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M Cipolloni, B Fresch, I Occhiuto, P Rukin, K G Komarova, A Cecconello, I Willner, R D Levine, F Remacle, E Collini
Elucidating the role of quantum coherences in energy migration within biological and artificial multichromophoric antenna systems is the subject of an intense debate. It is also a practical matter because of the decisive implications for understanding the biological processes and engineering artificial materials for solar energy harvesting. A supramolecular rhodamine heterodimer on a DNA scaffold was suitably engineered to mimic the basic donor-acceptor unit of light-harvesting antennas. Ultrafast 2D electronic spectroscopic measurements allowed identifying clear features attributable to a coherent superposition of dimer electronic and vibrational states contributing to the coherent electronic charge beating between the donor and the acceptor...
August 17, 2017: Physical Chemistry Chemical Physics: PCCP
Timo Paschen, Michael Förster, Michael Krüger, Christoph Lemell, Georg Wachter, Florian Libisch, Thomas Madlener, Joachim Burgdörfer, Peter Hommelhoff
In this article, we present coherent control of above-threshold photoemission from a tungsten nanotip achieving nearly perfect modulation. Depending on the pulse delay between fundamental ([Formula: see text]) and second harmonic ([Formula: see text]) pulses of a femtosecond fiber laser at the nanotip, electron emission is significantly enhanced or depressed during temporal overlap. Electron emission is studied as a function of pulse delay, optical near-field intensities, DC bias field and final photoelectron energy...
June 17, 2017: Journal of Modern Optics
Iaroslav Gnilitskyi, Thibault J-Y Derrien, Yoann Levy, Nadezhda M Bulgakova, Tomáš Mocek, Leonardo Orazi
Highly regular laser-induced periodic surface structures (HR-LIPSS) have been fabricated on surfaces of Mo, steel alloy and Ti at a record processing speed on large areas and with a record regularity in the obtained sub-wavelength structures. The physical mechanisms governing LIPSS regularity are identified and linked with the decay length (i.e. the mean free path) of the excited surface electromagnetic waves (SEWs). The dispersion of the LIPSS orientation angle well correlates with the SEWs decay length: the shorter this length, the more regular are the LIPSS...
August 16, 2017: Scientific Reports
Sizuo Luo, Wenhui Hu, Jiaqi Yu, Xiaokai Li, Lanhai He, Chuncheng Wang, Fuchun Liu, Dajun Ding
Strong field sequential ionization of symmetric-top CH3I molecules is studied experimentally by using a combined method of femtosecond laser induced impulsive alignment and time-of-flight mass spectrometry. Both alignment and angular dependent ion yields have been measured and the sequential ionization of multi-electron has been discussed. It's find that the maximum ionization happens when the polarization of probe laser is perpendicular to the internuclear axis of molecules, and the signal of fragment ions peaks at the polarization of probe laser is parallel to the internuclear axis of molecules...
August 16, 2017: Journal of Physical Chemistry. A
Victoria Kathryn Meader, Mallory G John, Collin J Rodrigues, Katharine Moore Tibbetts
Free electrons and H2O2 formed in an optical breakdown plasma are found to di- rectly control the kinetics of [AuCl4]- reduction to form Au nanoparticles (AuNPs) during femtosecond laser-assisted synthesis of AuNPs. The formation rates of both free electrons and H2O2 strongly depend on the energy and duration of the 800 nm laser pulses over the ranges of 10 - 2400 μJ and 30 - 1500 fs. By monitoring the conversion of [AuCl4]- to AuNPs using in situ UV-vis spectroscopy during laser irradiation, the first- and second-order rate constants in the autocatalytic rate law, k1 and k2, were extracted and compared to the computed free electron densities and experimentally measured H2O2 formation rates...
August 16, 2017: Journal of Physical Chemistry. A
M Oujja, S Psilodimitrakopoulos, E Carrasco, M Sanz, A Philippidis, A Selimis, P Pouli, G Filippidis, M Castillejo
The nonlinear optical microscopy (NLM) modalities of Multi-Photon Excited Fluorescence (MPEF) and Third Harmonic Generation (THG) have been combined in this work to characterize as a function of depth with micrometric resolution the type and extent of morphological and photochemical modifications that take place upon ultraviolet (UV) pulsed laser removal of a dammar varnish layer applied on a photosensitive substrate. The latter consists on a layer of the synthetic polymer poly-methyl methacrylate doped with a photosensitizer, the aromatic compound 1,4-di[2-(5-phenyloxazolyl)] benzene, that strongly fluoresces upon UV light illumination...
August 16, 2017: Physical Chemistry Chemical Physics: PCCP
Rundong Zhao, Yanoar Pribadi Sarwono, Rui-Qin Zhang
The tunneling lifetime of an electron escaping from an atom is calculated using a projected Green's function method, combining with the radial potential of the atom which is obtained from density functional theory. Results of the calculated electron tunneling lifetimes in model systems such as a quantum dot are shown to be comparable with other theoretical studies. For the first time, we have obtained the tunneling lifetimes of electrons escaping from a series of atoms (He, Ne, Ar, Kr, H, Li, Na, K) under a static electric field...
August 14, 2017: Journal of Chemical Physics
Denis S Kharenko, Innokentiy S Zhdanov, Anastasia E Bednyakova, Evgeniy V Podivilov, Mikhail P Fedoruk, Alexander Apolonski, Sergei K Turitsyn, Sergey A Babin
A high-energy (0.93 nJ) all-fiber erbium femtosecond oscillator operating in the telecom spectral range is proposed and realized. The laser cavity, built of commercially available fibers and components, combines polarization maintaining (PM) and non-PM parts providing stable generation of highly chirped (chirp parameter 40) pulses compressed in an output piece of standard PM fiber to 165 fs. The results of the numerical simulation agree well with the experiment. The analyzed intracavity pulse dynamics enables the classification of the generated pulses as dissipative solitons...
August 15, 2017: Optics Letters
Feng Zhou, Wei Ji
We develop a theoretical model to quantify the two-photon absorption (2 PA) coefficients of monolayer MoS2. Based on two-dimensional excitons, our model reveals the 2 PA coefficient spectrum on the order of 0.01-0.1 cm/MW in the near-infrared for monolayer MoS2. As compared to the band theory for bulk semiconductors, these coefficients are enhanced by at least one order of magnitude. Our model is in agreement with light-intensity-dependent photocurrent measurements on a monolayer MoS2, subband photodetector with femtosecond laser pulses...
August 15, 2017: Optics Letters
Shunnong Zhang, Zuanming Jin, Xiumei Liu, Wanying Zhao, Xian Lin, Chao Jing, Guohong Ma
We report the broadband terahertz (THz) radiation in ferromagnetic half-metallic Heusler alloy Co2MnSn thin film upon the irradiation of a femtosecond laser pulse at room temperature. The magnetic-, sample symmetry-, and pump fluence-dependent THz emission reveals that the THz radiation is originated from the magnetic-dipole radiation, i.e., the light-induced subpicosecond demagnetization. In addition, by optical pump-THz probe spectroscopy, we found that the photoexcited increase of the scattering rate of hot carriers thereby leads to the photoinduced negative THz conductivity in Co2MnSn thin film...
August 15, 2017: Optics Letters
M Blum, W Sekundo
Refractive lenticule extraction (ReLEx/SMILE) is a refractive surgical method developed by the authors in stages primarily for correction of myopia and myopic astigmatism, in which a femtosecond laser is exclusively used. In the (ReLEx/SMILE) method a refractive lenticule is generated by the femtosecond laser, which is subsequently extracted through a small incision. Opening of the corneal surface with a flap and use of an excimer laser is no longer necessary. In 2013 the method was newly assessed and classified by the Joint Commisssion for Refractive Surgery (KRC) of the Professional Association of Ophthalmologists (BVA) and the German Ophthalmological Society (DOG)...
August 14, 2017: Der Ophthalmologe: Zeitschrift der Deutschen Ophthalmologischen Gesellschaft
Francesco Itri, Daria Maria Monti, Marco Chino, Roberto Vinciguerra, Carlo Altucci, Angela Lombardi, Renata Piccoli, Leila Birolo, Angela Arciello
The identification of protein-protein interaction networks in living cells is becoming increasingly fundamental to elucidate main biological processes and to understand disease molecular bases on a system-wide level. We recently described a method (LUCK, Laser UV Cross-linKing) to cross-link interacting protein surfaces in living cells by UV laser irradiation. By using this innovative methodology, that does not require any protein modification or cell engineering, here we demonstrate that, upon UV laser irradiation of HeLa cells, a direct interaction between GAPDH and alpha-enolase was "frozen" by a cross-linking event...
August 11, 2017: Biochemical and Biophysical Research Communications
Mehra S Sidhu, Bhupesh Kumar, Kamal P Singh
Spider silk is a tough, elastic and lightweight biomaterial, although there is a lack of tools available for non-invasive processing of silk structures. Here we show that nonlinear multiphoton interactions of silk with few-cycle femtosecond pulses allow the processing and heterostructuring of the material in ambient air. Two qualitatively different responses, bulging by multiphoton absorption and plasma-assisted ablation, are observed for low- and high-peak intensities, respectively. Plasma ablation allows us to make localized nanocuts, microrods, nanotips and periodic patterns with minimal damage while preserving molecular structure...
August 14, 2017: Nature Materials
Mingyang Ji, Mahesh B Dawadi, Alexandria R LaSalla, Yuan Sun, David A Modarelli, Jon Robert Parquette
Nanostructured materials having multiple, discrete domains of sorted components are particularly important to create efficient optoelectronics. The construction of multicomponent nanostructures from self-assembled components is exceptionally challenging due to the propensity of noncovalent materials to undergo structural reorganization in the presence of excipient polymers. This work demonstrates that polymer-nanotube composites comprised of a self-assembled nanotube wrapped with two conjugated polymers could be assembled using a layer-by-layer approach...
August 14, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Meng Zhang, Lijuan Wang, Dongping Zhong
Photolyase, a flavoenzyme containing flavin adenine dinucleotide (FAD) molecule as a catalytic cofactor, repairs UV-induced DNA damage of cyclobutane pyrimidine dimer (CPD) and pyrimidine-pyrimidone (6-4) photoproduct using blue light. The FAD cofactor, conserved in the whole protein superfamily of photolyase/cryptochromes, adopts a unique folded configuration at the active site that plays a critical functional role in DNA repair. Here, we review our comprehensive characterization of the dynamics of flavin cofactor and its repair photocycles by different classes of photolyases on the most fundamental level...
August 9, 2017: Archives of Biochemistry and Biophysics
Hong Wang, Yi Hu, Shivaraj Yellappa, Michael B Thomas, R G Waruna Jinadasa, Alex Matus, Max Shulman, Francis D'souza
A novel class of β-functionalized push-pull zinc opp-dibenzoporphyrins were designed, synthesized and utilized as sensitizers for dye-sensitized solar cells. Spectral, electrochemical and computational studies were systematically performed to evaluate their spectral coverage, redox behavior and electronic structures. These porphyrins displayed much broader spectral coverage and more facile oxidation upon extension of π-conjugation. Free-energy calculations and femtosecond transient absorption studies (charge injection rate in the range of 1011 s-1) suggest efficient charge injection from the excited singlet state of porphyrin to the conduction band of the TiO2...
August 11, 2017: Chemistry, An Asian Journal
Raphael Thon, Wutharath Chin, Didier Chamma, Jean-Pierre Galaup, Aimeric Ouvrard, Bernard Bourguignon, Claudine Crépin
Methane solids present more than one accessible crystalline phase at low temperature at zero pressure. We trap W(CO)6 in CH4 and CD4 matrices between 8 and 35 K to probe the interaction between an impurity and its surrounding molecular solid under various physical conditions. Linear and nonlinear vibrational spectroscopies of W(CO)6 highlight different kinds of interaction and reveal new and remarkable signatures of the phase transition of methane. The structures in the absorption band of the antisymmetric CO stretching mode exhibit a clear modification at the transition between phase II and phase I in CH4 and motional narrowing is observed upon temperature increase...
December 7, 2016: Journal of Chemical Physics
O Hüter, F Temps
The radiationless electronic relaxation and α -CC bond fission dynamics of jet-cooled acetone in the S1 (nπ(*)) state and in high-lying 3p and 3d Rydberg states have been investigated by femtosecond time-resolved mass spectrometry and photoelectron imaging. The S1 state was accessed by absorption of a UV pump photon at selected wavelengths between λ = 320 and 250 nm. The observed acetone mass signals and the S1 photoelectron band decayed on sub-picosecond time scales, consistent with a recently proposed ultrafast structural relaxation of the molecules in the S1 state away from the Franck-Condon probe window...
December 7, 2016: Journal of Chemical Physics
Christian Frydendahl, Taavi Repän, Mathias Geisler, Sergey M Novikov, Jonas Beermann, Andrei V Lavrinenko, Sanshui Xiao, Sergey I Bozhevolnyi, N Asger Mortensen, Nicolas Stenger
Controlling and confining light by exciting plasmons in resonant metallic nanostructures is an essential aspect of many new emerging optical technologies. Here we explore the possibility of controllably reconfiguring the intrinsic optical properties of semi-continuous gold films, by inducing permanent morphological changes with a femtosecond (fs)-pulsed laser above a critical power. Optical transmission spectroscopy measurements show a correlation between the spectra of the morphologically modified films and the wavelength, polarization, and the intensity of the laser used for alteration...
August 10, 2017: Nanoscale
Yalun Wang, Xiao Han, Wang Xi, Jinyu Li, Anna Wang Roe, Ping Lu, Jun Qian
Deep-tissue imaging is of great significance to biological applications. In this paper, a deep-red emissive luminogen 2,3-bis(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl) fumaronitrile (TPATCN) with aggregation-induced emission (AIE) feature is prepared. TPATCN molecules were then encapsulated within a polymeric matrix of Pluronic F-127 to form nanoparticles (NPs). TPATCN NPs exhibit bright three-photon fluorescence (3PF) in deep-red region, together with high chemical stability, good photostability, and biocompatibility...
August 10, 2017: Advanced Healthcare Materials
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