-04-01

Proposed for the first time almost 30 years ago, the research on radio frequency linacs for hadron therapy experienced a sparkling interest in the past decade. The different projects found a common ground on a relatively high rf operating frequency of 3 GHz, taking advantage of the availability of affordable and reliable commercial klystrons at this frequency. This article presents for the first time the design of a proton therapy linac, called TULIP all-linac, from the source up to 230 MeV. In the first part, we will review the rationale of linacs for hadron therapy. We then divided this paper in two main sections: first, we will discuss the rf design of the different accelerating structures that compose TULIP; second, we will present the beam dynamics design of the different linac sections.

Intensity-Modulated Advanced X-ray Source (IMAXS) for Homeland Security Applications

NASA Astrophysics Data System (ADS)

Langeveld, Willem G. J.; Johnson, William A.; Owen, Roger D.; Schonberg, Russell G.

2009-03-01

X-ray cargo inspection systems for the detection and verification of threats and contraband require high x-ray energy and high x-ray intensity to penetrate dense cargo. On the other hand, low intensity is desirable to minimize the radiation footprint. A collaboration between HESCO/PTSE Inc., Schonberg Research Corporation and Rapiscan Laboratories, Inc. has been formed in order to design and build an Intensity-Modulated Advanced X-ray Source (IMAXS). Such a source would allow cargo inspection systems to achieve up to two inches greater imaging penetration capability, while retaining the same average radiation footprint as present fixed-intensity sources. Alternatively, the same penetration capability can be obtained as with conventional sources with a reduction of the average radiation footprint by about a factor of three. The key idea is to change the intensity of the source for each x-ray pulse based on the signal strengths in the inspection system detector array during the previous pulse. In this paper we describe methods to accomplish pulse-to-pulse intensity modulation in both S-band (2998 MHz) and X-band (9303 MHz) linac sources, with diode or triode (gridded) electron guns. The feasibility of these methods has been demonstrated. Additionally, we describe a study of a shielding design that would allow a 6 MV X-band source to be used in mobile applications.

RFI-Based Ion Linac Systems

NASA Astrophysics Data System (ADS)

Swenson, Donald A.

A new company, Ion Linac Systems, Inc., has been formed to promote the development, manufacture, and marketing of intense, RFI-based, Ion Linac Systems. The Rf Focused Interdigital (RFI) linac structure was invented by the author while at Linac Systems, LLC. The first step, for the new company, will be to correct a flaw in an existing RFI-based linac system and to demonstrate "good transmission" through the system. The existing system, aimed at the BNCT medical application, is designed to produce a beam of 2.5 MeV protons with an average beam current of 20 mA. In conjunction with a lithium target, it will produce an intense beam of epithermal neutrons. This system is very efficient, requiring only 180 kW of rf power to produce a 50 kW proton beam. In addition to the BNCT medical application, the RFI-based systems should represent a powerful neutron generator for homeland security, defence applications, cargo container inspection, and contraband detection. The timescale to the demonstration of "good transmission" is early fall of this year. Our website is www.ionlinacs.com.

Resonant excitation of high order modes in the 3.9 GHz cavity of the Linac Coherent Light Source

NASA Astrophysics Data System (ADS)

Lunin, A.; Khabiboulline, T.; Solyak, N.; Sukhanov, A.; Yakovlev, V.

2018-02-01

Construction of the Linac Coherent Light Source II (LCLS-II) is underway for the world's first hard x-ray free-electron laser. A central part of the LCLS-II project is a 4 GeV superconducting radio frequency electron linac that will operate in the continuous wave (cw) mode. The linac is segmented into four sections named as L 0 , L 1 , L 2 , and L 3 . Two 3.9 GHz cryomodules, each housing of eight third-harmonic cavities similar to the cavities developed for the European X-ray Free Electron Laser (XFEL), will be used in section L 1 of the linac for linearizing the longitudinal beam profile. In this paper, we present a study of trapped high order modes (HOMs) excited by a cw electron beam in the third-harmonic cavities of the LCLS-II linac. A detailed comparison of the original XFEL design and the LCLS-II design with a modified end group is performed in order to estimate the effect of a reduced beam pipe aperture on the efficiency of HOM damping. Furthermore, we apply a statistical analysis of the eigenmode spectrum for the estimation of the probability of resonant HOM losses and influence of HOMs on beam dynamics.

Combined observations of Arctic sea ice with near-coincident colocated X-band, C-band, and L-band SAR satellite remote sensing and helicopter-borne measurements

NASA Astrophysics Data System (ADS)

Johansson, A. M.; King, J. A.; Doulgeris, A. P.; Gerland, S.; Singha, S.; Spreen, G.; Busche, T.

2017-01-01

In this study, we compare colocated near-coincident X-, C-, and L-band fully polarimetry SAR satellite images with helicopter-borne ice thickness measurements acquired during the Norwegian Young sea ICE 2015 (N-ICE2015) expedition in the region of the Arctic Ocean north of Svalbard in April 2015. The air-borne surveys provide near-coincident snow plus ice thickness, surface roughness data, and photographs. This unique data set allows us to investigate how the different frequencies can complement one another for sea ice studies, but also to raise awareness of limitations. X-band and L-band satellite scenes were shown to be a useful complement to the standard SAR frequency for sea ice monitoring (C-band) for lead ice and newly formed sea ice identification. This may be in part be due to the frequency but also the high spatial resolution of these sensors. We found a relatively low correlation between snow plus ice thickness and surface roughness. Therefore, in our dataset ice thickness cannot directly be observed by SAR which has important implications for operational ice charting based on automatic segmentation.

E+ Transition in GaAs1-xNx and GaAs1-xBix Due to Isoelectronic-Impurity-Induced Perturbation of the Conduction Band

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fluegel, B.; Mascarenhas, A.; Ptak, A. J.

2007-01-01

An above-band-gap transition E{sub +} is experimentally observed in the dilute GaAs{sub 1-x}Bi{sub x} alloy. Precise measurements at very low dilutions are made of the above-band-gap transition E{sub +} that is observed in GaAs{sub 1-x}N{sub x}, making it possible to compare the behavior of the different isoelectronic traps Bi and N in the common host GaAs with respect to their perturbation to the host electronic structure. We suggest that the origin of the E{sub +} level observed in GaAs is not the isolated isoelectronic impurity level N{sub x}, as is presumed in the band-anticrossing model, but rather the isoelectronic-impurity-induced perturbationmore » of the conduction band L{sub 6}{sup c}.« less

Electrical and band structural analyses of Ti1-x Al x O y films grown by atomic layer deposition on p-type GaAs

NASA Astrophysics Data System (ADS)

An, Youngseo; Mahata, Chandreswar; Lee, Changmin; Choi, Sungho; Byun, Young-Chul; Kang, Yu-Seon; Lee, Taeyoon; Kim, Jiyoung; Cho, Mann-Ho; Kim, Hyoungsub

2015-10-01

Amorphous Ti1-x Al x O y films in the Ti-oxide-rich regime (x  <  0.5) were deposited on p-type GaAs via atomic layer deposition with titanium isopropoxide, trimethylaluminum, and H2O precursor chemistry. The electrical properties and energy band alignments were examined for the resulting materials with their underlying substrates, and significant frequency dispersion was observed in the accumulation region of the Ti-oxide-rich Ti1-x Al x O y films. Although a further reduction in the frequency dispersion and leakage current (under gate electron injection) could be somewhat achieved through a greater addition of Al-oxide in the Ti1-x Al x O y film, the simultaneous decrease in the dielectric constant proved problematic in finding an optimal composition for application as a gate dielectric on GaAs. The spectroscopic band alignment measurements of the Ti-oxide-rich Ti1-x Al x O y films indicated that the band gaps had a rather slow increase with the addition of Al-oxide, which was primarily compensated for by an increase in the valance band offset, while a nearly-constant conduction band offset with a negative electron barrier height was maintained.

The application of airborne imaging radars (L and X-band) to earth resources problems

NASA Technical Reports Server (NTRS)

Drake, B.; Shuchman, R. A.; Bryan, M. L.; Larson, R. W.; Liskow, C. L.; Rendleman, R. A.

1974-01-01

A multiplexed synthetic aperture Side-Looking Airborne Radar (SLAR) that simultaneously images the terrain with X-band (3.2 cm) and L-band (23.0 cm) radar wavelengths was developed. The Feasibility of using multiplexed SLAR to obtain useful information for earth resources purposes. The SLAR imagery, aerial photographs, and infrared imagery are examined to determine the qualitative tone and texture of many rural land-use features imaged. The results show that: (1) Neither X- nor L-band SLAR at moderate and low depression angles can directly or indirectly detect pools of water under standing vegetation. (2) Many of the urban and rural land-use categories present in the test areas can be identified and mapped on the multiplexed SLAR imagery. (3) Water resources management can be done using multiplexed SLAR. (4) Drainage patterns can be determined on both the X- and L-band imagery.

Direct Band Gap Gallium Antimony Phosphide (GaSbxP1−x) Alloys

PubMed Central

Russell, H. B.; Andriotis, A. N.; Menon, M.; Jasinski, J. B.; Martinez-Garcia, A.; Sunkara, M. K.

2016-01-01

Here, we report direct band gap transition for Gallium Phosphide (GaP) when alloyed with just 1–2 at% antimony (Sb) utilizing both density functional theory based computations and experiments. First principles density functional theory calculations of GaSbxP1−x alloys in a 216 atom supercell configuration indicate that an indirect to direct band gap transition occurs at x = 0.0092 or higher Sb incorporation into GaSbxP1−x. Furthermore, these calculations indicate band edge straddling of the hydrogen evolution and oxygen evolution reactions for compositions ranging from x = 0.0092 Sb up to at least x = 0.065 Sb making it a candidate for use in a Schottky type photoelectrochemical water splitting device. GaSbxP1−x nanowires were synthesized by reactive transport utilizing a microwave plasma discharge with average compositions ranging from x = 0.06 to x = 0.12 Sb and direct band gaps between 2.21 eV and 1.33 eV. Photoelectrochemical experiments show that the material is photoactive with p-type conductivity. This study brings attention to a relatively uninvestigated, tunable band gap semiconductor system with tremendous potential in many fields. PMID:26860470

Measurements and Simulations of Nadir-Viewing Radar Returns from the Melting Layer at X- and W-Bands

NASA Technical Reports Server (NTRS)

Liao, Liang; Meneghini, Robert; Tian, Lin; Heymsfield, Gerald M.

2010-01-01

Simulated radar signatures within the melting layer in stratiform rain, namely the radar bright band, are checked by means of comparisons with simultaneous measurements of the bright band made by the EDOP (X-band) and CRS (W-band) airborne Doppler radars during the CRYSTAL-FACE campaign in 2002. A stratified-sphere model, allowing the fractional water content to vary along the radius of the particle, is used to compute the scattering properties of individual melting snowflakes. Using the effective dielectric constants computed by the conjugate gradient-fast Fourier transform (CGFFT) numerical method for X and W bands, and expressing the fractional water content of melting particle as an exponential function in particle radius, it is found that at X band the simulated radar bright-band profiles are in an excellent agreement with the measured profiles. It is also found that the simulated W-band profiles usually resemble the shapes of the measured bright-band profiles even though persistent offsets between them are present. These offsets, however, can be explained by the attenuation caused by cloud water and water vapor at W band. This is confirmed by the comparisons of the radar profiles made in the rain regions where the un-attenuated W-band reflectivity profiles can be estimated through the X- and W band Doppler velocity measurements. The bright-band model described in this paper has the potential to be used effectively for both radar and radiometer algorithms relevant to the TRMM and GPM satellite missions.

Energy dependence of the band-limited noise in black hole X-ray binaries★

NASA Astrophysics Data System (ADS)

Stiele, H.; Yu, W.

2015-10-01

Black hole low-mass X-ray binaries show a variety of variability features, which manifest as narrow peak-like structures superposed on broad noise components in power density spectra in the hard X-ray emission. In this work, we study variability properties of the band-limited noise component during the low-hard state for a sample of black hole X-ray binaries. We investigate the characteristic frequency and amplitude of the band-limited noise component and study covariance spectra. For observations that show a noise component with a characteristic frequency above 1 Hz in the hard energy band (4-8 keV), we found this very same component at a lower frequency in the soft band (1-2 keV). This difference in characteristic frequency is an indication that while both the soft and the hard band photons contribute to the same band-limited noise component, which likely represents the modulation of the mass accretion rate, the origin of the soft photons is actually further away from the black hole than the hard photons. Thus, the soft photons are characterized by larger radii, lower frequencies and softer energies, and are probably associated with a smaller optical depth for Comptonization up-scattering from the outer layer of the corona, or suggest a temperature gradient of the corona. We interpret this energy dependence within the picture of energy-dependent power density states as a hint that the contribution of the up-scattered photons originating in the outskirts of the Comptonizing corona to the overall emission in the soft band is becoming significant.

Two-photon absorption and upconversion luminescence of colloidal CsPbX3 quantum dots

NASA Astrophysics Data System (ADS)

Han, Qiuju; Wu, Wenzhi; Liu, Weilong; Yang, Qingxin; Yang, Yanqiang

2018-01-01

The nonlinear optical and the upconversion luminescence (UCL) properties of CsPbX3 (X = Br or its binary mixtures with Cl, I) quantum dots (QDs) are investigated by femtosecond open-aperture (OA) Z-scan and time-resolved luminescence techniques in nonresonant spectral region. The OA Z-scan results show that CsPbX3 QDs have strong reverse saturable absorption (RSA), which is ascribed to two-photon absorption. Partially changing halide composition from Cl to Br, to I, two-photon absorption cross sections become larger at the same laser excitation intensity. The composition-tunable nonlinear absorption should be attributed to the gradual decrease of the lowest direct band gaps with the halide substitute. Moreover, the strong UCL can be observed under near infrared femtosecond laser excitation. Halide composition-tunable UCL dynamics of CsPbX3 QDs is analyzed by use of two-exponential fitting with deconvolution. When CsPbX3 QDs have similar sizes (10-13 nm), with partially changing halide composition from Cl to Br, to I, the average UCL lifetime becomes longer due to the variation of Kane energy. Our findings suggest all-inorganic perovskite QDs can be used as excellent gain medium for high-performance frequency-upconversion lasers and provide reference to engineer such QDs toward practical optoelectronic applications.

Design concepts and performance of NASA X-band transponder (DST) for deep space spacecraft applications

NASA Technical Reports Server (NTRS)

Mysoor, Narayan R.; Perret, Jonathan D.; Kermode, Arthur W.

1991-01-01

The design concepts and measured performance characteristics of an X band (7162 MHz/8415 MHz) breadboard deep space transponder (DST) for future spacecraft applications, with the first use scheduled for the Comet Rendezvous Asteroid Flyby (CRAF) and Cassini missions in 1995 and 1996, respectively. The DST consists of a double conversion, superheterodyne, automatic phase tracking receiver, and an X band (8415 MHz) exciter to drive redundant downlink power amplifiers. The receiver acquires and coherently phase tracks the modulated or unmodulated X band (7162 MHz) uplink carrier signal. The exciter phase modulates the X band (8415 MHz) downlink signal with composite telemetry and ranging signals. The receiver measured tracking threshold, automatic gain control static phase error, and phase jitter characteristics of the breadboard DST are in good agreement with the expected performance. The measured results show a receiver tracking threshold of -158 dBm and a dynamic signal range of 88 dB.

Development of extreme ultraviolet and soft x-ray multilayer optics for scientific studies with femtosecond/attosecond sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aquila, Andrew Lee

The development of multilayer optics for extreme ultraviolet (EUV) radiation has led to advancements in many areas of science and technology, including materials studies, EUV lithography, water window microscopy, plasma imaging, and orbiting solar physics imaging. Recent developments in femtosecond and attosecond EUV pulse generation from sources such as high harmonic generation lasers, combined with the elemental and chemical specificity provided by EUV radiation, are opening new opportunities to study fundamental dynamic processes in materials. Critical to these efforts is the design and fabrication of multilayer optics to transport, focus, shape and image these ultra-fast pulses This thesis describes themore » design, fabrication, characterization, and application of multilayer optics for EUV femtosecond and attosecond scientific studies. Multilayer mirrors for bandwidth control, pulse shaping and compression, tri-material multilayers, and multilayers for polarization control are described. Characterization of multilayer optics, including measurement of material optical constants, reflectivity of multilayer mirrors, and metrology of reflected phases of the multilayer, which is critical to maintaining pulse size and shape, were performed. Two applications of these multilayer mirrors are detailed in the thesis. In the first application, broad bandwidth multilayers were used to characterize and measure sub-100 attosecond pulses from a high harmonic generation source and was performed in collaboration with the Max-Planck institute for Quantum Optics and Ludwig- Maximilians University in Garching, Germany, with Professors Krausz and Kleineberg. In the second application, multilayer mirrors with polarization control are useful to study femtosecond spin dynamics in an ongoing collaboration with the T-REX group of Professor Parmigiani at Elettra in Trieste, Italy. As new ultrafast x-ray sources become available, for example free electron lasers, the multilayer designs

7 Å resolution in protein two-dimensional-crystal X-ray diffraction at Linac Coherent Light Source

PubMed Central

Pedrini, Bill; Tsai, Ching-Ju; Capitani, Guido; Padeste, Celestino; Hunter, Mark S.; Zatsepin, Nadia A.; Barty, Anton; Benner, W. Henry; Boutet, Sébastien; Feld, Geoffrey K.; Hau-Riege, Stefan P.; Kirian, Richard A.; Kupitz, Christopher; Messerschmitt, Marc; Ogren, John I.; Pardini, Tommaso; Segelke, Brent; Williams, Garth J.; Spence, John C. H.; Abela, Rafael; Coleman, Matthew; Evans, James E.; Schertler, Gebhard F. X.; Frank, Matthias; Li, Xiao-Dan

2014-01-01

Membrane proteins arranged as two-dimensional crystals in the lipid environment provide close-to-physiological structural information, which is essential for understanding the molecular mechanisms of protein function. Previously, X-ray diffraction from individual two-dimensional crystals did not represent a suitable investigational tool because of radiation damage. The recent availability of ultrashort pulses from X-ray free-electron lasers (XFELs) has now provided a means to outrun the damage. Here, we report on measurements performed at the Linac Coherent Light Source XFEL on bacteriorhodopsin two-dimensional crystals mounted on a solid support and kept at room temperature. By merging data from about a dozen single crystal diffraction images, we unambiguously identified the diffraction peaks to a resolution of 7 Å, thus improving the observable resolution with respect to that achievable from a single pattern alone. This indicates that a larger dataset will allow for reliable quantification of peak intensities, and in turn a corresponding increase in the resolution. The presented results pave the way for further XFEL studies on two-dimensional crystals, which may include pump–probe experiments at subpicosecond time resolution. PMID:24914166

Resonant excitation of high order modes in the 3.9 GHz cavity of the Linac Coherent Light Source

DOE PAGES

Lunin, A.; Khabiboulline, T.; Solyak, N.; ...

2018-02-06

Construction of the Linac Coherent Light Source II (LCLS-II) is underway for the world’s first hard x-ray free-electron laser. A central part of the LCLS-II project is a 4 GeV superconducting radio frequency electron linac that will operate in the continuous wave (cw) mode. The linac is segmented into four sections named as L0, L1, L2, and L3. Two 3.9 GHz cryomodules, each housing of eight third-harmonic cavities similar to the cavities developed for the European X-ray Free Electron Laser (XFEL), will be used in section L1 of the linac for linearizing the longitudinal beam profile. Here in this paper, we presentmore » a study of trapped high order modes (HOMs) excited by a cw electron beam in the third-harmonic cavities of the LCLS-II linac. A detailed comparison of the original XFEL design and the LCLS-II design with a modified end group is performed in order to estimate the effect of a reduced beam pipe aperture on the efficiency of HOM damping. Furthermore, we apply a statistical analysis of the eigenmode spectrum for the estimation of the probability of resonant HOM losses and influence of HOMs on beam dynamics.« less

Low- Z polymer sample supports for fixed-target serial femtosecond X-ray crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feld, Geoffrey K.; Heymann, Michael; Benner, W. Henry

X-ray free-electron lasers (XFELs) offer a new avenue to the structural probing of complex materials, including biomolecules. Delivery of precious sample to the XFEL beam is a key consideration, as the sample of interest must be serially replaced after each destructive pulse. The fixed-target approach to sample delivery involves depositing samples on a thin-film support and subsequent serial introduction via a translating stage. Some classes of biological materials, including two-dimensional protein crystals, must be introduced on fixed-target supports, as they require a flat surface to prevent sample wrinkling. A series of wafer and transmission electron microscopy (TEM)-style grid supports constructedmore » of low- Z plastic have been custom-designed and produced. Aluminium TEM grid holders were engineered, capable of delivering up to 20 different conventional or plastic TEM grids using fixed-target stages available at the Linac Coherent Light Source (LCLS). As proof-of-principle, X-ray diffraction has been demonstrated from two-dimensional crystals of bacteriorhodopsin and three-dimensional crystals of anthrax toxin protective antigen mounted on these supports at the LCLS. In conclusion, the benefits and limitations of these low- Z fixed-target supports are discussed; it is the authors' belief that they represent a viable and efficient alternative to previously reported fixed-target supports for conducting diffraction studies with XFELs.« less

Observations of Heavy Rainfall in a Post Wildland Fire Area Using X-Band Polarimetric Radar

NASA Astrophysics Data System (ADS)

Cifelli, R.; Matrosov, S. Y.; Gochis, D. J.; Kennedy, P.; Moody, J. A.

2011-12-01

Polarimetric X-band radar systems have been used increasingly over the last decade for rainfall measurements. Since X-band radar systems are generally less costly, more mobile, and have narrower beam widths (for same antenna sizes) than those operating at lower frequencies (e.g., C and S-bands), they can be used for the "gap-filling" purposes for the areas when high resolution rainfall measurements are needed and existing operational radars systems lack adequate coverage and/or resolution for accurate quantitative precipitation estimation (QPE). The main drawback of X-band systems is attenuation of radar signals, which is significantly stronger compared to frequencies used by "traditional" precipitation radars operating at lower frequencies. The use of different correction schemes based on polarimetric data can, to a certain degree, overcome this drawback when attenuation does not cause total signal extinction. This presentation will focus on examining the use of high-resolution data from the NOAA Earth System Research Laboratory (ESRL) mobile X-band dual polarimetric radar for the purpose of estimating precipitation in a post-wildland fire area. The NOAA radar was deployed in the summer of 2011 to examine the impact of gap-fill radar on QPE and the resulting hydrologic response during heavy rain events in the Colorado Front Range in collaboration with colleagues from the National Center for Atmospheric Research (NCAR), Colorado State University (CSU), and the U.S. Geological Survey (USGS). A network of rain gauges installed by NCAR, the Denver Urban Drainage Flood Control District (UDFCD), and the USGS are used to compare with the radar estimates. Supplemental data from NEXRAD and the CSU-CHILL dual polarimetric radar are also used to compare with the NOAA X-band and rain gauges. It will be shown that rainfall rates and accumulations estimated from specific differential phase measurements (KDP) at X-band are in good agreement with the measurements from the gauge

An X-band spacecraft transponder for deep space applications - Design concepts and breadboard performance

NASA Technical Reports Server (NTRS)

Mysoor, Narayan R.; Perret, Jonathan D.; Kermode, Arthur W.

1992-01-01

The design concepts and measured performance characteristics are summarized of an X band (7162 MHz/8415 MHz) breadboard deep space transponder (DSP) for future spacecraft applications, with the first use scheduled for the Comet Rendezvous Asteroid Flyby (CRAF) and Cassini missions in 1995 and 1996, respectively. The DST consists of a double conversion, superheterodyne, automatic phase tracking receiver, and an X band (8415 MHz) exciter to drive redundant downlink power amplifiers. The receiver acquires and coherently phase tracks the modulated or unmodulated X band (7162 MHz) uplink carrier signal. The exciter phase modulates the band (8415 MHz) downlink signal with composite telemetry and ranging signals. The receiver measured tracking threshold, automatic gain control, static phase error, and phase jitter characteristics of the breadboard DST are in good agreement with the expected performance. The measured results show a receiver tracking threshold of -158 dBm and a dynamic signal range of 88 dB.

Terahertz Streaking of Few-Femtosecond Relativistic Electron Beams

NASA Astrophysics Data System (ADS)

Zhao, Lingrong; Wang, Zhe; Lu, Chao; Wang, Rui; Hu, Cheng; Wang, Peng; Qi, Jia; Jiang, Tao; Liu, Shengguang; Ma, Zhuoran; Qi, Fengfeng; Zhu, Pengfei; Cheng, Ya; Shi, Zhiwen; Shi, Yanchao; Song, Wei; Zhu, Xiaoxin; Shi, Jiaru; Wang, Yingxin; Yan, Lixin; Zhu, Liguo; Xiang, Dao; Zhang, Jie

2018-04-01

Streaking of photoelectrons with optical lasers has been widely used for temporal characterization of attosecond extreme ultraviolet pulses. Recently, this technique has been adapted to characterize femtosecond x-ray pulses in free-electron lasers with the streaking imprinted by far-infrared and terahertz (THz) pulses. Here, we report successful implementation of THz streaking for time stamping of an ultrashort relativistic electron beam, whose energy is several orders of magnitude higher than photoelectrons. Such an ability is especially important for MeV ultrafast electron diffraction (UED) applications, where electron beams with a few femtosecond pulse width may be obtained with longitudinal compression, while the arrival time may fluctuate at a much larger timescale. Using this laser-driven THz streaking technique, the arrival time of an ultrashort electron beam with a 6-fs (rms) pulse width has been determined with 1.5-fs (rms) accuracy. Furthermore, we have proposed and demonstrated a noninvasive method for correction of the timing jitter with femtosecond accuracy through measurement of the compressed beam energy, which may allow one to advance UED towards a sub-10-fs frontier, far beyond the approximate 100-fs (rms) jitter.

Computer-Automated Evolution of Spacecraft X-Band Antennas

NASA Technical Reports Server (NTRS)

Lohn, Jason D.; Homby, Gregory S.; Linden, Derek S.

2010-01-01

A document discusses the use of computer- aided evolution in arriving at a design for X-band communication antennas for NASA s three Space Technology 5 (ST5) satellites, which were launched on March 22, 2006. Two evolutionary algorithms, incorporating different representations of the antenna design and different fitness functions, were used to automatically design and optimize an X-band antenna design. A set of antenna designs satisfying initial ST5 mission requirements was evolved by use these algorithms. The two best antennas - one from each evolutionary algorithm - were built. During flight-qualification testing of these antennas, the mission requirements were changed. After minimal changes in the evolutionary algorithms - mostly in the fitness functions - new antenna designs satisfying the changed mission requirements were evolved and within one month of this change, two new antennas were designed and prototypes of the antennas were built and tested. One of these newly evolved antennas was approved for deployment on the ST5 mission, and flight-qualified versions of this design were built and installed on the spacecraft. At the time of writing the document, these antennas were the first computer-evolved hardware in outer space.

The DARHT Phase 2 Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

wolf, Zachary R.

2000-09-12

The second phase accelerator for the Dual Axis Hydrodynamic Test facility (DARHT) is designed to provide an electron beam pulse that is 2{mu}s long, 2kA, and 20 MeV in particle energy. The injector provides 3.2 MeV so that the linac need only provide 16.8 MeV. The linac is made with two types of induction accelerator cells. The first block of 8 cells have a 14 in. beam pipe compared to 10 in. in the remaining 80 cells. The other principal difference is that the first 8 cells have reduced volt-sec in their induction cores as a result of a largermore » diameter beam pipe. The cells are designed for very reliable high voltage operation. The insulator is Mycalex. Results from prototype tests are given including results from solenoid measurements. Each cell contains a solenoid for beam transport and a set of x-y correction coils to reduce corkscrew motion. Details of tests to determine RF mode impedances relevant to BBU generation are given. Blocks of cells are separated by intercells some of which contain transport solenoids. The intercells provide vacuum pumping stations as well. Issues of alignment and installation are discussed.« less

Ultrafast Magnetization Manipulation Using Single Femtosecond Light and Hot-Electron Pulses.

PubMed

Xu, Yong; Deb, Marwan; Malinowski, Grégory; Hehn, Michel; Zhao, Weisheng; Mangin, Stéphane

2017-11-01

Current-induced magnetization manipulation is a key issue for spintronic applications. This manipulation must be fast, deterministic, and nondestructive in order to function in device applications. Therefore, single- electronic-pulse-driven deterministic switching of the magnetization on the picosecond timescale represents a major step toward future developments of ultrafast spintronic systems. Here, the ultrafast magnetization dynamics in engineered Gd x [FeCo] 1- x -based structures are studied to compare the effect of femtosecond laser and hot-electron pulses. It is demonstrated that a single femtosecond hot-electron pulse causes deterministic magnetization reversal in either Gd-rich and FeCo-rich alloys similarly to a femtosecond laser pulse. In addition, it is shown that the limiting factor of such manipulation for perpendicular magnetized films arises from the formation of a multidomain state due to dipolar interactions. By performing time-resolved measurements under various magnetic fields, it is demonstrated that the same magnetization dynamics are observed for both light and hot-electron excitation, and that the full magnetization reversal takes place within 40 ps. The efficiency of the ultrafast current-induced magnetization manipulation is enhanced due to the ballistic transport of hot electrons before reaching the GdFeCo magnetic layer. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Beam-based measurements of long-range transverse wakefields in the Compact Linear Collider main-linac accelerating structure

DOE PAGES

Zha, Hao; Latina, Andrea; Grudiev, Alexej; ...

2016-01-20

The baseline design of CLIC (Compact Linear Collider) uses X-band accelerating structures for its main linacs. In order to maintain beam stability in multibunch operation, long-range transverse wakefields must be suppressed by 2 orders of magnitude between successive bunches, which are separated in time by 0.5 ns. Such strong wakefield suppression is achieved by equipping every accelerating structure cell with four damping waveguides terminated with individual rf loads. A beam-based experiment to directly measure the effectiveness of this long-range transverse wakefield and benchmark simulations was made in the FACET test facility at SLAC using a prototype CLIC accelerating structure. Furthermore,more » the experiment showed good agreement with the simulations and a strong suppression of the wakefields with an unprecedented minimum resolution of 0.1 V/(pC mm m).« less

Mini-RF S- and X-band Bistatic Observations of the Floor of Cabeus Crater

NASA Astrophysics Data System (ADS)

Patterson, Gerald Wesley; Stickle, Angela; Turner, Franklin; Jensen, James; Cahill, Joshua; Mini-RF Team

2017-10-01

The Mini-RF instrument aboard NASA’s Lunar Reconnaissance Orbiter (LRO) is a hybrid dual-polarized synthetic aperture radar (SAR) and operates in concert with the Arecibo Observatory (AO) and the Goldstone deep space communications complex 34 meter antenna DSS-13 to collect S- and X-band bistatic radar data of the Moon. Bistatic radar data provide a means to probe the near subsurface for the presence of water ice, which exhibits a strong response in the form of a Coherent Backscatter Opposition Effect (CBOE). This effect has been observed in radar data for the icy surfaces of the Galilean satellites, the polar caps of Mars, polar craters on Mercury, and terrestrial ice sheets in Greenland. Previous work using Mini-RF S-band (12.6 cm) bistatic data suggests the presence of a CBOE associated with the floor of the lunar south polar crater Cabeus. The LRO spacecraft has begun its third extended mission. For this phase of operations Mini-RF is leveraging the existing AO architecture to make S-band radar observations of additional polar craters (e.g., Haworth, Shoemaker, Faustini). The purpose of acquiring these data is to determine whether other polar craters exhibit the response observed for Cabeus. Mini-RF has also initiated a new mode of operation that utilizes the X-band (4.2cm) capability of the instrument receiver and a recently commissioned X/C-band transmitter within the Deep Space Network’s (DSN) Goldstone complex to collect bistatic X-band data of the Moon. The purpose of acquiring these data is to constrain the depth/thickness of materials that exhibit a CBOE response - with an emphasis on observing the floor of Cabeus. Recent Mini-RF X-band observations of the floors of the craters Cabeus do not show evidence for a CBOE. This would suggest that the upper ~0.5 meters of the regolith for the floor of Cabeus do not harber water ice in a form detectable at 4.2 cm wavelengths.

Photophysical properties of C60 colloids suspended in water with Triton X-100 surfactant: excited-state properties with femtosecond resolution.

PubMed

Clements, Andrew F; Haley, Joy E; Urbas, Augustine M; Kost, Alan; Rauh, R David; Bertone, Jane F; Wang, Fei; Wiers, Brian M; Gao, De; Stefanik, Todd S; Mott, Andrew G; Mackie, David M

2009-06-11

We examine the photophysics of a colloidal suspension of C(60) particles in a micellar solution of Triton X-100 and water, prepared via a new synthesis which allows high-concentration suspensions. The particle sizes are characterized by transmission electron microscopy and dynamic light scattering and found to be somewhat polydisperse in the range of 10-100 nm. The suspension is characterized optically by UV-vis spectroscopy, femtosecond transient absorption spectroscopy, laser flash photolysis, and z-scan. The ground-state absorbance spectrum shows a broad absorbance feature centered near 450 nm which is indicative of colloidal C(60). The transient absorption dynamics, presented for the first time with femtosecond resolution, are very similar to that of thin films of C(60) and indicate a strong quenching of the singlet excited state on short time scales and evidence of little intersystem crossing to a triplet excited state. Laser flash photolysis reveals that a triplet excited-state absorption spectrum, which is essentially identical in shape to that of molecular C(60) solutions, does indeed arise, but with much lower magnitude and somewhat shorter lifetime. Z-scan analysis confirms that the optical response of this material is dominated by nonlinear scattering.

Effect of Γ-X band mixing on the donor binding energy in a Quantum Wire

NASA Astrophysics Data System (ADS)

Vijaya Shanthi, R.; Jayakumar, K.; Nithiananthi, P.

2015-02-01

To invoke the technological applications of heterostructure semiconductors like Quantum Well (QW), Quantum Well Wire (QWW) and Quantum Dot (QD), it is important to understand the property of impurity energy which is responsible for the peculiar electronic & optical behavior of the Low Dimensional Semiconductor Systems (LDSS). Application of hydrostatic pressure P>35kbar drastically alters the band offsets leading to the crossover of Γ band of the well & X band of the barrier resulting in an indirect transition of the carrier and this effect has been studied experimentally and theoretically in a QW structure. In this paper, we have investigated the effect of Γ-X band mixing due to the application of hydrostatic pressure in a GaAs/AlxGa1-xAs QWW system. The results are presented and discussed for various widths of the wire.

Femtosecond x-ray scattering study of ultrafast photoinduced structural dynamics in solvated [ Co ( terpy ) 2 ] 2 +

DOE PAGES

Biasin, Elisa; van Driel, Tim Brandt; Kjær, Kasper S.; ...

2016-06-30

Here, we study the structural dynamics of photoexcited [Co(terpy) 2] 2+ in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitation event leads to elongation of the Co-N bonds, followed by coherent Co-N bond length oscillations arising from the impulsive excitation of a vibrational mode dominated by the symmetrical stretch of all six Co-N bonds. This mode has a period of 0.33 ps and decays on a subpicosecond time scale. We find that the equilibrium bond-elongated structure of themore » high spin state is established on a single-picosecond time scale and that this state has a lifetime of ~7 ps.« less

Inverse Compton scattering X-ray source yield optimization with a laser path folding system inserted in a pre-existent RF linac

NASA Astrophysics Data System (ADS)

Chaleil, A.; Le Flanchec, V.; Binet, A.; Nègre, J. P.; Devaux, J. F.; Jacob, V.; Millerioux, M.; Bayle, A.; Balleyguier, P.; Prazeres, R.

2016-12-01

An inverse Compton scattering source is under development at the ELSA linac of CEA, Bruyères-le-Châtel. Ultra-short X-ray pulses are produced by inverse Compton scattering of 30 ps-laser pulses by relativistic electron bunches. The source will be able to operate in single shot mode as well as in recurrent mode with 72.2 MHz pulse trains. Within this framework, an optical multipass system that multiplies the number of emitted X-ray photons in both regimes has been designed in 2014, then implemented and tested on ELSA facility in the course of 2015. The device is described from both geometrical and timing viewpoints. It is based on the idea of folding the laser optical path to pile-up laser pulses at the interaction point, thus increasing the interaction probability. The X-ray output gain measurements obtained using this system are presented and compared with calculated expectations.

Estimating tropical forest structure using LIDAR AND X-BAND INSAR

NASA Astrophysics Data System (ADS)

Palace, M. W.; Treuhaft, R. N.; Keller, M. M.; Sullivan, F.; Roberto dos Santos, J.; Goncalves, F. G.; Shimbo, J.; Neumann, M.; Madsen, S. N.; Hensley, S.

2013-12-01

Tropical forests are considered the most structurally complex of all forests and are experiencing rapid change due to anthropogenic and climatic factors. The high carbon stocks and fluxes make understanding tropical forests highly important to both regional and global studies involving ecosystems and climate. Large and remote areas in the tropics are prime targets for the use of remotely sensed data. Radar and lidar have previously been used to estimate forest structure, with an emphasis on biomass. These two remote sensing methods have the potential to yield much more information about forest structure, specifically through the use of X-band radar and waveform lidar data. We examined forest structure using both field-based and remotely sensed data in the Tapajos National Forest, Para, Brazil. We measured multiple structural parameters for about 70 plots in the field within a 25 x 15 km area that have TanDEM-X single-pass horizontally and vertically polarized radar interferometric data. High resolution airborne lidar were collected over a 22 sq km portion of the same area, within which 33 plots were co-located. Preliminary analyses suggest that X-band interferometric coherence decreases by about a factor of 2 (from 0.95 to 0.45) with increasing field-measured vertical extent (average heights of 7-25 m) and biomass (10-430 Mg/ha) for a vertical wavelength of 39 m, further suggesting, as has been observed at C-band, that interferometric synthetic aperture radar (InSAR) is substantially more sensitive to forest structure/biomass than SAR. Unlike InSAR coherence versus biomass, SAR power at X-band versus biomass shows no trend. Moreover, airborne lidar coherence at the same vertical wavenumbers as InSAR is also shown to decrease as a function of biomass, as well. Although the lidar coherence decrease is about 15% more than the InSAR, implying that lidar penetrates more than InSAR, these preliminary results suggest that X-band InSAR may be useful for structure and

SU-E-T-670: Radiotherapy Vault Shielding Evaluation Method for a Flattening Filter-Free (FFF) Linac-Practical Considerations and Recommendations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mihailidis, D

2015-06-15

Purpose: To date, there isn’t formal approach for flattening filter-free (FFF) linac vault shielding evaluation, thus, we propose an extension to NCRP#151 to accommodate the recent large number of FFF linac installations.Methods and Materials: We extended the approach in NCRP#151 to design two Truebeam vaults in our new cancer center for hypofractionated treatments. Monte Carlo calculations have characterized primary, scattered, leakage and neutron radiations from FFF-modes. These calculations have shown that: a) FFF primary beam is softer on the central-axis compared to flattening filtered (FF), b) the lateral dose profile is peaked on the central axis and less integral targetmore » current is required to generate the same tumor dose with the FF beam. Thus, the TVLs for FFF mode are smaller than those of the FF mode and the scatter functions of the FF mode (NCRP#151) may not be appropriate for FFF-mode, c) the neutron source strength and fluence for 18X-FFF is smaller than 18X-FF, but it is not of a concern here, no 18X-FFF-mode is available on the linac under investigation. Results: These barrier thickness are smaller (12% reduction on the average) than those computed for conventional FF mode with same realistic primary workload since, the primary TVLs used here are smaller and the WL is smaller than the conventional (almost half reduced), keeping the TADR in tolerance. Conclusions: A comprehensive method for shielding barrier calculations based on dedicated data for FFF-mode linacs is highly desired. Meanwhile, we provide an extension to NCRP#151 to accommodate the shielding design of such installations. It is also shown that if a vault is already designed for IMRT/VMAT and SABR hypofractionated treatments with FFF-mode linac, the vault can also be used for a FFF mode linac replacement, leaving some leeway for slightly higher workload on the FFF linac.« less

The modification of X and L band radar signals by monomolecular sea slicks

NASA Technical Reports Server (NTRS)

Huehnerfuss, H.; Alpers, W.; Cross, A.; Garrett, W. D.; Keller, W. C.; Plant, W. J.; Schuler, D. L.; Lange, P. A.; Schlude, F.

1983-01-01

One methyl oleate and two oleyl alcohol surface films were produced on the surface of the North Sea under comparable oceanographic and meteorological conditions in order to investigate their influence on X and L band radar backscatter. Signals are backscattered in these bands primarily by surface waves with lengths of about 2 and 12 cm, respectively, and backscattered power levels in both bands were reduced by the slicks. The reduction was larger at X band than at L band, however, indicating that shorter waves are more intensely damped by the surface films. The oleyl alcohol film caused greater attenuation of short gravity waves than the film of methyl oleate, thus demonstrating the importance of the physicochemical properties of films on the damping of wind-generated gravity capillary waves. Finally, these experiments indicate a distinct dependence of the degree of damping on the angle between wind and waves. Wind-generated waves traveling in the wind direction are more intensely damped by surface films than are waves traveling at large angles to the wind.

Femtosecond fibre laser stabilisation to an optical frequency standard using a KTP electro-optic crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nyushkov, B N; Pivtsov, V S; Koliada, N A

2015-05-31

A miniature intracavity KTP-based electro-optic phase modulator has been developed which can be used for effective stabilisation of an optical frequency comb of a femtosecond erbiumdoped fibre laser to an optical frequency standard. The use of such an electro-optic modulator (EOM) has made it possible to extend the working frequency band of a phase-locked loop system for laser stabilisation to several hundred kilohertz. We demonstrate that the KTP-based EOM is sufficiently sensitive even at a small optical length, which allows it to be readily integrated into cavities of femtosecond fibre lasers with high mode frequency spacings (over 100 MHz). (extrememore » light fields and their applications)« less

Energy band gap and spectroscopic studies in Mn{sub 1-x}Cu{sub x}WO{sub 4} (0 ≤ x ≤ 0.125)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mal, Priyanath; Rambabu, P.; Turpu, G. R.

2016-05-06

A study on the effect of nonmagnetic Cu{sup 2+} substitution at Mn{sup 2+} site on the structural and energy band gap of the MnWO{sub 4} is reported. Convenient solid state reaction route has been adopted for the synthesis of Mn{sub 1-x}Cu{sub x}WO{sub 4}. X-ray diffraction (XRD) pattern showed high crystalline quality of the prepared samples. Raman spectroscopic studies were carried out to understand the structural aspects of the doping. 15 Raman active modes were identified out of 18, predicted for wolframite type monoclinic structure of MnWO{sub 4}. UV-visible diffuse reflectance spectra were recorded and analyzed to get energy band gapmore » of the studied system and are found in the range of 2.5 eV to 2.04 eV with a systematic decrease with the increase in Cu{sup 2+} concentration. Energy band gap values are verified by Density Functional Theory calculations based on projector augmented wave (PAW) method. The calculated values are in good agreement with the experimental data.« less

Long-period fiber grating fabricated by 800 nm femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Zhang, Yani; Xi, Yaru; Liu, Sicong; Jiang, Peng; Zhao, Ya; Xu, Qiang

2018-02-01

In this paper, the long period fiber gratings (LPFGs) in standard SMF-28 telecommunication fibers without hydrogen loading were inscribed by using point-to-point direct writing method of femtosecond laser pulses with pulse duration of 100 fs, repetition rate of 1kHz and a central wavelength of 800 nm. The LPFGs with different spectral characteristics were fabricated by adjusting grating period, grating length and duty ratio. The results show that the resonant peak wavelengths shift to the long-wave direction with the increase of the grating length increasing. The variations of duty ratio will lead to the generation of resonance rejection band of LPFGs from singlepeak to multi-peak plus lesser out-of-band loss.

Dosimetric analysis of stereotactic body radiation therapy for pancreatic cancer using MR-guided Tri-60Co unit, MR-guided LINAC, and conventional LINAC-based plans.

PubMed

Ramey, Stephen James; Padgett, Kyle R; Lamichhane, Narottam; Neboori, Hanmath J; Kwon, Deukwoo; Mellon, Eric A; Brown, Karen; Duffy, Melissa; Victoria, James; Dogan, Nesrin; Portelance, Lorraine

2018-03-01

This study aims to perform a dosimetric comparison of 2 magnetic resonance (MR)-guided radiation therapy systems capable of performing online adaptive radiation therapy versus a conventional radiation therapy system for pancreas stereotactic body radiation therapy. Ten cases of patients with pancreatic adenocarcinoma previously treated in our institution were used for this analysis. MR-guided tri-cobalt 60 therapy (MR-cobalt) and MR-LINAC plans were generated and compared with conventional LINAC (volumetric modulated arc therapy) plans. The prescription dose was 40 Gy in 5 fractions covering 95% of the planning tumor volume for the 30 plans. The same organs at risk (OARs) dose constraints were used in all plans. Dose-volume-based indices were used to compare PTV coverage and OAR sparing. The conformity index of 40 Gy in 5 fractions covering 95% of the planning tumor volume demonstrated higher conformity in both LINAC-based plans compared with MR-cobalt plans. Although there was no difference in mean conformity index between LINAC and MR-LINAC plans (1.08 in both), there was a large difference between LINAC and MR-cobalt plans (1.08 vs 1.52). Overall, 79%, 72%, and 78% of critical structure dosimetric constraints were met with LINAC, MR-cobalt, and MR-LINAC plans, respectively. The MR-cobalt plans delivered more doses to all OARs compared with the LINAC plans. In contrast, the doses to the OARs of the MR-LINAC plans were similar to LINAC plans except in 2 cases: liver mean dose (MR-LINAC, 2 .8 Gy vs LINAC, 2.1 Gy) and volume of duodenum receiving at least 15 Gy (MR-LINAC, 13.2 mL vs LINAC, 15.4 mL). Both differences are likely not clinically significant. This study demonstrates that dosimetrically similar plans were achieved with conventional LINAC and MR-LINAC, whereas doses to OARs were statistically higher for MR-cobalt compared with conventional LINAC plans because of low-dose spillage. Given the improved tumor-tracking capabilities of MR-LINAC, further studies

Ka-band and X-band observations of the solar corona acquired during the Cassini 2001 superior conjunction

NASA Technical Reports Server (NTRS)

Morabito, D. D.

2002-01-01

Simultaneous dual-frequency Ka-band (32 GHz) and X-band (8.4 GHz) carrier signal data have been acquired during the superior conjunction of the Cassini spacecraft June 2001, using the NASA Deep Space Network's facilities located in Goldstone, California. The solar elongation angle of the observations varied from -4.1 degrees (-16 solar radii) to -0.6 degrees (-2.3 solar radii). The observed coronal and solar effects on the signals include spectral broadening, amplitude scintillation, phase scintillation, and increased noise. The measurements were generally consistent with existing solar models, except during solar transient events when the signatures of the measurements were observed to increase significantly above the quiet background levels. This is the second solar conjunction of Cassini for which simultaneous X/Ka data were acquired. Both solar conjunctions, conducted in May 2000 and June 2001, occurred near the peak of the current 11 year solar cycle.

TH-C-BRC-03: Emerging Linac Based SRS/SBRT Technologies with Modulated Arc Delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, L.

2016-06-15

The delivery techniques for SRS/SBRT have been under rapid developments in recent years, which pose new challenges to medical physicists ranging from planning and quality assurance to imaging and motion management. This educational course will provide a general overview of the latest delivery techniques in SRS/SBRT, and discuss the clinical processes to address the challenges of each technique with special emphasis on dedicated gamma-ray based device, robotic x-band linac-based system and conventional C-arm s-band linac-based SRS systems. (1). Gamma-ray based SRS/SRT: This is the gold standard of intracranial SRS. With the advent of precision imaging guidance and frameless patient positioningmore » capabilities, novel stereoscopic CBCT and automatic dose adaption solution are introduced to the Gamma-ray based SRS for the first time. The first North American system has been approved by the US regulatory for patient treatments in the spring of 2016. (2). Robotic SRS/SBRT system: A number of technological milestones have been developed in the past few years, including variable aperture collimator, sequential optimization technique, and the time reduction technique. Recently, a new robotic model allows the option of a multi-leaf collimator. These technological advances have reduced the treatment time and improved dose conformity significantly and could potentially expand the application of radiosurgery for the treatment of targets not previously suitable for robotic SRS/SBRT or fractionated stereotactic radiotherapy. These technological advances have created new demanding mandates on hardware and patient quality assurance (QA) tasks, as well as the need for updating/educating the physicists in the community on these requirements. (3). Conventional Linac based treatments: Modulated arc therapy (MAT) has gained wide popularities in Linac-based treatments in recent years due to its high delivery efficiency and excellent dose conformities. Recently, MAT has been

Serial femtosecond crystallography: A revolution in structural biology.

PubMed

Martin-Garcia, Jose M; Conrad, Chelsie E; Coe, Jesse; Roy-Chowdhury, Shatabdi; Fromme, Petra

2016-07-15

Macromolecular crystallography at synchrotron sources has proven to be the most influential method within structural biology, producing thousands of structures since its inception. While its utility has been instrumental in progressing our knowledge of structures of molecules, it suffers from limitations such as the need for large, well-diffracting crystals, and radiation damage that can hamper native structural determination. The recent advent of X-ray free electron lasers (XFELs) and their implementation in the emerging field of serial femtosecond crystallography (SFX) has given rise to a remarkable expansion upon existing crystallographic constraints, allowing structural biologists access to previously restricted scientific territory. SFX relies on exceptionally brilliant, micro-focused X-ray pulses, which are femtoseconds in duration, to probe nano/micrometer sized crystals in a serial fashion. This results in data sets comprised of individual snapshots, each capturing Bragg diffraction of single crystals in random orientations prior to their subsequent destruction. Thus structural elucidation while avoiding radiation damage, even at room temperature, can now be achieved. This emerging field has cultivated new methods for nanocrystallogenesis, sample delivery, and data processing. Opportunities and challenges within SFX are reviewed herein. Published by Elsevier Inc.

TU-H-BRA-03: Performance of a Clinical Gridded Electron Gun in Magnetic Fields: Implications for MRI-Linac Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whelan, B; Keall, P; Bazalova-Carter, M

Purpose: Recent advances towards MRI Linac radiotherapy have motivated a wide range of studies characterizing electromagnetic interactions between the two devices. One of the most sensitive components is the linac electron gun. To data, only non gridded (diode) guns have been investigated however, most linac vendors utilize gridded (triode) guns, which enable efficient and robust beam gating. The purpose of this study was to develop a realistic model of a gridded gun used clinically, and to characterize its performance in magnetic fields. Methods: The gridded electron gun used on Varian high energy machines was measured using 3D laser scanning quotedmore » as accurate to 0.1mm. Based on the scane, a detailed CAD mode was developed. From this, key geometry was extracted and a FEM model was developed (Opera/SCALA). Next, the high voltage (HV), grid voltage, and emission current were read from six dose matched TrueBeam linacs for the 6X, 10X and 15X photon modes (0 B-field). The mean values were used to represent each mode, which was simulated I constant magnetic fields from 0–200G in-line, and 0–35G perpendicular. Results: Experimentally measured HV, grid voltage, and emission current from 6X, 10X and 15X modes were respectively: 15±.03kV, 10±.08kV, 11±.03kV; 93±7V, 41±3V, and 70±6V; 327±27mA, 129±10mA, and 214±19mA. The error in simulated emission current of each mode was 3%,6%, and 3%. For in-line fields, 50% beam loss occurred at 114, 96, and 97G; for perpendicular; at 12, 13 and 14G. Sensitivity for a given geometry is primarily determined by HV setting. Conclusion: Future MRI-Linac systems will almost certainly use gridded guns. We present the first model of a clinical gridded gun, and match the experimental emission current to within 6% across three different operating modes. This clinical gun shows increased sensitivity to magnetic fields than previous work,and different modes show different sensitivity.« less

Nano-crystalline Magnesium Substituted Cadmium Ferrites as X-band Microwave Absorbers

NASA Astrophysics Data System (ADS)

Bhongale, S. R.; Ingawale, H. R.; Shinde, T. J.; Pubby, Kunal; Bindra Narang, Sukhleen; Vasambekar, P. N.

2017-11-01

The magnetic and electromagnetic properties of nanocrystalline spinel ferrites with chemical formula MgxCd1-xFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) prepared by oxalate co-precipitation method under microwave sintering technique were studied. The magnetic and dielectric parameters of ferrites were determined by using vibrating sample magnetometer (VSM) and vector network analyzer (VNA) respectively. Magnetic parameters such as saturation magnetizations (Ms), coercive force (Hc), remnant magnetization (Mr), Yafet-Kittel (Y-K) angle of ferrites were determined from hysteresis loops. The variation of real permittivity (ε‧), dielectric loss tangent (tanδe), real permeability (μ‧) and magnetic loss tangent (tanδm) with frequency and Mg2+content were studied in X-band frequency range. The values of ε‧, tanδe, μ‧ and tanδm of ferrites were observed to be in range of 4.2 - 6.12, 2.9 × 10-1 - 6 × 10-2, 0.6 - 1.12 and 4.5 × 10-1 - 2 × 10-3 respectively for the prepared compositions. The study of variation of reflection loss with frequency of all ferrites shows that ferrite with magnesium content x = 0.4 can be potential candidate for microwave applications in X-band.

Tunable band gap in Bi(Fe1-xMnx)O3 films

NASA Astrophysics Data System (ADS)

Xu, X. S.; Ihlefeld, J. F.; Lee, J. H.; Ezekoye, O. K.; Vlahos, E.; Ramesh, R.; Gopalan, V.; Pan, X. Q.; Schlom, D. G.; Musfeldt, J. L.

2010-05-01

In order to investigate band gap tunability in polar oxides, we measured the optical properties of a series of Bi(Fe1-xMnx)O3 thin films. The absorption response of the mixed metal solid solutions is approximately a linear combination of the characteristics of the two end members, a result that demonstrates straightforward band gap tunability in this system.

Modeling of silicon in femtosecond laser-induced modification regimes: accounting for ambipolar diffusion

NASA Astrophysics Data System (ADS)

Derrien, Thibault J.-Y.; Bulgakova, Nadezhda M.

2017-05-01

During the last decades, femtosecond laser irradiation of materials has led to the emergence of various applications based on functionalization of surfaces at the nano- and microscale. Via inducing a periodic modification on material surfaces (band gap modification, nanostructure formation, crystallization or amorphization), optical and mechanical properties can be tailored, thus turning femtosecond laser to a key technology for development of nanophotonics, bionanoengineering, and nanomechanics. Although modification of semiconductor surfaces with femtosecond laser pulses has been studied for more than two decades, the dynamics of coupling of intense laser light with excited matter remains incompletely understood. In particular, swift formation of a transient overdense electron-hole plasma dynamically modifies optical properties in the material surface layer and induces large gradients of hot charge carriers, resulting in ultrafast charge-transport phenomena. In this work, the dynamics of ultrafast laser excitation of a semiconductor material is studied theoretically on the example of silicon. A special attention is paid to the electron-hole pair dynamics, taking into account ambipolar diffusion effects. The results are compared with previously developed simulation models, and a discussion of the role of charge-carrier dynamics in localization of material modification is provided.

Origin of band gap bowing in dilute GaAs1-xNx and GaP1-xNx alloys: A real-space view

NASA Astrophysics Data System (ADS)

Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.

2013-07-01

The origin of the band gap bowing in dilute nitrogen doped gallium based III-V semiconductors is largely debated. In this paper we show the dilute GaAs1-xNx and GaP1-xNx as representative examples that the nitrogen-induced states close to the conduction band minimum propagate along the zigzag chains on the {110} planes. Thereby states originating from different N atoms interact with each other resulting in broadening of the nitrogen-induced states which narrows the band gap. Our modeling based on ab initio theoretical calculations explains the experimentally observed N concentration dependent band gap narrowing both qualitatively and quantitatively.

Coupled-cavity drift-tube linac

DOEpatents

Billen, James H.

1996-01-01

A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the .pi.-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is .beta..lambda., where .lambda. is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a .pi./2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range.

Insights into photosystem II from isomorphous difference Fourier maps of femtosecond X-ray diffraction data and quantum mechanics/molecular mechanics structural models

DOE PAGES

Wang, Jimin; Askerka, Mikhail; Brudvig, Gary W.; ...

2017-01-12

Understanding structure–function relations in photosystem II (PSII) is important for the development of biomimetic photocatalytic systems. X-ray crystallography, computational modeling, and spectroscopy have played central roles in elucidating the structure and function of PSII. Recent breakthroughs in femtosecond X-ray crystallography offer the possibility of collecting diffraction data from the X-ray free electron laser (XFEL) before radiation damage of the sample, thereby overcoming the main challenge of conventional X-ray diffraction methods. However, the interpretation of XFEL data from PSII intermediates is challenging because of the issues regarding data-processing, uncertainty on the precise positions of light oxygen atoms next to heavy metalmore » centers, and different kinetics of the S-state transition in microcrystals compared to solution. Lastly, we summarize recent advances and outstanding challenges in PSII structure–function determination with emphasis on the implementation of quantum mechanics/molecular mechanics techniques combined with isomorphous difference Fourier maps, direct methods, and high-resolution spectroscopy.« less

Insights into Photosystem II from Isomorphous Difference Fourier Maps of Femtosecond X-ray Diffraction Data and Quantum Mechanics/Molecular Mechanics Structural Models.

PubMed

Wang, Jimin; Askerka, Mikhail; Brudvig, Gary W; Batista, Victor S

2017-02-10

Understanding structure-function relations in photosystem II (PSII) is important for the development of biomimetic photocatalytic systems. X-ray crystallography, computational modeling, and spectroscopy have played central roles in elucidating the structure and function of PSII. Recent breakthroughs in femtosecond X-ray crystallography offer the possibility of collecting diffraction data from the X-ray free electron laser (XFEL) before radiation damage of the sample, thereby overcoming the main challenge of conventional X-ray diffraction methods. However, the interpretation of XFEL data from PSII intermediates is challenging because of the issues regarding data-processing, uncertainty on the precise positions of light oxygen atoms next to heavy metal centers, and different kinetics of the S-state transition in microcrystals compared to solution. Here, we summarize recent advances and outstanding challenges in PSII structure-function determination with emphasis on the implementation of quantum mechanics/molecular mechanics techniques combined with isomorphous difference Fourier maps, direct methods, and high-resolution spectroscopy.

Insights into photosystem II from isomorphous difference Fourier maps of femtosecond X-ray diffraction data and quantum mechanics/molecular mechanics structural models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jimin; Askerka, Mikhail; Brudvig, Gary W.

Understanding structure–function relations in photosystem II (PSII) is important for the development of biomimetic photocatalytic systems. X-ray crystallography, computational modeling, and spectroscopy have played central roles in elucidating the structure and function of PSII. Recent breakthroughs in femtosecond X-ray crystallography offer the possibility of collecting diffraction data from the X-ray free electron laser (XFEL) before radiation damage of the sample, thereby overcoming the main challenge of conventional X-ray diffraction methods. However, the interpretation of XFEL data from PSII intermediates is challenging because of the issues regarding data-processing, uncertainty on the precise positions of light oxygen atoms next to heavy metalmore » centers, and different kinetics of the S-state transition in microcrystals compared to solution. Lastly, we summarize recent advances and outstanding challenges in PSII structure–function determination with emphasis on the implementation of quantum mechanics/molecular mechanics techniques combined with isomorphous difference Fourier maps, direct methods, and high-resolution spectroscopy.« less

A discussion on the use of X-band SAR images in marine applications

NASA Astrophysics Data System (ADS)

Schiavulli, D.; Sorrentino, A.; Migliaccio, M.

2012-10-01

The Synthetic Aperture Radar (SAR) is able to generate images of the sea surface that can be exploited to extract geophysical information of environmental interest. In order to enhance the operational use of these data in the marine applications the revisit time is to be improved. This goal can be achieved by using SAR virtual or real constellations and/or exploiting new antenna technologies that allow huge swath and fine resolution. Within this framework, the presence of the Italian and German X-band SAR constellations is of special interest while the new SAR technologies are not nowadays operated. Although SAR images are considered to be independent of weather conditions, this is only partially true at higher frequencies, e.g. X-band. In fact, observations can present signature corresponding to high intensity precipitating clouds, i.e. rain cells. Further, ScanSAR images may be characterized by the presence of processing artifacts, called scalloping, that corrupt image interpretation. In this paper we review these key facts that are at the basis of an effective use of X-band SAR images for marine applications.

Nitrogen-Induced Perturbation of the Valence Band States in GaP1-xNx Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dudiy, S. V.; Zunger, A.; Felici, M.

2006-01-01

The effects of diluted nitrogen impurities on the valence- and conduction-band states of GaP{sub 1-x}N{sub x} have been predicted and measured experimentally. The calculation uses state-of-the-art atomistic modeling: we use large supercells with screened pseudopotentials and consider several random realizations of the nitrogen configurations. These calculations agree with photoluminescence excitation (PLE) measurements performed for nitrogen concentrations x up to 0.035 and photon energies up to 1 eV above the GaP optical-absorption edge, as well as with published ellipsometry data. In particular, a predicted nitrogen-induced buildup of the L character near the valence- and conduction-band edges accounts for the surprising broad-absorptionmore » plateau observed in PLE between the X{sub 1c} and the {Lambda}{sub 1c} critical points of GaP. Moreover, theory accounts quantitatively for the downward bowing of the indirect conduction-band edge and for the upward bowing of the direct transition with increasing nitrogen concentration. We review some of the controversies in the literature regarding the shifts in the conduction band with composition, and conclude that measured results at ultralow N concentration cannot be used to judge behavior at a higher concentration. In particular, we find that at the high concentrations of nitrogen studied here ({approx}1%) the conduction-band edge (CBE) is a hybridized state made from the original GaP X{sub 1c} band-edge state plus all cluster states. In this limit, the CBE plunges down in energy as the N concentration increases, in quantitative agreement with the measurements reported here. However, at ultralow nitrogen concentrations (<0.1%), the CBE is the nearly unperturbed host X{sub 1c}, which does not sense the nitrogen cluster levels. Thus, this state does not move energetically as nitrogen is added and stays pinned in energy, in agreement with experimental results.« less

Understanding the Femtosecond Laser-Solid Interaction Near and Beyond the Material Damage Threshold

DTIC Science & Technology

2016-05-23

study of the fundamentals of femtosecond laser damage as a function of various parameters, laser wavelength, pulsewidth, pulse number, experimental ... experimental observation without any free parameters. The brand new FSD Lab constructed under the BRI grant in the Physics Research Building at the Ohio... studied across a range of band-gaps for s- and p-polarized light and it is found that conventional theoretical prediction on laser damage threshold

Zn(x)Cd(1-x)Se nanomultipods with tunable band gaps: synthesis and first-principles calculations.

PubMed

Wei, Hao; Su, Yanjie; Han, Ziyi; Li, Tongtong; Ren, Xinglong; Yang, Zhi; Wei, Liangming; Cong, Fengsong; Zhang, Yafei

2013-06-14

In this paper, we demonstrate that ZnxCd1-xSe nanomultipods can be synthesized via a facile and nontoxic solution-based method. Interesting aspects of composition, morphology and optical properties were deeply explored. The value of Zn/(Zn+Cd) could be altered across the entire range from 0.08 to 0.86 by varying the ratio of cation precursor contents. The band gap energy could be linearly tuned from 1.88 to 2.48 eV with respect to the value of Zn/(Zn+Cd). The experiment also showed that oleylamine played a dominant role in the formation of multipod structure. A possible growth mechanism was further suggested. First-principles calculations of band gap energy and density of states in the Vienna ab initio simulation package code were performed to verify the experimental variation tendency of the band gap. Computational results indicated that dissimilarities of electronic band structures and orbital constitutions determined the tunable band gap of the as-synthesized nanomultipod, which might be promising for versatile applications in relevant areas of solar cells, biomedicine, sensors, catalysts and so on.

Nanosurgery of cells and chromosomes using near-infrared twelve-femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Uchugonova, Aisada; Lessel, Matthias; Nietzsche, Sander; Zeitz, Christian; Jacobs, Karin; Lemke, Cornelius; König, Karsten

2012-10-01

Laser-assisted surgery based on multiphoton absorption of near-infrared laser light has great potential for high precision surgery at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact laser method also supports contamination-free cell nanosurgery. In this paper we describe usage of an ultrashort femtosecond laser scanning microscope for sub-100 nm surgery of human cells and metaphase chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770 nm/830 nm) and an in situ pulse duration at the target ranging from 12 fs up to 3 ps was employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond laser pulses at low mean milliwatt powers for sub-100 nm surgery of cells and cellular organelles.

Design and simulation of RF MEMS SPST shunt and SPDT shunt-shunt switches for X-band and Ku-band applications

NASA Astrophysics Data System (ADS)

Lenka, Manas K.; Sharma, Amit; Sharma, Jaibir; DasGupta, Amitava

2012-10-01

This paper describes the design and simulation of RF MEMS SPST shunt and SPDT shunt-shunt switches with modified coplanar waveguide (CPW) configuration for X-band and Ku-band applications exhibiting high isolation and low insertion loss. By modifying the basic CPW structure for a six-strip membrane having length 720 μm, the resonant frequency can be reduced from 33.5 GHz to 13.5 GHz with isolation as high as -30 dB(-63 dB at resonant frequency) in Ku-band. Similar results are also found in case SPST and SPDT switches with other membrane types.

Clusters in intense x-ray pulses

NASA Astrophysics Data System (ADS)

Bostedt, Christoph

2012-06-01

Free-electron lasers can deliver extremely intense, coherent x-ray flashes with femtosecond pulse length, opening the door for imaging single nanoscale objects in a single shot. All matter irradiated by these intense x-ray pulses, however, will be transformed into a highly-excited non-equilibrium plasma within femtoseconds. During the x-ray pulse complex electron dynamics and the onset of atomic disorder will be induced, leading to a time-varying sample. We have performed first experiments about x-ray laser pulse -- cluster interaction with a combined spectroscopy and imaging approach at both, the FLASH free electron laser in Hamburg (Germany) and the LCLS x-ray free-electron laser in Stanford (California). Atomic clusters are ideal for investigating the light - matter interaction because their size can be tuned from the molecular to the bulk regime, thus allowing to distinguish between intra and inter atomic processes. Imaging experiments with xenon clusters show power-density dependent changes in the scattering patterns. Modeling the scattering data indicates that the optical constants of the clusters change during the femtosecond pulse due to the transient creation of high charge states. The results show that ultra fast scattering is a promising approach to study transient states of matter on a femtosecond time scale. Coincident recording of time-of-flight spectra and scattering patterns allows the deconvolution of focal volume and particle size distribution effects. Single-shot single-particle experiments with keV x-rays reveal that for the highest power densities an highly excited and hot cluster plasma is formed for which recombination is suppressed. Time resolved infrared pump -- x-ray probe experiments have started. Here, the clusters are pumped into a nanoplasma state and their time evolution is probed with femtosecond x-ray scattering. The data show strong variations in the scattering patterns stemming from electronic reconfigurations in the cluster

Coupled-cavity drift-tube linac

DOEpatents

Billen, J.H.

1996-11-26

A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the {pi}-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is {beta}{lambda}, where {lambda} is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a {pi}/2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range. 5 figs.

A common-aperture X- and S-band four-function feedcone. [hornfeed design for antennas of Deep Space Network

NASA Technical Reports Server (NTRS)

Withington, J. R.; Williams, W. F.

1982-01-01

Williams and Withington (1979) have considered a prototype X-S-band feedhorn which enabled simultaneous X- and S-band reception from a Cassegrain antenna. This feedhorn has quite successfully demonstrated an alternate method to the standard Deep Space Network (DSN) system of multiple subreflectors and dichroic plate for dual-band reception. In connection with a Network Consolidation Program, involving centralized control of existing antennas and construction of new reflector antennas, a second-generation feedhorn/combiner was conceived to show that this common-aperture feedhorn system was capable of performing all necessary functions the DSN would be called upon to perform with existing and future X-S-band spacecraft. Attention is given to the feedhorn concept, the combiner concept, the first and the second generation of the horn, Sand X-band tuning, and planned capabilities. The feedhorn greatly extends the state of the art in DSN performance and will enhance DSN capabilities in the future.

Understanding band alignments in semiconductor heterostructures: Composition dependence and type-I-type-II transition of natural band offsets in nonpolar zinc-blende AlxGa1 -xN /AlyGa1 -yN composites

NASA Astrophysics Data System (ADS)

Landmann, M.; Rauls, E.; Schmidt, W. G.

2017-04-01

The composition dependence of the natural band alignment at nonpolar AlxGa1 -xN /AlyGa1 -yN heterojunctions is investigated via hybrid functional based density functional theory. Accurate band-gap data are provided using Heyd-Scuseria-Ernzerhof (HSE) type hybrid functionals with a composition dependent exact-exchange contribution. The unstrained band alignment between zincblende (zb) AlxGa1 -xN semiconductor alloys is studied within the entire ternary composition range utilizing the Branch-point technique to align the energy levels related to the bulklike direct Γv→Γc and indirect, pseudodirect, respectively, Γv→Xc type transitions in zb-AlxGa1 -xN . While the zb-GaN/AlxGa1 -xN band edges consistently show a type-I alignment, the relative position of fundamental band edges changes to a type-II alignment in the Al-rich composition ranges of zb-AlxGa1 -xN /AlN and zb-AlxGa1 -xN /AlyGa1 -yN systems. The presence of a direct-indirect band-gap transition at xc=0.63 in zb-AlxGa1 -xN semiconductor alloys gives rise to a notably different composition dependence of band discontinuities in the direct and indirect energy-gap ranges. Below the critical direct-indirect Al/Ga-crossover concentration, the band offsets show a close to linear dependence on the alloy composition. In contrast, notable bowing characteristics of all band discontinuities are observed above the critical crossover composition.

High-Resolution Protein Structure Determination by Serial Femtosecond Crystallography

PubMed Central

Boutet, Sébastien; Lomb, Lukas; Williams, Garth J.; Barends, Thomas R. M.; Aquila, Andrew; Doak, R. Bruce; Weierstall, Uwe; DePonte, Daniel P.; Steinbrener, Jan; Shoeman, Robert L.; Messerschmidt, Marc; Barty, Anton; White, Thomas A.; Kassemeyer, Stephan; Kirian, Richard A.; Seibert, M. Marvin; Montanez, Paul A.; Kenney, Chris; Herbst, Ryan; Hart, Philip; Pines, Jack; Haller, Gunther; Gruner, Sol M.; Philipp, Hugh T.; Tate, Mark W.; Hromalik, Marianne; Koerner, Lucas J.; van Bakel, Niels; Morse, John; Ghonsalves, Wilfred; Arnlund, David; Bogan, Michael J.; Caleman, Carl; Fromme, Raimund; Hampton, Christina Y.; Hunter, Mark S.; Johansson, Linda C.; Katona, Gergely; Kupitz, Christopher; Liang, Mengning; Martin, Andrew V.; Nass, Karol; Redecke, Lars; Stellato, Francesco; Timneanu, Nicusor; Wang, Dingjie; Zatsepin, Nadia A.; Schafer, Donald; Defever, James; Neutze, Richard; Fromme, Petra; Spence, John C. H.; Chapman, Henry N.; Schlichting, Ilme

2013-01-01

Structure determination of proteins and other macromolecules has historically required the growth of high-quality crystals sufficiently large to diffract x-rays efficiently while withstanding radiation damage. We applied serial femtosecond crystallography (SFX) using an x-ray free-electron laser (XFEL) to obtain high-resolution structural information from microcrystals (less than 1 micrometer by 1 micrometer by 3 micrometers) of the well-characterized model protein lysozyme. The agreement with synchrotron data demonstrates the immediate relevance of SFX for analyzing the structure of the large group of difficult-to-crystallize molecules. PMID:22653729

Sub-femtosecond quantum dynamics of the strong-field ionization of water to the X ̃(2)B1 and Ã(2)A1 states of the cation.

PubMed

Jayachander Rao, B; Varandas, A J C

2015-03-07

Motivated by recent efforts to achieve sub-femtosecond structural resolution in various molecular systems, we have performed a femtosecond quantum dynamics study of the water cation in the X ̃(2)B1 and Ã(2)A1 electronic states. Autocorrelation functions for H2O(+) and D2O(+) are calculated for such electronic states by solving numerically the time-dependent Schrödinger equation. From the ratio of the squared autocorrelation functions of D2O(+) and H2O(+), the high-order harmonic generation signals are calculated. Substantial vibrational dynamics is found in the Ã(2)A1 state as compared to the one in X ̃(2)B1, which supports recent experimental findings of Farrell et al., Phys. Rev. Lett., 2011, 107, 083001. Maxima in the above ratio are also predicted at ∼1.1 fs and ∼1.6 fs for the X ̃(2)B1 and Ã(2)A1 states, respectively. The expectation values of the positions of the atoms in H2O(+) as a function of time reveal a strong excitation of the bending mode in the Ã(2)A1 state, which explains the observed vibrational dynamics. The peaks in the ratios of the squared autocorrelation functions are also explained in terms of the evolving geometries of the water cation.

Review: Serial Femtosecond Crystallography: A Revolution in Structural Biology

PubMed Central

Martin-Garcia, Jose M.; Conrad, Chelsie E.; Coe, Jesse; Roy-Chowdhury, Shatabdi; Fromme, Petra

2016-01-01

Macromolecular crystallography at synchrotron sources has proven to be the most influential method within structural biology, producing thousands of structures since its inception. While its utility has been instrumental in progressing our knowledge of structures of molecules, it suffers from limitations such as the need for large, well-diffracting crystals, and radiation damage that can hamper native structural determination. The recent advent of X-ray free electron lasers (XFELs) and their implementation in the emerging field of serial femtosecond crystallography (SFX) has given rise to a remarkable expansion upon existing crystallographic constraints, allowing structural biologists access to previously restricted scientific territory. SFX relies on exceptionally brilliant, micro-focused X-ray pulses, which are femtoseconds in duration, to probe nano/micrometer sized crystals in a serial fashion. This results in data sets comprised of individual snapshots, each capturing Bragg diffraction of single crystals in random orientations prior to their subsequent destruction. Thus structural elucidation while avoiding radiation damage, even at room temperature, can now be achieved. This emerging field has cultivated new methods for nanocrystallogenesis, sample delivery, and data processing. Opportunities and challenges within SFX are reviewed herein. PMID:27143509

Commercial Superconducting Electron Linac for Radioisotope Production

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grimm, Terry Lee; Boulware, Charles H.; Hollister, Jerry L.

2015-08-13

The majority of radioisotopes used in the United States today come from foreign suppliers or are generated parasitically in large government accelerators and nuclear reactors. Both of these restrictions limit the availability of radioisotopes and discourage the development and evaluation of new isotopes and for nuclear medicine, science, and industry. Numerous studies have been recommending development of dedicated accelerators for production of radioisotopes for over 20 years (Institute of Medicine, 1995; Reba, et al, 2000; National Research Council, 2007; NSAC 2009). The 2015 NSAC Long Range Plan for Isotopes again identified electron accelerators as an area for continued research andmore » development. Recommendation 1(c) from the 2015 NSAC Isotope report specifically identifies electron accelerators for continued funding for the purpose of producing medical and industrial radioisotopes. Recognizing the pressing need for new production methods of radioisotopes, the United States Congress passed the American Medical Isotope Production Act of 2012 to develop a domestic production of 99Mo and to eliminate the use of highly enriched uranium (HEU) in the production of 99Mo. One of the advantages of high power electron linear accelerators (linacs) is they can create both proton- and neutron-rich isotopes by generating high energy x-rays that knock out protons or neutrons from stable atoms or by fission of uranium. This allows for production of isotopes not possible in nuclear reactors. Recent advances in superconducting electron linacs have decreased the size and complexity of these systems such that they are economically competitive with nuclear reactors and large, high energy accelerators. Niowave, Inc. has been developing a radioisotope production facility based on a superconducting electron linac with liquid metal converters.« less

Composition dependence of band alignments in GaxIn1-xAsySb1-y heterojunctions lattice matched to GaSb and InAs

NASA Astrophysics Data System (ADS)

Shim, Kyurhee

2013-11-01

A theoretical model utilizing a universal tight binding method and a correlated function expansion technique is presented to calculate the valence band maximum (VBM) and the conduction band minimum (CBM) of the binary (GaAs, InAS, GaSb, and InSb) and quaternary alloy GaxIn1-xAsySb1-y systems. By organizing the relative positions of the VBM and CBM between semiconductors, the band alignments and band types in the heterojunctions are determined. A straddling (type-I) band alignment in InAs/GaAs, InSb/GaAs, and GaSb/InSb, staggered (type-II) band alignment in GaSb/GaAs, and broken (type-III) band alignment in InSb/InAs and InAs/GaSb are found respectively. In addition, the compositional variations of VBM, CBM, valence band offset, conduction band offset, and band type for the alloy GaxIn1-xAsySb1-y lattice matched on GaSb and InAs are obtained as increasing the composition x. A pronounced upward bowing for the VBM and a very slight upward bowing (almost linear) for CBM are found, respectively. By controlling the compositions (x, y), band type transitions occur. The GaxIn1-xAsySb1-y heterojunctions lattice matched to GaSb changes their band types from type-III at x ˜0→ to type-II at x = 0.07, and → to type-I at x = 0.38. In contrast, the GaxIn1-xAsySb1-y heterojunctions lattice matched to InAs changes their band types from type-II x ˜0→ to type-III at x = 0.32. Reasonable agreement is obtained between our theoretical results and existing experimental data.

Serial Femtosecond Crystallography Opens New Avenues for Structural Biology

PubMed Central

Coe, Jesse; Fromme, Petra

2016-01-01

Free electron lasers (FELs) provide X-ray pulses in the femtosecond time domain with up to 1012 higher photon flux than synchrotrons and open new avenues for the determination of difficult to crystallize proteins, like large complexes and human membrane proteins. While the X-ray pulses are so strong that they destroy any solid material, the crystals diffract before they are destroyed. The most successful application of FELs for biology has been the method of serial femtosecond crystallography (SFX) where nano or microcrystals are delivered to the FEL beam in a stream of their mother liquid at room temperature, which ensures the replenishment of the sample before the next X-ray pulse arrives. New injector technology allows also for the delivery of crystal in lipidic cubic phases or agarose, which reduces the sample amounts for an SFX data set by two orders of magnitude. Time-resolved SFX also allows for analysis of the dynamics of biomolecules, the proof of principle being recently shown for light-induced reactions in photosystem II and photoactive yellow protein. An SFX data sets consist of thousands of single crystal snapshots in random orientations, which can be analyzed now “on the fly” by data analysis programs specifically developed for SFX, but de-novo phasing is still a challenge, that might be overcome by two-color experiments or phasing by shape transforms. PMID:26786767

Interleaving lattice for the Argonne Advanced Photon Source linac

NASA Astrophysics Data System (ADS)

Shin, S.; Sun, Y.; Dooling, J.; Borland, M.; Zholents, A.

2018-06-01

To realize and test advanced accelerator concepts and hardware, a beam line is being reconfigured in the linac extension area (LEA) of the Argonne Advanced Photon Source (APS) linac. A photocathode rf gun installed at the beginning of the APS linac will provide a low emittance electron beam into the LEA beam line. The thermionic rf gun beam for the APS storage ring and the photocathode rf gun beam for the LEA beam line will be accelerated through the linac in an interleaved fashion. In this paper, the design studies for interleaving lattice realization in the APS linac is described with the initial experiment result.

Femtosecond Laser-Assisted Descemetorhexis: A Novel Technique in Descemet Membrane Endothelial Keratoplasty.

PubMed

Pilger, Daniel; von Sonnleithner, Christoph; Bertelmann, Eckart; Joussen, Antonia M; Torun, Necip

2016-10-01

To explore the feasibility of femtosecond laser-assisted descemetorhexis (DR) to facilitate Descemet membrane endothelial keratoplasty (DMEK) surgery. Six pseudophakic patients suffering from Fuchs' endothelial dystrophy underwent femtosecond laser-assisted DMEK surgery. DR was performed using the LenSx femtosecond laser, followed by manual removal of the Descemet membrane. Optical coherence tomography images were used to measure DR parameters. Patients were followed up for 1 month to examine best corrected visual acuity, endothelial cell loss, flap detachment, and structure of the anterior chamber of the eye. The diameter of the DR approximated the intended diameter closely [mean error of 34 μm (0.45%) and 54 μm (0.67%) in the x- and y-diameter, respectively] and did not require manual correction. The median visual acuity increased from 0.4 logMAR (range 0.6-0.4 logMAR) preoperative to 0.2 logMAR (range 0-0.4 logMAR) postoperative. The median endothelial cell loss was 22% (range 7%-34%). No clinically significant flap detachments were noted. All patients had clear corneas after surgery, and no side effects or damage to structures of the anterior chamber were noted. Femtosecond laser-assisted DR is a safe and precise method for facilitating DMEK surgery.

Analysis of HOM Problems in the C-ADS Main Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Burn; Ng, King Yuen

2017-05-18

Excitation of higher-order modes (HOMs) in superconducting cavities may severely affect the operation of the main linac in the Chinese Accelerator Driven System (CADS). Preliminary analysis is made on the effects of beam dynamic, which includes possible longitudinal and transverse emittance enlargements, as well as the possibility of beam breakup. Suggestions are given for further investigation. Comparison is made between the C-ADS and the Fermilab Project X.

Tailoring of optical band gap by varying Zn content in Cd{sub 1-x}Zn{sub x}S thin films prepared by spray pyrolysis method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Vipin, E-mail: vipinkumar28@yahoo.co.in; Sharma, D. K.; Agrawal, Sonalika

Cd{sub 1-X}Zn{sub X}S thin films (X = 0.2, 0.4, 0.6, 0.8) have been grown on glass substrate by spray pyrolysis technique using equimolar concentration aqueous solution of cadmium chloride, zinc acetate and thiourea. Prepared thin films have been characterized by UV-VIS spectrophotometer. The optical band gap of the films has been studied by transmission spectra in wavelength range 325-600nm. It has been observed that optical band gap increases with increasing zinc concentration. The optical band gap of these thin films varies from 2.59 to 3.20eV with increasing Zn content.

Multichannel X-Band Dielectric-Resonator Oscillator

NASA Technical Reports Server (NTRS)

Mysoor, Narayan; Dennis, Matthew; Cook, Brian

2006-01-01

A multichannel dielectric-resonator oscillator (DRO), built as a prototype of a local oscillator for an X-band transmitter or receiver, is capable of being electrically tuned among and within 26 adjacent frequency channels, each 1.16 MHz wide, in a band ranging from 7,040 to 7,070 GHz. The tunability of this oscillator is what sets it apart from other DROs, making it possible to use mass-produced oscillator units of identical design in diverse X-band applications in which there are requirements to use different fixed frequencies or to switch among frequency channels. The oscillator (see figure) includes a custom-designed voltage-controlled-oscillator (VCO) monolithic microwave integrated circuit (MMIC), a dielectric resonator disk (puck), and two varactor-coupling circuits, all laid out on a 25-mil (0.635-mm)-thick alumina substrate having a length and width of 17.8 mm. The resonator disk has a diameter of 8.89 mm and a thickness of 4.01 mm. The oscillator is mounted in an 8.9-mm-deep cavity in a metal housing. The VCO MMIC incorporates a negative- resistance oscillator amplifier along with a buffer amplifier. The resonator disk is coupled to a microstrip transmission line connected to the negative-resistance port of the VCO MMIC. The two varactor-coupling circuits include microstrip lines, laid out orthogonally to each other, for coupling with the resonator disk. Each varactor microstrip line is DC-coupled to an external port via a microwave choke. One varactor is used for coarse tuning to select a channel; the other varactor is used (1) for fine tuning across the 1.16-MHz width of each channel and (2) as a feedback port for a phase-lock loop. The resonator disk is positioned to obtain (1) the most desirable bandwidth, (2) relatively tight coupling with the microstrip connected to the coarse-tuning varactor, and (3) relatively loose coupling with the microstrip connected to the fine-tuning varactor. Measurements of performance showed that the oscillator can be

Accurate determination of the valence band edge in hard x-ray photoemission spectra using GW theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lischner, Johannes, E-mail: jlischner597@gmail.com; Department of Physics and Department of Materials and the Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, London SW7 2AZ; Nemšák, Slavomír

We introduce a new method for determining accurate values of the valence-band maximum in x-ray photoemission spectra. Specifically, we align the sharpest peak in the valence-band region of the experimental spectrum with the corresponding feature of a theoretical valence-band density of states curve from ab initio GW theory calculations. This method is particularly useful for soft and hard x-ray photoemission studies of materials with a mixture of valence-band characters, where strong matrix element effects can render standard methods for extracting the valence-band maximum unreliable. We apply our method to hydrogen-terminated boron-doped diamond, which is a promising substrate material for novelmore » solar cell devices. By carrying out photoemission experiments with variable light polarizations, we verify the accuracy of our analysis and the general validity of the method.« less

Nanosurgery of cells and chromosomes using near-infrared twelve-femtosecond laser pulses.

PubMed

Uchugonova, Aisada; Lessel, Matthias; Nietzsche, Sander; Zeitz, Christian; Jacobs, Karin; Lemke, Cornelius; König, Karsten

2012-10-01

ABSTRACT. Laser-assisted surgery based on multiphoton absorption of near-infrared laser light has great potential for high precision surgery at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact laser method also supports contamination-free cell nanosurgery. In this paper we describe usage of an ultrashort femtosecond laser scanning microscope for sub-100 nm surgery of human cells and metaphase chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770  nm/830  nm) and an in situ pulse duration at the target ranging from 12 fs up to 3 ps was employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond laser pulses at low mean milliwatt powers for sub-100 nm surgery of cells and cellular organelles.

Crossbar H-mode drift-tube linac design with alternative phase focusing for muon linac

NASA Astrophysics Data System (ADS)

Otani, M.; Futatsukawa, K.; Hasegawa, K.; Kitamura, R.; Kondo, Y.; Kurennoy, S.

2017-07-01

We have developed a Crossbar H-mode (CH) drift-tube linac (DTL) design with an alternative phase focusing (APF) scheme for a muon linac, in order to measure the anomalous magnetic moment and electric dipole moment (EDM) of muons at the Japan Proton Accelerator Research Complex (J-PARC). The CH-DTL accelerates muons from β = v/c = 0.08 to 0.28 at an operational frequency of 324 MHz. The design and results are described in this paper.

Femtosecond Optical and X-Ray Measurement of the Semiconductor-to-Metal Transition in VO2

NASA Astrophysics Data System (ADS)

Cavalleri, Andrea; Toth, Csaba; Squier, Jeff; Siders, Craig; Raksi, Ferenc; Forget, Patrick; Kieffer, Jean-Claude

2001-03-01

While the use of ultrashort visible pulses allows access to ultrafast changes in the optical properties during phase transitions, measurement of the correlation between atomic movement and electronic rearrangement has proven more elusive. Here, we report on the conjunct measurement of ultrafast electronic and structural dynamics during a semiconductor-to-metal phase transition in VO2. Rearrangement of the unit cell from monoclinic to rutile (measured by ultrafast x-ray diffraction) is accompanied by a sharp increase in the electrical conductivity and perturbation of the optical properties (measured with ultrafast visible spectroscopy). Ultrafast x-ray diffraction experiments were performed using femtosecond bursts of Cu-Ka from a laser generated plasma source. A clear rise of the diffraction signal originating from the impulsively generated metallic phase was observable on the sub-picosecond timescale. Optical experiments were performed using time-resolved microscopy, providing temporally and spatially resolved measurements of the optical reflectivity at 800 nm. The data indicate that the reflectivity of the low-temperature semiconducting solid is driven to that of the equilibrium, high-temperature metallic phase within 400 fs after irradiation with a 50-fs laser pulse at fluences in excess of 10 mJ/cm2. In conclusion, the data presented in this contribution suggest that the semiconductor-to-metal transition in VO2 occurs within 500 fs after laser-irradiation. A nonthermal physical mechanism governs the re-arrangement.

Dynamical Study of Femtosecond-Laser-Ablated Liquid-Aluminum Nanoparticles Using Spatiotemporally Resolved X-Ray-Absorption Fine-Structure Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi

2007-10-19

We study the temperature evolution of aluminum nanoparticles generated by femtosecond laser ablation with spatiotemporally resolved x-ray-absorption fine-structure spectroscopy. We successfully identify the nanoparticles based on the L-edge absorption fine structure of the ablation plume in combination with the dependence of the edge structure on the irradiation intensity and the expansion velocity of the plume. In particular, we show that the lattice temperature of the nanoparticles is estimated from the L-edge slope, and that its spatial dependence reflects the cooling of the nanoparticles during plume expansion. The results reveal that the emitted nanoparticles travel in a vacuum as a condensedmore » liquid phase with a lattice temperature of about 2500 to 4200 K in the early stage of plume expansion.« less

Zn x Cd1-x S tunable band structure-directing photocatalytic activity and selectivity of visible-light reduction of CO2 into liquid solar fuels

NASA Astrophysics Data System (ADS)

Tang, Lanqin; Kuai, Libang; Li, Yichang; Li, Haijin; Zhou, Yong; Zou, Zhigang

2018-02-01

A series of Zn x Cd1-x S monodispersed nanospheres were successfully synthesized with tunable band structures. As-prepared Zn x Cd1-x S solid solutions show much enhanced photocatalytic efficiency for CO2 photoreduction in aqueous solutions under visible light irradiation, relative to pure CdS analog. Methanol (CH3OH) and acetaldehyde (CH3CHO) are the major products of CO2 photoreduction for the solid solutions with x = 0, 0.2, and 0.5. Interestingly, Zn0.8Cd0.2S photocatalyst with a wide band gap can also additionally generate ethanol (CH3CH2OH) besides CH3OH and CH3CHO. The balance between the band structure-directing redox capacity and light absorption should be considered to influence both product yield and selectivity of CO2 photoreduction. The possible photoreduction mechanism was tentatively proposed.

Initial Testing of the Mark-0 X-Band RF Gun at SLAC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlieks, Arnold; Adolphsen, C.; Dolgashev, V.

A new X-band RF gun (Mark-0) has been assembled, tuned and was tested in the ASTA facility at SLAC. This gun has been improved from an earlier gun used in Compton-scattering experiments at SLAC by the introduction of a racetrack dual-input coupler to reduce quadrupole fields. Waveguide-to-coupler irises were also redesigned to reduce surface magnetic fields and therefore peak pulse surface heating. Tests of this photocathode gun will allow us to gain early operational experience for beam tests of a new gun with further improvements (Mark-1) being prepared for SLAC's X-Band Test Area (XTA) program and the LLNL MEGa-ray program.more » Results of current testing up to {approx} 200 MV/m peak surface Electric fields are presented.« less

SLAC Linac Preparations for FACET

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erickson, R.; Bentson, L.; Kharakh, D.

The SLAC 3km linear electron accelerator has been cut at the two-thirds point to provide beams to two independent programs. The last third provides the electron beam for the Linac Coherent Light Source (LCLS), leaving the first two-thirds available for FACET, the new experimental facility for accelerator science and test beams. In this paper, we describe this separation and projects to prepare the linac for the FACET experimental program.

Project for the development of the linac based NCT facility in University of Tsukuba.

PubMed

Kumada, H; Matsumura, A; Sakurai, H; Sakae, T; Yoshioka, M; Kobayashi, H; Matsumoto, H; Kiyanagi, Y; Shibata, T; Nakashima, H

2014-06-01

A project team headed by University of Tsukuba launched the development of a new accelerator based BNCT facility. In the project, we have adopted Radio-Frequency Quadrupole (RFQ)+Drift Tube Linac (DTL) type linac as proton accelerators. Proton energy generated from the linac was set to 8MeV and average current was 10mA. The linac tube has been constructed by Mitsubishi Heavy Industry Co. For neutron generator device, beryllium is selected as neutron target material; high intensity neutrons are generated by the reaction with beryllium and the 80kW proton beam. Our team chose beryllium as the neutron target material. At present beryllium target system is being designed with Monte-Carlo estimations and heat analysis with ANSYS. The neutron generator consists of moderator, collimator and shielding. It is being designed together with the beryllium target system. We also acquired a building in Tokai village; the building has been renovated for use as BNCT treatment facility. It is noteworthy that the linac tube had been installed in the facility in September 2012. In BNCT procedure, several medical devices are required for BNCT treatment such as treatment planning system, patient positioning device and radiation monitors. Thus these are being developed together with the linac based neutron source. For treatment planning system, we are now developing a new multi-modal Monte-Carlo treatment planning system based on JCDS. The system allows us to perform dose estimation for BNCT as well as particle radiotherapy and X-ray therapy. And the patient positioning device can navigate a patient to irradiation position quickly and properly. Furthermore the device is able to monitor movement of the patient׳s position during irradiation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Flood Monitoring using X-band Dual-polarization Radar Network

NASA Astrophysics Data System (ADS)

Chandrasekar, V.; Wang, Y.; Maki, M.; Nakane, K.

2009-09-01

A dense weather radar network is an emerging concept advanced by the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA). Using multiple radars observing over a common will create different data outcomes depending on the characteristics of the radar units employed and the network topology. To define this a general framework is developed to describe the radar network space, and formulations are obtained that can be used for weather radar network characterization. Current weather radar surveillance networks are based upon conventional sensing paradigm of widely-separated, standalone sensing systems using long range radars that operate at wavelengths in 5-10 cm range. Such configuration has limited capability to observe close to the surface of the earth because of the earth's curvature but also has poorer resolution at far ranges. The dense network radar system, observes and measures weather phenomenon such as rainfall and severe weather close to the ground at higher spatial and temporal resolution compared to the current paradigm. In addition the dense network paradigm also is easily adaptable to complex terrain. Flooding is one of the most common natural hazards in the world. Especially, excessive development decreases the response time of urban watersheds and complex terrain to rainfall and increases the chance of localized flooding events over a small spatial domain. Successful monitoring of urban floods requires high spatiotemporal resolution, accurate precipitation estimation because of the rapid flood response as well as the complex hydrologic and hydraulic characteristics in an urban environment. This paper reviews various aspects in radar rainfall mapping in urban coverage using dense X-band dual-polarization radar networks. By reducing the maximum range and operating at X-band, one can ensure good azimuthal resolution with a small-size antenna and keep the radar beam closer to the ground. The networked topology helps to achieve satisfactory

Preliminary Analysis of X-Band and Ka-Band Radar for Use in the Detection of Icing Conditions Aloft

NASA Technical Reports Server (NTRS)

Reehorst, Andrew L.; Koenig, George G.

2004-01-01

NASA and the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) have an on-going activity to develop remote sensing technologies for the detection and measurement of icing conditions aloft. Radar has been identified as a strong tool for this work. However, since the remote detection of icing conditions with the intent to identify areas of icing hazard is a new and evolving capability, there are no set requirements for radar sensitivity. This work is an initial attempt to quantify, through analysis, the sensitivity requirements for an icing remote sensing radar. The primary radar of interest for cloud measurements is Ka-band, however, since NASA is currently using an X-band unit, this frequency is also examined. Several aspects of radar signal analysis were examined. Cloud reflectivity was calculated for several forms of cloud using two different techniques. The Air Force Geophysical Laboratory (AFGL) cloud models, with different drop spectra represented by a modified gamma distribution, were utilized to examine several categories of cloud formation. Also a fundamental methods approach was used to allow manipulation of the cloud droplet size spectra. And an analytical icing radar simulator was developed to examine the complete radar system response to a configurable multi-layer cloud environment. Also discussed is the NASA vertical pointing X-band radar. The radar and its data system are described, and several summer weather events are reviewed.

The Cryogenic AntiCoincidence detector for ATHENA X-IFU: a scientific assessment of the observational capabilities in the hard X-ray band

NASA Astrophysics Data System (ADS)

D'Andrea, M.; Lotti, S.; Macculi, C.; Piro, L.; Argan, A.; Gatti, F.

2017-12-01

ATHENA is a large X-ray observatory, planned to be launched by ESA in 2028 towards an L2 orbit. One of the two instruments of the payload is the X-IFU: a cryogenic spectrometer based on a large array of TES microcalorimeters, able to perform integral field spectrography in the 0.2-12 keV band (2.5 eV FWHM at 6 keV). The X-IFU sensitivity is highly degraded by the particle background expected in the L2 orbit, which is induced by primary protons of both galactic and solar origin, and mostly by secondary electrons. To reduce the particle background level and enable the mission science goals, the instrument incorporates a Cryogenic AntiCoincidence detector (CryoAC). It is a 4 pixel TES based detector, placed < 1 mm below the main array. In this paper we report a scientific assessment of the CryoAC observational capabilities in the hard X-ray band (E > 10 keV). The aim of the study has been to understand if the present detector design can be improved in order to enlarge the X-IFU scientific capability on an energy band wider than the TES array. This is beyond the CryoAC baseline, being this instrument aimed to operate as anticoincidence particle detector and not conceived to perform X-ray observations.

ARIEL e-LINAC: Commissioning and Development

NASA Astrophysics Data System (ADS)

Laxdal, R. E.; Zvyagintsev, V.

2016-09-01

A superconducting electron Linac (e-Linac) will be a part of the ARIEL facility for the production of radioactive ion beams (RIB) at TRIUMF. The e-Linac will consist of five 1.3GHz 9-cell cavities in three cryomodules delivering a 50MeV 10mA beam. The baseline operation will be single pass but a re-circulating ring is planned to allow either energy boost or energy recovery operation. The first stage of the accelerator which consists of two cryomodules has been successfully commissioned in 2014. The paper will discuss the superconducting radio-frequency (SRF) challenges of the accelerator. Cavities, crymodules and RF system design, preparation, and performance will be presented.

The localized effect of the Bi level on the valence band in the dilute bismuth GaBixAs1-x alloy

NASA Astrophysics Data System (ADS)

Zhao, Chuan-Zhen; Zhu, Min-Min; Wang, Jun; Wang, Sha-Sha; Lu, Ke-Qing

2018-05-01

The research on the temperature dependence of the band gap energy of the dilute bismuth GaBixAs1-x alloy has been done. It is found that its temperature insensitiveness is due to the enhanced localized character of the valence band state and the small decrease of the temperature coefficient for the conduction band minimum (CBM). The enhanced localized character of the valence band state is the main factor. In order to describe the localized effect of the Bi levels on the valence band, the localized energy is introduced into the Varshni's equation. It is found that the effect of the localized Bi level on the valence band becomes strong with increasing Bi content. In addition, it is found that the pressure dependence of the band gap energy of GaBixAs1-x does not seem to be influenced by the localized Bi levels. It is due to two factors. One is that the pressure dependence of the band gap energy is mainly determined by the D CBM of GaBixAs1-x. The D CBM of GaBixAs1-x is not influenced by the localized Bi levels. The other is that the small variation of the pressure coefficient for the D valence band maximum (VBM) state of GaBixAs1-x can be cancelled by the variation of the pressure coefficient for the D CBM state of GaBixAs1-x.

Design concepts and performance of NASA X-band (7162 MHz/8415 MHz) transponder for deep-space spacecraft applications

NASA Technical Reports Server (NTRS)

Mysoor, N. R.; Perret, J. D.; Kermode, A. W.

1991-01-01

The design concepts and measured performance characteristics are summarized of an X band (7162 MHz/8415 MHz) breadboard deep space transponder (DSP) for future spacecraft applications, with the first use scheduled for the Comet Rendezvous Asteroid Flyby (CRAF) and Cassini missions in 1995 and 1996, respectively. The DST consists of a double conversion, superheterodyne, automatic phase tracking receiver, and an X band (8415 MHz) exciter to drive redundant downlink power amplifiers. The receiver acquires and coherently phase tracks the modulated or unmodulated X band (7162 MHz) uplink carrier signal. The exciter phase modulates the X band (8415 MHz) downlink signal with composite telemetry and ranging signals. The receiver measured tracking threshold, automatic gain control, static phase error, and phase jitter characteristics of the breadboard DST are in good agreement with the expected performance. The measured results show a receiver tracking threshold of -158 dBm and a dynamic signal range of 88 dB.

Femtosecond Lasers and Corneal Surgical Procedures.

PubMed

Marino, Gustavo K; Santhiago, Marcony R; Wilson, Steven E

2017-01-01

Our purpose is to present a broad review about the principles, early history, evolution, applications, and complications of femtosecond lasers used in refractive and nonrefractive corneal surgical procedures. Femtosecond laser technology added not only safety, precision, and reproducibility to established corneal surgical procedures such as laser in situ keratomileusis (LASIK) and astigmatic keratotomy, but it also introduced new promising concepts such as the intrastromal lenticule procedures with refractive lenticule extraction (ReLEx). Over time, the refinements in laser optics and the overall design of femtosecond laser platforms led to it becoming an essential tool for corneal surgeons. In conclusion, femtosecond laser is a heavily utilized tool in refractive and nonrefractive corneal surgical procedures, and further technological advances are likely to expand its applications. Copyright 2017 Asia-Pacific Academy of Ophthalmology.

Large-area synthesis of monolayered MoS(2(1-x))Se(2x) with a tunable band gap and its enhanced electrochemical catalytic activity.

PubMed

Yang, Lei; Fu, Qi; Wang, Wenhui; Huang, Jian; Huang, Jianliu; Zhang, Jingyu; Xiang, Bin

2015-06-21

"Band gap engineering" in two-dimensional (2D) materials plays an important role in tailoring their physical and chemical properties. The tuning of the band gap is typically achieved by controlling the composition of the semiconductor alloys. However, large-area preparation of 2D alloys remains a major challenge. Here, we report the large-area synthesis of high-quality monolayered MoS2(1-x)Se2x with a size coverage of hundreds of microns using a chemical vapor deposition method. The photoluminescence (PL) spectroscopy results confirm the tunable band gap in MoS2(1-x)Se2x, which is modulated by varying the Se content. Atomic-scale analysis was performed and the chemical composition was characterized using high-resolution scanning transmission electron microscopy and X-ray photoemission spectroscopy. With the introduction of Se into monolayered MoS2, it leads to enhanced catalytic activity in an electrochemical reaction for hydrogen generation, compared to monolayered MoS2 and MoSe2. It is promising as a potential alternative to expensive noble metals.

Regenerative Amplification of Femtosecond Pulses: Design andConstruction of a sub-100fs, muon J Laser System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schumacher, Andreas B.

1996-10-01

Femtosecond lasers are a powerful tool for a wealth of applications in physics, chemistry and biology. In most cases, however, their use is fundamentally restricted to a rather narrow spectral range. This thesis deals with the construction and characterization of a femtosecond light source for spectroscopic applications which overcomes that restriction. It is demonstrated how the output of a continuously pumped Ti:sapphire femtosecond oscillator is amplified to the μJ level,while the pulse duration remains below 100 fs. A combination of continuous pumping, acousto-optic switching and Ti:Al 2O 3 as a gain medium allows amplification at high repetition rates. By focusingmore » the high energy pulses into a sapphire crystal, a broad-band continuum can be generated, extended in wavelengths over several hundred nanometers. To accomplish amplification of three orders of magnitude while maintaining the pulse length, a regenerative multipass amplifier system was built. The thesis describes theoretical design, realization and characterization of the system. Theoretical calculations and preliminary measurements were carried out and allow a critical evaluation of the final performance.« less

Synthesis and enhanced electrochemical catalytic performance of monolayer WS2(1-x) Se2x with a tunable band gap.

PubMed

Fu, Qi; Yang, Lei; Wang, Wenhui; Han, Ali; Huang, Jian; Du, Pingwu; Fan, Zhiyong; Zhang, Jingyu; Xiang, Bin

2015-08-26

The first realization of a tunable band-gap in monolayer WS2(1-x) Se2x is demonstrated. The tuning of the bandgap exhibits a strong dependence of S and Se content, as proven by PL spectroscopy. Because of its remarkable electronic structure, monolayer WS2(1-x) Se2x exhibits novel electrochemical catalytic activity and offers long-term electrocatalytic stability for the hydrogen evolution reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanostructure array plasmas generated by femtosecond pulses at highly relativistic intensities

NASA Astrophysics Data System (ADS)

Hollinger, R. C.; Wong, Y.; Wong, S.; Rockwood, A.; Glasby, J.; Shlyaptsev, V.; Rocca, J. J.; Capeluto, M. G.; Kaymak, V.; Pukhov, A.

2017-10-01

The irradiation of high aspect ratio ordered nanostructure arrays with ultra-high contrast femtosecond laser pulses of relativistic intensity provides a unique combination of nearly complete optical absorption and drastically enhanced light penetration into near-solid density targets. This allows the material to be volumetrically heated deep into the ultra-high energy density regime. In previous experiments we have shown that irradiation of Ni and Au nanostructures with femtosecond pulses focused to an intensity of 5x1018 Wcm-2 generate multi-KeV near solid density plasmas in which atoms are ionized to the Ni+26 and Au+52 charge states. Here we present the first results of the irradiation of nanostructure arrays with highly relativistic pulses of intensities up to 5x1021Wcm-2. Silver and Rhodium nanowire arrays were irradiated with frequency-doubled pulses of 30 fs duration from a petawatt-class Ti:Sa laser. Time integrated x-ray spectra show the presence of He-like and Li-like emission. Results of experiments conducted with a variety of different nanowires diameters with a range of interwire spacings will be presented and compared to the result of 3D particle-in-cell-simulations. This work was supported by the Fusion Energy Program, Office of Science of the U.S Department of Energy.

Femtosecond tracking of carrier relaxation in germanium with extreme ultraviolet transient reflectivity

NASA Astrophysics Data System (ADS)

Kaplan, Christopher J.; Kraus, Peter M.; Ross, Andrew D.; Zürch, Michael; Cushing, Scott K.; Jager, Marieke F.; Chang, Hung-Tzu; Gullikson, Eric M.; Neumark, Daniel M.; Leone, Stephen R.

2018-05-01

Extreme ultraviolet (XUV) transient reflectivity around the germanium M4 ,5 edge (3 d core-level to valence transition) at 30 eV is advanced to obtain the transient dielectric function of crystalline germanium [100] on femtosecond to picosecond time scales following photoexcitation by broadband visible-to-infrared (VIS/NIR) pulses. By fitting the transient dielectric function, carrier-phonon induced relaxations are extracted for the excited carrier distribution. The measurements reveal a hot electron relaxation rate of 3.2 ±0.2 ps attributed to the X -L intervalley scattering and a hot hole relaxation rate of 600 ±300 fs ascribed to intravalley scattering within the heavy hole (HH) band, both in good agreement with previous work. An overall energy shift of the XUV dielectric function is assigned to a thermally induced band gap shrinkage by formation of acoustic phonons, which is observed to be on a timescale of 4-5 ps, in agreement with previously measured optical phonon lifetimes. The results reveal that the transient reflectivity signal at an angle of 66∘ with respect to the surface normal is dominated by changes to the real part of the dielectric function, due to the near critical angle of incidence of the experiment (66∘-70∘) for the range of XUV energies used. This work provides a methodology for interpreting XUV transient reflectivity near core-level transitions, and it demonstrates the power of the XUV spectral region for measuring ultrafast excitation dynamics in solids.

Fixed-target protein serial microcrystallography with an x-ray free electron laser

PubMed Central

Hunter, Mark S.; Segelke, Brent; Messerschmidt, Marc; Williams, Garth J.; Zatsepin, Nadia A.; Barty, Anton; Benner, W. Henry; Carlson, David B.; Coleman, Matthew; Graf, Alexander; Hau-Riege, Stefan P.; Pardini, Tommaso; Seibert, M. Marvin; Evans, James; Boutet, Sébastien; Frank, Matthias

2014-01-01

We present results from experiments at the Linac Coherent Light Source (LCLS) demonstrating that serial femtosecond crystallography (SFX) can be performed to high resolution (~2.5 Å) using protein microcrystals deposited on an ultra-thin silicon nitride membrane and embedded in a preservation medium at room temperature. Data can be acquired at a high acquisition rate using x-ray free electron laser sources to overcome radiation damage, while sample consumption is dramatically reduced compared to flowing jet methods. We achieved a peak data acquisition rate of 10 Hz with a hit rate of ~38%, indicating that a complete data set could be acquired in about one 12-hour LCLS shift using the setup described here, or in even less time using hardware optimized for fixed target SFX. This demonstration opens the door to ultra low sample consumption SFX using the technique of diffraction-before-destruction on proteins that exist in only small quantities and/or do not produce the copious quantities of microcrystals required for flowing jet methods. PMID:25113598

Linear Accelerator (LINAC)

MedlinePlus

... equipment? How is safety ensured? What is this equipment used for? A linear accelerator (LINAC) is the ... Therapy (SBRT) . top of page How does the equipment work? The linear accelerator uses microwave technology (similar ...

A new design of an S/X dual band circular slot antenna for radar applications.

PubMed

Ghnimi, Said; Wali, Rawia; Gharsallh, Ali; Razban, Tchanguiz

2013-01-01

A novel design of dual-band slot antenna with a circular patch for radar applications is presented and studied. It is fed by a micro-strip line and built on a FR-4 substrate with a whole size of 18 x 30 mm2. A dual band printed antenna is created by introducing slots on the radiating element. By this, two bandwidth, covering C and X band, are achieved. In order to obtain a good fundamental antenna design, the initial studies were carried out theoretically, using CST Microwave Studio simulation software. In this case, the frequency range at return loss < 10 dB is 5.24 - 6.16 GHz for low frequency and is 7.9 -11.7 GHz for high frequency. In addition, the proposed antenna has good radiation characteristics and stable gains over the whole operating bands. A prototype of antenna is fabricated and tested. Experimental data show good agreement between simulated and measured results.

Effects of microstructure banding on hydrogen assisted fatigue crack growth in X65 pipeline steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ronevich, Joseph A.; Somerday, Brian P.; San Marchi, Chris W.

Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. Thus the reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impededmore » hydrogen diffusion across the banded pearlite.« less

Effects of microstructure banding on hydrogen assisted fatigue crack growth in X65 pipeline steels

DOE PAGES

Ronevich, Joseph A.; Somerday, Brian P.; San Marchi, Chris W.

2015-09-10

Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. Thus the reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impededmore » hydrogen diffusion across the banded pearlite.« less

Dynamics of Molecular Emission Features from Nanosecond, Femtosecond Laser and Filament Ablation Plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harilal, Sivanandan S.; Yeak, J.; Brumfield, Brian E.

2016-06-15

The evolutionary paths of molecular species and nanoparticles in laser ablation plumes are not well understood due to the complexity of numerous physical processes that occur simultaneously in a transient laser-plasma system. It is well known that the emission features of ions, atoms, molecules and nanoparticles in a laser ablation plume strongly depend on the laser irradiation conditions. In this letter we report the temporal emission features of AlO molecules in plasmas generated using a nanosecond laser, a femtosecond laser and filaments generated from a femtosecond laser. Our results show that, at a fixed laser energy, the persistence of AlOmore » is found to be highest and lowest in ns and filament laser plasmas respectively while molecular species are formed at early times for both ultrashort pulse (fs and filament) generated plasmas. Analysis of the AlO emission band features show that the vibrational temperature of AlO decays rapidly in filament assisted laser ablation plumes.« less

Ultrafast pre-breakdown dynamics in Al₂O₃SiO₂ reflector by femtosecond UV laser spectroscopy.

PubMed

Du, Juan; Li, Zehan; Xue, Bing; Kobayashi, Takayoshi; Han, Dongjia; Zhao, Yuanan; Leng, Yuxin

2015-06-29

Ultrafast carrier dynamics in Al2O3/SiO2 high reflectors has been investigated by UV femtosecond laser. It is identified by laser spectroscopy that, the carrier dynamics contributed from the front few layers of Al2O3 play a dominating role in the initial laser-induced damage of the UV reflector. Time-resolved reflection decrease after the UV excitation is observed, and conduction electrons is found to relaxed to a mid-gap defect state locating about one photon below the conduction band . To interpret the laser induced carrier dynamics further, a theoretical model including electrons relaxation to a mid-gap state is built, and agrees very well with the experimental results.. To the best of our knowledge, this is the first study on the pre-damage dynamics in UV high reflector induced by femtosecond UV laser.

Femtosecond lasers for microsurgery of cornea

NASA Astrophysics Data System (ADS)

Vartapetov, Sergei K.; Khudyakov, D. V.; Lapshin, Konstantin E.; Obidin, Aleksei Z.; Shcherbakov, Ivan A.

2012-03-01

The review of femtosecond laser installations for medical applications is given and a new femtosecond ophthalmologic system for creation of a flap of corneal tissue during the LASIK operation is described. An all-fibre femtosecond laser emitting ~400-fs pulses at 1067 nm is used. The pulse repetition rate can vary from 200 kHz up to 1 MHz. The output energy of the femtosecond system does not exceed 1 μJ. A specially developed objective with small spherical and chromatic aberrations is applied to focus laser radiation to an area of an eye cornea. The size of the focusing spot does not exceed 3 μm. To process the required area, scanning by a laser beam is applied with a speed no less than 5 m s-1. At a stage of preliminary tests of the system, the Κ8 glass, organic PMMA glass and specially prepared agarose gels are used as a phantom of an eye. The femtosecond system is successfully clinically tested on a plenty of eyes of a pig and on several human eyes. The duration of the procedure of creation of a corneal flap does not exceed 20 s.

Rye Canyon X-ray noise test: One-third octave-band data

NASA Technical Reports Server (NTRS)

Willshire, W. L., Jr.

1983-01-01

Acoustic data were obtained for the 25 ft. diameter X-wing rotor model during performance testing of the rotor system in hover. Data collected at the outdoor whirl tower test facility with a twelve microphone array were taken for approximately 150 test conditions comprised of various combinations of RPM, blade pressure ratio (BPR), and blade angle of attack (collective). The three test parameters had four values of RPM from 404 to 497, twelve values of BPR from 1.0 to 2.1, and six values of collective from 0.0 deg to 8.5 deg. Fifteen to twenty seconds of acoustic data were reduced to obtain an average 1/3 octave band spectrum for each microphone for each test condition. The complete, as measured, 1/3 octave band results for all the acoustic data are listed. Another part of the X-wing noise test was the acoustic calibration of the Rye Canyon whirl tower bowl. Corrections were computed which, when applied to as measured data, yield estimates of the free field X-wing noise. The free field estimates provide a more realistic measure of the rotor system noise levels. Trend analysis of the three test parameters on noise level were performed.

Mini-RF S- and X-Band Bistatic Radar Observations of the Moon

NASA Astrophysics Data System (ADS)

Patterson, G. W.; Carter, L. M.; Stickle, A. M.; Cahill, J. T. S.; Nolan, M. C.; Morgan, G. A.; Schroeder, D. M.; Mini-RF Team

2018-04-01

The Mini-RF instrument onboard the NASA LRO mission is collecting S- and X-band bistatic radar data to provide new insights regarding regolith development on the Moon, the diversity of lunar volcanism, and the current inventory of polar ice.

Magnetic shielding investigation for a 6 MV in-line linac within the parallel configuration of a linac-MR system.

PubMed

Santos, D M; St Aubin, J; Fallone, B G; Steciw, S

2012-02-01

In our current linac-magnetic resonance (MR) design, a 6 MV in-line linac is placed along the central axis of the MR's magnet where the MR's fringe magnetic fields are parallel to the overall electron trajectories in the linac waveguide. Our previous study of this configuration comprising a linac-MR SAD of 100 cm and a 0.5 T superconducting (open, split) MR imager. It showed the presence of longitudinal magnetic fields of 0.011 T at the electron gun, which caused a reduction in target current to 84% of nominal. In this study, passive and active magnetic shielding was investigated to recover the linac output losses caused by magnetic deflections of electron trajectories in the linac within a parallel linac-MR configuration. Magnetic materials and complex shield structures were used in a 3D finite element method (FEM) magnetic field model, which emulated the fringe magnetic fields of the MR imagers. The effects of passive magnetic shielding was studied by surrounding the electron gun and its casing with a series of capped steel cylinders of various inner lengths (26.5-306.5 mm) and thicknesses (0.75-15 mm) in the presence of the fringe magnetic fields from a commercial MR imager. In addition, the effects of a shield of fixed length (146.5 mm) with varying thicknesses were studied against a series of larger homogeneous magnetic fields (0-0.2 T). The effects of active magnetic shielding were studied by adding current loops around the electron gun and its casing. The loop currents, separation, and location were optimized to minimize the 0.011 T longitudinal magnetic fields in the electron gun. The magnetic field solutions from the FEM model were added to a validated linac simulation, consisting of a 3D electron gun (using OPERA-3d/scala) and 3D waveguide (using comsol Multiphysics and PARMELA) simulations. PARMELA's target current and output phase-space were analyzed to study the linac's output performance within the magnetic shields. The FEM model above agreed within 1

Femtosecond laser-induced structural difference in fused silica with a non-reciprocal writing process

NASA Astrophysics Data System (ADS)

Song, Hui; Dai, Ye; Song, Juan; Ma, Hongliang; Yan, Xiaona; Ma, Guohong

2017-04-01

In this paper, we report a non-reciprocal writing process for inducing asymmetric microstructure using a femtosecond laser with tilted pulse fronts in fused silica. The shape of the induced microstructure at the focus closely depends on the laser scan direction. An elongated end is observed as a kind of structural difference between the written lines with two reverse scans along + x and - x, which further leads to a birefringence intensity difference. We also find a bifurcation in the head region of the induced microstructure between the written lines along x and y. That process results from the focal intensity distortion caused by the pulse front tilt by comparing the simulated intensity distribution with the experimental results. The current results demonstrate that the pulse front tilt not only affects the free electron excitation at the focus but also further distorts the shape of the induced microstructure during a high-energy femtosecond laser irradiation. These results offer a route to fabricate optical elements by changing the spatiotemporal characteristics of ultrashort pulses.

Optical characterization of type-I to type-II band alignment transition in GaAs/Al x Ga1-x As quantum rings grown by droplet epitaxy

NASA Astrophysics Data System (ADS)

Su, Linlin; Wang, Ying; Guo, Qinglin; Li, Xiaowei; Wang, Shufang; Fu, Guangsheng; Mazur, Yuriy I.; E Ware, Morgan; Salamo, Gregory J.; Liang, Baolai; Huffaker, Diana L.

2017-08-01

Optical properties of GaAs/Al x Ga1-x As quantum rings (QRs) grown on GaAs (1 0 0) by droplet epitaxy have been investigated as a function of the Al-composition in the Al x Ga1-x As barrier. A transition from type-I to type-II band alignment is observed for the QRs via photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. While x  ⩽  0.45, the QR PL spectra show a blue-shift and an increasing intensity with increasing Al-composition, revealing the enhancement of quantum confinement in the QRs with type-I band alignment. While x  ⩾  0.60, the characteristic large blue-shift with excitation intensity and the much longer lifetime indicate the realization of a type-II band alignment. Due to the height fluctuation of QR structures grown by droplet epitaxy mode, it is not the large blue-shift of emission energy, but the long lifetime that becomes the more important feature to identify the type-II band alignment.

An X-band phase-locked relativistic backward wave oscillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Y.; Science and Technology on High Power Microwave Laboratory, Mianyang 621900; Li, Z. H.

2015-08-15

For the purpose of coherent high power microwave combining at high frequency band, an X-band phase-locked relativistic backward wave oscillator is presented and investigated. The phase-locking of the oscillator is accomplished by modulation of the electron beam before it reaches the oscillator. To produce a bunched beam with an acceptable injected RF power requirement, an overmoded input cavity is employed to provide initial density modulation. And a buncher cavity is introduced to further increase the modulation depth. When the beam enters the oscillator, the modulation depth is enough to lock the frequency and phase of the output microwave generated bymore » the oscillator. Particle-in-cell simulation shows that an input power of 90 kW is sufficient to lock the frequency and phase of 1.5 GW output microwave with locking bandwidth of 60 MHz.« less

Signature of Arctic first-year ice melt pond fraction in X-band SAR imagery

NASA Astrophysics Data System (ADS)

Fors, Ane S.; Divine, Dmitry V.; Doulgeris, Anthony P.; Renner, Angelika H. H.; Gerland, Sebastian

2017-03-01

In this paper we investigate the potential of melt pond fraction retrieval from X-band polarimetric synthetic aperture radar (SAR) on drifting first-year sea ice. Melt pond fractions retrieved from a helicopter-borne camera system were compared to polarimetric features extracted from four dual-polarimetric X-band SAR scenes, revealing significant relationships. The correlations were strongly dependent on wind speed and SAR incidence angle. Co-polarisation ratio was found to be the most promising SAR feature for melt pond fraction estimation at intermediate wind speeds (6. 2 m s-1), with a Spearman's correlation coefficient of 0. 46. At low wind speeds (0. 6 m s-1), this relation disappeared due to low backscatter from the melt ponds, and backscatter VV-polarisation intensity had the strongest relationship to melt pond fraction with a correlation coefficient of -0. 53. To further investigate these relations, regression fits were made both for the intermediate (R2fit = 0. 21) and low (R2fit = 0. 26) wind case, and the fits were tested on the satellite scenes in the study. The regression fits gave good estimates of mean melt pond fraction for the full satellite scenes, with less than 4 % from a similar statistics derived from analysis of low-altitude imagery captured during helicopter ice-survey flights in the study area. A smoothing window of 51 × 51 pixels gave the best reproduction of the width of the melt pond fraction distribution. A considerable part of the backscatter signal was below the noise floor at SAR incidence angles above ˜ 40°, restricting the information gain from polarimetric features above this threshold. Compared to previous studies in C-band, limitations concerning wind speed and noise floor set stricter constraints on melt pond fraction retrieval in X-band. Despite this, our findings suggest new possibilities in melt pond fraction estimation from X-band SAR, opening for expanded monitoring of melt ponds during melt season in the future.

Electron transfer in a virtual quantum state of LiBH4 induced by strong optical fields and mapped by femtosecond x-ray diffraction.

PubMed

Stingl, J; Zamponi, F; Freyer, B; Woerner, M; Elsaesser, T; Borgschulte, A

2012-10-05

Transient polarizations connected with a spatial redistribution of electronic charge in a mixed quantum state are induced by optical fields of high amplitude. We determine for the first time the related transient electron density maps, applying femtosecond x-ray powder diffraction as a structure probe. The prototype ionic material LiBH4 driven nonresonantly by an intense sub-40 fs optical pulse displays a large-amplitude fully reversible electron transfer from the BH4(-) anion to the Li+ cation during excitation. Our results establish this mechanism as the source of the strong optical polarization which agrees quantitatively with theoretical estimates.

DSN 63 64-meter antenna S- and X-band efficiency and system noise temperature calibrations, July 1986

NASA Technical Reports Server (NTRS)

Slobin, S. D.

1987-01-01

The Deep Space Network (DSN) 64-meter antenna in Spain (DSN 63) has been calibrated prior to its upgrading to a 70-meter high efficiency configuration in preparation for the Voyager Neptune encounter in August 1989. The S-band (2285 MHz) and X-band (8420 MHz) effective area efficiency and system noise temperature calibrations were carried out during July 1986 to establish a baseline system performance for this station. It is expected that the 70-meter will result in at least a 1.9 dB G/T improvement at X-band relative to the 64-meter baseline reference.

Status Of the ILC Main Linac Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saini, Arun; Kapin, Valery; Solyak, Nikolay

2017-05-01

International Linear collider (ILC) is a proposed accelerator facility which is primarily based on two 11-km long superconducting main linacs. In this paper we present recent updates on the main linac design and discuss changes made in order to meet specification outlined in the technical design report (TDR).

Energy-band alignment of (HfO2)x(Al2O3)1-x gate dielectrics deposited by atomic layer deposition on β-Ga2O3 (-201)

NASA Astrophysics Data System (ADS)

Yuan, Lei; Zhang, Hongpeng; Jia, Renxu; Guo, Lixin; Zhang, Yimen; Zhang, Yuming

2018-03-01

Energy band alignments between series band of Al-rich high-k materials (HfO2)x(Al2O3)1-x and β-Ga2O3 are investigated using X-Ray Photoelectron Spectroscopy (XPS). The results exhibit sufficient conduction band offsets (1.42-1.53 eV) in (HfO2)x(Al2O3)1-x/β-Ga2O3. In addition, it is also obtained that the value of Eg, △Ec, and △Ev for (HfO2)x(Al2O3)1-x/β-Ga2O3 change linearly with x, which can be expressed by 6.98-1.27x, 1.65-0.56x, and 0.48-0.70x, respectively. The higher dielectric constant and higher effective breakdown electric field of (HfO2)x(Al2O3)1-x compared with Al2O3, coupled with sufficient barrier height and lower gate leakage makes it a potential dielectric for high voltage β-Ga2O3 power MOSFET, and also provokes interest in further investigation of HfAlO/β-Ga2O3 interface properties.

Spin splitting in band structures of BiTeX (X=Cl, Br, I) monolayers

NASA Astrophysics Data System (ADS)

Hvazdouski, D. C.; Baranava, M. S.; Stempitsky, V. R.

2018-04-01

In systems with breaking of inversion symmetry a perpendicular electric field arises that interacts with the conduction electrons. It may give rise to electron state splitting even without influence of external magnetic field due to the spin-orbital interaction (SOI). Such a removal of the spin degeneracy is called the Rashba effect. Nanostructure with the Rashba effect can be part of a spin transistor. Spin degeneracy can be realized in a channel from a material of this type without additive of magnetic ions. Lack of additive increases the charge carrier mobility and reliability of the device. Ab initio simulations of BiTeX (X=Cl, Br, I) monolayers have been carried out using VASP wherein implemented DFT method. The study of this structures is of interest because such sort of structures can be used their as spin-orbitronics materials. The crystal parameters of BiTeCl, BiTeBr, BiTeI have been determined by the ionic relaxation and static calculations. It is necessary to note that splitting of energy bands occurs in case of SOI included. The values of the Rashba coefficient aR (in the range from 6.25 to 10.00 eV·Å) have high magnitudes for spintronics materials. Band structure of monolayers structures have ideal Rashba electron gas, i.e. there no other energy states near to Fermi level except Rashba states.

Nature of the abnormal band gap narrowing in highly crystalline Zn1-xCoxO nanorods

NASA Astrophysics Data System (ADS)

Qiu, Xiaoqing; Li, Liping; Li, Guangshe

2006-03-01

Highly crystalline Zn1-xCoxO nanorods were prepared using a hydrothermal method. With increasing Co2+ dopant concentration, the lattice volume enlarged considerably, which is associated with the enhanced repulsive interactions of defect dipole moments on the wall surfaces. This lattice modification produced a significant decrease in band gap energies with its magnitude that followed the relationship, ΔEg=ΔE0•(e-x/B-1), where x and B are Co2+ dopant concentration and a constant, respectively. The abnormal band gap energies were indicated to originate from the sp-d exchange interactions that are proportional to the square of lattice volume.

Practical application of cross correlation technique to measure jitter of master-oscillator-power-amplifier laser system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Młyńczak, J.; Sawicz-Kryniger, K.; Fry, A. R.

2014-01-01

The Linac coherent light source (LCLS) at the SLAC National Accelerator Laboratory (SLAC) is the world’s first hard X-ray free electron laser (XFEL) and is capable of producing high-energy, femtosecond duration X-ray pulses. A common technique to study fast timescale physical phenomena, various “pump/probe” techniques are used. In these techniques there are two lasers, one optical and one X-ray, that work as a pump and as a probe to study dynamic processes in atoms and molecules. In order to resolve phenomena that occur on femtosecond timescales, it is imperative to have very precise timing between the optical lasers and X-raysmore » (on the order of ~ 20 fs or better). The lasers are synchronized to the same RF source that drives the accelerator and produces the X-ray laser. However, elements in the lasers cause some drift and time jitter, thereby de-synchronizing the system. This paper considers cross-correlation technique as a way to quantify the drift and jitter caused by the regenerative amplifier of the ultrafast optical laser.« less

The continuous and discrete molecular orbital x-ray bands from Xe(q+) (12≤q≤29) +Zn collisions.

PubMed

Guo, Yipan; Yang, Zhihu; Hu, Bitao; Wang, Xiangli; Song, Zhangyong; Xu, Qiumei; Zhang, Boli; Chen, Jing; Yang, Bian; Yang, Jie

2016-07-29

In this paper, the x-ray emissions are measured by the interaction of 1500-3500 keV Xe(q+) (q = 12, 15, 17, 19, 21, 23, 26 and 29) ions with Zn target. When q < 29, we observe Ll, Lα, Lβ1, Lβ2 and Lγ characteristic x-rays from Xe(q+) ions and a broad M-shell molecular orbital (MO) x-ray band from the transient quasi-molecular levels. It is found that their yields quickly increase with different rates as the incident energy increases. Besides, the widths of the broad MO x-ray bands are about 0.9-1.32 keV over the energy range studied and are proportional to v(1/2) (v = projectile velocity). Most remarkably, when the projectile charge state is 29, the broad x-ray band separates into several narrow discrete spectra, which was never observed before in this field.

X-ray absorption and reflection as probes of the GaN conduction bands: Theory and experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B.

1997-04-01

X-ray absorption measurements are a well-known probe of the unoccupied states in a material. The same information can be obtained by using glancing angle X-ray reflectivity. In spite of several existing band structure calculations of the group III nitrides and previous optical studies in UV range, a direct probe of their conduction band densities of states is of interest. The authors performed a joint experimental and theoretical investigation using both of these experimental techniques for wurtzite GaN.

Time-resolved imaging of the microbunching instability and energy spread at the Linac Coherent Light Source

DOE PAGES

Ratner, D.; Behrens, C.; Ding, Y.; ...

2015-03-09

The microbunching instability (MBI) is a well known problem for high brightness electron beams and has been observed at accelerator facilities around the world. Free-electron lasers (FELs) are particularly susceptible to MBI, which can distort the longitudinal phase space and increase the beam’s slice energy spread (SES). Past studies of MBI at the Linac Coherent Light Source (LCLS) relied on optical transition radiation to infer the existence of microbunching. With the development of the x-band transverse deflecting cavity (XTCAV), we can for the first time directly image the longitudinal phase space at the end of the accelerator and complete amore » comprehensive study of MBI, revealing both detailed MBI behavior as well as insights into mitigation schemes. The fine time resolution of the XTCAV also provides the first LCLS measurements of the final SES, a critical parameter for many advanced FEL schemes. As a result, detailed MBI and SES measurements can aid in understanding MBI mechanisms, benchmarking simulation codes, and designing future high- brightness accelerators.« less

Femtosecond lasers for microsurgery of cornea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vartapetov, Sergei K; Khudyakov, D V; Lapshin, Konstantin E

The review of femtosecond laser installations for medical applications is given and a new femtosecond ophthalmologic system for creation of a flap of corneal tissue during the LASIK operation is described. An all-fibre femtosecond laser emitting {approx}400-fs pulses at 1067 nm is used. The pulse repetition rate can vary from 200 kHz up to 1 MHz. The output energy of the femtosecond system does not exceed 1 {mu}J. A specially developed objective with small spherical and chromatic aberrations is applied to focus laser radiation to an area of an eye cornea. The size of the focusing spot does not exceedmore » 3 {mu}m. To process the required area, scanning by a laser beam is applied with a speed no less than 5 m s{sup -1}. At a stage of preliminary tests of the system, the {Kappa}8 glass, organic PMMA glass and specially prepared agarose gels are used as a phantom of an eye. The femtosecond system is successfully clinically tested on a plenty of eyes of a pig and on several human eyes. The duration of the procedure of creation of a corneal flap does not exceed 20 s.« less

Femtosecond phacoemulsification: the business and the medicine.

PubMed

Uy, Harvey S; Edwards, Keith; Curtis, Nick

2012-01-01

PURPOSE FOR REVIEW: Phacoemulsification is the preferred method for cataract surgery in the developed world. The number of phacoemulsification procedures performed annually is expected to increase as the population ages. Femtosecond cataract surgery offers several surgical advantages over conventional phacoemulsification and has already attained commercial application in some countries. The purpose of this review is to outline the benefits, risks and commercial issues of femtosecond lasers as applied to cataract surgery. Cataract surgeons are adopting femtosecond technology to perform laser capsulotomy, lens fragmentation, clear cornea incisions and limbal relaxing incisions. Femtosecond lasers clearly perform these surgical steps with greater precision and reproducibility. Further benefits such as improved postoperative refractive results and reduced complication rates are being investigated. Commercial issues have invariably arisen such as cost of installation and operation, value proposition and return on investment. Femtosecond cataract surgery is an evolving procedure that can potentially lead to better and safer surgical outcomes. This review presents the currently available scientific evidence and discusses some of the relevant financial issues concerning this technology.

Incidence of rainbow glare after laser in situ keratomileusis flap creation with a 60 kHz femtosecond laser.

PubMed

Bamba, Sonya; Rocha, Karolinne M; Ramos-Esteban, Jerome C; Krueger, Ronald R

2009-06-01

To report the incidence of and factors associated with rainbow glare after laser in situ keratomileusis (LASIK) flap creation with a 60 kHz femtosecond laser. Department of Refractive Surgery, Cleveland Clinic Cole Eye Institute, Cleveland, Ohio, USA. Consecutive patients having LASIK by the same surgeon were questioned during postoperative examinations or by telephone about postoperative rainbow glare (radiating colors around a white light at night). Femtosecond laser (IntraLase) settings included pulse frequency 60 kHz, flap thickness 90 to 110 mum, and spot/line separation 8 mum. Raster energy was 0.8 microJ (75% of eyes) and 1.0 to 1.1 microJ (25%). Excimer laser ablation was performed with the LADAR 4000 or 6000 platform using custom or conventional treatments. Of 260 consecutive patients, 256 (98.5%) were successfully contacted. Fifteen patients (28 eyes) reported postoperative rainbow glare (5.8%), described as 4 to 12 bands of color around a white light, with 6 bands most common. The symptom did not correlate with refractive error, age, or sex but was more frequent at 1.0 microJ or 1.1 microJ raster energy (11.6%) than at 0.8 microJ (4.1%). The incidence followed a bimodal distribution, with the first grouping due to inadequate alignment and higher energy just after laser installation and the second just before a later maintenance service call. Rainbow glare is a mild optical side effect of femtosecond LASIK. In this study, higher raster energy levels and length of time between service calls were associated with the occurrence of rainbow glare.

Detection of carbon monoxide (CO) in sooting hydrocarbon flames using femtosecond two-photon laser-induced fluorescence (fs-TPLIF)

NASA Astrophysics Data System (ADS)

Wang, Yejun; Kulatilaka, Waruna D.

2018-01-01

Ultrashort-pulse, femtosecond (fs)-duration, two-photon laser-induced fluorescence (fs-TPLIF) measurements of carbon monoxide (CO) are reported in rich, sooting hydrocarbon flames. CO-TPLIF detection using conventional nanosecond or picosecond lasers are often plagued by photochemical interferences, specifically under fuel-rich flames conditions. In the current study, we investigate the commonly used CO two-photon excitation scheme of the B1Σ+ ← X1Σ+ electronic transition, using approximately 100-fs-duration excitation pulses. Fluorescence emission was observed in the Ångström band originating from directly populated B1Σ+ upper state, as well as, in the third positive band from collisionally populated b3Σ+ upper state. The current work was focused on the Ångström band emission. Interference from nascent C2 emissions originating from hot soot particles in the flame could be reduced to a negligible level using a narrower detection gate width. In contrast, avoiding interferences from laser-generated C2 Swan-band emissions required specific narrowband spectral filtering in sooting flame conditions. The observed less than quadratic laser pulse energy dependence of the TPLIF signal suggests the presence of strong three-photon ionization and stimulated emission processes. In a range of CH4/air and C2H4/air premixed flames investigated, the measured CO fluorescence signals agree well with the calculated equilibrium CO number densities. Reduced-interference CO-TPLIF imaging in premixed C2H4/O2/N2 jet flames is also reported.

X-Band, 17-Watt Solid-State Power Amplifier

NASA Technical Reports Server (NTRS)

Mittskus, Anthony; Stone, Ernest; Boger, William; Burgess, David; Honda, Richard; Nuckolls, Carl

2005-01-01

An advanced solid-state power amplifier that can generate an output power of as much as 17 W at a design operating frequency of 8.4 GHz has been designed and constructed as a smaller, lighter, less expensive alternative to traveling-wave-tube X-band amplifiers and to prior solid-state X-band power amplifiers of equivalent output power. This amplifier comprises a monolithic microwave integrated circuit (MMIC) amplifier module and a power-converter module integrated into a compact package (see Figure 1). The amplifier module contains an input variable-gain amplifier (VGA), an intermediate driver stage, a final power stage, and input and output power monitors (see Figure 2). The VGA and the driver amplifier are 0.5-m GaAs-based metal semiconductor field-effect transistors (MESFETs). The final power stage contains four parallel high-efficiency, GaAs-based pseudomorphic high-electron-mobility transistors (PHEMTs). The gain of the VGA is voltage-variable over a range of 10 to 24 dB. To provide for temperature compensation of the overall amplifier gain, the gain-control voltage is generated by an operational-amplifier circuit that includes a resistor/thermistor temperature-sensing network. The driver amplifier provides a gain of 14 dB to an output power of 27 dBm to drive the four parallel output PHEMTs, each of which is nominally capable of putting out as much as 5 W. The driver output is sent to the input terminals of the four parallel PHEMTs through microstrip power dividers; the outputs of these PHEMTs are combined by microstrip power combiners (which are similar to the microstrip power dividers) to obtain the final output power of 17 W.

Femtosecond x rays link melting of charge-density wave correlations and light-enhanced coherent transport in YB a 2 C u 3 O 6.6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Först, M.; Frano, A.; Kaiser, S.

2014-11-17

In this study, we use femtosecond resonant soft x-ray diffraction to measure the optically stimulated ultrafast changes of charge density wave correlations in underdoped YBa₂Cu₃O₆.₆. We find that when coherent interlayer transport is enhanced by optical excitation of the apical oxygen distortions, at least 50% of the in-plane charge density wave order is melted. These results indicate that charge ordering and superconductivity may be competing up to the charge ordering transition temperature, with the latter becoming a hidden phase that is accessible only by nonlinear phonon excitation.

Fluorinated graphene oxide for enhanced S and X-band microwave absorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sudeep, P. M.; TIFR-Centre for Interdisciplinary Sciences, Tata Institute of Fundamental Research, Hyderabad 500075; Vinayasree, S.

2015-06-01

Here we report the microwave absorbing properties of three graphene derivatives, namely, graphene oxide (GO), fluorinated GO (FGO, containing 5.6 at. % Fluorine (F)), and highly FGO (HFGO, containing 23 at. % F). FGO is known to be exhibiting improved electrochemical and electronic properties when compared to GO. Fluorination modifies the dielectric properties of GO and hence thought of as a good microwave absorber. The dielectric permittivities of GO, FGO, and HFGO were estimated in the S (2 GHz to 4 GHz) and X (8 GHz to 12 GHz) bands by employing cavity perturbation technique. For this, suspensions containing GO/FGO/HFGO were made in N-Methylmore » Pyrrolidone (NMP) and were subjected to cavity perturbation. The reflection loss was then estimated and it was found that −37 dB (at 3.2 GHz with 6.5 mm thickness) and −31 dB (at 2.8 GHz with 6 mm thickness) in the S band and a reflection loss of −18 dB (at 8.4 GHz with 2.5 mm thickness) and −10 dB (at 11 GHz with 2 mm thickness) in the X band were achieved for 0.01 wt. % of FGO and HFGO in NMP, respectively, suggesting that these materials can serve as efficient microwave absorbers even at low concentrations.« less

The broad-band X-ray spectral variability of Mrk 841

NASA Technical Reports Server (NTRS)

George, I. M.; Nandra, K.; Fabian, A. C.; Turner, T. J.; Done, C.; Day, C. S. R.

1993-01-01

A detailed spectral analysis of five X-ray observations of Mrk 841 with the EXOSAT, Ginga, and ROSAT satellites is reported. Variability is apparent in both the soft (0.1-1.0 keV) and medium (1-20 keV) energy bands. Above, 1 keV, the spectra are adequately modeled by a power law with a strong emission line of equivalent width 450 eV. The large equivalent width of the emission line indicates a strongly enhanced reflection component of the source compared with other Seyferts observed with Ginga. The implications of the results of the analysis for physical models of the emission regions in this and other X-ray bright Seyferts are briefly examined.

Extraction of Late Summer Sea Ice Properties from Polarimetric SAR Features in C- and X-Band

NASA Astrophysics Data System (ADS)

Fors, Ane S.; Brekke, Camilla; Gerland, Sebastian; Doulgeris, Anthony P.; Eltoft, Torbjørn

2015-04-01

In this study we examine the potential use of six polarimetric features for interpretation of late summer sea ice types. Five high-resolution C and X-band scenes were recorded in the Fram Strait covering fast first-year and old sea ice. In addition sea ice thickness, surface roughness and melt pond fraction were collected during a helicopter flight at the study area. From the SAR scenes, six polarimetric features were extracted. Along sections of the track of the helicopter flight, the mean of the SAR features were compared to mean values of the properties measured during the helicopter flight. The results reveal relations between several of the SAR features and the geophysical properties measured in C-band, and weak relations in X-band.

Femtosecond laser in laser in situ keratomileusis

PubMed Central

Salomão, Marcella Q.; Wilson, Steven E.

2014-01-01

Flap creation is a critical step in laser in situ keratomileusis (LASIK). Efforts to improve the safety and predictability of the lamellar incision have fostered the development of femtosecond lasers. Several advantages of the femtosecond laser over mechanical microkeratomes have been reported in LASIK surgery. In this article, we review common considerations in management and complications of this step in femtosecond laser–LASIK and concentrate primarily on the IntraLase laser because most published studies relate to this instrument. PMID:20494777

The room temperature crystal structure of a bacterial phytochrome determined by serial femtosecond crystallography

DOE PAGES

Edlund, Petra; Takala, Heikki; Claesson, Elin; ...

2016-10-19

Phytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser. We find overall good agreement compared to a crystal structure at 1.35 Å resolution derived frommore » conventional crystallography at cryogenic temperatures, which we also report here. The thioether linkage between chromophore and protein is subject to positional ambiguity at the synchrotron, but is fully resolved with SFX. As a result, the study paves the way for time-resolved structural investigations of the phytochrome photocycle with time-resolved SFX.« less

The room temperature crystal structure of a bacterial phytochrome determined by serial femtosecond crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edlund, Petra; Takala, Heikki; Claesson, Elin

Phytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser. We find overall good agreement compared to a crystal structure at 1.35 Å resolution derived frommore » conventional crystallography at cryogenic temperatures, which we also report here. The thioether linkage between chromophore and protein is subject to positional ambiguity at the synchrotron, but is fully resolved with SFX. As a result, the study paves the way for time-resolved structural investigations of the phytochrome photocycle with time-resolved SFX.« less

DSN 100-meter X and S band microwave antenna design and performance

NASA Technical Reports Server (NTRS)

Williams, W. F.

1978-01-01

The RF performance is studied for large reflector antenna systems (100 meters) when using the high efficiency dual shaped reflector approach. An altered phase was considered so that the scattered field from a shaped surface could be used in the JPL efficiency program. A new dual band (X-S) microwave feed horn was used in the shaping calculations. A great many shaping calculations were made for various horn sizes and locations and final RF efficiencies are reported. A conclusion is reached that when using the new dual band horn, shaping should probably be performed using the pattern of the lower frequency

Laser-Induced Damage with Femtosecond Pulses

NASA Astrophysics Data System (ADS)

Kafka, Kyle R. P.

The strong electric fields of focused femtosecond laser pulses lead to non-equilibrium dynamics in materials, which, beyond a threshold intensity, causes laser-induced damage (LID). Such a strongly non-linear and non-perturbative process renders important LID observables like fluence and intensity thresholds and damage morphology (crater) extremely difficult to predict quantitatively. However, femtosecond LID carries a high degree of precision, which has been exploited in various micro/nano-machining and surface engineering applications, such as human eye surgery and super-hydrophobic surfaces. This dissertation presents an array of experimental studies which have measured the damage behavior of various materials under femtosecond irradiation. Precision experiments were performed to produce extreme spatio-temporal confinement of the femtosecond laser-solid damage interaction on monocrystalline Cu, which made possible the first successful direct-benchmarking of LID simulation with realistic damage craters. A technique was developed to produce laser-induced periodic surface structures (LIPSS) in a single pulse (typically a multi-pulse phenomenon), and was used to perform a pump-probe study which revealed asynchronous LIPSS formation on copper. Combined with 1-D calculations, this new experimental result suggests more drastic electron heating than expected. Few-cycle pulses were used to study the LID performance and morphology of commercial ultra-broadband optics, which had not been systematically studied before. With extensive surface analysis, various morphologies were observed, including LIPSS, swelling (blisters), simple craters, and even ring-shaped structures, which varied depending on the coating design, number of pulses, and air/vacuum test environment. Mechanisms leading to these morphologies are discussed, many of which are ultrafast in nature. The applied damage behavior of multi-layer dielectric mirrors was measured and compared between long pulse (150 ps

The Atomic, Molecular and Optical Science instrument at the Linac Coherent Light Source

DOE PAGES

Ferguson, Ken R.; Bucher, Maximilian; Bozek, John D.; ...

2015-05-01

The Atomic, Molecular and Optical Science (AMO) instrument at the Linac Coherent Light Source (LCLS) provides a tight soft X-ray focus into one of three experimental endstations. The flexible instrument design is optimized for studying a wide variety of phenomena requiring peak intensity. There is a suite of spectrometers and two photon area detectors available. An optional mirror-based split-and-delay unit can be used for X-ray pump–probe experiments. Recent scientific highlights illustrate the imaging, time-resolved spectroscopy and high-power density capabilities of the AMO instrument.

Femtosecond Electron and Photon Pulses Facility in Thailand

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rimjaem, S.; Thongbai, C.; Jinamoon, V.

Femtosecond electron and photon pulses facility has been established as SURIYA project at the Fast Neutron Research Facility (FNRF). Femtosecond electron bunches can be generated from a system consisting of an RF gun with a thermionic cathode, an alpha magnet as an magnetic bunch compressor, and a linear accelerator as a post acceleration section. Femtosecond electron pulses can be used directly or used as a source to produce equally short electromagnetic (EM) radiation pulses via certain kind of radiation production processes. At SURIYA project, we are interested especially in production of radiation in Far-infrared (FIR) regime. At these wavelengths, themore » radiation from femtosecond electron pulses is emitted coherently resulting in high intensity radiation. Overview of the facility, the generation of femtosecond electron bunches, the theoretical background of coherent transition radiation and the recent experimental results will be presented and discussed in this paper.« less

Composition and Band Gap Tailoring of Crystalline (GaN)1- x(ZnO) x Solid Solution Nanowires for Enhanced Photoelectrochemical Performance.

PubMed

Li, Jing; Liu, Baodan; Wu, Aimin; Yang, Bing; Yang, Wenjin; Liu, Fei; Zhang, Xinglai; An, Vladimir; Jiang, Xin

2018-05-07

Photoelectrochemical water splitting has emerged as an effective artificial photosynthesis technology to generate clean energy of H 2 from sunlight. The core issue in this reaction system is to develop a highly efficient photoanode with a large fraction of solar light absorption and greater active surface area. In this work, we take advantage of energy band engineering to synthesize (GaN) 1- x (ZnO) x solid solution nanowires with ZnO contents ranging from 10.3% to 47.6% and corresponding band gap tailoring from 3.08 to 2.77 eV on the basis of the Au-assisted VLS mechanism. The morphology of nanowires directly grown on the conductive substrate facilitates the charge transfer and simultaneously improves the surface reaction sites. As a result, a photocurrent approximately 10 times larger than that for a conventional powder-based photoanode is obtained, which indicates the potential of (GaN) 1- x (ZnO) x nanowires in the preparation of superior photoanodes for enhanced water splitting. It is anticipated that the water-splitting capability of (GaN) 1- x (ZnO) x nanowire can be further increased through alignment control for enhanced visible light absorption and reduction of charge transfer resistance.

Physics design of APT linac with normal conducting rf cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nath, S.; Billen, J.H.; Stovall, J.E.

The accelerator based production of tritium calls for a high-power, cw proton linac. Previous designs for such a linac use a radiofrequency quadrupole (RFQ), followed by a drift-tube linac (DTL) to an intermediate energy and a coupled-cavity linc (CCL) to the final energy. The Los Alamos design uses a high-energy (6.7 MeV) RFQ followed by the newly developed coupled-cavity drift-tube linac (CCDTL) and a CCL. This design accommodates external electromagnetic quadrupole lenses which provide a strong uniform focusing lattice from the end of the RFQ to the end of the CCL. The cell lengths in linacs of traditional design aremore » typically graded as a function of particle velocity. By making groups of cells symmetric in both the CCDTL and CCL, the cavity design as well as mechanical design and fabrication is simplified without compromising the performance. At higher energies, there are some advantages of using superconducting rf cavities. Currently, such schemes are under vigorous study. This paper describes the linac design based on normal conducting cavities and presents simulation results.« less

Overtaking collision effects in a cw double-pass proton linac

DOE PAGES

Tao, Yue; Qiang, Ji; Hwang, Kilean

2017-12-22

The recirculating superconducting proton linac has the advantage of reducing the number of cavities in the accelerator and the corresponding construction and operational costs. Beam dynamics simulations were done recently in a double-pass recirculating proton linac using a single proton beam bunch. For continuous wave (cw) operation, the high-energy proton bunch during the second pass through the linac will overtake and collide with the low-energy bunch during the first pass at a number of locations of the linac. These collisions might cause proton bunch emittance growth and beam quality degradation. Here, we study the collisional effects due to Coulomb space-chargemore » forces between the high-energy bunch and the low-energy bunch. Our results suggest that these effects on the proton beam quality would be small and might not cause significant emittance growth or beam blowup through the linac. A 10 mA, 500 MeV cw double-pass proton linac is feasible without using extra hardware for phase synchronization.« less

Overtaking collision effects in a cw double-pass proton linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Yue; Qiang, Ji; Hwang, Kilean

The recirculating superconducting proton linac has the advantage of reducing the number of cavities in the accelerator and the corresponding construction and operational costs. Beam dynamics simulations were done recently in a double-pass recirculating proton linac using a single proton beam bunch. For continuous wave (cw) operation, the high-energy proton bunch during the second pass through the linac will overtake and collide with the low-energy bunch during the first pass at a number of locations of the linac. These collisions might cause proton bunch emittance growth and beam quality degradation. Here, we study the collisional effects due to Coulomb space-chargemore » forces between the high-energy bunch and the low-energy bunch. Our results suggest that these effects on the proton beam quality would be small and might not cause significant emittance growth or beam blowup through the linac. A 10 mA, 500 MeV cw double-pass proton linac is feasible without using extra hardware for phase synchronization.« less

Cornell-BNL Electron Energy Recovery Linac FFAG Test Accelerator (CBETA)

NASA Astrophysics Data System (ADS)

Trbojevic, Dejan; Peggs, Steve; Berg, Scott; Brooks, Stephen; Mahler, George; Meot, Francois; Tsoupas, Nicholaos; Witte, Holger; Hoffstaetter, Georg; Bazarov, Ivan; Mayes, Christopher; Patterson, Ritchie; Smolenski, Karl; Li, Yulin; Dobbins, John; BNL Team; Cornell University Team

A novel energy recovery linac (ERL) with Non-Scaling Fixed Field Alternating Gradient (NS-FFAG) racetrack is being constructed as a result of collaboration of the Cornell University with Brookhaven National Laboratory. The existing injector and superconducting linac at Cornell University are being installed together with a single NS-FFAG arcs and straight section at the opposite side of the linac to form an ERL system. The 6 MeV electron beam from injector is transferred into the 36 MeV superconducting linac and accelerated by four successive passes: from 42 to 150 MeV using the same NS-FFAG structure made of permanent magnets. After the maximum energy of 150 MeV is reached, the electron beam is brought back to the linac with opposite Radio Frequency (RF) phase and with 4 passes electron energy is recovered and brought back to the initial energy of 6 MeV. This is going to be the first 4 pass superconducting ERL and the first NS-FFAG permanent magnet structure to bring the electron beam back to the linac.

A novel electron gun for inline MRI-linac configurations.

PubMed

Constantin, Dragoş E; Holloway, Lois; Keall, Paul J; Fahrig, Rebecca

2014-02-01

This work introduces a new electron gun geometry capable of robust functioning in the presence of a high strength external magnetic field for axisymmetric magnetic resonance imaging (MRI)-linac configurations. This allows an inline MRI-linac to operate without the need to isolate the linear accelerator (linac) using a magnetic shield. This MRI-linac integration approach not only leaves the magnet homogeneity unchanged but also provides the linac flexibility to move along the magnet axis of symmetry if the source to target distance needs to be adjusted. Simple electron gun geometry modifications of a Varian 600 C electron gun are considered and solved in the presence of an external magnetic field in order to determine a set of design principles for the new geometry. Based on these results, a new gun geometry is proposed and optimized in the fringe field of a 0.5 T open bore MRI magnet (GE Signa SP). A computer model for the 6 MeV Varian 600 C linac is used to determine the capture efficiency of the new electron gun-linac system in the presence of the fringe field of the same MRI scanner. The behavior of the new electron gun plus the linac system is also studied in the fringe fields of two other magnets, a 1.0 T prototype open bore magnet and a 1.5 T GE Conquest scanner. Simple geometrical modifications of the original electron gun geometry do not provide feasible solutions. However, these tests show that a smaller transverse cathode diameter with a flat surface and a slightly larger anode diameter could alleviate the current loss due to beam interactions with the anode in the presence of magnetic fields. Based on these findings, an initial geometry resembling a parallel plate capacitor with a hole in the anode is proposed. The optimization procedure finds a cathode-anode distance of 5 mm, a focusing electrode angle of 5°, and an anode drift tube length of 17.1 mm. Also, the linac can be displaced with ± 15 cm along the axis of the 0.5 T magnet without capture

A novel electron gun for inline MRI-linac configurations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Constantin, Dragoş E., E-mail: dragos.constantin@varian.com; Fahrig, Rebecca; Holloway, Lois

2014-02-15

Purpose: This work introduces a new electron gun geometry capable of robust functioning in the presence of a high strength external magnetic field for axisymmetric magnetic resonance imaging (MRI)-linac configurations. This allows an inline MRI-linac to operate without the need to isolate the linear accelerator (linac) using a magnetic shield. This MRI-linac integration approach not only leaves the magnet homogeneity unchanged but also provides the linac flexibility to move along the magnet axis of symmetry if the source to target distance needs to be adjusted. Methods: Simple electron gun geometry modifications of a Varian 600C electron gun are considered andmore » solved in the presence of an external magnetic field in order to determine a set of design principles for the new geometry. Based on these results, a new gun geometry is proposed and optimized in the fringe field of a 0.5 T open bore MRI magnet (GE Signa SP). A computer model for the 6 MeV Varian 600C linac is used to determine the capture efficiency of the new electron gun-linac system in the presence of the fringe field of the same MRI scanner. The behavior of the new electron gun plus the linac system is also studied in the fringe fields of two other magnets, a 1.0 T prototype open bore magnet and a 1.5 T GE Conquest scanner. Results: Simple geometrical modifications of the original electron gun geometry do not provide feasible solutions. However, these tests show that a smaller transverse cathode diameter with a flat surface and a slightly larger anode diameter could alleviate the current loss due to beam interactions with the anode in the presence of magnetic fields. Based on these findings, an initial geometry resembling a parallel plate capacitor with a hole in the anode is proposed. The optimization procedure finds a cathode-anode distance of 5 mm, a focusing electrode angle of 5°, and an anode drift tube length of 17.1 mm. Also, the linac can be displaced with ±15 cm along the axis of the 0

A novel electron gun for inline MRI-linac configurations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Constantin, Dragoş E., E-mail: dragos.constantin@varian.com; Fahrig, Rebecca; Holloway, Lois

Purpose: This work introduces a new electron gun geometry capable of robust functioning in the presence of a high strength external magnetic field for axisymmetric magnetic resonance imaging (MRI)-linac configurations. This allows an inline MRI-linac to operate without the need to isolate the linear accelerator (linac) using a magnetic shield. This MRI-linac integration approach not only leaves the magnet homogeneity unchanged but also provides the linac flexibility to move along the magnet axis of symmetry if the source to target distance needs to be adjusted. Methods: Simple electron gun geometry modifications of a Varian 600C electron gun are considered andmore » solved in the presence of an external magnetic field in order to determine a set of design principles for the new geometry. Based on these results, a new gun geometry is proposed and optimized in the fringe field of a 0.5 T open bore MRI magnet (GE Signa SP). A computer model for the 6 MeV Varian 600C linac is used to determine the capture efficiency of the new electron gun-linac system in the presence of the fringe field of the same MRI scanner. The behavior of the new electron gun plus the linac system is also studied in the fringe fields of two other magnets, a 1.0 T prototype open bore magnet and a 1.5 T GE Conquest scanner. Results: Simple geometrical modifications of the original electron gun geometry do not provide feasible solutions. However, these tests show that a smaller transverse cathode diameter with a flat surface and a slightly larger anode diameter could alleviate the current loss due to beam interactions with the anode in the presence of magnetic fields. Based on these findings, an initial geometry resembling a parallel plate capacitor with a hole in the anode is proposed. The optimization procedure finds a cathode-anode distance of 5 mm, a focusing electrode angle of 5°, and an anode drift tube length of 17.1 mm. Also, the linac can be displaced with ±15 cm along the axis of the 0

Band gap and mobility of epitaxial perovskite BaSn1 -xHfxO3 thin films

NASA Astrophysics Data System (ADS)

Shin, Juyeon; Lim, Jinyoung; Ha, Taewoo; Kim, Young Mo; Park, Chulkwon; Yu, Jaejun; Kim, Jae Hoon; Char, Kookrin

2018-02-01

A wide band-gap perovskite oxide BaSn O3 is attracting much attention due to its high electron mobility and oxygen stability. On the other hand, BaHf O3 was recently reported to be an effective high-k gate oxide. Here, we investigate the band gap and mobility of solid solutions of BaS n1 -xH fxO3 (x =0 -1 ) (BSHO) as a basis to build advanced perovskite oxide heterostructures. All the films were epitaxially grown on MgO substrates using pulsed laser deposition. Density functional theory calculations confirmed that Hf substitution does not create midgap states while increasing the band gap. From x-ray diffraction and optical transmittance measurements, the lattice constants and the band-gap values are significantly modified by Hf substitution. We also measured the transport properties of n -type La-doped BSHO films [(Ba ,La ) (Sn ,Hf ) O3 ] , investigating the feasibility of modulation doping in the BaSn O3/BSHO heterostructures. The Hall measurement data revealed that, as the Hf content increases, the activation rate of the La dopant decreases and the scattering rate of the electrons sharply increases. These properties of BSHO films may be useful for applications in various heterostructures based on the BaSn O3 system.

Evaluating the potential use of a high-resolution X-band polarimetric radar observations in Urban Hydrology

NASA Astrophysics Data System (ADS)

Anagnostou, Marios N.; Kalogiros, John; Marzano, Frank S.; Anagnostou, Emmanouil N.; Baldini, Luca; Nikolopoulos, EfThymios; Montopoli, Mario; Picciotti, Errico

2014-05-01

The Mediterranean area concentrates the major natural risks related to the water cycle, including heavy precipitation and flash-flooding during the fall season. Every year in central and south Europe we witness several fatal and economical disasters from severe storm rainfall triggering Flash Floods, and its impacts are increasing worldwide, but remain very difficult to manage. The spatial scale of flash flood occurrence is such that its vulnerability is often focused on dispersed urbanization, transportation and tourism infrastructures (De Marchi and Scolobig 2012). Urbanized and industrialized areas shows peculiar hydrodynamic and meteo-oceanographic features and they concentrate the highest rates of flash floods and fatal disasters. The main causes of disturbance being littoral urban development and harbor activities, the building of littoral rail- and highways, and the presence of several polluted discharges. All the above mentioned characteristics limit our ability to issue timely flood warnings. Precipitation estimates based on raingauge networks are usually associated with low coverage density, particularly at high altitudes. On the other hand, operational weather radar networks may provide valuable information of precipitation at these regimes but reliability of their estimates is often limited due to retrieval (e.g. variability in the reflectivity-to-rainfall relationship) and spatial extent constrains (e.g. blockage issues, overshooting effects). As a result, we currently lack accurate precipitation estimates over urban complex terrain areas, which essentially means that we lack accurate knowledge of the triggering factor for a number of hazards like flash floods and debris flows/landslides occurring in those areas. A potential solution to overcome sampling as well as retrieval uncertainty limitations of current observational networks might be the use of network of low-power dual-polarization X-band radars as complement to raingauges and gap-filling to

Formation of aggregated nanoparticle spheres through femtosecond laser surface processing

NASA Astrophysics Data System (ADS)

Tsubaki, Alfred T.; Koten, Mark A.; Lucis, Michael J.; Zuhlke, Craig; Ianno, Natale; Shield, Jeffrey E.; Alexander, Dennis R.

2017-10-01

A detailed structural and chemical analysis of a class of self-organized surface structures, termed aggregated nanoparticle spheres (AN-spheres), created using femtosecond laser surface processing (FLSP) on silicon, silicon carbide, and aluminum is reported in this paper. AN-spheres are spherical microstructures that are 20-100 μm in diameter and are composed entirely of nanoparticles produced during femtosecond laser ablation of material. AN-spheres have an onion-like layered morphology resulting from the build-up of nanoparticle layers over multiple passes of the laser beam. The material properties and chemical composition of the AN-spheres are presented in this paper based on scanning electron microscopy (SEM), focused ion beam (FIB) milling, transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX) analysis. There is a distinct difference in the density of nanoparticles between concentric rings of the onion-like morphology of the AN-sphere. Layers of high-density form when the laser sinters nanoparticles together and low-density layers form when nanoparticles redeposit while the laser ablates areas surrounding the AN-sphere. The dynamic nature of femtosecond laser ablation creates a variety of nanoparticles that make-up the AN-spheres including Si/C core-shell, nanoparticles that directly fragmented from the base material, nanoparticles with carbon shells that retarded oxidation, and amorphous, fully oxidized nanoparticles.

Acoustic Injectors for Drop-On-Demand Serial Femtosecond Crystallography.

PubMed

Roessler, Christian G; Agarwal, Rakhi; Allaire, Marc; Alonso-Mori, Roberto; Andi, Babak; Bachega, José F R; Bommer, Martin; Brewster, Aaron S; Browne, Michael C; Chatterjee, Ruchira; Cho, Eunsun; Cohen, Aina E; Cowan, Matthew; Datwani, Sammy; Davidson, Victor L; Defever, Jim; Eaton, Brent; Ellson, Richard; Feng, Yiping; Ghislain, Lucien P; Glownia, James M; Han, Guangye; Hattne, Johan; Hellmich, Julia; Héroux, Annie; Ibrahim, Mohamed; Kern, Jan; Kuczewski, Anthony; Lemke, Henrik T; Liu, Pinghua; Majlof, Lars; McClintock, William M; Myers, Stuart; Nelsen, Silke; Olechno, Joe; Orville, Allen M; Sauter, Nicholas K; Soares, Alexei S; Soltis, S Michael; Song, Heng; Stearns, Richard G; Tran, Rosalie; Tsai, Yingssu; Uervirojnangkoorn, Monarin; Wilmot, Carrie M; Yachandra, Vittal; Yano, Junko; Yukl, Erik T; Zhu, Diling; Zouni, Athina

2016-04-05

X-ray free-electron lasers (XFELs) provide very intense X-ray pulses suitable for macromolecular crystallography. Each X-ray pulse typically lasts for tens of femtoseconds and the interval between pulses is many orders of magnitude longer. Here we describe two novel acoustic injection systems that use focused sound waves to eject picoliter to nanoliter crystal-containing droplets out of microplates and into the X-ray pulse from which diffraction data are collected. The on-demand droplet delivery is synchronized to the XFEL pulse scheme, resulting in X-ray pulses intersecting up to 88% of the droplets. We tested several types of samples in a range of crystallization conditions, wherein the overall crystal hit ratio (e.g., fraction of images with observable diffraction patterns) is a function of the microcrystal slurry concentration. We report crystal structures from lysozyme, thermolysin, and stachydrine demethylase (Stc2). Additional samples were screened to demonstrate that these methods can be applied to rare samples. Copyright © 2016 Elsevier Ltd. All rights reserved.

Acoustic Injectors for Drop-On-Demand Serial Femtosecond Crystallography

DOE PAGES

Roessler, Christian G.; Agarwal, Rakhi; Allaire, Marc; ...

2016-03-17

X-ray free-electron lasers (XFELs) provide very intense X-ray pulses suitable for macromolecular crystallography. Each X-ray pulse typically lasts for tens of femtoseconds and the interval between pulses is many orders of magnitude longer. Here we describe two novel acoustic injection systems that use focused sound waves to eject picoliter to nanoliter crystal-containing droplets out of microplates and into the X-ray pulse from which diffraction data are collected. The on-demand droplet delivery is synchronized to the XFEL pulse scheme, resulting in X-ray pulses intersecting up to 88% of the droplets. We tested several types of samples in a range of crystallizationmore » conditions, wherein the overall crystal hit ratio (e.g., fraction of images with observable diffraction patterns) is a function of the microcrystal slurry concentration. Lastly, we report crystal structures from lysozyme, thermolysin, and stachydrine demethylase (Stc2). In addition, samples were screened to demonstrate that these methods can be applied to rare samples« less

Acoustic Injectors for Drop-On-Demand Serial Femtosecond Crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roessler, Christian G.; Agarwal, Rakhi; Allaire, Marc

X-ray free-electron lasers (XFELs) provide very intense X-ray pulses suitable for macromolecular crystallography. Each X-ray pulse typically lasts for tens of femtoseconds and the interval between pulses is many orders of magnitude longer. Here we describe two novel acoustic injection systems that use focused sound waves to eject picoliter to nanoliter crystal-containing droplets out of microplates and into the X-ray pulse from which diffraction data are collected. The on-demand droplet delivery is synchronized to the XFEL pulse scheme, resulting in X-ray pulses intersecting up to 88% of the droplets. We tested several types of samples in a range of crystallizationmore » conditions, wherein the overall crystal hit ratio (e.g., fraction of images with observable diffraction patterns) is a function of the microcrystal slurry concentration. We report crystal structures from lysozyme, thermolysin, and stachydrine demethylase (Stc2). Additional samples were screened to demonstrate that these methods can be applied to rare samples.« less

Acoustic Injectors for Drop-On-Demand Serial Femtosecond Crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roessler, Christian G.; Agarwal, Rakhi; Allaire, Marc

X-ray free-electron lasers (XFELs) provide very intense X-ray pulses suitable for macromolecular crystallography. Each X-ray pulse typically lasts for tens of femtoseconds and the interval between pulses is many orders of magnitude longer. Here we describe two novel acoustic injection systems that use focused sound waves to eject picoliter to nanoliter crystal-containing droplets out of microplates and into the X-ray pulse from which diffraction data are collected. The on-demand droplet delivery is synchronized to the XFEL pulse scheme, resulting in X-ray pulses intersecting up to 88% of the droplets. We tested several types of samples in a range of crystallizationmore » conditions, wherein the overall crystal hit ratio (e.g., fraction of images with observable diffraction patterns) is a function of the microcrystal slurry concentration. Lastly, we report crystal structures from lysozyme, thermolysin, and stachydrine demethylase (Stc2). In addition, samples were screened to demonstrate that these methods can be applied to rare samples« less

Waveguide detuning caused by transverse magnetic fields on a simulated in-line 6 MV linac.

PubMed

St Aubin, J; Steciw, S; Fallone, B G

2010-09-01

Due to the close proximity of the linear accelerator (linac) to the magnetic resonance (MR) imager in linac-MR systems, it will be subjected to magnet fringe fields larger than the Earth's magnetic field of 5 x 10(-5) T. Even with passive or active shielding designed to reduce these fields, some magnitude of the magnetic field is still expected to intersect the linac, causing electron deflection and beam loss. This beam loss, resulting from magnetic fields that cannot be eliminated with shielding, can cause a detuning of the waveguide due to excessive heating. The detuning, if significant, could lead to an even further decrease in output above what would be expected strictly from electron deflections caused by an external magnetic field. Thus an investigation of detuning was performed through various simulations. According to the Lorentz force, the electrons will be deflected away from their straight course to the target, depositing energy as they impact the linac copper waveguide. The deposited energy would lead to a heating and deformation of the copper structure resulting in resonant frequency changes. PARMELA was used to determine the mean energy and fraction of total beam lost in each linac cavity. The energy deposited into the copper waveguide from the beam losses caused by transverse magnetic fields was calculated using the Monte Carlo program DOSRZnrc. From the total energy deposited, the rise in temperature and ultimately the deformation of the structure was estimated. The deformed structure was modeled using the finite element method program COMSOL MULTIPHYSICS to determine the change in cavity resonant frequency. The largest changes in resonant frequency were found in the first two accelerating cavities for each field strength investigated. This was caused by a high electron fluence impacting the waveguide inner structures coupled with their low kinetic energies. At each field strength investigated, the total change in accelerator frequency was less than

Femtosecond parabolic pulse shaping in normally dispersive optical fibers.

PubMed

Sukhoivanov, Igor A; Iakushev, Sergii O; Shulika, Oleksiy V; Díez, Antonio; Andrés, Miguel

2013-07-29

Formation of parabolic pulses at femtosecond time scale by means of passive nonlinear reshaping in normally dispersive optical fibers is analyzed. Two approaches are examined and compared: the parabolic waveform formation in transient propagation regime and parabolic waveform formation in the steady-state propagation regime. It is found that both approaches could produce parabolic pulses as short as few hundred femtoseconds applying commercially available fibers, specially designed all-normal dispersion photonic crystal fiber and modern femtosecond lasers for pumping. The ranges of parameters providing parabolic pulse formation at the femtosecond time scale are found depending on the initial pulse duration, chirp and energy. Applicability of different fibers for femtosecond pulse shaping is analyzed. Recommendation for shortest parabolic pulse formation is made based on the analysis presented.

Photoinduced coherent acoustic phonon dynamics inside Mott insulator Sr2IrO4 films observed by femtosecond X-ray pulses

NASA Astrophysics Data System (ADS)

Zhang, Bing-Bing; Liu, Jian; Wei, Xu; Sun, Da-Rui; Jia, Quan-Jie; Li, Yuelin; Tao, Ye

2017-04-01

We investigate the transient photoexcited lattice dynamics in a layered perovskite Mott insulator Sr2IrO4 film by femtosecond X-ray diffraction using a laser plasma-based X-ray source. The ultrafast structural dynamics of Sr2IrO4 thin films are determined by observing the shift and broadening of (0012) Bragg diffraction after excitation by 1.5 eV and 3.0 eV pump photons for films with different thicknesses. The observed transient lattice response can be well interpreted as a distinct three-step dynamics due to the propagation of coherent acoustic phonons generated by photoinduced quasiparticles (QPs). Employing a normalized phonon propagation model, we found that the photoinduced angular shifts of the Bragg peak collapse into a universal curve after introducing normalized coordinates to account for different thicknesses and pump photon energies, pinpointing the origin of the lattice distortion and its early evolution. In addition, a transient photocurrent measurement indicates that the photoinduced QPs are charge neutral excitons. Mapping the phonon propagation and correlating its dynamics with the QP by ultrafast X-ray diffraction (UXRD) establish a powerful way to study electron-phonon coupling and uncover the exotic physics in strongly correlated systems under nonequilibrium conditions.

Excitation energy dependence of excited states dynamics in all- trans-carotenes determined by femtosecond absorption and fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Kosumi, Daisuke; Yanagi, Kazuhiro; Nishio, Tomohiro; Hashimoto, Hideki; Yoshizawa, Masayuki

2005-06-01

Ultrafast relaxation kinetics in β-carotene and lycopene has been investigated by femtosecond absorption and fluorescence spectroscopies using tunable excitation pulses. The transient signals induced by the photoexcitation with larger excess energy have broader bands and longer lifetimes both in the 11Bu+and21Ag- excited states. The excess vibrational energy remains longer than several picoseconds and slows the relaxation kinetics in carotenoids.

A laser-Compton scattering prototype experiment at 100 MeV linac of Shanghai Institute of Applied Physics.

PubMed

Luo, W; Xu, W; Pan, Q Y; Cai, X Z; Chen, J G; Chen, Y Z; Fan, G T; Fan, G W; Guo, W; Li, Y J; Liu, W H; Lin, G Q; Ma, Y G; Shen, W Q; Shi, X C; Xu, B J; Xu, J Q; Xu, Y; Zhang, H O; Yan, Z; Yang, L F; Zhao, M H

2010-01-01

As a prototype of the Shanghai Laser Electron Gamma Source in the Shanghai Synchrotron Radiation Facility, an x-ray source based on laser-Compton scattering (LCS) has been installed at the terminal of the 100 MeV linac of the Shanghai Institute of Applied Physics. LCS x-rays are generated by interactions between Q-switched Nd:yttrium aluminum garnet laser pulses [with wavelength of 1064 nm and pulse width of 21 ns (full width at half maximum)] and electron bunches [with energy of 108 MeV and pulse width of 0.95 ns (rms)] at an angle of 42 degrees between laser and electron beam. In order to measure the energy spectrum of LCS x-rays, a Si(Li) detector along the electron beam line axis is positioned at 9.8 m away from a LCS chamber. After background subtraction, the LCS x-ray spectrum with the peak energy of 29.1+/-4.4|(stat)+/-2.1|(syst) keV and the peak width (rms) of 7.8+/-2.8|(stat)+/-0.4|(syst) keV is observed. Normally the 100 MeV linac operates with the electron macropulse charge of 1.0 nC/pulse, and the electron and laser collision repetition rate of 20 Hz. Therefore, the total LCS x-ray flux of (5.2+/-2.0) x 10(2) Hz can be achieved.

Linac design for the European spallation source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klein, H.

1995-10-01

A study group has started to develop a conceptual design for a European Spallation Source (ESS). This pulsed 5 MW source presently consists of a 1.334 GeV linac and two compressor rings. In the following mainly the high intensity linac part will be discussed, which has some features of interest for accelerators for transmutation of radioactive waste too.

High-resolution F T spectrum of A 2 Π r - X 2 Σ + band system of MgCl

NASA Astrophysics Data System (ADS)

Saksena, M. D.; Deo, M. N.; Sunanda, K.; Behere, S. H.; Jadhav, Ashok

2011-03-01

The emission spectrum of the A 2 Π r - X 2 Σ + band system of MgCl molecule (360-380 nm) has been recorded on BOMEM DA8 Fourier transform spectrometer at an apodized resolution of 0.035 cm-1. The spectra have been excited under flowing conditions in a demountable stainless steel hollow cathode lamp (400 V, 250 mA) containing anhydrous MgCl2 and Ar. The resulting spectra are very intense and the 0-0, 1-1, 1-0 bands of A 2 Π 1/2- X 2 Σ + sub-transition and the 0-0 band of A 2 Π 3/2- X 2 Σ + sub-transition have been rotationally analyzed. Improved molecular constants have been derived using a least-squares fit program in which optical data of earlier analyzed 0-1 and 0-2 bands ( A 2 Π 1/2- X 2 Σ +) was also included. The Λ-doubling constants in the v' = 0, 1 levels of the A 2 Π 1/2 sub-state are as expected, i.e. p 1 > p 0, where as it is found that the spin-doubling constants of the v″ = 0, 1 and 2 levels of the ground state X 2 Σ +, decrease with the increase in v, i.e. γ 0 > γ 1 > γ 2. This is indicative of the presence of some nearby state, influencing the spin-doubling.

Band-gap tailoring and visible-light-driven photocatalytic performance of porous (GaN)1-x(ZnO)x solid solution.

PubMed

Wu, Aimin; Li, Jing; Liu, Baodan; Yang, Wenjin; Jiang, Yanan; Liu, Lusheng; Zhang, Xinglai; Xiong, Changmin; Jiang, Xin

2017-02-21

(GaN) 1-x (ZnO) x solid solution has attracted extensive attention due to its feasible band-gap tunability and excellent photocatalytic performance in overall water splitting. However, its potential application in the photodegradation of organic pollutants and environmental processing has rarely been reported. In this study, we developed a rapid synthesis process to fabricate porous (GaN) 1-x (ZnO) x solid solution with a tunable band gap in the range of 2.38-2.76 eV for phenol photodegradation. Under visible-light irradiation, (GaN) 0.75 (ZnO) 0.25 solid solution achieved the highest photocatalytic performance compared to other (GaN) 1-x (ZnO) x solid solutions with x = 0.45, 0.65 and 0.85 due to its higher redox capability and lower lattice deformation. Slight Ag decoration with a content of 1 wt% on the surface of the (GaN) 0.75 (ZnO) 0.25 solid solution leads to a significant enhancement in phenol degradation, with a reaction rate eight times faster than that of pristine (GaN) 0.75 (ZnO) 0.25 . Interestingly, phenol in aqueous solution (10 mg L -1 ) can also be completely degraded within 60 min, even under the direct exposure of sunlight irradiation. The photocurrent response indicates that the enhanced photocatalytic activity of (GaN) 0.75 (ZnO) 0.25 /Ag is directly induced by the improved transfer efficiency of the photogenerated electrons at the interface. The excellent phenol degradation performance of (GaN) 1-x (ZnO) x /Ag further broadens their promising photocatalytic utilization in environmental processing, besides in overall water splitting for hydrogen production.

Late-summer sea ice segmentation with multi-polarisation SAR features in C and X band

NASA Astrophysics Data System (ADS)

Fors, Ane S.; Brekke, Camilla; Doulgeris, Anthony P.; Eltoft, Torbjørn; Renner, Angelika H. H.; Gerland, Sebastian

2016-02-01

In this study, we investigate the potential of sea ice segmentation by C- and X-band multi-polarisation synthetic aperture radar (SAR) features during late summer. Five high-resolution satellite SAR scenes were recorded in the Fram Strait covering iceberg-fast first-year and old sea ice during a week with air temperatures varying around 0 °C. Sea ice thickness, surface roughness and aerial photographs were collected during a helicopter flight at the site. Six polarimetric SAR features were extracted for each of the scenes. The ability of the individual SAR features to discriminate between sea ice types and their temporal consistency were examined. All SAR features were found to add value to sea ice type discrimination. Relative kurtosis, geometric brightness, cross-polarisation ratio and co-polarisation correlation angle were found to be temporally consistent in the investigated period, while co-polarisation ratio and co-polarisation correlation magnitude were found to be temporally inconsistent. An automatic feature-based segmentation algorithm was tested both for a full SAR feature set and for a reduced SAR feature set limited to temporally consistent features. In C band, the algorithm produced a good late-summer sea ice segmentation, separating the scenes into segments that could be associated with different sea ice types in the next step. The X-band performance was slightly poorer. Excluding temporally inconsistent SAR features improved the segmentation in one of the X-band scenes.

Search for the OH (X(2)Pi) Meinel band emission in meteors as a tracer of mineral water in comets: detection of N(2)(+) (A-X)

NASA Technical Reports Server (NTRS)

Jenniskens, Peter; Laux, Christophe O.

2004-01-01

We report the discovery of the N(2)(+) A-X Meinel band in the 780-840 nm meteor emission from two Leonid meteoroids that were ejected less than 1000 years ago by comet 55P/Tempel-Tuttle. Our analysis indicates that the N(2)(+) molecule is at least an order of magnitude less abundant than expected, possibly as a result of charge transfer reactions with meteoric metal atoms. This new band was found while searching for rovibrational transitions in the X(2)Pi electronic ground state of OH (the OH Meinel band), a potential tracer of water bound to minerals in cometary matter. The electronic A-X transition of OH has been identified in other Leonid meteors. We did not detect this OH Meinel band, which implies that the excited A state is not populated by thermal excitation but by a mechanism that directly produces OH in low vibrational levels of the excited A(2)Sigma state. Ultraviolet dissociation of atmospheric or meteoric water vapor is such a mechanism, as is the possible combustion of meteoric organics.

Band gap and band offset of (GaIn)(PSb) lattice matched to InP

NASA Astrophysics Data System (ADS)

Köhler, F.; Böhm, G.; Meyer, R.; Amann, M.-C.

2005-07-01

Metastable (GaxIn1-x)(PySb1-y) layers were grown on (001) InP substrates by gas source molecular beam epitaxy. Low-temperature photoluminescence spectroscopy was applied to these heterostructures and revealed spatially indirect band-to-band recombination of electrons localized in the InP with holes in the (GaxIn1-x)(PySb1-y). In addition, samples with layer thicknesses larger than 100nm showed direct PL across the band gap of (GaxIn1-x)(PySb1-y). Band-gap energies and band offset energies of (GaxIn1-x)(PySb1-y) relative to InP were derived from these PL data. A strong bowing parameter was observed.

Ultrafast Carrier dynamics of InxGa1-xN nanostructures grown directly on Si(111)

NASA Astrophysics Data System (ADS)

Kumar, Praveen; Devi, Pooja; Rodriguez⁠, P. E. D. S.; Kumar, Manish; Shivling, V. D.; Noetzel, Richard; Sharma, Chhavi; Sinha, R. K.; Kumar, Mahesh

2018-05-01

We show a flux dependence changes in structural, optical and electronic properties of InxGa1-xN nanostructures (NSs) namely nanocolumns (NCs), nanoflakes (NFs) and nanowall network (NWN) grown directly on Si(111) surface. Field emission scanning electron microscopy (FESEM) images were recorded to see morphological changes from NFs to NCs and NWNc etc, while high-resolution X-ray diffraction (HRXRD) ω-2θ scans were used to determine In incorporation. The maximum In incorporation was observed to be 20, 33 and 38% for the sharp transition from NFs to NCs and NWNs, respectively. The charge carrier dynamics of these grown NSs were probed using Ultrafast Femtosecond Transient Absorption Spectroscopy (UFTAS) with excitation at 350 nm pump wavelength. The UFTAS studies show the comparative charge carriers dynamics of the NWS, NCs and NFs. The charge carrier studies show a higher lifetime in NWNs as compare to NCs and NFs. Further, to examine electronic structure and level of degeneracy of these NSs, core-level and valence band spectra were analyzed by X-ray photoelectron spectroscopy (XPS), which manifest the upward band bending ranging from 0.2 eV to 0.4 eV.

AgRISTARS. Supporting research: MARS x-band scatterometer

NASA Technical Reports Server (NTRS)

Ulaby, F. T. (Principal Investigator); Gabel, P. F., Jr.; Brunfeldt, D. R.

1981-01-01

The design, construction, and data collection procedures of the mobile agricultural radar sensor (MARS) x band scatterometer are described. This system is an inexpensive, highly mobile, truck mounted FM-CW radar operating at a center frequency of 10.2 GHz. The antennas, which allow for VV and VH polarizations, are configured in a side looking mode that allows for drive by data collection. This configuration shortens fieldwork time considerably while increasing statistical confidence in the data. Both internal calibration, via a delay line, and external calibration with a Luneberg lens are used to calibrate the instrument in terms of sigma(o). The radar scattering cross section per unit area, sigma(o), is found using the radar equation.

Femtosecond laser refractive surgery: small-incision lenticule extraction vs. femtosecond laser-assisted LASIK.

PubMed

Lee, Jimmy K; Chuck, Roy S; Park, Choul Yong

2015-07-01

Small-incision lenticule extraction (SMILE) is a novel technique devised to correct refractive errors. SMILE circumvents excimer laser photoablation of cornea, as the stromal lenticule cut by femtosecond laser is removed manually. Smaller incisions and preservation of anterior corneal biomechanical strength have been suggested as some of the advantages of SMILE over femtosecond laser-assisted LASIK (FS-LASIK). In this review, we compared previous published results of SMILE and FS-LASIK. The advantage, efficacy and safety of SMILE are compared with FS-LASIK. SMILE achieved similar efficacy, predictability and safety as FS-LASIK. Greater preservations of corneal biomechanical strength and corneal nerves were observed in SMILE when compared with LASIK or PRK. Additionally, the incidence of postoperative dry eye syndrome was found to be less problematic in SMILE than in FS-LASIK. SMILE is a promising new surgery for refractive error correction. Prospective and retrospective studies of SMILE have shown that results of SMILE are similar to FS-LASIK. With advances in femtosecond laser technology, SMILE may gain greater acceptance in the future.

Femtosecond movies of water near interfaces at sub-Angstrom resolution

NASA Astrophysics Data System (ADS)

Coridan, Robert; Hwee Lai, Ghee; Schmidt, Nathan; Abbamonte, Peter; Wong, Gerard C. L.

2010-03-01

The behavior of liquid water near interfaces with nanoscopic variations in chemistry influences a broad range of phenomena in biology. Using inelastic x-ray scattering (IXS) data from 3rd-generation synchrotron x-ray sources, we reconstruct the Greens function of liquid water, which describes the å-scale spatial and femtosecond-scale temporal evolution of density fluctuations. We extend this response function formalism to reconstruct the evolution of hydration structures near dynamic surfaces with different charge distributions, in order to define more precisely the molecular signature of hydrophilicity and hydrophobicity. Moreover, we investigate modifications to surface hydration structures and dynamics as the size of hydrophilic and hydrophobic patches are varied.

Effects of femtosecond laser radiation on the skin

NASA Astrophysics Data System (ADS)

Rogov, P. Yu; Bespalov, V. G.

2016-08-01

A mathematical model of linear and nonlinear processes is presented occurring under the influence of femtosecond laser radiation on the skin. There was held an analysis and the numerical solution of an equation system describing the dynamics of the electron and phonon subsystems were received. The results can be used to determine the maximum permissible levels of energy generated by femtosecond laser systems and the establishment of Russian laser safety standards for femtosecond laser systems.

Frequency choice of eRHIC SRF linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, W.; Ben-Zvi, I.; Roser, T.

2016-01-05

eRHIC is a FFAG lattice-based multipass ERL. The eRHIC SRF linac has been decided to change from 422 MHz 5-cell cavity to 647 MHz 5-cell cavity. There are several considerations affecting the frequency choice for a high-current multipass-ERL: the beam structure, bunch length, energy spread, beam-break-up (BBU) threshold, SRF loss considerations. Beyond the physics considerations, cost and complexity or risk is an important consideration for the frequency choice, especially when we are designing a machine to be built in a few years. Although there are some benefits of using a 422 MHz cavity for eRHIC ERL, however, there are somemore » very critical drawbacks, including lack of facilities to fabricate a 422 MHz 5-cell cavity, very few facilities to process such a cavity and no existing facility to test the cavity anywhere. As the cavity size is big and its weight is large, it is difficult to handle it during fabrication, processing and testing, and no one has experience in this area. As the cavity size is large, the cryomodule becomes big as well. All of these considerations drive the risk of building eRHIC ERL with 422 MHz cavities to a very high level. Therefore, a decision was made to change the frequency of main linac to be 647 MHz 5-cell cavities. This note will compare these two linacs: 422MHz 5-cell cavity linac and 647Mz 5-cell cavity SRF linac, from both practical point of view and physics point of view.« less

SU-E-T-119: Dosimetric and Mechanical Characteristics of Elekta Infinity LINAC with Agility MLC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, J; Xu, Q; Xue, J

2014-06-01

Purpose: Elekta Infinity is the one of the latest generation LINAC with unique features. Two Infinity LINACs are recently commissioned at our institution. The dosimetric and mechanical characteristics of the machines are presented. Methods: Both Infinity LINACs with Agility MLC (160 leaves with 0.5 cm leaf width) are configured with five electron energies (6, 9, 12, 15, and 18 MeV) and two photon energies (6 and 15 MV). One machine has additional photon energy (10 MV). The commissioning was performed by following the manufacturer's specifications and AAPM TG recommendations. Beam data of both electron and photon beams are measured withmore » scanning ion chambers and linear diode array. Machines are adjusted to have the dosimetrically equivalent characteristics. Results: The commissioning of mechanical and imaging system meets the tolerances by TG recommendations. The PDD{sub 10} of various field sizes for 6 and 15 MV shows < 0.5% difference between two machines. For each electron beams, R{sub 80} matches with < 0.4 mm difference. The symmetry and flatness agree within 0.8% and 0.9% differences for photon beams, respectively. For electron beams, the differences of the symmetry and flatness are within 1.2% and 0.8%, respectively. The mean inline penumbras for 6, 10, and 15 MV are respectively 5.1±0.24, 5.6±0.07, and 5.9±0.10 mm for 10x10 cm at 10 cm depth. The crossline penumbras are larger than inline penumbras by 2.2, 1.4, and 1.0 mm, respectively. The MLC transmission factor with interleaf leakage is 0.5 % for all photon energies. Conclusion: The dosimetric and mechanical characteristics of two Infinity LINACs show good agreements between them. Although the Elekta Infinity has been used in many institutions, the detailed characteristics of the machine have not been reported. This study provides invaluable information to understand the Infinity LINAC and to compare the quality of commissioning data for other LINACs.« less

German national femtosecond technology project (FST)

NASA Astrophysics Data System (ADS)

Dausinger, Friedrich

2002-06-01

The German federal government started the funding of a national project intended to exploit the potential of femtosecond technology. In a forgoing competition five research consortia had been successful and have started now together with an adjoin research consortium their investigations in the following fields: (i) micro-machining of technical materials for microstructuring and drilling, (ii) medical therapy in: ophthalmology, dentistry, neurology and ear surgery, (iii) metrology, (iv) laser safety, (v) x- ray generation. Lasers, systems and technologies required in these potential fields of applications will be investigated. The program aims at industrial success and is dominated by industrial partners, therefore. The more fundamental research is done in university institutes and research centers.

Landsat Data Continuity Mission (LDCM) - Optimizing X-Band Usage

NASA Technical Reports Server (NTRS)

Garon, H. M.; Gal-Edd, J. S.; Dearth, K. W.; Sank, V. I.

2010-01-01

The NASA version of the low-density parity check (LDPC) 7/8-rate code, shortened to the dimensions of (8160, 7136), has been implemented as the forward error correction (FEC) schema for the Landsat Data Continuity Mission (LDCM). This is the first flight application of this code. In order to place a 440 Msps link within the 375 MHz wide X band we found it necessary to heavily bandpass filter the satellite transmitter output . Despite the significant amplitude and phase distortions that accompanied the spectral truncation, the mission required BER is maintained at < 10(exp -12) with less than 2 dB of implementation loss. We utilized a band-pass filter designed ostensibly to replicate the link distortions to demonstrate link design viability. The same filter was then used to optimize the adaptive equalizer in the receiver employed at the terminus of the downlink. The excellent results we obtained could be directly attributed to the implementation of the LDPC code and the amplitude and phase compensation provided in the receiver. Similar results were obtained with receivers from several vendors.

Theoretical band structure of the superconducting antiperovskite oxide Sr3-xSnO

NASA Astrophysics Data System (ADS)

Ikeda, Atsutoshi; Fukumoto, Toshiyuki; Oudah, Mohamed; Hausmann, Jan Niklas; Yonezawa, Shingo; Kobayashi, Shingo; Sato, Masatoshi; Tassel, Cédric; Takeiri, Fumitaka; Takatsu, Hiroshi; Kageyama, Hiroshi; Maeno, Yoshiteru

2018-05-01

In order to investigate the position of the strontium deficiency in superconductive Sr3-xSnO, we synthesized and measured X-ray-diffraction patterns of Sr3-xSnO (x ∼ 0.5). Because no clear peaks originating from superstructures were observed, strontium deficiency is most likely to be randomly distributed. We also performed first-principles band-structure calculations on Sr3-xSnO (x = 0, 0.5) using two methods: full-potential linearized-augmented plane-wave plus local orbitals method and the Korringa-Kohn-Rostoker Green function method combined with the coherent potential approximation. We revealed that the Fermi energy of Sr3-xSnO in case of x ∼ 0.5 is about 0.8 eV below the original Fermi energy of the stoichiometric Sr3SnO, where the mixing of the valence p and conduction d orbitals are considered to be small.

Femtosecond laser-induced herringbone patterns

NASA Astrophysics Data System (ADS)

Garcell, Erik M.; Lam, Billy; Guo, Chunlei

2018-06-01

Femtosecond laser-induced herringbone patterns are formed on copper (Cu). These novel periodic structures are created following s-polarized, large incident angle, femtosecond laser pulses. Forming as slanted and axially symmetric laser-induced periodic surface structures along the side walls of ablated channels, the result is a series of v-shaped structures that resemble a herringbone pattern. Fluence mapping, incident angle studies, as well as polarization studies have been conducted and provide a clear understanding of this new structure.

Pressure dependence of band-gap and phase transitions in bulk CuX (X = Cl, Br, I)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Azhikodan, Dilna; Nautiyal, Tashi; Sharma, S.

2016-05-06

Usually a phase transition, in theoretical studies, is explored or verified by studying the total energy as a function of the volume considering various plausible phases. The intersection point, if any, of the free energy vs. volume curves for the different phases is then the indicator of the phase transition(s). The question is, can the theoretical study of a single phase alone indicate a phase transition? i.e. can we look beyond the phase under consideration through such a study? Using density-functional theory, we report a novel approach to suggest phase transition(s) through theoretical study of a single phase. Copper halidesmore » have been engaged for this study. These are direct band-gap semiconductors, with zinc blende structure at ambient conditions, and are reported to exhibit many phase transitions. We show that the study of volume dependence of energy band-gap in a single phase facilitates looking beyond the phase under consideration. This, when translated to pressures, reflects the phase transition pressures for CuX (X = Cl, Br, I) with an encouraging accuracy. This work thus offers a simple, yet reliable, approach based on electronic structure calculations to investigate new semiconducting materials for phase changes under pressure.« less

Evaluation of the JPL X-band 32 element active array. [for deep space communication

NASA Technical Reports Server (NTRS)

Boreham, J. F.; Postal, R. B.; Conroy, B. L.

1979-01-01

Tests performed on an X-band 32-element active array are described. Antenna pattern characteristics of the array were tested in its standard operating mode as well as several degraded performance modes, including failures of 1, 2, 3, 4, 8, 16, and 31 elements. Additionally, the array was characterized with the addition of a metallic shroud, and also characterized versus rf drive level and at a single off-axis electronic beamsteered position. Characterization was performed on several of the 3/4-watt, three-stage, X-band solid-state power amplifier modules. The characterization included swept amplitude response, amplitude and phase versus temperature from -20 to +60 C, and intermodulation distortion of selected modules. The array is described and conclusions and recommendations based upon the experience and results achieved are included.

The Linac Coherent Light Source: Recent Developments and Future Plans

DOE PAGES

Schoenlein, R. W.; Boutet, S.; Minitti, M. P.; ...

2017-08-18

The development of X-ray free-electron lasers (XFELs) has launched a new era in X-ray science by providing ultrafast coherent X-ray pulses with a peak brightness that is approximately one billion times higher than previous X-ray sources. The Linac Coherent Light Source (LCLS) facility at the SLAC National Accelerator Laboratory, the world’s first hard X-ray FEL, has already demonstrated a tremendous scientific impact across broad areas of science. Here in this paper, a few of the more recent representative highlights from LCLS are presented in the areas of atomic, molecular, and optical science; chemistry; condensed matter physics; matter in extreme conditions;more » and biology. This paper also outlines the near term upgrade (LCLS-II) and motivating science opportunities for ultrafast X-rays in the 0.25–5 keV range at repetition rates up to 1 MHz. Future plans to extend the X-ray energy reach to beyond 13 keV (<1 Å) at high repetition rate (LCLS-II-HE) are envisioned, motivated by compelling new science of structural dynamics at the atomic scale.« less

Energy Recovery Linacs for Light Source Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

George Neil

2011-04-01

Energy Recovery Linacs are being considered for applications in present and future light sources. ERLs take advantage of the continuous operation of superconducting rf cavities to accelerate high average current beams with low losses. The electrons can be directed through bends, undulators, and wigglers for high brightness x ray production. They are then decelerated to low energy, recovering power so as to minimize the required rf drive and electrical draw. When this approach is coupled with advanced continuous wave injectors, very high power, ultra-short electron pulse trains of very high brightness can be achieved. This paper will review the statusmore » of worldwide programs and discuss the technology challenges to provide such beams for photon production.« less

Femtosecond imaging of nonlinear acoustics in gold.

PubMed

Pezeril, Thomas; Klieber, Christoph; Shalagatskyi, Viktor; Vaudel, Gwenaelle; Temnov, Vasily; Schmidt, Oliver G; Makarov, Denys

2014-02-24

We have developed a high-sensitivity, low-noise femtosecond imaging technique based on pump-probe time-resolved measurements with a standard CCD camera. The approach used in the experiment is based on lock-in acquisitions of images generated by a femtosecond laser probe synchronized to modulation of a femtosecond laser pump at the same rate. This technique allows time-resolved imaging of laser-excited phenomena with femtosecond time resolution. We illustrate the technique by time-resolved imaging of the nonlinear reshaping of a laser-excited picosecond acoustic pulse after propagation through a thin gold layer. Image analysis reveals the direct 2D visualization of the nonlinear acoustic propagation of the picosecond acoustic pulse. Many ultrafast pump-probe investigations can profit from this technique because of the wealth of information it provides over a typical single diode and lock-in amplifier setup, for example it can be used to image ultrasonic echoes in biological samples.

Design and Simulation of Microstrip Hairpin Bandpass Filter with Open Stub and Defected Ground Structure (DGS) at X-Band Frequency

NASA Astrophysics Data System (ADS)

Hariyadi, T.; Mulyasari, S.; Mukhidin

2018-02-01

In this paper we have designed and simulated a Band Pass Filter (BPF) at X-band frequency. This filter is designed for X-band weather radar application with 9500 MHz center frequency and bandwidth -3 dB is 120 MHz. The filter design was performed using a hairpin microstrip combined with an open stub and defected ground structure (DGS). The substrate used is Rogers RT5880 with a dielectric constant of 2.2 and a thickness of 1.575 mm. Based on the simulation results, it is found that the filter works on frequency 9,44 - 9,56 GHz with insertion loss value at pass band is -1,57 dB.

Native structure of photosystem II at 1.95 Å resolution viewed by femtosecond X-ray pulses.

PubMed

Suga, Michihiro; Akita, Fusamichi; Hirata, Kunio; Ueno, Go; Murakami, Hironori; Nakajima, Yoshiki; Shimizu, Tetsuya; Yamashita, Keitaro; Yamamoto, Masaki; Ago, Hideo; Shen, Jian-Ren

2015-01-01

Photosynthesis converts light energy into biologically useful chemical energy vital to life on Earth. The initial reaction of photosynthesis takes place in photosystem II (PSII), a 700-kilodalton homodimeric membrane protein complex that catalyses photo-oxidation of water into dioxygen through an S-state cycle of the oxygen evolving complex (OEC). The structure of PSII has been solved by X-ray diffraction (XRD) at 1.9 ångström resolution, which revealed that the OEC is a Mn4CaO5-cluster coordinated by a well defined protein environment. However, extended X-ray absorption fine structure (EXAFS) studies showed that the manganese cations in the OEC are easily reduced by X-ray irradiation, and slight differences were found in the Mn-Mn distances determined by XRD, EXAFS and theoretical studies. Here we report a 'radiation-damage-free' structure of PSII from Thermosynechococcus vulcanus in the S1 state at a resolution of 1.95 ångströms using femtosecond X-ray pulses of the SPring-8 ångström compact free-electron laser (SACLA) and hundreds of large, highly isomorphous PSII crystals. Compared with the structure from XRD, the OEC in the X-ray free electron laser structure has Mn-Mn distances that are shorter by 0.1-0.2 ångströms. The valences of each manganese atom were tentatively assigned as Mn1D(III), Mn2C(IV), Mn3B(IV) and Mn4A(III), based on the average Mn-ligand distances and analysis of the Jahn-Teller axis on Mn(III). One of the oxo-bridged oxygens, O5, has significantly longer distances to Mn than do the other oxo-oxygen atoms, suggesting that O5 is a hydroxide ion instead of a normal oxygen dianion and therefore may serve as one of the substrate oxygen atoms. These findings provide a structural basis for the mechanism of oxygen evolution, and we expect that this structure will provide a blueprint for the design of artificial catalysts for water oxidation.

SU-E-T-624: Portal Dosimetry Commissioning of Multiple (6) Varian TrueBeam Linacs Equipped with PortalVision DMI MV Imager

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weldon, M; DiCostanzo, D; Grzetic, S

2015-06-15

Purpose: To show that a single model for Portal Domisetry (PD) can be established for beam-matched TrueBeam™ linacs that are equipped with the DMI imager (43×43cm effective area). Methods: Our department acquired 6 new TrueBeam™s, 4 “Slim” and 2 “Edge” models. The Slims were equipped with 6 and 10MV photons, and the Edges with 6MV. MLCs differed between the Slims and Edges (Millennium 120 vs HD-MLC respectively). PD model was created from data acquired using a single linac (Slim). This includes maximum field size profile, as well as output factors and acquired measured fluence using the DMI imager. All identicalmore » linacs were beam-matched, profiles were within 1% at maximum field size at a variety of depths. The profile correction file was generated from 40×40 profile acquired at 5cm depth, 95cm SSD, and was adjusted for deviation at the field edges and corners. The PD model and profile correction was applied to all six TrueBeam™s and imagers. A variety of jaw only and sliding window (SW) MLC test fields, as well as TG-119 and clinical SW and VMAT plans were run on each linac to validate the model. Results: For 6X and 10X, field by field comparison using 3mm/3% absolute gamma criteria passed 90% or better for all cases. This was also true for composite comparisons of TG-199 and clinical plans, matching our current department criteria. Conclusion: Using a single model per photon energy for PD for the TrueBeam™ equipped with a DMI imager can produce clinically acceptable results across multiple identical and matched linacs. It is also possible to use the same PD model despite different MLCs. This can save time during commissioning and software updates.« less

Real-Time Atmospheric Phase Fluctuation Correction Using a Phased Array of Widely Separated Antennas: X-Band Results and Ka-Band Progress

NASA Astrophysics Data System (ADS)

Geldzahler, B.; Birr, R.; Brown, R.; Grant, K.; Hoblitzell, R.; Miller, M.; Woods, G.; Argueta, A.; Ciminera, M.; Cornish, T.; D'Addario, L.; Davarian, F.; Kocz, J.; Lee, D.; Morabito, D.; Tsao, P.; Jakeman-Flores, H.; Ott, M.; Soloff, J.; Denn, G.; Church, K.; Deffenbaugh, P.

2016-09-01

NASA is pursuing a demonstration of coherent uplink arraying at 7.145-7.190 GHz (X-band) and 30-31 GHz (Kaband) using three 12m diameter COTS antennas separated by 60m at the Kennedy Space Center in Florida. In addition, we have used up to three 34m antennas separated by 250m at the Goldstone Deep Space Communication Complex in California at X-band 7.1 GHz incorporating real-time correction for tropospheric phase fluctuations. Such a demonstration can enable NASA to design and establish a high power, high resolution, 24/7 availability radar system for (a) tracking and characterizing observations of Near Earth Objects (NEOs), (b) tracking, characterizing and determining the statistics of small-scale (≤10cm) orbital debris, (c) incorporating the capability into its space communication and navigation tracking stations for emergency spacecraft commanding in the Ka band era which NASA is entering, and (d) fielding capabilities of interest to other US government agencies. We present herein the results of our phased array uplink combining at near 7.17 and 8.3 GHz using widely separated antennas demonstrations at both locales, the results of a study to upgrade from a communication to a radar system, and our vision for going forward in implementing a high performance, low lifecycle cost multi-element radar array.

Investigation of an X-band gigawatt long pulse multi-beam relativistic klystron amplifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Zhenbang; Huang, Hua; Lei, Lurong

2015-09-15

To achieve a gigawatt-level long pulse radiation power in X-band, a multi-beam relativistic klystron amplifier is proposed and studied experimentally. By introducing 18 electron drift tubes and extended interaction cavities, the power capacity of the device is increased. A radiation power of 1.23 GW with efficiency of 41% and amplifier gain of 46 dB is obtained in the particle-in-cell simulation. Under conditions of a 10 Hz repeat frequency and an input RF power of 30 kW, a radiation power of 0.9 GW, frequency of 9.405 GHz, pulse duration of 105 ns, and efficiency of 30% is generated in the experiment, and the amplifier gain is aboutmore » 45 dB. Both the simulation and the experiment prove that the multi-beam relativistic klystron amplifier can generate a long pulse GW-level radiation power in X-band.« less

Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra

DOE PAGES

Wolf, Thomas; Holzmeier, Fabian; Wagner, Isabella; ...

2017-07-01

Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine's neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependentmore » dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.« less

Optical device fabrication using femtosecond laser processing with glass-hologram

NASA Astrophysics Data System (ADS)

Suzuki, Jun'ichi; Arima, Yasunori; Tanaka, Shuhei

2011-03-01

Using femtosecond laser processing with glass-hologram, fabrication of 1cm-long straight waveguide and X-coupler is reported in this paper. We design and fabricate 4-level glass-hologram which generates 1cm-long straight line intensity. We fabricate 1cm-long waveguides inside fused silica at one shot exposure with the glass-hologram. We investigate the waveguide performance of near field pattern and propagation loss at wavelength of 1550nm. The near field pattern is almost circular shape. The propagation loss at 1550nm is estimated to be < 1.0 dB/cm. As an example of an optical device consisting of straight waveguides, we fabricate X-coupler or 2x2 coupler using straight line waveguides, and observe the output power ratio depending on crossing angle.

Femtosecond laser processing of NiPd single and 5x(Ni/Pd) multilayer thin films

NASA Astrophysics Data System (ADS)

Petrović, S.; Gaković, B.; Zamfirescu, M.; Radu, C.; Peruško, D.; Radak, B.; Ristoscu, C.; Zdravković, S.; Luculescu, C. L.; Mihailescu, I. N.

2017-09-01

Modification of single and complex nickel-palladium samples by laser processing in the femtosecond time domain was studied. The samples were processed by focused Ti:Sapphire laser beam (Clark CPA-2101) with 775 nm laser wavelength, 2 kHz repetition rate, 200 fs pulse duration. The laser-induced morphological modifications have shown dependence on the applied fluences and number of laser pulses. The formed surface nanostructures on the single NiPd/Si and multilayer 5x(Ni/Pd)/Si systems are compared with individual Ni and Pd thin films. The results show an increase in surface roughness, formation of parallel periodic surface structures, appearance of hydrodynamic features and ablation of surface material. At low number of pulses (less than 10 pulses) and low pulse energies range (not over 1.7 μJ), the two types of laser-induced periodic surface structure (LIPSS) can be observed: low and high spatial frequency LIPSS (HSFL and LSFL). For all samples, the measured LSFL periods were 720 nm for the ripples created solely on thin film surfaces during the single pulse action. In the case of the multi-pulse irradiation, the periodicities of created LSFLs on the all investigated thin films have shown tendency to reduction with increasing of pulse energies.

Femtosecond laser structuring of titanium implants

NASA Astrophysics Data System (ADS)

Vorobyev, A. Y.; Guo, Chunlei

2007-06-01

In this study we perform the first femtosecond laser surface treatment of titanium in order to determine the potential of this technology for surface structuring of titanium implants. We find that the femtosecond laser produces a large variety of nanostructures (nanopores, nanoprotrusions) with a size down to 20 nm, multiple parallel grooved surface patterns with a period on the sub-micron level, microroughness in the range of 1-15 μm with various configurations, smooth surface with smooth micro-inhomogeneities, and smooth surface with sphere-like nanostructures down to 10 nm. Also, we have determined the optimal conditions for producing these surface structural modifications. Femtosecond laser treatment can produce a richer variety of surface structures on titanium for implants and other biomedical applications than long-pulse laser treatments.

High incidence of rainbow glare after femtosecond laser assisted-LASIK using the upgraded FS200 femtosecond laser.

PubMed

Zhang, Yu; Chen, Yue-Guo

2018-03-05

To compare the incidence of rainbow glare (RG) after femtosecond laser assisted-LASIK (FS-LASIK) using the upgraded FS200 femtosecond laser with different flap cut parameter settings. A consecutive series of 129 patients (255 eyes) who underwent FS-LASIK for correcting myopia and/or astigmatism using upgraded WaveLight FS200 femtosecond laser with the original settings was included in group A. Another consecutive series of 129 patients (255 eyes) who underwent FS-LASIK using upgraded WaveLight FS200 femtosecond laser with flap cut parameter settings changed (decreased pulse energy, spot and line separation) was included in group B. The incidence and fading time of RG, confocal microscopic image and postoperative clinical results were compared between the two groups. There were no differences between the two groups in age, baseline refraction, excimer laser ablation depth, postoperative uncorrected visual acuity and refraction. The incidence rate of RG in group A (35/255, 13.73%) was significantly higher than that in group B (4/255, 1.57%) (P < 0.05). The median fading time was 3 months in group A and 1 month in group B (P > 0.05).The confocal microscopic images showed wider laser spot spacing in group A than group B. The incidence of RG was significantly correlated with age and grouping (P < 0.05). The upgraded FS200 femtosecond laser with original flap cut parameter settings could increase the incidence of RG. The narrower grating size and lower pulse energy could ameliorate this side effect.

Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhattacherjee, Aditi, E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu; Attar, Andrew R., E-mail: abhattacherjee@berkeley.edu, E-mail: andrewattar@berkeley.edu; Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720

2016-03-28

Femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy based on a high-harmonic generation source is used to study the 266 nm induced A-band photodissociation dynamics of allyl iodide (CH{sub 2} =CHCH{sub 2}I). The photolysis of the C—I bond at this wavelength produces iodine atoms both in the ground ({sup 2}P{sub 3/2}, I) and spin-orbit excited ({sup 2}P{sub 1/2}, I*) states, with the latter as the predominant channel. Using XUV absorption at the iodine N{sub 4/5} edge (45–60 eV), the experiments constitute a direct probe of not only the long-lived atomic iodine reaction products but also the fleeting transition state region ofmore » the repulsive n{sub I}σ{sup ∗}{sub C—I} excited states. Specifically, three distinct features are identified in the XUV transient absorption spectrum at 45.3 eV, 47.4 eV, and 48.4 eV (denoted transients A, B, and C, respectively), which arise from the repulsive valence-excited nσ{sup ∗} states and project onto the high-lying core-excited states of the dissociating molecule via excitation of 4d(I) core electrons. Transients A and B originate from 4d(I) → n(I) core-to-valence transitions, whereas transient C is best assigned to a 4d(I) →σ{sup ∗}(C—I) transition. The measured differential absorbance of these new features along with the I/I* branching ratios known from the literature is used to suggest a more definitive assignment, albeit provisional, of the transients to specific dissociative states within the A-band manifold. The transients are found to peak around 55 fs–65 fs and decay completely by 145 fs–185 fs, demonstrating the ability of XUV spectroscopy to map the evolution of reactants into products in real time. The similarity in the energies of transients A and B with analogous features observed in methyl iodide [Attar et al. J. Phys. Chem. Lett. 6, 5072, (2015)] together with the new observation of transient C in the present work provides a more complete picture of the valence

Band bending at ferroelectric surfaces and interfaces investigated by x-ray photoelectron spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Apostol, Nicoleta Georgiana, E-mail: nicoleta.apostol@infim.ro

2014-11-24

This work reports on the use of X-ray photoelectron spectroscopy to quantify band bending at ferroelectric free surfaces and at their interfaces with metals. Surfaces exhibiting out-of-plane ferroelectric polarization are characterized by a band bending, due to the formation of a dipole layer at the surface, composed by the uncompensated polarization charges (due to ionic displacement) and to the depolarization charge sheet of opposite sign, composed by mobile charge carriers, which migrate near surface, owing to the depolarization electric field. To this surface band bending due to out-of-plane polarization states, metal-semiconductor Schottky barriers must be considered additionally when ferroelectrics aremore » covered by metal layers. It is found that the net band bending is not always an algebraic sum of the two effects discussed above, since sometimes the metal is able to provide additional charge carriers, which are able to fully compensate the surface charge of the ferroelectric, up to the vanishing of the ferroelectric band bending. The two cases which will be discussed in more detail are Au and Cu deposited by molecular beam epitaxy on PbZr{sub 0.2}Ti{sub 0.8}O{sub 3}(001) single crystal thin layers, prepared by pulsed laser deposition. Gold forms unconnected nanoparticles, and their effect on the band bending is the apparition of a Schottky band bending additional to the band bending due to the out-of-plane polarization. Copper, starting with a given thickness, forms continuous metal layers connected to the ground of the system, and provide electrons in sufficient quantity to compensate the band bending due to the out-of-plane polarization.« less

Atmospheric dayglow diagnostics involving the O2(b-X) Atmospheric band emission: Global Oxygen and Temperature (GOAT) mapping

NASA Astrophysics Data System (ADS)

Slanger, T. G.; Pejaković, D. A.; Kostko, O.; Matsiev, D.; Kalogerakis, K. S.

2017-03-01

The terrestrial dayglow displays prominent emission features from the 0-0 and 1-1 bands of the O2 Atmospheric band system in the 760-780 nm region. We present an analysis of observations in this wavelength region recorded by the Space Shuttle during the Arizona Airglow Experiment. A major conclusion is that the dominant product of O(1D) + O2 energy transfer is O2(b, v = 1), a result that corroborates our previous laboratory studies. Moreover, critical to the interpretation of dayglow is the possible interference by N2 and N2+ bands in the 760-780 nm region, where the single-most important component is the N2 1PG 3-1 band that overlaps with the O2(b-X) 0-0 band. When present, this background must be accounted for to reveal the O2(b-X) 0-0 and 1-1 bands for altitudes at which the O2 and N2/N2+ emissions coincide. Finally, we exploit the very different collisional behavior of the two lowest O2(b) vibrational levels to outline a remote sensing technique that provides information on Atmospheric composition and temperature from space-based observations of the 0-0 and 1-1 O2 atmospheric bands.

Electromagnetic properties of absorber fabric coated with BaFe12O19/MWCNTs/PANi nanocomposite in X and Ku bands frequency

NASA Astrophysics Data System (ADS)

Afzali, Arezoo; Mottaghitalab, Vahid; Seyyed Afghahi, Seyyed Salman; Jafarian, Mojtaba; Atassi, Yomen

2017-11-01

Current investigation focuses on the electromagnetic properties of nonwoven fabric coated with BaFe12O19 (BHF) /MWCNTs/PANi nanocomposite in X and Ku bands. The BHF/MWCNTs and BHF/MWCNTs/PANi nanocomposites are prepared using the sol gel and in-situ polymerization methods respectively. The absorbent fabric was prepared based on applying a 40 wt% of BHF/MWCNTs/PANi nanocomposite in silicon resin on nonwoven fabric via roller coating technique The X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and vector network analysis (VNA) are used to peruse microstructural, magnetic and electromagnetic features of the composite and absorber fabric respectively. The microscopic images of the fabric coated with magnetic nanocomposite shows a homogenous layer of nanoparticles on the fabric surface. The maximum reflection loss of binary nano-composite BHF/MWCNTs was measured about -28.50 dB at 11.72 GHz with 1.7 GHz bandwidth (RL < -10 dB) in X band. Moreover in Ku band, the maximum reflection loss is -29.66 dB at 15.78 GHz with 3.2 GHz bandwidths. Also the ternary nanocomposite BHF/MWCNTs/PANi exhibits a broad band absorber over a wide range of X band with a maximum reflection loss of -36.2 dB at 10.2 GHz with 1.5 GHz bandwidth and in the Ku band has arrived a maximum reflection loss of -37.65 dB at 12.84 GHz with 2.43 GHz bandwidth. This result reflects the synergistic effect of the different components with different loss mechanisms. As it is observed due to the presence of PANi in the structure of nanocomposite, the amount of absorption has increased extraordinarily. The absorber fabric exhibits a maximum reflection loss of -24.2 dB at 11.6 GHz with 4 GHz bandwidth in X band. However, in Ku band, the absorber fabric has had the maximum absorption in 16.88 GHz that is about -24.34 dB with 6 GHz bandwidth. Therefore, results indicate that the fabric samples coated represents appreciable maximum absorption value of more than 99% in

Development of a scintillating G-GEM detector for a 6-MeV X-band Linac for medical applications

NASA Astrophysics Data System (ADS)

Fujiwara, T.; Tanaka, S.; Mitsuya, Y.; Takahashi, H.; Tagi, K.; Kusano, J.; Tanabe, E.; Yamamoto, M.; Nakamura, N.; Dobashi, K.; Tomita, H.; Uesaka, M.

2013-12-01

We recently developed glass gas electron multipliers (G-GEMs) with an entirely new process using photo-etchable glass. The photo-etchable glass used for the substrate is called PEG3 (Hoya Corporation). Taking advantage of low outgassing material, we have envisioned a medical application of G-GEMs. A two-dimensional position-sensitive dosimetry system based on a scintillating gas detector is being developed for real-time dose distribution monitoring in X-ray radiation therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside of which G-GEM structures are mounted. Photons produced by the excited Ar/CF4 gas molecules during the gas multiplication in the GEM holes are detected by a mirror-lens-CCD-camera system. We found that the intensity distribution of the measured light spot is proportional to the 2D dose distribution. In this work, we report on the first results from a scintillating G-GEM detector for a position-sensitive X-ray beam dosimeter.

Crystal structure of CO-bound cytochrome c oxidase determined by serial femtosecond X-ray crystallography at room temperature.

PubMed

Ishigami, Izumi; Zatsepin, Nadia A; Hikita, Masahide; Conrad, Chelsie E; Nelson, Garrett; Coe, Jesse D; Basu, Shibom; Grant, Thomas D; Seaberg, Matthew H; Sierra, Raymond G; Hunter, Mark S; Fromme, Petra; Fromme, Raimund; Yeh, Syun-Ru; Rousseau, Denis L

2017-07-25

Cytochrome c oxidase (C c O), the terminal enzyme in the electron transfer chain, translocates protons across the inner mitochondrial membrane by harnessing the free energy generated by the reduction of oxygen to water. Several redox-coupled proton translocation mechanisms have been proposed, but they lack confirmation, in part from the absence of reliable structural information due to radiation damage artifacts caused by the intense synchrotron radiation. Here we report the room temperature, neutral pH (6.8), damage-free structure of bovine C c O (bC c O) in the carbon monoxide (CO)-bound state at a resolution of 2.3 Å, obtained by serial femtosecond X-ray crystallography (SFX) with an X-ray free electron laser. As a comparison, an equivalent structure was obtained at a resolution of 1.95 Å, from data collected at a synchrotron light source. In the SFX structure, the CO is coordinated to the heme a 3 iron atom, with a bent Fe-C-O angle of ∼142°. In contrast, in the synchrotron structure, the Fe-CO bond is cleaved; CO relocates to a new site near Cu B , which, in turn, moves closer to the heme a 3 iron by ∼0.38 Å. Structural comparison reveals that ligand binding to the heme a 3 iron in the SFX structure is associated with an allosteric structural transition, involving partial unwinding of the helix-X between heme a and a 3 , thereby establishing a communication linkage between the two heme groups, setting the stage for proton translocation during the ensuing redox chemistry.

SU-F-E-17: A Dedicated Teaching and Research Linac as a Stepping Stone to Introduce Medical Physics to Students

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beaulieu, L; Archambault, L; Universite Laval, Quebec, Quebec

Purpose: This work describes how a non-clinical, research and teaching Linac is used as an extremely motivating and exciting way to introduce students to medical physics. Methods: The dedicated facility was inaugurated in 2014. The facility is composed of a fully equipped and functional state-of-the-art Varian TrueBeam Linac and a complete set of physics instruments and QA phantoms for the Linac and onboard imaging. The Linac bunker and treatment console are oversized such that a class of 12–15 can comfortably fit, seated if needed for longer sessions. A 3cr undergraduate laboratory course that includes medical imaging, x-ray source characterization (mAs,more » kVp, and filtering) and many others including an introductory Linac laboratory was created. The latter is composed of one general 4-hours session and a weekly 4-hours session for teams of two students. The general session includes a hands-on presentation of the Linac, its environment and a formal safety and radiation protection course (with an exam). Results: Since the winter of 2015, senior undergraduate (total of 15) pursuing either the medical physics or the biomedical engineering tracks can register. At the Linac, the students are allowed full control of the experiments, including set-up and irradiation. Supervisor intervention is limited to safety concerns for students or equipment. Measurements of output factors using two chambers (regular and small field) for various field sizes (1×1 to 30×30 cm{sup 2}) and of detailed depth-dose curves for 6 MV, 6 and 12 MeV beams are to be performed and discussed in a formal report. Conclusion: Full access to, and control of, a Linac is the high point of this course. It provides a glimpse of medical physics and generates an experimental background for those continuing to CAMPEP programs. This dedicated, non-clinical facility further enable enhance CAMPEP graduate teaching and research activities not possible with a clinical device.« less

High-speed femtosecond pump-probe spectroscopy with a smart pixel detector array.

PubMed

Bourquin, S; Prasankumar, R P; Kärtner, F X; Fujimoto, J G; Lasser, T; Salathé, R P

2003-09-01

A new femtosecond pump-probe spectroscopy technique is demonstrated that permits the high-speed, parallel acquisition of pump-probe measurements at multiple wavelengths. This is made possible by use of a novel, two-dimensional smart pixel detector array that performs amplitude demodulation in real time on each pixel. This detector array can not only achieve sensitivities comparable with lock-in amplification but also simultaneously performs demodulation of probe transmission signals at multiple wavelengths, thus permitting rapid time- and wavelength-resolved femtosecond pump-probe spectroscopy. Measurements on a thin sample of bulk GaAs are performed across 58 simultaneous wavelengths. Differential probe transmission changes as small as approximately 2 x 10(-4) can be measured over a 5-ps delay scan in only approximately 3 min. This technology can be applied to a wide range of pump-probe measurements in condensed matter, chemistry, and biology.

Initial Atomic Motion Immediately Following Femtosecond-Laser Excitation in Phase-Change Materials.

PubMed