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A I Chernov, M A Kozhaev, I V Savochkin, D V Dodonov, P M Vetoshko, A K Zvezdin, V I Belotelov
In most of the previous studies of the spin wave optical generation in magnetic dielectrics, the backward volume spin waves were excited. Here we modified the parameters of the circularly polarized optical pump beams emitted by femtosecond laser to reveal surface spin waves in bismuth iron garnet thin film. Beams that are larger than 10 μm in diameter generate both surface and volume spin waves with only one spectral peak near the ferromagnetic resonance. On the contrary, narrower beams excite predominantly surface spin waves of higher frequency, providing an additional peak in the spin wave spectrum...
January 15, 2017: Optics Letters
Boju Gai, Yukun Sun, Haneol Lim, Huandong Chen, Joseph Faucher, Minjoo L Lee, Jongseung Yoon
Large-scale deployment of GaAs solar cells in terrestrial photovoltaics demands significant cost reduction for preparing device-quality epitaxial materials. Although multilayer epitaxial growth in conjunction with printing-based materials assemblies has been proposed as a promising route to achieve this goal, their practical implementation remains challenging owing to the degradation of materials properties and resulting nonuniform device performance between solar cells grown in different sequences. Here we report an alternative approach to circumvent these limitations and enable multilayer-grown GaAs solar cells with uniform photovoltaic performance...
January 11, 2017: ACS Nano
Hao Song, Dan Ruan, Wenyang Liu, V Andrew Stenger, Rolf Pohmann, Maria A Fernandez Seara, Tejas Nair, Sungkyu Jung, Jingqin Luo, Yuichi Motai, Jingfei Ma, John D Hazle, H Michael Gach
PURPOSE: Respiratory motion prediction using an artificial neural network (ANN) was integrated with pseudocontinuous arterial spin labeling (pCASL) MRI to allow free-breathing perfusion measurements in the kidney. In this study, we evaluated the performance of the ANN to accurately predict the location of the kidneys during image acquisition. METHODS: A pencil-beam navigator was integrated with a pCASL sequence to measure lung/diaphragm motion during ANN training and the pCASL transit delay...
January 11, 2017: Medical Physics
R Kramer, V F Cassola, M E A Andrade, M W C de Araújo, D J Brenner, H J Khoury
The purpose of bowtie filters in CT scanners is to homogenize the x-ray intensity measured by the detectors in order to improve the image quality and at the same time to reduce the dose to the patient because of the preferential filtering near the periphery of the fan beam. For CT dosimetry, especially for Monte Carlo calculations of organ and tissue absorbed doses to patients, it is important to take the effect of bowtie filters into account. However, material composition and dimensions of these filters are proprietary...
January 10, 2017: Physics in Medicine and Biology
U P Gomes, D Ercolani, V Zannier, S Battiato, E Ubyivovk, V Mikhailovskii, Y Murata, S Heun, F Beltram, L Sorba
We report on the heterogeneous nucleation of catalyst-free InAs nanowires on Si(111) substrates by chemical beam epitaxy. We show that nanowire nucleation is enhanced by sputtering the silicon substrate with energetic particles. We argue that particle bombardment introduces lattice defects on the silicon surface that serve as preferential nucleation sites. The formation of these nucleation sites can be controlled by the sputtering parameters, allowing the control of nanowire density in a wide range. Nanowire nucleation is accompanied by unwanted parasitic islands, but careful choice of annealing and growth temperature allows us to strongly reduce the relative density of these islands and to realize samples with high nanowire yield...
January 10, 2017: Nanotechnology
Mark V Mishra, Sameer Aggarwal, Soren M Bentzen, Nancy Knight, Minesh P Mehta, William F Regine
PURPOSE: To review and assess ongoing proton beam therapy (PBT) clinical trials and to identify major gaps. METHODS AND MATERIALS: Active PBT clinical trials were identified from and the World Health Organization International Clinical Trials Platform Registry. Data on clinical trial disease site, age group, projected patient enrollment, expected start and end dates, study type, and funding source were extracted. RESULTS: A total of 122 active PBT clinical trials were identified, with target enrollment of >42,000 patients worldwide...
February 1, 2017: International Journal of Radiation Oncology, Biology, Physics
C Fair, R Shanley, J Rogosheske, A Lazaryan, B McClune, C G Brunstein, V Bachanova
No abstract text is available yet for this article.
January 9, 2017: Bone Marrow Transplantation
Yang Wu, Xuepeng Qiu, Hongwei Liu, Jingbo Liu, Yan Chen, Lin Ke, Hyunsoo Yang
We report a highly efficient tunable THz reflector in graphene. By applying a small gate voltage (up to �� 3 V), the reflectance of graphene is modulated from a minimum of 0.79% to a maximum of 33.4% using graphene/ionic liquid structures at room temperature, and the reflection tuning is uniform within a wide spectral range (0.1 ��� 1.5 THz). Our observation is explained by the Drude model, which describes the THz wave-induced intraband transition in graphene. This tunable reflectance of graphene may contribute to broadband THz mirrors, deformable THz mirrors, variable THz beam splitters and other optical components...
January 9, 2017: Nanotechnology
P Piersimoni, J Ramos-Méndez, T Geoghegan, V A Bashkirov, R W Schulte, B A Faddegon
PURPOSE: To determine the dependence of the accuracy in reconstruction of relative stopping power (RSP) with proton computerized tomography (pCT) scans on the purity of the proton beam and the technological complexity of the pCT scanner using standard phantoms and a digital representation of a pediatric patient. METHODS: The Monte Carlo method was applied to simulate the pCT scanner, using both a pure proton beam (uniform 200 MeV mono-energetic, parallel beam) and the Northwestern Medicine Chicago Proton Center (NMCPC) clinical beam in uniform scanning mode...
November 22, 2016: Medical Physics
M Brouard, S D S Gordon, A Hackett Boyle, C G Heid, B Nichols, V Walpole, F J Aoiz, S Stolte
The integral steric asymmetry for the inelastic scattering of NO(X) by a variety of collision partners was recorded using a crossed molecular beam apparatus. The initial state of the NO(X, v = 0, j = 1/2, Ω=1/2, ϵ=-1,f) molecule was selected using a hexapole electric field, before the NO bond axis was oriented in a static electric field, allowing probing of the scattering of the collision partner at either the N- or O-end of the molecule. Scattered NO molecules were state selectively probed using (1 + 1') resonantly enhanced multiphoton ionisation, coupled with velocity-map ion imaging...
January 7, 2017: Journal of Chemical Physics
Patrick W McLaughlin, Adam L Liss, Paul L Nguyen, Dean G Assimos, Anthony V D'Amico, Alexander R Gottschalk, Gary S Gustafson, Sameer R Keole, Stanley L Liauw, Shane Lloyd, Benjamin Movsas, Bradley R Prestidge, Timothy N Showalter, Al V Taira, Neha Vapiwala, Brian J Davis
PURPOSE: To present the most updated American College of Radiology consensus guidelines formed from an expert panel on treatment of locally advanced, high-risk prostate cancer METHODS:: The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer-reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios...
January 4, 2017: American Journal of Clinical Oncology
S S Stafeev, A G Nalimov, M V Kotlyar, D Gibson, S Song, L O'Faolain, V V Kotlyar
We have investigated a four-sector transmission polarization converter (4-SPC) for a wavelength of 633 nm, that enables the conversion of a linearly polarized incident beam into a mixture of linearly and azimuthally polarized beams. It was numerically shown that by placing a Fresnel zone plate of focal length 532 nm immediately after the 4-SPC, the incident light can be focused into an oblong subwavelength focal spot whose size is smaller than the diffraction limit (with width and breadth, respectively, measuring FWHM = 0...
December 26, 2016: Optics Express
Erik J Bochove, V S Rao Gudimetla
We propose a self-consistency condition based on the extended Huygens-Fresnel principle, which we apply to the propagation kernel of the mutual coherence function of a partially coherent laser beam propagating through a turbulent atmosphere. The assumption of statistical independence of turbulence in neighboring propagation segments leads to an integral equation in the propagation kernel. This integral equation is satisfied by a Gaussian function, with dependence on the transverse coordinates that is identical to the previous Gaussian formulation by Yura [Appl...
January 1, 2017: Journal of the Optical Society of America. A, Optics, Image Science, and Vision
Christopher V Poulton, Matthew J Byrd, Manan Raval, Zhan Su, Nanxi Li, Erman Timurdogan, Douglas Coolbaugh, Diedrik Vermeulen, Michael R Watts
We demonstrate passive large-scale nanophotonic phased arrays in a CMOS-compatible silicon photonic platform. Silicon nitride waveguides are used to allow for higher input power and lower phase variation compared to a silicon-based distribution network. A phased array at an infrared wavelength of 1550 nm is demonstrated with an ultra-large aperture size of 4  mm×4  mm, achieving a record small and near diffraction-limited spot size of 0.021°×0.021° with a side lobe suppression of 10 dB. A main beam power of 400 mW is observed...
January 1, 2017: Optics Letters
E A Zlobina, S I Kablukov, A A Wolf, A V Dostovalov, S A Babin
High beam quality and narrow spectrum have been obtained in a Raman fiber laser based on a 1.1 km long graded-index fiber directly pumped by a multimode 915 nm laser diode. The generation of a near-diffraction-limited beam at 954 nm with M<sup>2</sup>≤1.27 and Δλ=0.42  nm at an output power above 10 W is enabled by a cavity mirror made of a special fiber Bragg grating inscribed by a femtosecond technique in the central part of the graded-index fiber core.
January 1, 2017: Optics Letters
Victor V Kotlyar, Alexey A Kovalev, Alexey P Porfirev
We theoretically study a Gaussian optical beam with an embedded off-axis optical vortex. We also experimentally generate such an asymmetric Gaussian optical vortex by using an off-axis spiral phase plate. It is shown that depending on the shift distance the laser beam has the form of a crescent, which is rotated upon propagation. An analytical expression is obtained for the orbital angular momentum of such a beam, which appears to be fractional. When the shift increases, the greater the number of spirality of the phase plate or the "fork" hologram, the slower the momentum decreases...
January 1, 2017: Optics Letters
Ilya A Fedorov, Alexander E Ulanov, Yury V Kurochkin, A I Lvovsky
We propose and implement a new scheme of generating the optical Einstein-Podolsky-Rosen entangled state. Parametric down-conversion in two nonlinear crystals, positioned back-to-back in the waist of a pump beam, produces single-mode squeezed vacuum states in orthogonal polarization modes; a subsequent beam splitting entangles them and generates the Einstein-Podolsky-Rosen state. The technique takes advantage of the strong nonlinearity associated with type-0 phase-matching configuration while, at the same time, eliminating the need for actively stabilizing the optical phase between the two single-mode squeezers...
January 1, 2017: Optics Letters
Yuan-Qing Huang, Rong Huang, Qing-Lu Liu, Chang-Cheng Zheng, Ji-Qiang Ning, Yong Peng, Zi-Yang Zhang
In this paper, we demonstrated the fabrication of one-dimensional (1D) and two-dimensional (2D) periodic nanostructures on III-V GaAs substrates utilizing laser direct writing (LDW) technique. Metal thin films (Ti) and phase change materials (Ge2Sb2Te5 (GST) and Ge2Sb1.8Bi0.2Te5 (GSBT)) were chosen as photoresists to achieve small feature sizes of semiconductor nanostructures. A minimum feature size of about 50 nm about a quarter of the optical diffraction limit was obtained on the photoresists, and 1D III-V semiconductor nanolines with a minimum width of 150 nm were successfully acquired on the GaAs substrate which was smaller than the best results acquired on Si substrate ever reported...
December 2017: Nanoscale Research Letters
K Masterova, A Sethi, D Anderson, V Prabhu, I Rusu, S Gros, E Melian
PURPOSE: Frameless Stereotactic radiosurgery (SRS) is increasingly used in the clinic. Cone-Beam CT (CBCT) to simulation-CT match has replaced the 3-dimensional coordinate based set up using a stereotactic localizing frame. The SRS frame however served as both a localizing and immobilizing device. We seek to measure the quality of frameless (mask based) and frame based immobilization and evaluate its impact on target dose. METHODS: Each SRS patient was set up by kV on-board imaging (OBI) and then fine-tuned with CBCT...
June 2016: Medical Physics
D Cao, M Jermoumi, V Mehta, D Shepard
PURPOSE: Clinical implementation of gated lung SBRT requires tools to verify the accuracy of the target positioning on a daily basis. This is a particular challenge on Elekta linacs where the XVI imaging system does not interface directly to any commercial gating solution. In this study, we used the Elekta's intra-fractional imaging functionality to perform the pretreatment CBCT verifications and evaluated both the image quality and gating accuracy. METHODS: To use intrafraction imaging tools for pretreatment verifications, we planned a 360-degree arc with 1mmx5mm MLC opening...
June 2016: Medical Physics
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