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Intense pulse light

Paul Hoerner, H Bernhard Schlegel
The angular dependence of ionization by linear and circularly polarized light has been examined for N2, NH3, H2O, CO2, CH2O pyrazine, methyloxirane, and vinyloxirane. Time dependent configuration interaction with single excitations and a complex absorbing potential was used to simulate ionization by a seven cycle 800 nm cosine squared pulse with intensities ranging from 0.56x10^14 W cm^-2 to 5.05x10^14 W cm^-2. The shapes of the ionization yield for linearly polarized light can be understood primarily in terms of the nodal structure of the highest occupied orbitals...
January 18, 2017: Journal of Physical Chemistry. A
Asaf Dahan, Assaf Levanon, Mordechai Katz, Haim Suchowski
We introduce a generalization of the adiabatic frequency conversion method for an efficient conversion of ultrashort pulses in the full nonlinear regime. Our analysis takes into account dispersion as well as two-photon processes and Kerr effect, allowing complete analysis of any three waves with arbitrary phase mismatched design and any nonlinear optical process. We use this analysis to design an efficient and robust second harmonic generation, the most widely used nonlinear process for both fundamental and applied research...
January 16, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Ryan J Martinie, Elizabeth J Blaesi, Carsten Krebs, J Martin Bollinger, Alexey Silakov, Christopher J Pollock
High-valent iron and manganese complexes effect some of the most challenging biochemical reactions known, including hydrocarbon and water oxidations associated with the global carbon cycle and oxygenic photosynthesis, respectively. Their extreme reactivity presents an impediment to structural characterization, but their biological importance and potential chemical utility have, nevertheless, motivated extensive efforts toward that end. Several such intermediates accumulate during activation of class I ribonucleotide reductase (RNR) β subunits, which self-assemble dimetal cofactors with stable one-electron oxidants that serve to initiate the enzyme's free-radical mechanism...
January 11, 2017: Journal of the American Chemical Society
Iko Hyppänen, Niina Perälä, Riikka Arppe, Michael Schäferling, Tero Soukka
The luminescence intensity ratio (LIR) of the green emissions of the near-infrared excited NaYF4:Yb3+,Er3+ nanocrystals is a promising method for temperature sensing. Here, the influence of excitation power density, excitation pulse length, excitation wavelength, silica shell, and solvent on the LIR and its temperature response is reported. Primary objective is to study the LIR mechanism and the impact of measurement and environmental parameters on the calibration and precision of the LIR. The LIR value is demonstrated to be unaffected by the excitation intensity in the studied range...
January 10, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
M S Hur, B Ersfeld, A Noble, H Suk, D A Jaroszynski
Ultra-intense, narrow-bandwidth, electromagnetic pulses have become important tools for exploring the characteristics of matter. Modern tuneable high-power light sources, such as free-electron lasers and vacuum tubes, rely on bunching of relativistic or near-relativistic electrons in vacuum. Here we present a fundamentally different method for producing narrow-bandwidth radiation from a broad spectral bandwidth current source, which takes advantage of the inflated radiation impedance close to cut-off in a medium with a plasma-like permittivity...
January 10, 2017: Scientific Reports
M J Delgado-González, M M Sánchez-Guillén, M V García-Moreno, M C Rodríguez-Dodero, C García-Barroso, D A Guillén-Sánchez
During the ageing of brandies, many physicochemical processes take place involving the distilled spirit and the wood of the casks. Because of these reactions, the polyphenolic content of brandies and their content of organic acids increase with the ageing. These reactions are slow, and the ageing of high-quality brandies takes several years. In this paper, the development of a system that uses the circulation of the wine distillate through encapsulated American oak chips and the application of ultrasound energy with the aim of producing aged wine spirits has been carried out, and the influences of the operation variables over the characteristics of the produced drink have been measured...
May 2017: Ultrasonics Sonochemistry
Valdemar Stankevič, Gediminas Račiukaitis, Francesca Bragheri, Xuewen Wang, Eugene G Gamaly, Roberto Osellame, Saulius Juodkazis
Understanding of material behaviour at nanoscale under intense laser excitation is becoming critical for future application of nanotechnologies. Nanograting formation by linearly polarised ultra-short laser pulses has been studied systematically in fused silica for various pulse energies at 3D laser printing/writing conditions, typically used for the industrial fabrication of optical elements. The period of the nanogratings revealed a dependence on the orientation of the scanning direction. A tilt of the nanograting wave vector at a fixed laser polarisation was also observed...
January 9, 2017: Scientific Reports
Dong Yoon Oh, Ki Youl Yang, Connor Fredrick, Gabriel Ycas, Scott A Diddams, Kerry J Vahala
Short duration, intense pulses of light can experience dramatic spectral broadening when propagating through lengths of optical fibre. This continuum generation process is caused by a combination of nonlinear optical effects including the formation of dispersive waves. Optical analogues of Cherenkov radiation, these waves allow a pulse to radiate power into a distant spectral region. In this work, efficient and coherent dispersive wave generation of visible to ultraviolet light is demonstrated in silica waveguides on a silicon chip...
January 9, 2017: Nature Communications
Jing Lian, Yide Ma, Yurun Ma, Bin Shi, Jizhao Liu, Zhen Yang, Yanan Guo
PURPOSE: As gallbladder diseases including gallstone and cholecystitis are mainly diagnosed by using ultra-sonographic examinations, we propose a novel method to segment the gallbladder and gallstones in ultrasound images. METHODS: The method is divided into five steps. Firstly, a modified Otsu algorithm is combined with the anisotropic diffusion to reduce speckle noise and enhance image contrast. The Otsu algorithm separates distinctly the weak edge regions from the central region of the gallbladder...
January 6, 2017: International Journal of Computer Assisted Radiology and Surgery
Sungeun Jo, Hong Jin Kong, Hyochoong Bang, Jae-Wan Kim, Jomsool Kim, Soungwoong Choi
An innovative flash LIDAR (light detection and ranging) system with high spatial resolution and high range precision is proposed in this paper. The proposed system consists of a polarization modulating Pockels cell (PMPC) and a micro-polarizer CCD camera (MCCD). The Pockels cell changes its polarization state with respect to time after a laser pulse is emitted from the system. The polarization state of the laser-return pulse depends on the arrival time. The MCCD measures the intensity of the returning laser pulse to calculate the polarization state, which gives the range...
December 26, 2016: Optics Express
B Liu, H Bromberger, A Cartella, T Gebert, M Först, A Cavalleri
We report on the generation of high-energy (1.9 μJ) far-infrared pulses tunable between 4 and 18 THz frequency. Emphasis is placed on tunability and on minimizing the bandwidth of these pulses to less than 1 THz, as achieved by difference-frequency mixing of two linearly chirped near-infrared pulses in the organic nonlinear crystal DSTMS. As the two near-infrared pulses are derived from amplification of the same white light continuum, their carrier envelope phase fluctuations are mutually correlated, and hence the difference-frequency THz field exhibits absolute phase stability...
January 1, 2017: Optics Letters
Anatoly A Svidzinsky, Hichem Eleuch, Marlan O Scully
If an electromagnetic pulse is detuned from atomic transition frequency by amount Δ>1/τ, where τ is the turn-on time of the pulse, then atomic population adiabatically follows the pulse intensity without causing Rabi oscillations. Here we show that, if initially, the atom has nonzero coherence, then the adiabatic pulse yields Rabi oscillations of atomic population ρ<sub>aa</sub>(t), and we obtain analytical solutions for ρ<sub>aa</sub>(t). Our findings can be useful for achieving generation of coherent light in the backward direction in the QASER scheme in which modulation of the coupling between light and atoms is produced by Rabi oscillations...
January 1, 2017: Optics Letters
P Black, Y Na, C Wuu
PURPOSE: Cherenkov light emission has been shown to correlate with ionizing radiation (IR) dose delivery in solid tissue. In order to properly correlate Cherenkov light images with real time dose delivery in a patient, we must account for geometric and intensity distortions arising from observation angle, as well as the effect of monitor units (MU) and field size on Cherenkov light emission. To test the feasibility of treatment field verification, we first focused on Cherenkov light emission efficiency based on MU and known field size (FS)...
June 2016: Medical Physics
S Goddu, B Sun, K Grantham, T Zhao, T Zhang, J Bradley, S Mutic
PURPOSE: Proton therapy (PT) delivery is complex and extremely dynamic. Therefore, quality assurance testing is vital, but highly time-consuming. We have developed a High-Speed Scintillation-Camera-System (HS-SCS) for simultaneously measuring multiple beam characteristics. METHODS: High-speed camera was placed in a light-tight housing and dual-layer neutron shield. HS-SCS is synchronized with a synchrocyclotron to capture individual proton-beam-pulses (PBPs) at ∼504 frames/sec...
June 2016: Medical Physics
Juan Sun, Hao Deng, Ningwu Liu, Hongliang Wang, Benli Yu, Jingsong Li
We developed a laser absorption sensor based on a pulsed, broadband tunable external cavity quantum cascade laser (ECQCL) centered at 1285 cm(-1). Unlike traditional infrared spectroscopy system, a quartz crystal tuning fork (QCTF) as a light detector was used for laser signal detection. Fast Fourier transform was applied to extract vibration intensity information of QCTF. The sensor system is successfully tested on nitrous oxide (N2O) spectroscopy measurements and compared with a standard infrared detector...
December 2016: Review of Scientific Instruments
B Kramer, J Wunderlich, P Muranyi
Non-thermal disinfection technologies are gaining increasing interest in the field of minimally processed food in order to improve the microbial safety or to extend the shelf life. Especially fresh-cut produce or meat and fish products are vulnerable to microbial spoilage but due to their sensitivity, they require gentle preservation measures. The application of intense light pulses (PL) of a broad spectral range comprising ultraviolet, visible and near infrared irradiation is currently investigated as a potentially suitable technology to reduce microbial loads on different food surfaces or in beverages...
December 29, 2016: Journal of Applied Microbiology
Wei-Peng Li, Chia-Hao Su, Ling-Chuan Tsao, Chun-Ting Chang, Ya-Ping Hsu, Chen-Sheng Yeh
Carbon monoxide (CO) causes the dysfunction of mitochondria to induce the apoptosis of cancer cells giving a promising choice as an emerging treatment. The currently reported CO-based complexes still suffer from many limitations. Synthesis of CO-release carriers in the manner of on-demand control is highly anticipated. In this study, we present a near-infrared (NIR) light-responsive CO-delivery nanocarrier, a PEGylated iron carbonyl derivatized Prussian blue (PB) nanoparticle (NP). Taking the structural characteristic containing Fe(3+)-N≡C-Fe(2+) unit, the -CN(-) served as the active sites for the coordination of iron carbonyl, while the surface Fe sites chelated with the amine-functionalized polyethylene glycol (NH2-PEG6000-NH2) to yield PEGylated PB NPs carrying CO...
December 27, 2016: ACS Nano
Christina Schwarz, Robin Sharma, William S Fischer, Mina Chung, Grazyna Palczewska, Krzysztof Palczewski, David R Williams, Jennifer J Hunter
Two-photon ophthalmoscopy has potential for in vivo assessment of function of normal and diseased retina. However, light safety of the sub-100 fs laser typically used is a major concern and safety standards are not well established. To test the feasibility of safe in vivo two-photon excitation fluorescence (TPEF) imaging of photoreceptors in humans, we examined the effects of ultrashort pulsed light and the required light levels with a variety of clinical and high resolution imaging methods in macaques. The only measure that revealed a significant effect due to exposure to pulsed light within existing safety standards was infrared autofluorescence (IRAF) intensity...
December 1, 2016: Biomedical Optics Express
Mark van Gastel, Sander Stuijk, Gerard de Haan
Continuous monitoring of respiration is essential for early detection of critical illness. Current methods require sensors attached to the body and/or are not robust to subject motion. Alternative camera-based solutions have been presented using motion vectors and remote photoplethysmography. In this work, we present a non-contact camera-based method to detect respiration, which can operate in both visible and dark lighting conditions by detecting the respiratory-induced colour differences of the skin. We make use of the close similarity between skin colour variations caused by the beating of the heart and those caused by respiration, leading to a much improved signal quality compared to single-channel approaches...
December 1, 2016: Biomedical Optics Express
Gonzalo Arias-Gil, Frank Walter Ohl, Kentaroh Takagaki, Michael Thomas Lippert
Optogenetics is one of the most important techniques in neurophysiology, with potential clinical applications. However, the strong light needed may cause harmful temperature rises. So far, there are no methods to reliably estimate brain heating and safe limits in actual optogenetic experiments. We used thermal imaging to directly measure such temperature rises at the surface of live mouse brains during laser illumination with wavelengths and intensities typical for optogenetics. We then modeled the temperature rise with a simple logarithmic model...
October 2016: Neurophotonics
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