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Michael Förster, Timo Paschen, Michael Krüger, Christoph Lemell, Georg Wachter, Florian Libisch, Thomas Madlener, Joachim Burgdörfer, Peter Hommelhoff
We demonstrate coherent control of multiphoton and above-threshold photoemission from a single solid-state nanoemitter driven by a fundamental and a weak second harmonic laser pulse. Depending on the relative phase of the two pulses, electron emission is modulated with a contrast of the oscillating current signal of up to 94%. Electron spectra reveal that all observed photon orders are affected simultaneously and similarly. We confirm that photoemission takes place within 10 fs. Accompanying simulations indicate that the current modulation with its large contrast results from two interfering quantum pathways leading to electron emission...
November 18, 2016: Physical Review Letters
Leonardo Mastropasqua, Roberta Calienno, Claudia Curcio, Rodolfo Mastropasqua, Mario Nubile, Niccolò Salgari, Manuela Lanzini
PURPOSE: To detect corneal inflammation and apoptosis induced after small incision lenticule extraction (SMILE) at different refractive corrections for moderate to high values of myopia. METHODS: Fifty patients (50 eyes) suffering from medium to high myopia (spherical equivalent refraction from -3.75 to -10.00 diopters (D) with refractive astigmatism under -0.75 D) underwent SMILE in order to correct myopic error. In vivo evaluation was done by corneal confocal microscopy (IVCM) and ex vivo by immunohistochemistry...
December 2, 2016: Current Eye Research
Lara Martínez-Fernández, Giovanni Granucci, Marvin Pollum, Carlos Crespo-Hernández, Maurizio Persico, Ines Corral Perez
Photosensitization of DNA by thionucleosides is a promising photo-chemotherapeutic treatment option for a variety of malignancies. DNA metabolization of thiated prodrugs can lead to cell death upon exposure to a low dose of UVA light. The exact mechanisms of thionucleoside phototoxicity are still not fully understood. In this work, we have combined femtosecond broadband transient absorption experiments with state-of-the-art molecular simulations to provide mechanistic insights for the ultrafast and efficient population of the triplet-state in the UVA-activated pyrimidine anticancer drug: 4-thiothymine...
December 2, 2016: Chemistry: a European Journal
M J MacDonald, T Gorkhover, B Bachmann, M Bucher, S Carron, R N Coffee, R P Drake, K R Ferguson, L B Fletcher, E J Gamboa, S H Glenzer, S Göde, S P Hau-Riege, D Kraus, J Krzywinski, A L Levitan, K-H Meiwes-Broer, C P O'Grady, T Osipov, T Pardini, C Peltz, S Skruszewicz, M Swiggers, C Bostedt, T Fennel, T Döppner
Atomic clusters can serve as ideal model systems for exploring ultrafast (∼100 fs) laser-driven ionization dynamics of dense matter on the nanometer scale. Resonant absorption of optical laser pulses enables heating to temperatures on the order of 1 keV at near solid density conditions. To date, direct probing of transient states of such nano-plasmas was limited to coherent x-ray imaging. Here we present the first measurement of spectrally resolved incoherent x-ray scattering from clusters, enabling measurements of transient temperature, densities, and ionization...
November 2016: Review of Scientific Instruments
Z Chen, P Hering, S B Brown, C Curry, Y Y Tsui, S H Glenzer
To study the rapid evolution of AC conductivity from ultrafast laser excited warm dense matter (WDM), a spatial chirp single-shot method is developed utilizing a crossing angle pump-probe configuration. The pump beam is shaped individually in two spatial dimensions so that it can provide both sufficient laser intensity to excite the material to warm dense matter state and a uniform time window of up to 1 ps with sub-100 fs FWHM temporal resolution. Temporal evolution of AC conductivity in laser excited warm dense gold was also measured...
November 2016: Review of Scientific Instruments
S Ter-Avetisyan, A Andreev, K Platonov, J H Sung, S K Lee, H W Lee, J Y Yoo, P K Singh, H Ahmed, C Scullion, K F Kakolee, T W Jeong, P Hadjisolomou, M Borghesi
A significant level of back reflected laser energy was measured during the interaction of ultra-short, high contrast PW laser pulses with solid targets at 30° incidence. 2D PIC simulations carried out for the experimental conditions show that at the laser-target interface a dynamic regular structure is generated during the interaction, which acts as a grating (quasi-grating) and reflects back a significant amount of incident laser energy. With increasing laser intensity above 10<sup>18</sup> W/cm<sup>2</sup> the back reflected fraction increases due to the growth of the surface modulation to larger amplitudes...
November 28, 2016: Optics Express
Maoxiang Hou, Feng Zhu, Ying Wang, Yiping Wang, Changrui Liao, Shen Liu, Peixiang Lu
A gas pressure sensor based on an antiresonant reflecting guidance mechanism in a hollow-core fiber (HCF) with an open microchannel is experimentally demonstrated for gas pressure sensing. The microchannel was created on the ring cladding of the HCF by femtosecond laser drilling to provide an air-core pressure equivalent to the external environment. The HCF cladding functions as an antiresonant reflecting waveguide, which induces sharp periodic lossy dips in the transmission spectrum. The proposed sensor exhibits a high pressure sensitivity of 3...
November 28, 2016: Optics Express
E Hertz, F Billard, G Karras, P Béjot, B Lavorel, O Faucher
We present a method to finely tailor ultraviolet femtosecond laser pulses using a pulse shaper with ability in the infrared/visible spectral range. We have developed to that end a frequency doubling module in which the up-conversion mechanism is carried out in the Fourier plane of a 4 f -line. The pulse shaper is used to imprint a spectral phase and/or amplitude onto the fundamental pulse. The shaped pulse is then frequency doubled through the module which transfers the applied spectral shaping to the second harmonic field in a predictable manner...
November 28, 2016: Optics Express
C G E Alfieri, A Diebold, F Emaury, E Gini, C J Saraceno, U Keller
We present semiconductor saturable absorber mirrors (SESAMs) that can potentially support femtosecond pulses from ultrafast thin disk lasers (TDLs) with high average power approaching the kW-power level and high pulse energy in the range of 100 µJ to 1 mJ at megahertz pulse repetition rates. For high-power operation, the SESAM parameters will ultimately limit the shortest pulse duration from a soliton mode-locked laser before mode locking instabilities such as multiple pulsing instabilities and continuous wave (cw) breakthrough start to occur...
November 28, 2016: Optics Express
Jake Fontana, Melissa Maldonado, Nicholas Charipar, Scott A Trammell, Rafaela Nita, Jawad Naciri, Alberto Pique, Banahalli Ratna, Anderson S L Gomes
We created centimeter-scale area metasurfaces consisting of a quasi-hexagonally close packed monolayer of gold nanospheres capped with alkanethiol ligands on glass substrates using a directed self-assembly approach. We experimentally characterized the morphology and the linear and nonlinear optical properties of metasurfaces. We show these metasurfaces, with interparticle gaps of 0.6 nm, are modeled well using a classical (without charge transfer) description. We find a large dispersion of linear refractive index, ranging from values less than vacuum, 0...
November 28, 2016: Optics Express
Ben McMillen, Christos Athanasiou, Yves Bellouard
The use of femtosecond lasers to introduce controlled stress states has recently been demonstrated in silica glass. We use this technique, in combination with chemical etching, to generate and control stress-induced birefringence over a well-defined region of interest, demonstrating direct-write wave plates with precisely tailored retardance levels. This tailoring enables the fabrication of laser-written polarization optics that can be tuned to any wavelength for which silica is transparent, and with a clear aperture free of any laser modifications...
November 28, 2016: Optics Express
Alexey Ermolov, Heli Valtna-Lukner, John Travers, Philip St J Russell
A multi-shot transient-grating cross-correlation frequency-resolved optical gating (FROG) is implemented for the characterization of nanojoule-scale, few-femtosecond, deep-ultraviolet pulses. In theory, the system can characterize pulses with a bandwidth extending from below 200 nm to above 1.5 μm. It is experimentally shown that a 200 THz (50 nm) wide dispersive wave centered at 275 nm, generated in a gas-filled HC-PCF, has a temporal duration of 4 fs. The numerical simulations agree well with the experiment...
December 1, 2016: Optics Letters
So-Yoen Kim, Yang-Jin Cho, Ah-Rang Lee, Ho-Jin Son, Won-Sik Han, Dae Won Cho, Sang Ook Kang
The influence of π-conjugation structural changes on photoinduced electron transfer (PET) and intramolecular charge transfer (ICT) processes in π-conjugated donor (D)-acceptor (A) dyads (D-π-A) was investigated. Three types of D-π-A dyads were prepared through the modification of the structure of their π-conjugated linker, including D-π-A (1) and D-πtw-A (2) having a twisted π-conjugation, and D-π-Si-π-A (3) with a π-conjugation severed by a Si-atom. In these dyads, carbazole (Cz) and oxadiazole (Oz) moieties act as an electron donor and acceptor, respectively...
December 1, 2016: Physical Chemistry Chemical Physics: PCCP
Ahmed M Elsied, Nicholas C Termini, Prasoon K Diwakar, Ahmed Hassanein
The dynamic characteristics of the ions emitted from ultrashort laser interaction with materials were studied. A series of successive experiments were conducted for six different elements (C, Al, Cu, Mo, Gd, and W) using 40 fs, 800 nm Ti: Sapphire laser. Time-of-flight (TOF) ion profile was analyzed and charge emission dependencies were investigated. The effects of incident laser interaction with each element were studied over a wide range of laser fluences (0.8 J/cm(2) to 24 J/cm(2)) corresponding to laser intensities (2...
December 1, 2016: Scientific Reports
David Gauthier, Enrico Allaria, Marcello Coreno, Ivan Cudin, Hugo Dacasa, Miltcho Boyanov Danailov, Alexander Demidovich, Simone Di Mitri, Bruno Diviacco, Eugenio Ferrari, Paola Finetti, Fabio Frassetto, David Garzella, Swen Künzel, Vincent Leroux, Benoît Mahieu, Nicola Mahne, Michael Meyer, Tommaso Mazza, Paolo Miotti, Giuseppe Penco, Lorenzo Raimondi, Primož Rebernik Ribič, Robert Richter, Eléonore Roussel, Sebastian Schulz, Luca Sturari, Cristian Svetina, Mauro Trovò, Paul Andreas Walker, Marco Zangrando, Carlo Callegari, Marta Fajardo, Luca Poletto, Philippe Zeitoun, Luca Giannessi, Giovanni De Ninno
Chirped pulse amplification in optical lasers is a revolutionary technique, which allows the generation of extremely powerful femtosecond pulses in the infrared and visible spectral ranges. Such pulses are nowadays an indispensable tool for a myriad of applications, both in fundamental and applied research. In recent years, a strong need emerged for light sources producing ultra-short and intense laser-like X-ray pulses, to be used for experiments in a variety of disciplines, ranging from physics and chemistry to biology and material sciences...
December 1, 2016: Nature Communications
Karima Chah, Damien Kinet, Christophe Caucheteur
New dual temperature and strain sensor has been designed using eccentric second-order fiber Bragg gratings produced in standard single-mode optical fiber by point-by-point direct writing technique with tight focusing of 800 nm femtosecond laser pulses. With thin gold coating at the grating location, we experimentally show that such gratings exhibit a transmitted amplitude spectrum composed by the Bragg and cladding modes resonances that extend in a wide spectral range exceeding one octave. An overlapping of the first order and second order spectrum is then observed...
November 30, 2016: Scientific Reports
Germano Leal Ehlke, Ronald R Krueger
Myopia is a generally benign refractive error with an increasing prevalence worldwide. It can be corrected temporarily with glasses and contact lenses and permanently with laser vision correction. The 2 main procedures currently being performed for myopia correction are photorefractive keratectomy and laser-assisted in situ keratomileusis. Each technique has its advantages, but they appear to yield similar visual outcomes 1 year after surgery. Laser vision correction for myopia was considered a paradigm shift because healthy eyes could now undergo a surgical procedure to permanently and safely correct the error by altering the center of the cornea, which was previously off limits because of the potential for loss of transparency...
November 2016: Asia-Pacific Journal of Ophthalmology
Fabian Rupp, Katharina Chevalier, Michèle Graf, Markus Schmitz, Harald Kelm, Anneken Grün, Manuel Zimmer, Markus Gerhards, Christoph van Wüllen, Hans-Jörg Krüger, Rolf Diller
A comprehensive spectroscopic and structural investigation of [CoII(L-N4tBu2)(dbsq)][B(p-C6H4Cl)4] (1, L-N4tBu2 = N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane, dbsq1- = 3,5-di-tert-butylsemiquinonate), the first known octahedral complex with a low-spin (ls) CoII semiquinonate ground state, is reported. Above 200 K, solids as well as solutions of 1 exhibit thermally induced spin-crossover (SCO) from the ls to the high-spin (hs) CoII semiquinonate state instead of the frequently observed valence tautomerism from ls CoIII catecholate to hs CoII semiquinonate...
November 29, 2016: Chemistry: a European Journal
Sebastian Schott, Lea Ress, Jan Hrušák, Patrick Nuernberger, Tobias Brixner
Trihalide anions are linear molecules that can be photodissociated with ultraviolet (UV) light. Whereas deep-UV excitation leads to three-body dissociation, for near-UV excitation just one molecular bond is cleaved, which notionally opens up the possibility for different fragmentation patterns. Here, we explore whether the dihalide fragment is formed as an anionic or neutral species and whether heteronuclear trihalides can lead to two different dihalides. The analysis is based on pronounced wavepacket dynamics induced by femtosecond UV pulses and associated both with the initial trihalide and the nascent dihalide species...
November 29, 2016: Physical Chemistry Chemical Physics: PCCP
Takashi Nakano, Sean M Mackay, Eng Wui Tan, Keshav M Dani, Jeff Wickens
External control over rapid and precise release of chemicals in the brain potentially provides a powerful interface with neural activity. Optical manipulation techniques, such as optogenetics and caged compounds, enable remote control of neural activity and behavior with fine spatiotemporal resolution. However, these methods are limited to chemicals that are naturally present in the brain or chemically suitable for caging. Here, we demonstrate the ability to interface with neural functioning via a wide range of neurochemicals released by stimulating loaded liposomal nanostructures with femtosecond lasers...
November 2016: ENeuro
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