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https://www.readbyqxmd.com/read/29160708/photophysics-of-zinc-porphyrin-aggregates-in-dilute-water-ethanol-solutions
#1
Amy L Stevens, Neeraj Kumar Joshi, Matthew F Paige, Ronald Paul Steer
Dimeric and multimeric aggregates of a model metalloporphyrin, zinc tetraphenylporphyrin (ZnTPP), have been produced in a controlled manner by incrementally increasing the water content of dilute aqueous ethanol solutions. Steady state absorption, fluorescence emission and fluorescence excitation spectra have been measured to identify the aggregates present as a function of solvent composition. The dynamics of the excited states of the aggregates produced initially by excitation in the Soret region have been measured by ultrafast fluorescence upconversion techniques...
November 21, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/29152535/time-zero-determination-for-fel-pump-probe-studies-based-on-ultrafast-melting-of-bismuth
#2
S W Epp, M Hada, Y Zhong, Y Kumagai, K Motomura, S Mizote, T Ono, S Owada, D Axford, S Bakhtiarzadeh, H Fukuzawa, Y Hayashi, T Katayama, A Marx, H M Müller-Werkmeister, R L Owen, D A Sherrell, K Tono, K Ueda, F Westermeier, R J D Miller
A common challenge for pump-probe studies of structural dynamics at X-ray free-electron lasers (XFELs) is the determination of time zero (T0)-the time an optical pulse (e.g., an optical laser) arrives coincidently with the probe pulse (e.g., a XFEL pulse) at the sample position. In some cases, T0 might be extracted from the structural dynamics of the sample's observed response itself, but generally, an independent robust method is required or would be superior to the inferred determination of T0. In this paper, we present how the structural dynamics in ultrafast melting of bismuth can be exploited for a quickly performed, reliable and accurate determination of T0 with a precision below 20 fs and an overall experimental accuracy of 50 fs to 150 fs (estimated)...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/29148819/unveiling-structural-motions-of-a-highly-fluorescent-superphotoacid-by-locking-and-fluorinating-the-gfp-chromophore-in-solution
#3
Cheng Chen, Weimin Liu, Mikhail S Baranov, Nadezhda S Baleeva, Ilia V Yampolsky, Liangdong Zhu, Yanli Wang, Alexandra Shamir, Kyril M Solntsev, Chong Fang
Super-photoacidity involves ultrafast proton motions implicated in numerous chemical and biological processes. We used conformational locking and strategic addition of electron-withdrawing substituents to synthesize a new GFP-chromophore analog: p-HO-3,5-diF-BDI:BF2 (diF). It is highly fluorescent and exhibits excited-state proton transfer (ESPT) in various solvents, placing it among the strongest photoacids. Tunable femtosecond stimulated Raman spectroscopy with unique resonance conditions and transient absorption are complementarily employed to elucidate structural basis for super-photoacidity...
November 17, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/29147002/capturing-an-initial-intermediate-during-the-p450nor-enzymatic-reaction-using-time-resolved-xfel-crystallography-and-caged-substrate
#4
Takehiko Tosha, Takashi Nomura, Takuma Nishida, Naoya Saeki, Kouta Okubayashi, Raika Yamagiwa, Michihiro Sugahara, Takanori Nakane, Keitaro Yamashita, Kunio Hirata, Go Ueno, Tetsunari Kimura, Tamao Hisano, Kazumasa Muramoto, Hitomi Sawai, Hanae Takeda, Eiichi Mizohata, Ayumi Yamashita, Yusuke Kanematsu, Yu Takano, Eriko Nango, Rie Tanaka, Osamu Nureki, Osami Shoji, Yuka Ikemoto, Hironori Murakami, Shigeki Owada, Kensuke Tono, Makina Yabashi, Masaki Yamamoto, Hideo Ago, So Iwata, Hiroshi Sugimoto, Yoshitsugu Shiro, Minoru Kubo
Time-resolved serial femtosecond crystallography using an X-ray free electron laser (XFEL) in conjunction with a photosensitive caged-compound offers a crystallographic method to track enzymatic reactions. Here we demonstrate the application of this method using fungal NO reductase, a heme-containing enzyme, at room temperature. Twenty milliseconds after caged-NO photolysis, we identify a NO-bound form of the enzyme, which is an initial intermediate with a slightly bent Fe-N-O coordination geometry at a resolution of 2...
November 17, 2017: Nature Communications
https://www.readbyqxmd.com/read/29144140/specific-monitoring-of-excited-state-symmetry-breaking-by-femtosecond-broadband-fluorescence-upconversion-spectroscopy
#5
Joseph S Beckwith, Arnulf Rosspeintner, Giuseppe Licari, Markus Lunzer, Brigitte Holzer, Johannes Fröhlich, Eric Vauthey
Most quadrupolar molecules designed for large two-photon absorption cross section have been shown to undergo symmetry breaking upon excitation to the S1 state. This was originally deduced from their strong fluorescence solvatochromism and later visualized in real time using transient infrared spectroscopy. For molecules not containing clear IR marker modes, however, a specific real-time observation of the symmetry breaking process remains lacking. Here we show that this process can be resolved using broadband fluorescence upconversion spectroscopy by monitoring the instantaneous emission transition dipole moment...
November 20, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/29141390/-the-clinical-analysis-of-corneal-interface-fluid-syndrome-after-laser-lamellar-corneal-refractive-surgery
#6
K J Lin, J Chen, W Lin, X D Lin, Y M Zhou, L D Zheng, Y Tong
Objective: To analysis, the clinical characteristics, refractive changes, and clinical treatment of interface fluid syndrome after laser lamellar corneal refractive surgery. Methods: During Dec. 2010 to Apr. 2016. In total 6 cases(9 eyes), 3 cases were bilateral, 3 cases were unilateral. Five patients were male and 1 was female. The age of the patients ranged from 20 to 29 years was (24.83±4.02) years. Six cases(9 eyes)of IFS were diagnosed at our hospital. The history and complete ophthalmic examination that include Slit-lamp examination, Slit-lamp photography, refraction, corneal thickness measurement, corneal endothelial cell counting, IOP, anterior segment OCT(AS-OCT), exams were recorded...
November 11, 2017: [Zhonghua Yan Ke za Zhi] Chinese Journal of Ophthalmology
https://www.readbyqxmd.com/read/29140363/snapshot-second-harmonic-generation-polarimeter-based-on-spectral-analysis
#7
Matthieu Dubreuil, Sylvain Rivet, Yann Le Grand
A new high-speed second-harmonic generation (SHG) polarimetric method is reported. It is based on the spectral analysis of the SHG radiation emitted by a nonlinear medium excited with circularly polarized femtosecond laser pulses. The setup uses only passive components for polarization encoding and a fast spectrometer for spectral analysis. The method is validated on a z-cut quartz plate, then on a collagen-rich biological tissue with a view to single image polarization-resolved SHG microscopy.
November 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/29140361/self-referenced-octave-wide-subharmonic-gap-optical-parametric-oscillator-centered-at-3%C3%A2-%C3%A2-%C3%AE-m-and-pumped-by-an-er-fiber-laser
#8
Qitian Ru, Zachary E Loparo, XiaoSheng Zhang, Sean Crystal, Subith Vasu, Peter G Schunemann, Konstantin L Vodopyanov
We report an octave-wide mid-IR spectrum (2.3-4.8 μm) obtained from a subharmonic optical parametric oscillator (OPO) based on a newly developed nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP), which was synchronously pumped by a femtosecond 1560 nm fiber laser. We proved that the octave-wide output is in the form of a single frequency comb. The observed f-to-2f frequency beats, originating directly from the OPO, can be used for self-referencing and phase locking of the pump laser comb with no need for supercontinuum generation...
November 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/29140359/ns-duration-transient-bragg-gratings-in-silica-fibers
#9
Avishay Shamir, Aviran Halstuch, Yonatan Sivan, Amiel A Ishaaya
We demonstrate, for the first time to our knowledge, fast all-optical switching in standard silica fibers, based on a transient Bragg grating. The grating is implemented in the fiber using an immunization photo-pretreatment process, followed by side illumination with femtosecond laser pulses through a suitable phase mask. Each pulse is nonlinearly absorbed, creating a thermal grating that is washed out by thermal diffusion. Reflections measured from such gratings are characterized by a very fast rise time, nanoseconds duration, and a high extinction ratio...
November 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/29140342/fiber-format-dual-comb-coherent-raman-spectrometer
#10
Nicola Coluccelli, Christopher R Howle, Kenneth McEwan, Yuchen Wang, Toney Teddy Fernandez, Alessio Gambetta, Paolo Laporta, Gianluca Galzerano
We demonstrate a fiber-format system for dual-comb coherent anti-Stokes Raman scattering spectroscopy. The system is based on two ytterbium fiber (Yb) femtosecond lasers at repetition frequencies of 94 MHz, a Yb amplifier, and a photonic crystal fiber for spectral broadening and generation of pulses with a central wavelength of 1040 nm and durations in the sub-20-fs regime. We observed Raman spectra of acetonitrile and ethyl acetate with spectral coverage from 100 to 1300  cm(-1), resolution of 8  cm(-1), and a signal-to-noise ratio of around 100, when averaging over 10 acquisitions...
November 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/29140334/carrier-envelope-offset-stabilization-of-a-ghz-repetition-rate-femtosecond-laser-using-opto-optical-modulation-of-a-sesam
#11
Sargis Hakobyan, Valentin J Wittwer, Kutan Gürel, Aline S Mayer, Stéphane Schilt, Thomas Südmeyer
We demonstrate, to the best of our knowledge, the first carrier-envelope offset (CEO) frequency stabilization of a GHz femtosecond laser based on opto-optical modulation (OOM) of a semiconductor saturable absorber mirror (SESAM). The 1.05-GHz laser is based on a Yb:CALGO gain crystal and emits sub-100-fs pulses with 2.1-W average power at a center wavelength of 1055 nm. The SESAM plays two key roles: it starts and stabilizes the mode-locking operation and is simultaneously used as an actuator to control the CEO frequency...
November 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/29139483/surface-enhanced-raman-spectroscopy-bottlenecks-and-future-directions
#12
Rajapandiyan Panneerselvam, Guo-Kun Liu, Yao-Hui Wang, Jun-Yang Liu, Song-Yuan Ding, Jian-Feng Li, De-Yin Wu, Zhong-Qun Tian
In this feature article, we discuss in detail developmental bottleneck issues in Raman spectroscopy in its early stages and surface-enhanced Raman spectroscopy (SERS) in the past four decades. We divide SERS research into two different directions with different targets. Fundamental research is extending the limits of SERS to single-molecule, sub-nanometer resolution and femtosecond processes. In contrast, practical research is expanding the range of applications with the aim of providing versatile analytical tools for surface, materials, life, environmental, forensic and food sciences and also commercial instruments for use in daily life...
November 15, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/29137707/use-of-chemical-conversion-for-determination-of-nitrated-aromatic-hydrocarbons-using-femtosecond-ionization-mass-spectrometry
#13
Takuya Fujii, Tomoko Imasaka, Totaro Imasaka
A sample containing nitrated aromatic hydrocarbons (NPAHs) was injected into the sample inlet port of a gas chromatograph (GC), along with hydrazine, a reducing reagent. The analytes that eluted from the GC column were measured by mass spectrometry (MS) using an ultraviolet femtosecond laser as the ionization source. When no reducing reagent was used, large numbers of polycyclic aromatic hydrocarbons (PAHs) including NPAHs were observed in the two-dimensional GC/MS display. In contrast, when hydrazine was present, reduced forms of NPAHs, which included amino PAHs, were detected...
December 15, 2017: Analytica Chimica Acta
https://www.readbyqxmd.com/read/29134403/femtosecond-lenticule-extraction-performed-on-a-wrong-meridian-and-effectively-reversed-by-excimer-laser-ablation
#14
Alper Agca, Yusuf Yildirim, Burçin Kepez Yildiz, Dilek Yasa, Ali Demircan, Ahmet Demirok
No abstract text is available yet for this article.
November 13, 2017: Lasers in Medical Science
https://www.readbyqxmd.com/read/29133789/effect-of-time-delayed-feedback-on-the-interaction-of-a-dimer-system-with-its-environment
#15
M Farhat, S Kais, F H Alharbi
In this work, we report modeling of non-Markovian open quantum systems, consisting of an excitonic dimer that displays memory effect due to time delayed interaction with its environment. We, indeed investigate the effect of these time delays on quantum coherence and excitation dynamical behavior in the time domain generally considered for photosynthetic experiments (few hundred femtoseconds). In particular, we show that the coherence is maintained for periods proportional to time delays. Additionally, if delay is taken into account, coupling to the environment can be tuned to lower values, unlike in previous studies...
November 13, 2017: Scientific Reports
https://www.readbyqxmd.com/read/29131227/controlling-electron-and-energy-transfer-paths-by-selective-excitation-in-a-zinc-porphyrin-bodipy-c60-multi-modular-triad
#16
Christopher O Obondi, Gary N Lim, Priscilla Martinez, Varghese Swamy, Francis D'Souza
A multi-modular donor-acceptor triad composed of zinc porphyrin, BF2-chelated dipyrromethene (BODIPY), and C60 was newly synthesized, with the BODIPY entity at the central position. Using absorbance and emission spectral, electrochemical redox, and computational optimization results, energy level diagrams for the ZnP-BODIPY dyad and ZnP-BODIPY-C60 triad were constructed to envision the different photochemical events upon selective excitation of the BODIPY and ZnP entities. By transient absorption spectral studies covering a wide femtosecond-to-millisecond time scale, evidence for the different photochemical events and their kinetic information was secured...
November 13, 2017: Nanoscale
https://www.readbyqxmd.com/read/29131161/rapid-virtual-hematoxylin-and-eosin-histology-of-breast-tissue-specimens-using-a-compact-fluorescence-nonlinear-microscope
#17
Lucas C Cahill, Michael G Giacomelli, Tadayuki Yoshitake, Hilde Vardeh, Beverly E Faulkner-Jones, James L Connolly, Chi-Kuang Sun, James G Fujimoto
Up to 40% of patients undergoing breast conserving surgery for breast cancer require repeat surgeries due to close to or positive margins. The lengthy processing required for evaluating surgical margins by standard paraffin-embedded histology precludes its use during surgery and therefore, technologies for rapid evaluation of surgical pathology could improve the treatment of breast cancer by reducing the number of surgeries required. We demonstrate real-time histological evaluation of breast cancer surgical specimens by staining specimens with acridine orange (AO) and sulforhodamine 101 (SR101) analogously to hematoxylin and eosin (H&E) and then imaging the specimens with fluorescence nonlinear microscopy (NLM) using a compact femtosecond fiber laser...
November 13, 2017: Laboratory Investigation; a Journal of Technical Methods and Pathology
https://www.readbyqxmd.com/read/29129082/first-principles-study-of-electron-injection-and-defects-at-the-tio2-ch3nh3pbi3-interface-of-perovskite-solar-cells
#18
Jun Haruyama, Keitaro Sodeyama, Ikutaro Hamada, Liyuan Han, Yoshitaka Tateyama
We investigated electron injection rates and vacancy defect properties by performing first-principles calculations on the interface of an anatase-TiO2(001) and a tetragonal CH3NH3PbI3(110) (MAPbI3(110)). We found that the coupling matrix element between the lowest unoccupied molecular orbital of MAPbI3 and the TiO2 conduction band (CB) minimum is negligibly small, the indication being that electron-injection times for low-energy excited states are quite long (more than several tens of picoseconds). We also found that higher-lying CB states coupled more strongly; injection was expected to take place on a femtosecond time scale...
November 16, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/29127301/femtosecond-time-resolved-observation-of-butterfly-vibration-in-electronically-excited-o-fluorophenol
#19
Fengzi Ling, Shuai Li, Xinli Song, Yanmei Wang, Jinyou Long, Bing Zhang
The butterfly vibration during the hydrogen tunneling process in electronically excited o-fluorophenol has been visualized in real time by femtosecond time-resolved ion yield spectroscopy coupled with time-resolved photoelectron imaging technique. A coherent superposition of out-of-plane C-F butterfly motions is prepared in the first excited electronic state (S1). As the C-F bond vibrates with respect to the aromatic ring, the nuclear geometry varies periodically, leading to the corresponding variation in the photoionization channel...
November 10, 2017: Scientific Reports
https://www.readbyqxmd.com/read/29125720/charge-transfer-from-carbon-nanotubes-to-silicon-in-flexible-carbon-nanotube-silicon-solar-cells
#20
Xiaokai Li, Marina Mariano, Lyndsey McMillon-Brown, Jing-Shun Huang, Matthew Y Sfeir, Mark A Reed, Yeonwoong Jung, André D Taylor
Mechanical fragility and insufficient light absorption are two major challenges for thin flexible crystalline Si-based solar cells. Flexible hybrid single-walled carbon nanotube (SWNT)/Si solar cells are demonstrated by applying scalable room-temperature processes for the fabrication of solar-cell components (e.g., preparation of SWNT thin films and SWNT/Si p-n junctions). The flexible SWNT/Si solar cells present an intrinsic efficiency ≈7.5% without any additional light-trapping structures. By using these solar cells as model systems, the charge transport mechanisms at the SWNT/Si interface are investigated using femtosecond transient absorption...
November 10, 2017: Small
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