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Femtosecond laser

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https://www.readbyqxmd.com/read/28225007/full-3d-modelling-of-pulse-propagation-enables-efficient-nonlinear-frequency-conversion-with-low-energy-laser-pulses-in-a-single-element-tripler
#1
Tomasz M Kardaś, Michał Nejbauer, Paweł Wnuk, Bojan Resan, Czesław Radzewicz, Piotr Wasylczyk
Although new optical materials continue to open up access to more and more wavelength bands where femtosecond laser pulses can be generated, light frequency conversion techniques are still indispensable in filling the gaps on the ultrafast spectral scale. With high repetition rate, low pulse energy laser sources (oscillators) tight focusing is necessary for a robust wave mixing and the efficiency of broadband nonlinear conversion is limited by diffraction as well as spatial and temporal walk-off. Here we demonstrate a miniature third harmonic generator (tripler) with conversion efficiency exceeding 30%, producing 246 fs UV pulses via cascaded second order processes within a single laser beam focus...
February 22, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28219079/light-induced-structural-changes-and-the-site-of-o-o-bond-formation-in-psii-caught-by-xfel
#2
Michihiro Suga, Fusamichi Akita, Michihiro Sugahara, Minoru Kubo, Yoshiki Nakajima, Takanori Nakane, Keitaro Yamashita, Yasufumi Umena, Makoto Nakabayashi, Takahiro Yamane, Takamitsu Nakano, Mamoru Suzuki, Tetsuya Masuda, Shigeyuki Inoue, Tetsunari Kimura, Takashi Nomura, Shinichiro Yonekura, Long-Jiang Yu, Tomohiro Sakamoto, Taiki Motomura, Jing-Hua Chen, Yuki Kato, Takumi Noguchi, Kensuke Tono, Yasumasa Joti, Takashi Kameshima, Takaki Hatsui, Eriko Nango, Rie Tanaka, Hisashi Naitow, Yoshinori Matsuura, Ayumi Yamashita, Masaki Yamamoto, Osamu Nureki, Makina Yabashi, Tetsuya Ishikawa, So Iwata, Jian-Ren Shen
Photosystem II (PSII) is a huge membrane-protein complex consisting of 20 different subunits with a total molecular mass of 350 kDa for a monomer. It catalyses light-driven water oxidation at its catalytic centre, the oxygen-evolving complex (OEC). The structure of PSII has been analysed at 1.9 Å resolution by synchrotron radiation X-rays, which revealed that the OEC is a Mn4CaO5 cluster organized in an asymmetric, 'distorted-chair' form. This structure was further analysed with femtosecond X-ray free electron lasers (XFEL), providing the 'radiation damage-free' structure...
February 20, 2017: Nature
https://www.readbyqxmd.com/read/28217747/insights-into-photosystem-ii-from-isomorphous-difference-fourier-maps-of-femtosecond-x-ray-diffraction-data-and-quantum-mechanics-molecular-mechanics-structural-models
#3
REVIEW
Jimin Wang, Mikhail Askerka, Gary W Brudvig, Victor S Batista
Understanding structure-function relations in photosystem II (PSII) is important for the development of biomimetic photocatalytic systems. X-ray crystallography, computational modeling, and spectroscopy have played central roles in elucidating the structure and function of PSII. Recent breakthroughs in femtosecond X-ray crystallography offer the possibility of collecting diffraction data from the X-ray free electron laser (XFEL) before radiation damage of the sample, thereby overcoming the main challenge of conventional X-ray diffraction methods...
February 10, 2017: ACS Energy Lett
https://www.readbyqxmd.com/read/28215341/dissection-and-characterization-of-microtubule-bundles-in-the-mitotic-spindle-using-femtosecond-laser-ablation
#4
R Buđa, K Vukušić, I M Tolić
The mitotic spindle is a highly organized and dynamic structure required for segregation of the genetic material into two daughter cells. Although most of the individual players involved in building the spindle have been characterized in vitro, a general understanding of how all of the spindle players act together in vivo is still missing. Hence, in recent years, experiments have focused on introducing mechanical perturbations of the spindle on a micron scale, thereby providing insight into its function and organization, as well as into forces acting in the spindle...
2017: Methods in Cell Biology
https://www.readbyqxmd.com/read/28211728/electron-vortices-in-femtosecond-multiphoton-ionization
#5
D Pengel, S Kerbstadt, D Johannmeyer, L Englert, T Bayer, M Wollenhaupt
Multiphoton ionization of potassium atoms with a sequence of two counter-rotating circularly polarized femtosecond laser pulses produces vortex-shaped photoelectron momentum distributions in the polarization plane describing Archimedean spirals. The pulse sequences are produced by polarization shaping and the three-dimensional photoelectron distributions are tomographically reconstructed from velocity map imaging measurements. We show that perturbative ionization leads to electron vortices with c_{6} rotational symmetry...
February 3, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28210504/comparison-of-maximum-stretch-forces-between-femtosecond-laser-assisted-capsulotomy-and-continuous-curvilinear-capsulorhexis
#6
Mari Takagi, Takashi Kojima, Kei Ichikawa, Yoshiki Tanaka, Yukihito Kato, Rie Horai, Akeno Tamaoki, Kazuo Ichikawa
The current study reports comparing the postoperative mechanical properties of the anterior capsule between femtosecond laser capsulotomy (FLC) and continuous curvilinear capsulorhexis (CCC) of variable size and shape in porcine eyes. All CCCs were created using capsule forceps. Irregular or eccentric CCCs were also created to simulate real cataract surgery. For FLC, capsulotomies 5.3 mm in diameter were created using the LenSx® (Alcon) platform. Fresh porcine eyes were used in all experiments. The edges of the capsule openings were pulled at a constant speed using two L-shaped jigs...
2017: Journal of Ophthalmology
https://www.readbyqxmd.com/read/28210176/femtosecond-astigmatic-keratotomy-for-postkeratoplasty-astigmatism
#7
Nasser Al Sabaani, Salem Al Malki, Mohanna Al Jindan, Abdullah Al Assiri, Samar Al Swailem
PURPOSE: To evaluate the initial outcomes of femtosecond laser arcuate keratotomies (AK) to correct high astigmatism after keratoplasty. METHODS: This retrospective non-comparative interventional study included 52 consecutive patients (52 eyes) who underwent Intralase-enabled arcuate keratotomies. Changes in uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BCVA), mean refractive and keratometric astigmatism, preoperative and postoperative manifest refraction and complications were the main outcome measures...
July 2016: Saudi Journal of Ophthalmology: Official Journal of the Saudi Ophthalmological Society
https://www.readbyqxmd.com/read/28203055/resident-surgeon-efficiency-in-femtosecond-laser-assisted-cataract-surgery
#8
Andrew C Pittner, Brian R Sullivan
PURPOSE: Comparison of resident surgeon performance efficiencies in femtosecond laser-assisted cataract surgery (FLACS) versus conventional phacoemulsification. PATIENTS AND METHODS: A retrospective cohort study was conducted on consecutive patients undergoing phacoemulsification cataract surgery performed by senior ophthalmology residents under the supervision of 1 attending physician during a 9-month period in a large Veterans Affairs medical center. Medical records were reviewed for demographic information, preoperative nucleus grade, femtosecond laser pretreatment, operative procedure times, total operating room times, and surgical complications...
2017: Clinical Ophthalmology
https://www.readbyqxmd.com/read/28202732/atomic-structure-of-granulin-determined-from-native-nanocrystalline-granulovirus-using-an-x-ray-free-electron-laser
#9
Cornelius Gati, Dominik Oberthuer, Oleksandr Yefanov, Richard D Bunker, Francesco Stellato, Elaine Chiu, Shin-Mei Yeh, Andrew Aquila, Shibom Basu, Richard Bean, Kenneth R Beyerlein, Sabine Botha, Sébastien Boutet, Daniel P DePonte, R Bruce Doak, Raimund Fromme, Lorenzo Galli, Ingo Grotjohann, Daniel R James, Christopher Kupitz, Lukas Lomb, Marc Messerschmidt, Karol Nass, Kimberly Rendek, Robert L Shoeman, Dingjie Wang, Uwe Weierstall, Thomas A White, Garth J Williams, Nadia A Zatsepin, Petra Fromme, John C H Spence, Kenneth N Goldie, Johannes A Jehle, Peter Metcalf, Anton Barty, Henry N Chapman
To understand how molecules function in biological systems, new methods are required to obtain atomic resolution structures from biological material under physiological conditions. Intense femtosecond-duration pulses from X-ray free-electron lasers (XFELs) can outrun most damage processes, vastly increasing the tolerable dose before the specimen is destroyed. This in turn allows structure determination from crystals much smaller and more radiation sensitive than previously considered possible, allowing data collection from room temperature structures and avoiding structural changes due to cooling...
February 15, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28198887/femtosecond-two-photon-planar-laser-induced-fluorescence-of-carbon-monoxide-in-flames
#10
Daniel R Richardson, Sukesh Roy, James R Gord
Two-photon, planar laser-induced fluorescence (TP-PLIF) of carbon monoxide was performed in steady and driven flames using femtosecond (fs) laser pulses at 1 kHz. Excitation radiation at 230.1 nm (full-width at half-maximum bandwidth of 270  cm<sup>-1</sup>) was used to pump many rovibrational two-photon transitions in the B<sup>1</sup>∑<sup>+</sup>←X<sup>1</sup>∑<sup>+</sup> system. Visible fluorescence in the range 362-516 nm was captured using an image intensifier and high-speed camera...
February 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28198871/generating-high-contrast-near-single-cycle-waveforms-with-third-order-dispersion-compensation
#11
Henry Timmers, Yuki Kobayashi, Kristina F Chang, Maurizio Reduzzi, Daniel M Neumark, Stephen R Leone
Femtosecond laser pulses lasting only a few optical periods hold the potential for probing and manipulating the electronic degrees of freedom within matter. However, the generation of high-contrast, few-cycle pulses in the high power limit still remains nontrivial. In this Letter, we present the application of ammonium dihydrogen phosphate (ADP) as an optical medium for compensating for the higher-order dispersion of a carrier-envelope stable few-cycle waveform centered at 735 nm. The ADP crystal is capable of removing the residual third-order dispersion present in the spectral phase of an input pulse, resulting in near-transform-limited 2...
February 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28198846/femtosecond-two-photon-laser-induced-fluorescence-of-krypton-for-high-speed-flow-imaging
#12
Yejun Wang, Cade Capps, Waruna D Kulatilaka
Ultrashort-pulse (femtosecond-duration) two-photon laser-induced fluorescence (fs-TPLIF) of an inert gas tracer krypton (Kr) is investigated. A detailed spectroscopic study of fluorescence channels followed by the 5p<sup>'</sup>←←4p excitation of Kr at 204.1 nm is reported. The experimental line positions in the 750-840 nm emission region agree well with the NIST Atomic Spectra Database. The present work provides an accurate listing of relative line strengths in this spectral region. In the range of laser pulse energies investigated, a quadratic dependence was observed between the Kr-TPLIF signal and the laser pulse energy...
February 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28192588/conventional-versus-inverted-side-cut-flaps-for-femtosecond-laser-assisted-lasik-laboratory-and-clinical-evaluation
#13
Vishal Jhanji, Tommy C Y Chan, Wai Ying Li, Rayne R Lim, Marco C Y Yu, Kasin Law, Peng Yi, Yolanda W Y Yip, Yumeng Wang, Tsz Kin Ng, Shyam S Chaurasia, Rajiv R Mohan
PURPOSE: To study the differences in early corneal cellular events and biomechanical properties after femtosecond laser-assisted LASIK performed using conventional or inverted side-cut angles. METHODS: In the laboratory study, left eyes of 24 rabbits underwent LASIK flap creation with a 70° or 115° side-cut. The contralateral eyes served as controls. The corneas were harvested 24 hours postoperatively. In the clinical study, 2 eyes of each patient (n = 29) were randomized to corneal flap creation with 70° or 115° side-cut angles during LASIK...
February 1, 2017: Journal of Refractive Surgery
https://www.readbyqxmd.com/read/28192584/laser-assisted-capsulotomy-centration-a-prospective-trial-comparing-pupil-versus-oct-based-scanned-capsule-centration
#14
Tim Schultz, Nikolaos Tsiampalis, H Burkhard Dick
PURPOSE: To investigate different capsulotomy centration methods for femtosecond laser-assisted cataract surgery. The overlap between intraocular lens (IOL) optic and lens capsule was measured with different centration methods and IOL types. METHODS: This was a prospective randomized clinical trial. Patients with cataract scheduled for femtosecond laser-assisted cataract surgery were assigned to one of four treatment groups: optical coherence tomography (OCT)-based scanned capsule centration (SCC) and three-piece IOL (SCC with three-piece IOL); scanned capsule centration and plate-haptic IOL (SCC with plate-haptic IOL); pupil centration (PC) and three-piece IOL (PC with three-piece IOL); or PC and plate-haptic IOL (PC with plate-haptic IOL)...
February 1, 2017: Journal of Refractive Surgery
https://www.readbyqxmd.com/read/28192300/efficiency-estimates-and-practical-aspects-of-an-optical-kerr-gate-for-time-resolved-luminescence-spectroscopy
#15
I Dmitruk, Ye Shynkarenko, A Dmytruk, D Aleksiuk, V Kadan, P Korenyuk, N Zubrilin, I Blonskiy
We report experience of assembling an optical Kerr gate setup at the Femtosecond Laser Center for collective use at the Institute of Physics of the National Academy of Sciences of Ukraine. This offers an inexpensive solution to the problem of time-resolved luminescence spectroscopy. Practical aspects of its design and alignment are discussed and its main characteristics are evaluated. Theoretical analysis and numerical estimates are performed to evaluate the efficiency and the response time of an optical Kerr gate setup for fluorescence spectroscopy with subpicosecond time resolution...
October 11, 2016: Methods and Applications in Fluorescence
https://www.readbyqxmd.com/read/28192297/controlling-and-tracking-of-colloidal-nanostructures-through-two-photon-fluorescence
#16
Dipankar Mondal, Debabrata Goswami
Multiphoton absorbing dye-coated trapped spherical bead at the focal plane of femtosecond optical tweezers shows nonlinear optical (NLO) phenomena. One such NLO process of two-photon fluorescence (TPF) has been used for the background-free imaging of a femtosecond laser-trapping event. Due to the high peak powers of femtosecond laser pulses with low average powers, it is possible to not only trap single nanospheres, but encourage optically directed self-assembly. The TPF signatures of trapped particles show evidence of such a directed self-assembly process which, in turn, can provide information about the structural dynamics during the process of cluster formation...
October 7, 2016: Methods and Applications in Fluorescence
https://www.readbyqxmd.com/read/28188490/a-review-of-laser-assisted-versus-traditional-phacoemulsification-cataract-surgery
#17
REVIEW
H Burkhard Dick, Tim Schultz
The use of femtosecond laser surgery improves the precision and reproducibility of corneal incisions and the capsular opening; it also reduces the amount of ultrasound energy required for lens nucleus work-up. The rate of complications reported so far appears to be low. There are a number of contraindications such as a history of cornea and/or glaucoma surgery and certain anatomical features like deep-set eyes, kyphosis, tremor, and obesity. Visual recovery and refractive results of both techniques are excellent...
February 10, 2017: Ophthalmology and Therapy
https://www.readbyqxmd.com/read/28187180/comparative-evaluation-of-visual-outcomes-and-corneal-asphericity-after-laser-assisted-in-situ-keratomileusis-with-the-six-dimension-amaris-excimer-laser-system
#18
JunJie Piao, Ying-Jun Li, Woong-Joo Whang, Mihyun Choi, Min Ji Kang, Jee Hye Lee, Geunyoung Yoon, Choun-Ki Joo
PURPOSE: To compare the visual and refractive outcomes after laser-assisted in situ keratomileusis (LASIK) surgery for correction of myopia or myopic astigmatism using a six-dimensional Amaris excimer laser. METHODS: In this retrospective cohort study, we enrolled 47 eyes of 28 patients (age: 19-36 years) with myopia or myopic astigmatism. We used the Custom Ablation Manager protocol and performed ablations with the SCHWIND AMARIS system. LASIK flaps were cut with an iFS Advanced Femtosecond Laser...
2017: PloS One
https://www.readbyqxmd.com/read/28182182/ultrafast-injection-locked-amplification-in-a-thin-film-distributed-feedback-microcavity
#19
Meng Wang, Xinping Zhang
Injection mode locking is an important technique to achieve high-performance laser sources. Although this technique has been utilized in conventional laser systems, it has not been applied in thin-film distributed feedback lasers based on nanoscale photonic structures. We demonstrate an ultrafast injection-locked amplifier by injecting femtosecond supercontinuum pulses into a polymer-coated DFB microcavity. The amplifier works in the time scale of picoseconds and a bandwidth of 1 nm, supplying an easily recollimatable laser beam with excellent transverse mode...
February 9, 2017: Nanoscale
https://www.readbyqxmd.com/read/28176960/pseudophakic-astigmatism-reduction-with-femtosecond-laser-assisted-corneal-arcuate-incisions-a-pilot-study
#20
Clayton Blehm, Richard Potvin
PURPOSE: The aim of this study was to assess the effectiveness of the Verion-LenSx guided arcuate incision technique to reduce refractive astigmatism in a pseudophakic population. PATIENTS AND METHODS: A prospective single-arm study was conducted in which one or both eyes of subjects required reduction of 1.0-2.0 D of refractive astigmatism after previous cataract surgery or refractive lens exchange. The surgeon used the refractive cylinder in the eye and the Woodcock astigmatism nomogram for preoperative planning, while the LenSx femtosecond laser with the Verion Image Guided System was used to create all arcuate incisions...
2017: Clinical Ophthalmology
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