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https://www.readbyqxmd.com/read/28914922/effect-of-nitrogen-doping-on-the-photoluminescence-intensity-of-graphene-quantum-dots
#1
Svette Reina Merden Santiago, Yee Ann Wong, Tzu-Neng Lin, Chiao-Hsin Chang, Chi-Tsu Yuan, Ji-Lin Shen
We have developed a facile, fast, and one-step synthetic method to prepare graphene quantum dots (GQDs) simultaneously with nitrogen (N) doping via pulsed laser ablation. The N-doped GQDs (N-GQDs) with an average size around 3 nm and an N/C atomic ratio of 33% have been obtained. The N-GQDs emit blue photoluminescence (PL), where the PL intensity enhances as the N doping increases. The PL enhancement for the N-GQDs with a factor as high as 25 has been achieved as compared to GQDs. The origin of the PL enhancement in GQDs after N doping is attributed to the increased densities of pyridinic and graphitic N...
September 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28900751/effect-of-wavelength-and-beam-width-on-penetration-in-light-tissue-interaction-using-computational-methods
#2
Caerwyn Ash, Michael Dubec, Kelvin Donne, Tim Bashford
Penetration depth of ultraviolet, visible light and infrared radiation in biological tissue has not previously been adequately measured. Risk assessment of typical intense pulsed light and laser intensities, spectral characteristics and the subsequent chemical, physiological and psychological effects of such outputs on vital organs as consequence of inappropriate output use are examined. This technical note focuses on wavelength, illumination geometry and skin tone and their effect on the energy density (fluence) distribution within tissue...
September 12, 2017: Lasers in Medical Science
https://www.readbyqxmd.com/read/28900164/enhancing-laser-driven-proton-acceleration-by-using-micro-pillar-arrays-at-high-drive-energy
#3
Dimitri Khaghani, Mathieu Lobet, Björn Borm, Loïc Burr, Felix Gärtner, Laurent Gremillet, Liana Movsesyan, Olga Rosmej, Maria Eugenia Toimil-Molares, Florian Wagner, Paul Neumayer
The interaction of micro- and nano-structured target surfaces with high-power laser pulses is being widely investigated for its unprecedented absorption efficiency. We have developed vertically aligned metallic micro-pillar arrays for laser-driven proton acceleration experiments. We demonstrate that such targets help strengthen interaction mechanisms when irradiated with high-energy-class laser pulses of intensities ~10(17-18) W/cm(2). In comparison with standard planar targets, we witness strongly enhanced hot-electron production and proton acceleration both in terms of maximum energies and particle numbers...
September 12, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28894271/laser-induced-linear-field-particle-acceleration-in-free-space
#4
Liang Jie Wong, Kyung-Han Hong, Sergio Carbajo, Arya Fallahi, Philippe Piot, Marin Soljačić, John D Joannopoulos, Franz X Kärtner, Ido Kaminer
Linear-field particle acceleration in free space (which is distinct from geometries like the linac that requires components in the vicinity of the particle) has been studied for over 20 years, and its ability to eventually produce high-quality, high energy multi-particle bunches has remained a subject of great interest. Arguments can certainly be made that linear-field particle acceleration in free space is very doubtful given that first-order electron-photon interactions are forbidden in free space. Nevertheless, we chose to develop an accurate and truly predictive theoretical formalism to explore this remote possibility when intense, few-cycle electromagnetic pulses are used in a computational experiment...
September 11, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28884244/lasers-and-intense-pulsed-light-ipl-association-with-cancerous-lesions
#5
Caerwyn Ash, Godfrey Town, Rebecca Whittall, Louise Tooze, Jaymie Phillips
The development and use of light and lasers for medical and cosmetic procedures has increased exponentially over the past decade. This review article focuses on the incidence of reported cases of skin cancer post laser or IPL treatment. The existing evidence base of over 25 years of laser and IPL use to date has not raised any concerns regarding its long-term safety with only a few anecdotal cases of melanoma post treatment over two decades of use; therefore, there is no evidence to suggest that there is a credible cancer risk...
September 7, 2017: Lasers in Medical Science
https://www.readbyqxmd.com/read/28883424/efficient-post-acceleration-of-protons-in-helical-coil-targets-driven-by-sub-ps-laser-pulses
#6
H Ahmed, S Kar, G Cantono, P Hadjisolomou, A Poye, D Gwynne, C L S Lewis, A Macchi, K Naughton, G Nersisyan, V Tikhonchuk, O Willi, M Borghesi
The characteristics of laser driven proton beams can be efficiently controlled and optimised by employing a recently developed helical coil technique, which exploits the transient self-charging of solid targets irradiated by intense laser pulses. Here we demonstrate a well collimated (<1° divergence) and narrow bandwidth (~10% energy spread) proton beamlet of ~10(7) particles at 10 ± 0.5 MeV obtained by irradiating helical coil targets with a few joules, sub-ps laser pulses at an intensity of ~2 × 10(19) W cm(-2)...
September 7, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28878232/holographic-writing-of-ink-based-phase-conjugate-nanostructures-via-laser-ablation
#7
Muhammad Waqas Khalid, Rajib Ahmed, Ali K Yetisen, Bader AlQattan, Haider Butt
The optical phase conjugation (OPC) through photonic nanostructures in coherent optics involves the utilization of a nonlinear optical mechanism through real-time processing of electromagnetic fields. Their applications include spectroscopy, optical tomography, wavefront sensing, and imaging. The development of functional and personalized holographic devices in the visible and near-infrared spectrum can be improved by introducing cost-effective, rapid, and high-throughput fabrication techniques and low-cost recording media...
September 6, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28872134/coulomb-explosion-imaging-as-a-tool-to-distinguish-between-stereoisomers
#8
Martin Pitzer, Kilian Fehre, Maksim Kunitski, Till Jahnke, Lothar Schmidt, Horst Schmidt-Böcking, Reinhard Dörner, Markus Schöffler
This article shows how the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) or the "reaction microscope" technique can be used to distinguish between enantiomers (stereoisomers) of simple chiral species on the level of individual molecules. In this approach, a gaseous molecular jet of the sample expands into a vacuum chamber and intersects with femtosecond (fs) laser pulses. The high intensity of the pulses leads to fast multiple ionization, igniting a so-called Coulomb Explosion that produces several cationic (positively charged) fragments...
August 18, 2017: Journal of Visualized Experiments: JoVE
https://www.readbyqxmd.com/read/28872125/measurements-of-long-range-electronic-correlations-during-femtosecond-diffraction-experiments-performed-on-nanocrystals-of-buckminsterfullerene
#9
Rebecca A Ryan, Sophie Williams, Andrew V Martin, Ruben A Dilanian, Connie Darmanin, Corey T Putkunz, David Wood, Victor A Streltsov, Michael W M Jones, Naylyn Gaffney, Felix Hofmann, Garth J Williams, Sebastien Boutet, Marc Messerschmidt, M Marvin Seibert, Evan K Curwood, Eugeniu Balaur, Andrew G Peele, Keith A Nugent, Harry M Quiney, Brian Abbey
The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered 'random'...
August 22, 2017: Journal of Visualized Experiments: JoVE
https://www.readbyqxmd.com/read/28871115/in-situ-visualization-of-multiple-filament-competition-dynamic-during-nonlinear-propagation-of-femtosecond-laser
#10
Pengfei Qi, Lie Lin, Qiang Su, Nan Zhang, Lu Sun, Weiwei Liu
In this work, multiple filamentation competition of femtosecond pulse in methanol is studied both experimentally and numerically. The visualization of multiple filamentation competition has been realized in the experiment performing the three-photon fluorescence of Coumarin 440. The random changes of multiple filamentation stemmed from the jitter of the peak laser intensity ratio of initial hot spots are first observed directly and visually, which can be well explained by a simplified (2D+1)-dimensional model...
September 4, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28863677/a-gated-thomson-parabola-spectrometer-for-improved-ion-and-neutral-atom-measurements-in-intense-laser-produced-plasmas
#11
Sheroy Tata, Angana Mondal, Soubhik Sarkar, Amit D Lad, M Krishnamurthy
Ions of high energy and high charge are accelerated from compact intense laser produced plasmas and are routinely analysed either by time of flight or Thomson parabola spectrometry. At the highest intensities where ion energies can be substantially large, both these techniques have limitations. Strong electromagnetic pulse noise jeopardises the arrival time measurement, and a bright central spot in the Thomson parabola spectrometer affects the signal to noise ratio of ion traces that approach close to the central spot...
August 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28861729/a-preliminary-randomized-clinical-trial-comparing-diode-laser-and-scalpel-periosteal-incision-during-implant-surgery-impact-on-postoperative-morbidity-and-implant-survival
#12
Aysan Shahnaz, Raika Jamali, Farnush Mohammadi, Afshin Khorsand, Neda Moslemi, Reza Fekrazad
The aim of this preliminary randomized clinical trial was to compare: (1) post-operative morbidity after application of laser or scalpel incision for flap advancement during implant surgery and bone grafting and (2) implant survival rate following flap advancement with laser or scalpel incision after 6 months of loading. Eighteen patients who were scheduled for dental implant placement and simultaneous bone grafting were randomly assigned to test or control groups. Diode laser (810 nm, 2 W, pulse interval 200 μs; pulse length 100 μs, 400-μm initiated fiber tip), or scalpel (control) was used to sever the periosteum to create a tension-free flap...
August 31, 2017: Lasers in Medical Science
https://www.readbyqxmd.com/read/28856913/effects-of-external-trigeminal-nerve-stimulation-etns-on-laser-evoked-cortical-potentials-lep-a-pilot-study-in-migraine-patients-and-controls
#13
Eleonora Vecchio, Eleonora Gentile, Giovanni Franco, Katia Ricci, Marina de Tommaso
Background Transcutaneous external supraorbital nerve stimulation has emerged as a treatment option for primary headache disorders, though its action mechanism is still unclear. Study aim In this randomized, sham-controlled pilot study we aimed to test the effects of a single external transcutaneous nerve stimulation session on pain perception and cortical responses induced by painful laser stimuli delivered to the right forehead and the right hand in a cohort of migraine without aura patients and healthy controls...
January 1, 2017: Cephalalgia: An International Journal of Headache
https://www.readbyqxmd.com/read/28853899/refractory-plasmonics-without-refractory-materials
#14
Gelon Albrecht, Stefan Kaiser, Harald Giessen, Mario Hentschel
Refractory plasmonics deals with metallic nanostructures that can withstand high temperatures and intense laser pulses. The common belief was that refractory materials such as TiN are necessary for this purpose. Here we show that refractory plasmonics is possible without refractory materials. We demonstrate that gold nanostructures which are overcoated with 4 and 40 nm Al2O3 (alumina) by an atomic layer deposition process or by thick IC1-200 resist can withstand temperatures of over 800 °C at ambient atmospheric conditions...
September 8, 2017: Nano Letters
https://www.readbyqxmd.com/read/28835700/effect-of-crystal-orientation-on-femtosecond-laser-induced-thermomechanical-responses-and-spallation-behaviors-of-copper-films
#15
Qi-Lin Xiong, Zhenhuan Li, Takayuki Kitamura
Ultrafast thermomechanical responses and spallation behaviours of monocrystal copper films irradiated by femtosecond laser pulse are investigated using molecular dynamics simulation (MDS). Films with 〈100〉, 〈110〉 and 〈111〉 crystal orientations along the thickness direction were studied. The results show that the crystal orientation has a significant effect on femtosecond laser-induced thermomechanical responses and spallation behaviors of monocrystal copper films. The discrepancy between normal stresses in copper films with different crystal orientation leads to distinct differences in lattice temperature...
August 23, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28831487/light-intensity-field-enhancement-life-induced-localized-edge-abrasion-of-silica-coated-silver-nanoprisms
#16
Rijil Thomas, Soo Zeng Fiona Phua, Sivaramapanicker Sreejith, Yanli Zhao, Cheong Boon Soh
Silver nanoprisms (AgNPrs) exhibit localized surface plasmon resonance (LSPR) in the near infrared (NIR) region of the electromagnetic spectrum. LSPR-driven electric field enhancement around AgNPr edges has been investigated in various studies. A coating of dielectric materials such as silica on the surface of the AgNPrs is employed to extend the application of these nanoparticles under biocompatible conditions and to increase the thermal stability. Upon interactions with optical excitation (pulsed laser excitation), the AgNPrs undergo light intensity field enhancement (LIFE) at the corners...
August 23, 2017: Nanoscale
https://www.readbyqxmd.com/read/28830172/rotational-dissociation-of-impulsively-aligned-van-der-waals-complexes
#17
Anders A Søndergaard, Robert E Zillich, Henrik Stapelfeldt
The nonadiabatic alignment dynamics of weakly bound molecule-atom complexes, induced by a moderately intense 300 fs nonresonant laser pulse, is calculated by direct numerical solution of the time-dependent Schrödinger equation. Our method propagates the wave function according to the coupled channel equations for the complex, which can be done in a very efficient and stable manner out to large times. We present results for two van der Waal complexes, CS2-He and HCCH-He, as respective examples of linear molecules with large and small moments of inertia...
August 21, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28829098/plasmon-driven-sub-picosecond-breathing-of-metal-nanoparticles
#18
Franco P Bonafé, Bálint Aradi, Mengxue Guan, Oscar A Douglas-Gallardo, Chao Lian, Sheng Meng, Thomas Frauenheim, Cristián G Sánchez
We present the first real-time atomistic simulation on the quantum dynamics of icosahedral silver nanoparticles under strong laser pulses, using time dependent density functional theory (TDDFT) molecular dynamics. We identify the emergence of sub-picosecond breathing-like radial oscillations starting immediately after laser pulse excitation, with increasing amplitude as the field intensity increases. The ultrafast dynamic response of nanoparticles to laser excitation points to a new mechanism other than equilibrium electron-phonon scattering previously assumed, which takes a much longer timescale...
August 31, 2017: Nanoscale
https://www.readbyqxmd.com/read/28828925/towards-ion-beam-therapy-based-on-laser-plasma-accelerators
#19
Leonhard Karsch, Elke Beyreuther, Wolfgang Enghardt, Malte Gotz, Umar Masood, Ulrich Schramm, Karl Zeil, Jörg Pawelke
Only few ten radiotherapy facilities worldwide provide ion beams, in spite of their physical advantage of better achievable tumor conformity of the dose compared to conventional photon beams. Since, mainly the large size and high costs hinder their wider spread, great efforts are ongoing to develop more compact ion therapy facilities. One promising approach for smaller facilities is the acceleration of ions on micrometre scale by high intensity lasers. Laser accelerators deliver pulsed beams with a low pulse repetition rate, but a high number of ions per pulse, broad energy spectra and high divergences...
August 22, 2017: Acta Oncologica
https://www.readbyqxmd.com/read/28827645/micron-scale-mapping-of-megagauss-magnetic-fields-using-optical-polarimetry-to-probe-hot-electron-transport-in-petawatt-class-laser-solid-interactions
#20
Gourab Chatterjee, Prashant Kumar Singh, A P L Robinson, D Blackman, N Booth, O Culfa, R J Dance, L A Gizzi, R J Gray, J S Green, P Koester, G Ravindra Kumar, L Labate, Amit D Lad, K L Lancaster, J Pasley, N C Woolsey, P P Rajeev
The transport of hot, relativistic electrons produced by the interaction of an intense petawatt laser pulse with a solid has garnered interest due to its potential application in the development of innovative x-ray sources and ion-acceleration schemes. We report on spatially and temporally resolved measurements of megagauss magnetic fields at the rear of a 50-μm thick plastic target, irradiated by a multi-picosecond petawatt laser pulse at an incident intensity of ~10(20) W/cm(2). The pump-probe polarimetric measurements with micron-scale spatial resolution reveal the dynamics of the magnetic fields generated by the hot electron distribution at the target rear...
August 21, 2017: Scientific Reports
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