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Femtosecond laser

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https://www.readbyqxmd.com/read/28748241/spectral-dependence-of-photoemission-in-multiphoton-ionization-of-no2-by-femtosecond-pulses-in-the-375-430-nm-range
#1
S Marggi Poullain, R Cireasa, C Cornaggia, M Simon, T Marin, R Guillemin, J C Houver, R R Lucchese, D Dowek
We investigate the multiphoton ionization of NO2 using tunable (430-375 nm) femtosecond pulses and photoelectron-photoion coincidence momentum spectroscopy. In order to understand the complex electronic and nuclear photodynamics at play following absorption of three to five photons, we also report extended photoionization calculations using correlated targets and coupled channels. Exploring the multiphoton dissociative ionization (MPDI) and multiphoton ionization (MPI) processes over such a broad energy range enables us to lend further support to our work carried out around 400 nm of a femtosecond laser [S...
July 27, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28747742/mid-infrared-femtosecond-laser-induced-damages-in-as2s3-and-as2se3-chalcogenide-glasses
#2
Chenyang You, Shixun Dai, Peiqing Zhang, Yinsheng Xu, Yingying Wang, Dong Xu, Rongping Wang
In this paper, we report the first measurements of mid-infrared (MIR) femtosecond laser-induced damage in two typical chalcogenide glasses, As2S3 and As2Se3. Damage mechanism is studied via optical microscopy, scanning electron microscopy and elemental analysis. By irradiating at 3, 4 and 5 μm with 150 fs ultrashort pulses, the evolution of crater features is presented with increasing laser fluence. The dependence of laser damage on the bandgap and wavelength is investigated and finally the laser-induced damage thresholds (LIDTs) of As2S3 and As2Se3 at 3 and 4 μm are calculated from the experimental data...
July 26, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28747621/evaluation-of-biomechanical-changes-in-myopia-patients-with-unsatisfactory-corneas-after-femto-second-laser-in-situ-keratomileusis-fs-lasik-concurrent-with-accelerated-corneal-collagen-cross-linking-using-corvis-st-two-year-follow-up-results
#3
Weiwei Xu, Ye Tao, Liqiang Wang, Yifei Huang
BACKGROUND Some myopia patients with unsatisfactory corneas consider corneal refractive surgery for different reasons. Accelerated corneal collagen crosslinking (ACXL) is an effective method to enhance the resistance of the cornea. The present investigation was designed to evaluate the changes of biomechanical properties in patients with myopia and thin corneas after femtosecond-laser in situ keratomileusis (FS-LASIK) concurrent with ACXL. MATERIAL AND METHODS A prospective study was designed. A total of 22 eyes of 11 myopia astigmatism patients with unsatisfactory corneas were enrolled...
July 27, 2017: Medical Science Monitor: International Medical Journal of Experimental and Clinical Research
https://www.readbyqxmd.com/read/28745661/-n-s-i-n-i-v-biomechanical-aspects-of-anterior-capsulotomy-in-cataract-surgery
#4
K S Avetisov, N A Bakhchieva, S E Avetisov, I A Novikov, N V Belikov, I V Khaydukova
This paper reviews studies on biomechanical properties of the anterior lens capsule. Early experiments in this field were more fundamental. Later studies were aimed mainly at assessing the mechanical stability of the capsule edge after manual or femtosecond laser capsulorhexis (capsulotomy) - an important step in modern minimally invasive phaco surgery. For biomechanical tests, ex vivo samples of human and animal anterior capsules were used. The results of the studies presented here are quite heterogeneous, which suggests the necessity of gaining further insight into the issue...
2017: Vestnik Oftalmologii
https://www.readbyqxmd.com/read/28745654/-analysis-of-corneal-biomechanical-changes-after-femtosecond-laser-assisted-laser-in-situ-keratomileusis-in-children-with-hyperopic-anisometropia
#5
I L Kulikova, O V Shlenskaya, N V Chapurin
AIM: to analyze corneal hysteresis (CH) and corneal resistance factor (RF) readings obtained with the Reichert Ocular Response Analyzer (ORA) before and after hyperopic femtolaser-assisted laser in situ keratomileusis (FS-LASIK) in children with anisometropia as well as to establish factors that may cause changes in these parameters. MATERIAL AND METHODS: CH and RF were evaluated before and 1.5 years after FS-LASIK performed on amblyopic eyes of 28 patients aged 6-14 years...
2017: Vestnik Oftalmologii
https://www.readbyqxmd.com/read/28745650/-comparative-analysis-of-corneal-aberrations-after-intrastromal-segments-and-myoring-implantation-using-femtosecond-laser-in-patients-with-keratoconus
#6
N P Pashtaev, N A Pozdeeva, M V Sinitsyn
AIM: to comparatively analyze corneal aberrations after intrastromal corneal segments (ICS) and MyoRing implantation using femtosecond laser in patients with stage II-III keratoconus (KC) by Pentacam examination. MATERIAL AND METHODS: We have operated on 135 patients (145 eyes) with stage II or III KC. Depending on surgical technique, all patients were divided into two groups. Group I consisted of patients with KC, who received optimized femtosecond laser-assisted MyoRing implantation, group II - of those, who received femtosecond laser-assisted ICS implantation...
2017: Vestnik Oftalmologii
https://www.readbyqxmd.com/read/28743976/nano-plasmonic-near-field-phase-matching-of-attosecond-pulses
#7
Tahir Shaaran, Rana Nicolas, Bianca Iwan, Milutin Kovacev, Hamed Merdji
Nano-structures excited by light can enhance locally the electric field when tuned to plasmonic resonances. This phenomenon can be used to boost non-linear processes such as harmonic generation in crystals or in gases, Raman excitation, and four wave mixing. Here we present a theoretical investigation of the near-field phase matching of attosecond pulses emitted by high-order harmonic generation (HHG) of an atom immersed in a multi-cycle femtosecond infrared laser field and a spatially inhomogeneous plasmonic field...
July 25, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28742840/glaucomatous-changes-in-lamina-pores-shape-within-the-lamina-cribrosa-using-wide-bandwidth-femtosecond-mode-locked-laser-oct
#8
Takuhei Shoji, Hiroto Kuroda, Masayuki Suzuki, Hisashi Ibuki, Makoto Araie, Shin Yoneya
PURPOSE: The lamina cribrosa (LC) is known to play a critical role in the pathogenesis of glaucoma. Although it has been reported that striae-shaped or slit-shaped lamina pores are more frequent in eyes with primary open angle glaucoma (POAG), this observation is based only on fundus photography. The primary object of this study is to perform layer-by-layer comparisons of the shape of lamina pores within the LC in vivo. DESIGN: Cross-sectional study. METHODS: Optic nerve head B-scans were obtained using custom-made broad-wavelength optical coherence tomography with a mode-locked laser...
2017: PloS One
https://www.readbyqxmd.com/read/28742366/femtosecond-laser-enhanced-amyloid-fibril-formation-of-insulin
#9
Tsung-Han Liu, Ken-Ichi Yuyama, Takato Hiramatsu, Naoki Yamamoto, Eri Chatani, Hiroshi Miyasaka, Teruki Sugiyama, Hiroshi Masuhara
Femtosecond (fs) laser-induced crystallization as a novel crystallization technique was proposed for the first time by our group, where crystallization time can be significantly shortened under fs laser irradiation. Similarly, we have further extended our investigation to amyloid fibril formation also known as a nucleation-dependence process. Here we demonstrate that necessary time for amyloid fibril formation can be much shortened by fs laser irradiation leading to favorable enhancement. The enhancement was confirmed by both spectral measurements and direct observations of amyloid fibrils...
July 25, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28741162/-scanning-electron-microscopic-investigations-of-cutting-edge-quality-in-lamellar-keratotomy-using-the-wavelight-femtosecond-laser-fs-200-what-influence-do-spot-distance-and-an-additional-tunnel-have
#10
T Hammer, T Höche, J Heichel
BACKGROUND: Femtosecond lasers (fs-lasers) are established cutting instruments for the creation of LASIK flaps. Previous studies often showed even rougher surfaces after application of fs-laser systems compared to lamellar keratotomy with mechanical microkeratomes. When cutting the cornea with fs-lasers, an intrastromal gas development occurs, which has a potentially negative influence on the cutting quality if the gas cannot be dissipated; therefore, manufacturers have chosen the way of gas assimilation in so-called pockets...
July 24, 2017: Der Ophthalmologe: Zeitschrift der Deutschen Ophthalmologischen Gesellschaft
https://www.readbyqxmd.com/read/28733116/a-bright-future-for-serial-femtosecond-crystallography-with-xfels
#11
REVIEW
Linda C Johansson, Benjamin Stauch, Andrii Ishchenko, Vadim Cherezov
X-ray free electron lasers (XFELs) have the potential to revolutionize macromolecular structural biology due to the unique combination of spatial coherence, extreme peak brilliance, and short duration of X-ray pulses. A recently emerged serial femtosecond (fs) crystallography (SFX) approach using XFEL radiation overcomes some of the biggest hurdles of traditional crystallography related to radiation damage through the diffraction-before-destruction principle. Intense fs XFEL pulses enable high-resolution room-temperature structure determination of difficult-to-crystallize biological macromolecules, while simultaneously opening a new era of time-resolved structural studies...
July 18, 2017: Trends in Biochemical Sciences
https://www.readbyqxmd.com/read/28731774/femtosecond-spin-current-pulses-generated-by-the-nonthermal-spin-dependent-seebeck-effect-and-interacting-with-ferromagnets-in-spin-valves
#12
Alexandr Alekhin, Ilya Razdolski, Nikita Ilin, Jan P Meyburg, Detlef Diesing, Vladimir Roddatis, Ivan Rungger, Maria Stamenova, Stefano Sanvito, Uwe Bovensiepen, Alexey Melnikov
Using the sensitivity of optical second harmonic generation to currents, we demonstrate the generation of 250-fs long spin current pulses in Fe/Au/Fe/MgO(001) spin valves. The temporal profile of these pulses indicates ballistic transport of hot electrons across a sub-100 nm Au layer. The pulse duration is primarily determined by the thermalization time of laser-excited hot carriers in Fe. Considering the calculated spin-dependent Fe/Au interface transmittance we conclude that a nonthermal spin-dependent Seebeck effect is responsible for the generation of ultrashort spin current pulses...
July 7, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28730997/improving-the-electrical-contact-at-a-pt-tio2-nanowire-interface-by-selective-application-of-focused-femtosecond-laser-irradiation
#13
Songling Xing, Luchan Lin, Guisheng Zou, Lei Liu, Peng Peng, Aiping Wu, Walter W Duley, Norman Zhou
In this paper, we show that tightly focused femtosecond laser irradiation is effective in improving nanojoining of an oxide nanowire (TiO2) to a metal electrode (Pt), and how this process can be used to modify contact states. Enhanced chemical bondings are created due to localized plasmonically enhanced optical absorption at the Pt/TiO2 interface as confirmed by finite element simulations of the localized field distribution during irradiation. Nano Auger electron spectroscopy shows that the resulting heterojunction is depleted in oxygen, suggesting that a TiO2-x layer is formed between the Pt electrode and the TiO2 nanowire...
July 21, 2017: Nanotechnology
https://www.readbyqxmd.com/read/28730109/human-eye-ocular-component-analysis-for-refractive-state-and-refractive-surgery
#14
Chao-Kai Chang, Jui-Teng Lin, Yong Zhang
AIM: To analyze the clinical factors influencing the human vision corrections via the changing of ocular components of human eye in various applications; and to analyze refractive state via a new effective axial length. METHODS: An effective eye model was introduced by the ocular components of human eye including refractive indexes, surface radius (r1, r2, R1, R2) and thickness (t, T) of the cornea and lens, the anterior chamber depth (S1) and the vitreous length (S2)...
2017: International Journal of Ophthalmology
https://www.readbyqxmd.com/read/28729560/adaptive-control-of-ion-yield-in-femtosecond-laser-post-ionization-for-secondary-ion-mass-spectrometry
#15
Dusan Lorenc, Monika Jerigova, Monika Stupavska, Dusan Velic
Secondary ion mass spectrometry is an excellent technique of analytical chemistry, where primary ions sputter a solid sample generating the secondary ions which are determined. Although the ion yield is inherently low, it can be enhanced by using a post-ionization of sputtered neutral species. Our novel approach integrates this technique with a near infrared femtosecond laser post-ionization based on an adaptive control through a laser pulse shaper. The shaping of the laser pulse provides adaptive control to select a mass peak of interest and to enhance this peak intensity...
July 20, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28720815/generation-of-spin-waves-by-a-train-of-fs-laser-pulses-a-novel-approach-for-tuning-magnon-wavelength
#16
I V Savochkin, M Jäckl, V I Belotelov, I A Akimov, M A Kozhaev, D A Sylgacheva, A I Chernov, A N Shaposhnikov, A R Prokopov, V N Berzhansky, D R Yakovlev, A K Zvezdin, M Bayer
Currently spin waves are considered for computation and data processing as an alternative to charge currents. Generation of spin waves by ultrashort laser pulses provides several important advances with respect to conventional approaches using microwaves. In particular, focused laser spot works as a point source for spin waves and allows for directional control of spin waves and switching between their different types. For further progress in this direction it is important to manipulate with the spectrum of the optically generated spin waves...
July 18, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28717563/multiphoton-in-vivo-imaging-with-a-femtosecond-semiconductor-disk-laser
#17
Fabian F Voigt, Florian Emaury, Philipp Bethge, Dominik Waldburger, Sandro M Link, Stefano Carta, Alexander van der Bourg, Fritjof Helmchen, Ursula Keller
We use an ultrafast diode-pumped semiconductor disk laser (SDL) to demonstrate several applications in multiphoton microscopy. The ultrafast SDL is based on an optically pumped Vertical External Cavity Surface Emitting Laser (VECSEL) passively mode-locked with a semiconductor saturable absorber mirror (SESAM) and generates 170-fs pulses at a center wavelength of 1027 nm with a repetition rate of 1.63 GHz. We demonstrate the suitability of this laser for structural and functional multiphoton in vivo imaging in both Drosophila larvae and mice for a variety of fluorophores (including mKate2, tdTomato, Texas Red, OGB-1, and R-CaMP1...
July 1, 2017: Biomedical Optics Express
https://www.readbyqxmd.com/read/28717198/controlled-modification-of-biomolecules-by-ultrashort-laser-pulses-in-polar-liquids
#18
Vitaly Gruzdev, Dmitry Korkin, Brian P Mooney, Jesper F Havelund, Ian Max Møller, Jay J Thelen
Targeted chemical modification of peptides and proteins by laser pulses in a biologically relevant environment, i.e. aqueous solvent at room temperature, allows for accurate control of biological processes. However, the traditional laser methods of control of chemical reactions are applicable only to a small class of photosensitive biomolecules because of strong and ultrafast perturbations from biomolecule-solvent interactions. Here, we report excitation of harmonics of vibration modes of solvent molecules by femtosecond laser pulses to produce controlled chemical modifications of non-photosensitive peptides and proteins in polar liquids under room conditions...
July 17, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28716900/structural-insights-into-the-extracellular-recognition-of-the-human-serotonin-2b-receptor-by-an-antibody
#19
Andrii Ishchenko, Daniel Wacker, Mili Kapoor, Ai Zhang, Gye Won Han, Shibom Basu, Nilkanth Patel, Marc Messerschmidt, Uwe Weierstall, Wei Liu, Vsevolod Katritch, Bryan L Roth, Raymond C Stevens, Vadim Cherezov
Monoclonal antibodies provide an attractive alternative to small-molecule therapies for a wide range of diseases. Given the importance of G protein-coupled receptors (GPCRs) as pharmaceutical targets, there has been an immense interest in developing therapeutic monoclonal antibodies that act on GPCRs. Here we present the 3.0-Å resolution structure of a complex between the human 5-hydroxytryptamine 2B (5-HT2B) receptor and an antibody Fab fragment bound to the extracellular side of the receptor, determined by serial femtosecond crystallography with an X-ray free-electron laser...
July 17, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28716114/visumax-femtolasik-versus-moria-m2-microkeratome-in-mild-to-moderate-myopia-efficacy-safety-predictability-aberrometric-changes-and-flap-thickness-predictability
#20
Magda A Torky, Yousif A Al Zafiri, Abeer M Khattab, Rania K Farag, Eman A Awad
INTRODUCTION: This is an interventional prospective clinical study which was conducted to evaluate the efficacy, safety, predictability, ocular aberrations, and flap thickness predictability of Visumax femtosecond laser (FSL) compared to Moria M2 microkeratome (MK) in mild to moderate myopia. METHODS: This study included 60 eyes who were divided into two groups. Thirty eyes in group (I) in which the flap was created with Visumax FSL, while in group II (30 eyes) the Moria M2 MK was used...
July 17, 2017: BMC Ophthalmology
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