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Dimitar Popmintchev, Benjamin R Galloway, Ming-Chang Chen, Franklin Dollar, Christopher A Mancuso, Amelia Hankla, Luis Miaja-Avila, Galen O'Neil, Justin M Shaw, Guangyu Fan, Skirmantas Ališauskas, Giedrius Andriukaitis, Tadas Balčiunas, Oliver D Mücke, Audrius Pugzlys, Andrius Baltuška, Henry C Kapteyn, Tenio Popmintchev, Margaret M Murnane
Recent advances in high-order harmonic generation have made it possible to use a tabletop-scale setup to produce spatially and temporally coherent beams of light with bandwidth spanning 12 octaves, from the ultraviolet up to x-ray photon energies >1.6  keV. Here we demonstrate the use of this light for x-ray-absorption spectroscopy at the K- and L-absorption edges of solids at photon energies near 1 keV. We also report x-ray-absorption spectroscopy in the water window spectral region (284-543 eV) using a high flux high-order harmonic generation x-ray supercontinuum with 10^{9}  photons/s in 1% bandwidth, 3 orders of magnitude larger than has previously been possible using tabletop sources...
March 2, 2018: Physical Review Letters
G K Selikhanov, M S Fando, M V Dontsova, A G Gabdulkhakov
This review contains recent data on serial femtosecond X-ray crystallography (SFX), based on a femtosecond X-ray free electron laser, as well as, on the possibilities of its application for studying photosensitive proteins. Development of this method began rather recently, and it has already shown its effectiveness and some unique advantages over conventional X-ray structural analysis. This technology is especially promising for structural studies of membrane proteins and for kinetic studies. The main principle of the method, the possibility of its application in structural biology, its advantages and disadvantages, as well as its prospects for further development are analyzed in this review...
January 2018: Biochemistry. Biokhimii︠a︡
K Beltako, F Michelini, N Cavassilas, L Raymond
Nanoscale molecular-electronic devices and machines are emerging as promising functional elements, naturally flexible and efficient, for next-generation technologies. A deeper understanding of carrier dynamics in molecular junctions is expected to benefit many fields of nanoelectronics and power devices. We determine time-resolved charge current flowing at the donor-acceptor interface in molecular junctions connected to metallic electrodes by means of quantum transport simulations. The current is induced by the interaction of the donor with a Gaussian-shape femtosecond laser pulse...
March 14, 2018: Journal of Chemical Physics
Benjamin Stauch, Vadim Cherezov
G protein-coupled receptors (GPCRs) represent a large superfamily of membrane proteins that mediate cell signaling and regulate a variety of physiological processes in the human body. Structure-function studies of this superfamily were enabled a decade ago by multiple breakthroughs in technology that included receptor stabilization, crystallization in a membrane environment, and microcrystallography. The recent emergence of X-ray free-electron lasers (XFELs) has further accelerated structural studies of GPCRs and other challenging proteins by overcoming radiation damage and providing access to high-resolution structures and dynamics using micrometer-sized crystals...
March 15, 2018: Annual Review of Biophysics
Yuly Vesga, Carlos Diaz, Jeanne Crassous, Florencio E Hernandez
Herein, we report on the theoretical-experimental analysis of the two photon absorption and circular dichroism spectra of 1-(2-pyridyl)-4-methoxy-carbo[6]helicene derivative (P6). The primary outcomes of our investigation on this particular helicene derivative with a donor-acceptor motif on one end led to two important conclusions: 1) The lengthening of the π-electron delocalization within the helical core of P6 predominantly increases the contribution of the magnetic transition dipole moment to the TPCD signal; 2) The electric transition quadrupole moment contribution to the TPCD signal is enhanced by the intramolecular charge transfer (ICT) produced by the donor-acceptor combination on one end of the molecule...
March 15, 2018: Journal of Physical Chemistry. A
Ondřej Novák, Peter R Krogen, Tobias Kroh, Tomáš Mocek, Franz X Kärtner, Kyung-Han Hong
We report on a femtosecond ∼8.5  μm, ∼2  μJ source based on the intrapulse difference-frequency generation (DFG) of 2.1 μm pulses in an AgGaSe2 (AGSe) crystal. Compared to the conventional ∼0.8 or 1 μm near-infrared (IR) pulses, a ∼2  μm driver for intrapulse DFG can provide more efficient conversion into the wavelengths longer than 5 μm due to a lower quantum defect and is more suitable for the non-oxide nonlinear crystals that have a relatively low bandgap energy. Using 26 fs, 2...
March 15, 2018: Optics Letters
Can Cihan, Abdullah Muti, Isinsu Baylam, Askin Kocabas, Umit Demirbas, Alphan Sennaroglu
We report, to the best of our knowledge, the shortest femtosecond pulses generated from a Kerr-lens mode-locked (KLM) Alexandrite laser operating near 750 nm. The Alexandrite gain medium was pumped with a continuous-wave (cw), 532 nm laser, and the performance of both the short and extended resonators was investigated. The use of an extended cavity eliminated the multi-wavelength spectral instabilities observed during the cw operation of the short cavity. Furthermore, since the repetition rate of the Alexandrite laser was reduced from 107 to 5...
March 15, 2018: Optics Letters
N K Stevenson, C T A Brown, J-M Hopkins, M D Dawson, C Kränkel, A A Lagatsky
We report on the first demonstration, to the best of our knowledge, of a diode-pumped Tm:LuScO3 laser. Efficient and broadly tunable continuous wave operation in the 1973-2141 nm region and femtosecond mode-locking through the use of an ion-implanted InGaAsSb quantum-well-based semiconductor saturable absorber mirror are realized. When mode-locked, near-transform-limited pulses as short as 170 fs were generated at 2093 nm with an average output power of 113 mW and a pulse repetition frequency of 115.2 MHz...
March 15, 2018: Optics Letters
B E Malyugin, N S Anisimova
In certain cases intraoperative pupil dilation during cataract surgery may be necessary to improve the visualization of intraocular structures and assure the atraumatic nature of surgical manipulations. The article reviews a wide range of pupil expanders, their historical aspects and possibilities of their application in modern cataract surgery.
2018: Vestnik Oftalmologii
N P Pashtaev, N A Pozdeeva, V V Zotov, M V Sinitsyn, M A Shcheglova
AIM: to conduct a comparative experimental study of the effect of the use of intracorneal implants during femtosecond laser-assisted intrastromal pocket (IP) and intrastromal tunnel (IT) formation on the strength properties of the cornea. MATERIAL AND METHODS: The experimental study was performed on 24 corneas of 12 rabbit eyes enucleated 1 month after slaughtering. All eyes were divided into 6 groups according to the method of operation. IP and IT were created with IntraLase FS 60 kHz femtolaser...
2018: Vestnik Oftalmologii
Zhaoxiang Liu, Jinping Yao, Jinming Chen, Bo Xu, Wei Chu, Ya Cheng
The generation of laserlike narrow bandwidth emissions from nitrogen molecular ions (N_{2}^{+}) generated in intense near- and mid infrared femtosecond laser fields has aroused much interest because of the mysterious physics underlying such a phenomenon. Here, we perform a pump-probe measurement on the nonlinear interaction of rotational quantum wave packets of N_{2}^{+} generated in midinfrared (e.g., at a wavelength centered at 1580 nm) femtosecond laser fields with an ultrashort probe pulse whose broad spectrum overlaps both P- and R-branch rotational transition lines between the electronic states N_{2}^{+}(B^{2}Σ_{u}^{+},v^{'}=0) and N_{2}^{+}(X^{2}Σ_{g}^{+},v=0)...
February 23, 2018: Physical Review Letters
Khaldoun Saleh, Jacques Millo, Baptiste Marechal, Benoît Dubois, Ahmed Bakir, Alexandre Didier, Clément Lacroûte, Yann Kersalé
A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.
March 14, 2018: Scientific Reports
Alden Curtis, Chase Calvi, James Tinsley, Reed Hollinger, Vural Kaymak, Alexander Pukhov, Shoujun Wang, Alex Rockwood, Yong Wang, Vyacheslav N Shlyaptsev, Jorge J Rocca
Nuclear fusion is regularly created in spherical plasma compressions driven by multi-kilojoule pulses from the world's largest lasers. Here we demonstrate a dense fusion environment created by irradiating arrays of deuterated nanostructures with joule-level pulses from a compact ultrafast laser. The irradiation of ordered deuterated polyethylene nanowires arrays with femtosecond pulses of relativistic intensity creates ultra-high energy density plasmas in which deuterons (D) are accelerated up to MeV energies, efficiently driving D-D fusion reactions and ultrafast neutron bursts...
March 14, 2018: Nature Communications
J S Green, N Booth, R J Dance, R J Gray, D A MacLellan, A Marshall, P McKenna, C D Murphy, C P Ridgers, A P L Robinson, D Rusby, R H H Scott, L Wilson
A key issue in realising the development of a number of applications of high-intensity lasers is the dynamics of the fast electrons produced and how to diagnose them. We report on measurements of fast electron transport in aluminium targets in the ultra-intense, short-pulse (<50 fs) regime using a high resolution temporally and spatially resolved optical probe. The measurements show a rapidly (≈0.5c) expanding region of Ohmic heating at the rear of the target, driven by lateral transport of the fast electron population inside the target...
March 14, 2018: Scientific Reports
Yang Bai, Hannelore Bové, Tim S Nawrot, Benoit Nemery
BACKGROUND: Carbon load in airway macrophages (AM) has been proposed as an internal marker to assess long-term exposure to combustion-derived pollutant particles. However, it is not known how this biomarker is affected by changes in exposure. We studied the clearance kinetics of black carbon (BC) in AM, obtained by sputum induction, in a one-year panel study. METHODS: AM BC was measured 8 times with 6 weeks intervals in healthy young subjects: 15 long-term residents in Leuven, Belgium (BE, mean annual PM10 20-30 μg/m3 ) and 30 newcomers having arrived recently (< 3 weeks) in Leuven from highly polluted cities (mean annual PM10  > 50 μg/m3 ) in low and middle-income countries (LMIC, n = 15), or from low to moderately polluted cities in high-income countries (HIC, n = 15)...
March 14, 2018: Particle and Fibre Toxicology
Gregory A Babbitt, Jamie S Mortensen, Erin E Coppola, Lily E Adams, Justin K Liao
Traditional informatics in comparative genomics work only with static representations of biomolecules (i.e., sequence and structure), thereby ignoring the molecular dynamics (MD) of proteins that define function in the cell. A comparative approach applied to MD would connect this very short timescale process, defined in femtoseconds, to one of the longest in the universe: molecular evolution measured in millions of years. Here, we leverage advances in graphics-processing-unit-accelerated MD simulation software to develop a comparative method of MD analysis and visualization that can be applied to any two homologous Protein Data Bank structures...
March 13, 2018: Biophysical Journal
Mehdi Shajari, Emanuel Wanner, Vladimir Rusev, Shervin Mir Mohi Sefat, Wolfgang J Mayer, Thomas Kohnen, Siegfried Priglinger, Daniel Kook
PURPOSE: To compare corneal densitometry values after Femtosecond Laser-Assisted In Situ Keratomileusis (Fs-LASIK) and Small Incision Lenticule Extraction (SMILE) using Scheimpflug Imaging. METHODS: Our retrospective clinical trial included a total of 146 eyes where 57 eyes underwent Fs-LASIK and 89 eyes underwent SMILE. Examinations with a Pentacam Scheimpflug device (Oculus, Wetzlar, Germany) were performed before surgery, 1 week, 1 month, 3 months, 6 months, and 1 year after surgery...
March 14, 2018: Current Eye Research
Elizabeth S Ryland, Ming-Fu Lin, Max A Verkamp, Kaili Zhang, Kristin Benke, Michaela Carlson, Josh Vura-Weis
Iron porphyrins are the active sites of many natural and artificial catalysts, and their photoinduced dynamics have been described as either relaxation into a vibrationally hot ground state or as a cascade through metal-centered states. In this work, we directly probe the metal center of iron(III) tetraphenyl porphyrin chloride (FeTPPCl) using femtosecond M2,3 -edge x-ray absorption near-edge structure (XANES) spectroscopy. Photoexcitation at 400 nm produces a (π, π*) state that evolves in 70 fs to an iron(II) ligand-to-metal charge transfer (LMCT) state...
March 14, 2018: Journal of the American Chemical Society
Daiki Kato, Hayato Sakai, Yasuyuki Araki, Takehiko Wada, Nikolai V Tkachenko, Taku Hasobe
Photophysical control and switching on organic-inorganic hybrid interfaces are of great interest in diverse fundamental and applicative research areas. 6,13-Bis(triisopropylsilylethynyl)pentacene (TP) is well-known to exhibit efficient singlet fission (SF) for generation of high-yield triplet excited states in aggregated forms, whereas perylenediimide (PDI) ensembles show the characteristic excimer formation. Additionally, a combination of pentacene (electron donor: D) and PDI (electron acceptor: A) is expected to undergo an efficient photoinduced electron transfer (PET), and absorption of two chromophores combined covers the entire visible region...
March 14, 2018: Physical Chemistry Chemical Physics: PCCP
Ana R Bastos, Carlos M S Vicente, Rui Oliveira-Silva, Nuno J O Silva, Marta Tacão, João P da Costa, Mário Lima, Paulo S André, Rute A S Ferreira
The development of portable low-cost integrated optics-based biosensors for photonics-on-a-chip devices for real-time diagnosis are of great interest, offering significant advantages over current analytical methods. We report the fabrication and characterization of an optical sensor based on a Mach-Zehnder interferometer to monitor the growing concentration of bacteria in a liquid medium. The device pattern was imprinted on transparent self-patternable organic-inorganic di-ureasil hybrid films by direct UV-laser, reducing the complexity and cost production compared with lithographic techniques or three-dimensional (3D) patterning using femtosecond lasers...
March 12, 2018: Sensors
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