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Femtosecond laser

V L R Jacques, C Laulhé, N Moisan, S Ravy, D Le Bolloc'h
We report on time-resolved x-ray diffraction measurements following femtosecond laser excitation in pure bulk chromium. Comparing the evolution of incommensurate charge-density-wave (CDW) and atomic lattice reflections, we show that, a few nanoseconds after laser excitation, the CDW undergoes different structural changes than the atomic lattice. We give evidence for a transient CDW shear strain that breaks the lattice point symmetry. This strain is characteristic of sliding CDWs, as observed in other incommensurate CDW systems, suggesting the laser-induced CDW sliding capability in 3D systems...
October 7, 2016: Physical Review Letters
J M Glownia, A Natan, J P Cryan, R Hartsock, M Kozina, M P Minitti, S Nelson, J Robinson, T Sato, T van Driel, G Welch, C Weninger, D Zhu, P H Bucksbaum
Time-resolved femtosecond x-ray diffraction patterns from laser-excited molecular iodine are used to create a movie of intramolecular motion with a temporal and spatial resolution of 30 fs and 0.3 Å. This high fidelity is due to interference between the nonstationary excitation and the stationary initial charge distribution. The initial state is used as the local oscillator for heterodyne amplification of the excited charge distribution to retrieve real-space movies of atomic motion on ångstrom and femtosecond scales...
October 7, 2016: Physical Review Letters
Qiangbing Guo, Meixi Ji, Yunhua Yao, Meng Liu, Zhi-Chao Luo, Shian Zhang, Xiaofeng Liu, Jianrong Qiu
Here, we show that solution-processed Cu-Sn-S semiconductor nanocrystals (NCs) demonstrate a tunable localized surface plasmon resonance band in the near infrared region, where strong saturable absorption occurs. A saturable absorber based on these plasmonic NCs enables the construction of a stable mode-locked femtosecond fiber laser operating at the telecommunication band.
October 20, 2016: Nanoscale
Andreas Brenneis, Felix Schade, Simon Drieschner, Florian Heimbach, Helmut Karl, Jose A Garrido, Alexander W Holleitner
For future on-chip communication schemes, it is essential to integrate nanoscale materials with an ultrafast optoelectronic functionality into high-frequency circuits. The atomically thin graphene has been widely demonstrated to be suitable for photovoltaic and optoelectronic devices because of its broadband optical absorption and its high electron mobility. Moreover, the ultrafast relaxation of photogenerated charge carriers has been verified in graphene. Here, we show that dual-gated graphene junctions can be functional parts of THz-circuits...
October 20, 2016: Scientific Reports
Timothy V Roberts
No abstract text is available yet for this article.
September 2016: Clinical & Experimental Ophthalmology
Alper Ağca, Ahmet Demirok, Yusuf Yıldırım, Ali Demircan, Dilek Yaşa, Ceren Yeşilkaya, İrfan Perente, Muhittin Taşkapılı
Small-incision lenticule extraction (SMILE) is an alternative to laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for the correction of myopia and myopic astigmatism. SMILE can be performed for the treatment of myopia ≤-12 D and astigmatism ≤5 D. The technology is currently only available in the VisuMax femtosecond laser platform. It offers several advantages over LASIK and PRK; however, hyperopia treatment, topography-guided treatment, and cyclotorsion control are not available in the current platform...
2016: Clinical Ophthalmology
Petra Edlund, Heikki Takala, Elin Claesson, Léocadie Henry, Robert Dods, Heli Lehtivuori, Matthijs Panman, Kanupriya Pande, Thomas White, Takanori Nakane, Oskar Berntsson, Emil Gustavsson, Petra Båth, Vaibhav Modi, Shatabdi Roy-Chowdhury, James Zook, Peter Berntsen, Suraj Pandey, Ishwor Poudyal, Jason Tenboer, Christopher Kupitz, Anton Barty, Petra Fromme, Jake D Koralek, Tomoyuki Tanaka, John Spence, Mengning Liang, Mark S Hunter, Sebastien Boutet, Eriko Nango, Keith Moffat, Gerrit Groenhof, Janne Ihalainen, Emina A Stojković, Marius Schmidt, Sebastian Westenhoff
Phytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser...
October 19, 2016: Scientific Reports
Juan Gros-Otero, Montserrat Garcia-Gonzalez, Miguel A Teus, MariLuz Iglesias-Iglesias, Carlos Gimenez-Vallejo
PURPOSE: To compare femtosecond laser-assisted sub-Bowman keratomileusis (FSBK) versus laser-assisted subepithelial keratomileusis (LASEK) to correct moderate to high myopic astigmatism. METHODS: Retrospective, nonrandomized, interventional, comparative case series. A total of eight hundred and fifty-two eyes with myopic astigmatism of -1.5 diopters (D) or higher were included in the study. We compared 427 eyes treated with FSBK versus 425 eyes treated with LASEK with or without mitomycin C...
October 13, 2016: Journal of Optometry
Alexei Smolyaninov, Mu-Han Yang, Lin Pang, Yeshaiahu Fainman
A high-density array of plasmonic coaxial nanoantennas is used to enhance the two-photon absorption (TPA) process in a conventional silicon photodetector from a mode-locked 76 MHz Ti:sapphire laser over a spectral range from 1340 to 1550 nm. This enhanced TPA was used to generate an interferometric autocorrelation trace of a 150 fs laser pulse. Unlike second-harmonic generation, this technique does not require phase matching or a bulky crystal and can be used on a low-cost integrated silicon platform over a wide range of near-IR wavelengths compatible with modern commercial tunable femtosecond sources...
October 1, 2016: Optics Letters
Belén Sotillo, Vibhav Bharadwaj, J P Hadden, Masaaki Sakakura, Andrea Chiappini, Toney Teddy Fernandez, Stefano Longhi, Ottavia Jedrkiewicz, Yasuhiko Shimotsuma, Luigino Criante, Roberto Osellame, Gianluca Galzerano, Maurizio Ferrari, Kiyotaka Miura, Roberta Ramponi, Paul E Barclay, Shane Michael Eaton
Diamond is a promising platform for sensing and quantum processing owing to the remarkable properties of the nitrogen-vacancy (NV) impurity. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532 nm laser light, even at room temperature. The NV's states are isolated from environmental perturbations making their spin coherence comparable to trapped ions. An important breakthrough would be in connecting, using waveguides, multiple diamond NVs together optically...
October 17, 2016: Scientific Reports
Haomin Wang, Le Wang, Xiaoji G Xu
Scattering-type scanning near-field optical microscopy (s-SNOM) allows spectroscopic imaging with spatial resolution below the diffraction limit. With suitable light sources, s-SNOM is instrumental in numerous discoveries at the nanoscale. So far, the light sources have been limited to continuous wave or high-repetition-rate pulsed lasers. Low-repetition-rate pulsed sources cannot be used, due to the limitation of the lock-in detection mechanism that is required for current s-SNOM techniques. Here, we report a near-field signal extraction method that enables low-repetition-rate pulsed light sources...
October 17, 2016: Nature Communications
Muath Nairat, Vadim V Lozovoy, Marcos Dantus
While the interaction of atoms in strong fields is well understood, the same cannot be said about molecules. We consider how dissociative ionization of molecules depends on the quality of the femtosecond laser pulses, in particular, the presence of third- and fourth-order dispersion. We find that high-order dispersion (HOD) unexpectedly results in order-of-magnitude enhanced ion yields, along with the factor of three greater kinetic energy release compared to transform-limited pulses with equal peak intensities...
October 16, 2016: Journal of Physical Chemistry. A
M Bitter, V Milner
The periodically kicked rotor is a paradigm system for studying quantum effects on classically chaotic dynamics. The wave function of the quantum rotor localizes in angular momentum space, similarly to Anderson localization of the electronic wave function in disordered solids. Here, we observe dynamical localization in a system of true quantum rotors by subjecting nitrogen molecules to periodic sequences of femtosecond pulses. Exponential distribution of the molecular angular momentum-the hallmark of dynamical localization-is measured directly by means of coherent Raman scattering...
September 30, 2016: Physical Review Letters
Manli Liu, Jianchao Wang, Wen Zhong, Danyang Wang, Yugui Zhou, Quan Liu
PURPOSE: To evaluate the clinical results of suction loss in eyes during small incision lenticule extraction (SMILE). METHODS: This prospective paired-eye case study enrolled 8,490 eyes of 4,296 patients, of which 35 eyes experienced suction loss during the SMILE procedure while being treated for myopia or myopic astigmatism. The eyes with suction loss were re-treated with SMILE, femtosecond laser-assisted LASIK (FS-LASIK), or pseudo SMILE, and the fellow eyes were treated with SMILE...
October 1, 2016: Journal of Refractive Surgery
Tommy C Y Chan, Marco C Y Yu, Alex L K Ng, George P M Cheng, Jiamei Zhang, Yan Wang, Vishal Jhanji
PURPOSE: To analyze the visual and refractive outcomes of LASIK with and without simultaneous cross-linking for correction of myopia. METHODS: Patients who received femtosecond laser-assisted LASIK with and without adjunctive cross-linking according to patient's preference were examined longitudinally for 6 months. Patients with myopic manifest refraction spherical equivalent of 5.00 diopters (D) or greater and estimated residual stromal thickness of greater than 250 µm were included...
October 1, 2016: Journal of Refractive Surgery
Barry D Bruner, Zdeněk Mašín, Matteo Negro, Felipe Morales, Danilo Brambila, Michele Devetta, Davide Faccialà, Alex G Harvey, Misha Ivanov, Yann Mairesse, Serguei Patchkovskii, Valeria Serbinenko, Hadas Soifer, Salvatore Stagira, Caterina Vozzi, Nirit Dudovich, Olga Smirnova
High harmonic generation (HHG) spectroscopy has opened up a new frontier in ultrafast science, where electronic dynamics can be measured on an attosecond time scale. The strong laser field that triggers the high harmonic response also opens multiple quantum pathways for multielectron dynamics in molecules, resulting in a complex process of multielectron rearrangement during ionization. Using combined experimental and theoretical approaches, we show how multi-dimensional HHG spectroscopy can be used to detect and follow electronic dynamics of core rearrangement on sub-laser cycle time scales...
September 26, 2016: Faraday Discussions
Jongwoo Song, Younah Lee, Boa Jin, Jongdeok An, Hyunmin Park, Hoon Park, Myounghee Lee, Chan Im
To achieve intrinsically light-weight flexible photovoltaic devices, a bulk-heterojunction-type active layer with a narrow-bandgap polymer is still considered as one of the most important candidates. Therefore, detailed information about the charge transfer efficiency from a photo-excited species on an electron-donating polymer to an electron acceptor is an important factor, given that it is among the most fundamental quantitative measures to understand the solar power conversion efficiency, in particular at the initial stage followed by primary exciton formation...
September 29, 2016: Physical Chemistry Chemical Physics: PCCP
Veniamin A Borin, Sergey M Matveev, Darya S Budkina, Patrick Z El-Khoury, Alexander N Tarnovsky
Femtosecond transient absorption measurements powered by 40 fs laser pulses reveal that ultrafast isomerization takes place upon S1 excitation of both CH2I2 and CHBr3 in the gas phase. The photochemical conversion process is direct and intramolecular, i.e., it proceeds without caging media that have long been implicated in the photo-induced isomerization of polyhalogenated alkanes in condensed phases. Using multistate complete active space second order perturbation theory (MS-CASPT2) calculations, we investigate the structure of the photochemical reaction paths connecting the photoexcited species to their corresponding isomeric forms...
October 10, 2016: Physical Chemistry Chemical Physics: PCCP
Xiaolong He, Anurup Datta, Woongsik Nam, Luis M Traverso, Xianfan Xu
Controlled fabrication of single and multiple nanostructures far below the diffraction limit using a method based on laser induced periodic surface structure (LIPSS) is presented. In typical LIPSS, multiple lines with a certain spatial periodicity, but often not well-aligned, were produced. In this work, well-controlled and aligned nanowires and nanogrooves with widths as small as 40 nm and 60 nm with desired orientation and length are fabricated. Moreover, single nanowire and nanogroove were fabricated based on the same mechanism for forming multiple, periodic structures...
October 10, 2016: Scientific Reports
Seunghwoi Han, Hyunwoong Kim, Yong Woo Kim, Young-Jin Kim, Seungchul Kim, In-Yong Park, Seung-Woo Kim
Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures. Here a metal-sapphire nanostructure is devised to provide a solid tip as the HHG emitter, replacing commonly used gaseous atoms. The fabricated solid tip is made of monocrystalline sapphire surrounded by a gold thin-film layer, and intended to produce EUV harmonics by the inter- and intra-band oscillations of electrons driven by the incident laser...
October 10, 2016: Nature Communications
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