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A Fognini, T U Michlmayr, A Vaterlaus, Y Acremann
The ultrafast demagnetization process allows for the generation of femtosecond spin current pulses. Here, we present a thermodynamic model of the spin current generation process, based on the chemical potential gradients as the driving force for the spin current. We demonstrate that the laser-induced spin current can be estimated by an easy to understand diffusion model.
April 25, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Chun Hong Yoon, Hasan DeMirci, Raymond G Sierra, E Han Dao, Radman Ahmadi, Fulya Aksit, Andrew L Aquila, Alexander Batyuk, Halilibrahim Ciftci, Serge Guillet, Matt J Hayes, Brandon Hayes, Thomas J Lane, Meng Liang, Ulf Lundström, Jason E Koglin, Paul Mgbam, Yashas Rao, Theodore Rendahl, Evan Rodriguez, Lindsey Zhang, Soichi Wakatsuki, Sébastien Boutet, James M Holton, Mark S Hunter
We provide a detailed description of selenobiotinyl-streptavidin (Se-B SA) co-crystal datasets recorded using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS) for selenium single-wavelength anomalous diffraction (Se-SAD) structure determination. Se-B SA was chosen as the model system for its high affinity between biotin and streptavidin where the sulfur atom in the biotin molecule (C10H16N2O3S) is substituted with selenium. The dataset was collected at three different transmissions (100, 50, and 10%) using a serial sample chamber setup which allows for two sample chambers, a front chamber and a back chamber, to operate simultaneously...
April 25, 2017: Scientific Data
Zhao-Xin Lao, Yan-Lei Hu, Deng Pan, Ren-Yan Wang, Chen-Chu Zhang, Jin-Cheng Ni, Bing Xu, Jia-Wen Li, Dong Wu, Jia-Ru Chu
Long microchannels with thin walls, small width, and nanoholes or irregular shaped microgaps, which are similar to capillaries or cancerous vessels, are urgently needed to simulate the physiological activities in human body. However, the fabrication of such channels remains challenging. Here, microchannels with designable holes are manufactured by combining laser printing with line-contact capillary-force assembly. Two microwalls are first printed by femtosecond laser direct-writing, and subsequently driven to collapse into a channel by the capillary force that arises in the evaporation of developer...
April 25, 2017: Small
L Rapp, R Meyer, L Furfaro, C Billet, R Giust, F Courvoisier
We develop a novel concept for ultra-high speed cleaving of crystalline materials with femtosecond lasers. Using Bessel beams in single shot, fracture planes can be induced nearly all along the Bessel zone in sapphire. For the first time, we show that only for a pulse duration below 650 fs, a single fracture can be induced in sapphire, while above this duration, cracks appear in all crystallographic orientations. We determine the influential parameters which are polarization direction, crystallographic axes and scanning direction...
April 17, 2017: Optics Express
Yunbao Zheng, Haiying Liu, Jin Xiang, Qiaofeng Dai, Min Ouyang, Shaolong Tie, Sheng Lan
Gold nanoflowers with feature sizes ranging from several tenths to several hundred nanometers were synthesized by using the one-pot method. They were formed by the self-organization of gold nanoparticles of several nanometers and exhibited broad extinction spectra in the near infrared spectral range. Randomly distributed hot spots originating from the strongly localized modes were generated in gold nanoflowers and their appearances exhibited strong dependences on both the polarization and wavelength of the excitation light...
April 17, 2017: Optics Express
Biao Sun, Jiaqi Luo, Zhiyu Yan, Kun Liu, Junhua Ji, Ying Zhang, Qi Jie Wang, Xia Yu
We propose and demonstrate a broadly wavelength tunable mode-locked thulium-doped all-fiber laser, delivering sub-400 femtosecond (fs) pulses and tuning from 1867 nm to 2010 nm. The tunable range of 143 nm, to our best knowledge, is the widest in the femtosecond mode-locked thulium-doped fiber lasers (TDFLs). The broadly tunable range and femtosecond pulse oscillation attribute to the large free spectral range and bandwidth of the fiber-based Lyot filter, benefiting from the hybrid device based compact configuration...
April 17, 2017: Optics Express
Yan Zhang, Yinsheng Xu, Chenyang You, Dong Xu, Junzhou Tang, Peiqing Zhang, Shixun Dai
Chemical stoichiometric Ge-As-S glasses were prepared, and their thermal properties, refractive index (n), optical bandgap, Raman gain, and femtosecond laser damage were examined. Results revealed that the n and density (ρ) of the glasses decreased as Ge concentration increased, whereas the bandgap and glass transition temperature (Tg) increased. The Raman gain coefficients (g<sub>R</sub>) of the samples were calculated on the basis of spontaneous Raman scattering spectra. g<sub>R</sub> decreased from 2...
April 17, 2017: Optics Express
T Petersen, J D Zuegel, J Bromage
A high-energy, extended-cavity femtosecond BiBO optical parametric oscillator synchronously pumped by a 1.0-ps, 1030-nm Yb:YAG, thin-disk pump laser is presented. The oscillator operated near degeneracy in a noncollinear interaction geometry, producing signal wavelength tunability from 1.99 to 2.20 μm. The signal pulses have an average power exceeding 2 W, producing 455-fs pulses at 7.08 MHz with energies up to 350 nJ, showing increased potential for tunable sources of scalable ultrafast pulses in the infrared...
April 17, 2017: Optics Express
Xian Zhou, Yutang Dai, Joseph Muna Karanja, Fufei Liu, Minghong Yang
Hydrogen gas sensing properties of Pt-WO<sub>3</sub> films on spiral microstructured fiber Bragg grating (FBG) has been demonstrated. Pt-WO<sub>3</sub> film was prepared by hydrothermal method. The spiral microsturctured FBG was fabricated using femtosecond laser. Spiral microstructure FBG hydrogen sensor can detect hydrogen concentration from 0.02% H<sub>2</sub> to 4% H<sub>2</sub> at room temperature, and the response time is shortened from a few minutes to 10~30 s...
April 17, 2017: Optics Express
Dmitri Tsyboulski, Natalia Orlova, Peter Saggau
We present a frequency-multiplexed multi-site two-photon imaging method utilizing amplitude modulation of femtosecond laser pulses in the MHz range to tag each excitation beam and the corresponding fluorescence signals with specific frequencies. The frequency tags are generated with an interferometric scheme employing acousto-optic deflectors (AODs) to achieve precise spatial overlap of femtosecond laser pulses with periodically varying phase shift. Creating matching excitation beam patterns in each interferometer arm using multiple AOD driving frequencies, and subsequently overlapping these matching patterns, results in multiple encoded excitation beams with unique beat frequencies available for scanning...
April 17, 2017: Optics Express
Dong Shuo, Jie Lian, Mark H Jhon, Yinthai Chan, Zhi-Heng Loh
Femtosecond optical pump-probe spectroscopy resolves hitherto unobserved coherent acoustic phonons in colloidal CdSe/CdS core/shell nanoplatelets (NPLs). With increasing pump fluence, the frequency of the in-plane acoustic mode increases from 5.2 to 10.7 cm(-1), whereas the frequency of the out-of-plane mode remains at ~20 cm(-1). Analysis of the oscillation phases suggests that the coherent acoustic phonon generation mechanism transitions from displacive excitation to sub-picosecond Auger hole trapping with increasing pump fluence...
April 24, 2017: Nano Letters
Lewis A Baker, Sarah L Clark, Scott Habershon, Vasilios G Stavros
The ultrafast photoprotection mechanisms in operation of ethylhexyl triazone (EHT, octyl triazone), an approved ultraviolet-B (UV-B) chemical filter for commercial sunscreens, remain elusive, with a notable absence of ultrafast time-resolved measurements. These large organic molecules are of increasing interest as they are suspected to be less likely to penetrate the skin than some of the smaller approved filters, thereby reducing the possible adverse effects from sunscreen products. We apply femtosecond transient absorption spectroscopy with electronic structure calculations to unravel the complete photodeactivation mechanism that EHT undergoes after UV-B irradiation...
April 24, 2017: Journal of Physical Chemistry Letters
Roman V Kazantsev, Adam J Dannenhoffer, Adam S Weingarten, Brian T Phelan, Boris Harutyunyan, Taner Aytun, Ashwin Narayanan, Daniel J Fairfield, Job Boekhoven, Hiroaki Sai, Andrew Senesi, Pascual I O'Dogherty, Liam C Palmer, Michael J Bedzyk, Michael R Wasielewski, Samuel I Stupp
The energy landscape of a supramolecular material can include different molecular packing configurations that differ in stability and function. We report here on a thermally driven crystalline order transition in the landscape of supramolecular nanostructures formed by charged chromophore amphiphiles in salt-containing aqueous solutions. An irreversible transition was observed from a metastable to a stable crystal phase within the nanostructures. In the stable crystalline phase, the molecules end up organized in a short scroll morphology at high ionic strengths and as long helical ribbons at lower salt content...
April 24, 2017: Journal of the American Chemical Society
Xiaochun Gong, Cheng Lin, Feng He, Qiying Song, Kang Lin, Qinying Ji, Wenbin Zhang, Junyang Ma, Peifen Lu, Yunquan Liu, Heping Zeng, Weifeng Yang, Jian Wu
A phase-controlled orthogonal two-color (OTC) femtosecond laser pulse is employed to probe the time delay of photoelectron emission in the strong-field ionization of atoms. The OTC field spatiotemporally steers the emission dynamics of the photoelectrons and meanwhile allows us to unambiguously distinguish the main and sideband peaks of the above-threshold ionization spectrum. The relative phase shift between the main and sideband peaks, retrieved from the phase-of-phase of the photoelectron spectrum as a function of the laser phase, gradually decreases with increasing electron energy, and becomes zero for the fast electron which is mainly produced by the rescattering process...
April 7, 2017: Physical Review Letters
B B Zhou, X Liu, H R Guo, X L Zeng, X F Chen, H P Chung, Y H Chen, M Bache
We show that a temporal soliton can induce resonant radiation by three-wave mixing nonlinearities. This constitutes a new class of resonant radiation whose spectral positions are parametrically tunable. The experimental verification is done in a periodically poled lithium niobate crystal, where a femtosecond near-IR soliton is excited and resonant radiation waves are observed exactly at the calculated soliton phase-matching wavelengths via the sum- and difference-frequency generation nonlinearities. This extends the supercontinuum bandwidth well into the mid IR to span 550-5000 nm, and the mid-IR edge is parametrically tunable over 1000 nm by changing the three-wave mixing phase-matching condition...
April 7, 2017: Physical Review Letters
Aaron Sisto, Clem Stross, Marc W van der Kamp, Michael O'Connor, Simon McIntosh-Smith, Graham T Johnson, Edward G Hohenstein, Fred R Manby, David R Glowacki, Todd J Martinez
We recently outlined an efficient multi-tiered parallel ab initio excitonic framework that utilizes time dependent density functional theory (TDDFT) to calculate ground and excited state energies and gradients of large supramolecular complexes in atomistic detail - enabling us to undertake non-adiabatic simulations which explicitly account for the coupled anharmonic vibrational motion of all the constituent atoms in a supramolecular system. Here we apply that framework to the 27 coupled bacterio-chlorophyll-a chromophores which make up the LH2 complex, using it to compute an on-the-fly nonadiabatic surface-hopping (SH) trajectory of electronically excited LH2...
April 21, 2017: Physical Chemistry Chemical Physics: PCCP
Zhe Guang, Michelle Rhodes, Rick Trebino
Ultrashort pulses emerging from multimode optical fibers are spatiotemporally complex, because inside these fibers the modes have different spatial intensity patterns and experience different propagation velocities and dispersions. To determine the spatiotemporal field from multimode fibers, we applied a technique for the complete measurement of the output pulses called a spatially and temporally resolved intensity and phase evaluation device: full information from a single hologram. It yields the complete electric field over space and time from multiple digital holograms, simultaneously recorded at different frequencies on a single camera frame...
April 20, 2017: Applied Optics
Lena Grimmelsmann, Alireza Marefat Khah, Christian Spies, Christof Hättig, Patrick Nuernberger
Many synthetic DNA minor groove binders exhibit a strong increase in fluorescence when bound to DNA. The pharmaceutical-relevant berenil (diminazene aceturate) is an exception with an extremely low fluorescence quantum yield (on the order of 10(-4)). We investigate the ultrafast excited-state dynamics of this triazene by femtosecond time-resolved fluorescence experiments in water, ethylene glycol, and buffer and bound to the enzyme β-trypsin, the minor groove of AT-rich DNA, and G-quadruplex DNA. Ab initio calculations provide additional mechanistic insight...
April 20, 2017: Journal of Physical Chemistry Letters
Stefano Ponzoni, Simona Achilli, Chiara Pintossi, Giovanni Drera, Luigi Sangaletti, Paola Castrucci, Maurizio De Crescenzi, Stefania Pagliara
Despite the astonishing values of the power conversion efficiency reached, in just less than a decade, by the carbon nanotube / silicon (CNT/Si) solar cells, many doubts remain on the underlying transport mechanisms across the CNT/Si heterojunction. Here, by combining transient optical spectroscopy in the femtosecond timescale, X-ray photoemission and a systematic tracking of I-V curves across all phases of the interlayer SiOx growth at the interface, we grasp the mechanism that adequately preserves charge separation at the junction, hindering the photoexcited carrier recombination...
April 20, 2017: ACS Applied Materials & Interfaces
Ehsan Kheradpezhouh, Julian M C Choy, Vincent R Daria, Ehsan Arabzadeh
TRPA1 is a non-selective cation channel involved in pain sensation and neurogenic inflammation. Although TRPA1 is well established in a number of organs including the nervous system, its presence and function in the mammalian cortex remains unclear. Here, we demonstrate the expression of TRPA1 in rodent somatosensory cortex through immunostaining and investigate its functional activation by whole-cell electrophysiology, Ca(2+) imaging and two-photon photoswitching. Application of TRPA1 agonist (AITC) and antagonist (HC-030031) produced significant modulation of activity in layer 5 (L5) pyramidal neurons in both rats and mice; AITC increased intracellular Ca(2+) concentrations and depolarized neurons, and both effects were blocked by HC-030031...
April 2017: Open Biology
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