The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
M Dinescu - One of the best experts on this subject based on the ideXlab platform.
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comparison of 193nm and 308nm laser liquid printing by Shadowgraphy imaging
Applied Surface Science, 2013Co-Authors: A Pallapapavlu, Thomas Lippert, Alexander Wokaun, James Shawstewart, Thomas Mattle, Valentina Dinca, M DinescuAbstract:Over the last years laser-induced forward transfer has emerged as a versatile and powerful tool for engineering surfaces with active compounds. Soft, easily damageable materials can be transferred using a triazene polymer as a sacrificial layer which acts as a pressure generator and at the same time protects the material from direct laser irradiation. To understand and optimize the transfer process of biomolecules in liquid solution by using an intermediate triazene polymer photosensitive layer, Shadowgraphy imaging is carried out. Two laser systems i.e. an ArF laser operating at 193 nm and a XeCl laser operating at 308 nm are applied for the transfer. Solutions with 50% v/v glycerol concentration are prepared and the influence of the triazene polymer sacrificial layer thickness (60 nm) on the deposits is studied. The Shadowgraphy images reveal a pronounced difference between laser-induced forward transfer using 193 nm or 308 nm, i.e. very different shapes of the ejected liquid.
Christian Willert - One of the best experts on this subject based on the ideXlab platform.
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Tomographic Shadowgraphy for three-dimensional reconstruction of instantaneous spray distributions
Experiments in Fluids, 2012Co-Authors: Joachim Klinner, Christian WillertAbstract:Tomographic Shadowgraphy is an image-based optical technique capable of reconstructing the three dimensional instantaneous spray distributions within a given volume. The method is based on a multiple view imaging setup with inline illumination provided by current-pulsed LEDs, which results in droplet shadows being projected onto multiple sensor planes. Each camera records image pairs with short inter-framing times that allow the trajectories of the individual droplets to be estimated using conventional three-dimensional particle tracking approaches. The observed volume is calibrated with a traversed micro-target. A comparison is made between several photogrammetric and polynomial least-square camera calibration techniques regarding their accuracy in deep volume calibration at magnifications close to unity. A calibration method based on volume calibration from multiple planar homographies at equally spaced z -planes was found to produce the most reliable calibration. The combination of back-projected images at each voxel plane efficiently reproduces the droplet positions in three-dimensional space by line-of-sight (LOS) intensity reconstruction. Further improvement of the reconstruction can be achieved by iterative tomographic reconstruction, namely simultaneous multiplicative algebraic reconstruction technique (SMART). The quality of spray reconstruction is investigated using experimental data from multiple view shadowgraphs of hollow cone and flat fan water sprays. The investigations are further substantiated with simulations using synthetic data.
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Tomographic Spray Shadowgraphy - A Feasibility Study
2011Co-Authors: Joachim Klinner, Christian WillertAbstract:This contribution introduces tomographic Shadowgraphy, a volume resolving imaging technique which is capable of recovering the liquid phase of a spray both spatially and temporally. The method is based on a multiple view camera setup with inline illumination provided by current pulsed LEDs which results in droplet shadows being projected onto the sensor plane. Each camera records image pairs with short interframing times which allows the trajectories of the individual droplets to be estimated using conventional three-dimensional particle tracking approaches. The observed volume is calibrated with a traversed micro target. A comparison is made between several photogrammetric and polynomial least square camera calibration techniques regarding their accuracy in deep volume calibration at magnifications close to unity. A calibration method based on volume calibration from multiple planar homographies at equally spaced z-planes was found to produce the most reliable calibration. Sequential combination of back-projected images at each voxel plane efficiently reproduces the droplet positions in three-dimensional space. The quality of spray reconstruction is investigated using experimental data from multiple view shadowgraphs of a hollow cone spray.
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Tomographic Shadowgraphy for spray diagnostics
2011Co-Authors: Joachim Klinner, Christian WillertAbstract:This contribution introduces 3-D Shadowgraphy which is capable of resolving the placement of the liquid phase within a certain spray volume both spatially and temporally. The method is based on a multiple view camera setup and inline illumination provided by current pulsed LEDs. The quality of spray reconstruction was investigated using experimental data from multiple view shadowgraphs of hollow cone and flat fan water sprays. After calibration and determination of a 3-D mapping function for each view a line-of-sight (LOS) intensity reconstruction was implemented. After sequential combination of back-projected images at each voxel plane of the volume the 3-D droplet and ligament positions can be readily obtained. Further improvement of intensity reconstruction may be achieved by a iterative tomographic reconstruction, namely multiplicative algebraic reconstruction technique (SMART). These improvements are documented by comparing slices of the averaged 3-D shadowgraph intensity of the hollow cone spray orthogonal to the flow. The investigations were further substantiated with simulations using synthetic data to estimate reconstruction quality at increasing droplet densities.
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on the implementation of tomographic Shadowgraphy for spray diagnostics
2011Co-Authors: Joachim Klinner, Christian WillertAbstract:This contribution introduces 3-D Shadowgraphy which is capable of resolving the placement of the liquid phase within a certain spray volume both spatially and temporally. The method is based on a multiple view camera setup and inline illumination provided by current pulsed LEDs. The observed volume is calibrated with a traversed micro target. A comparison is made between several photogrammetric and polynomial least square camera calibration techniques regarding their accuracy in deep volume calibration at magnifications close to 1 : 1. A new calibration method is suggested which derives volume calibration from multiple planar homographies at equally spaced z-planes. After an sequential combination of back-projected images at each voxel plane the 3-D droplet positions can be readily obtained. The quality of spray reconstruction was investigated using experimental data from multiple view shadowgraphs of hollow cone and flat fan water sprays. The investigations were further substantiated with simulations using synthetic data.
Mohinder S Yadav - One of the best experts on this subject based on the ideXlab platform.
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multiple laser based high speed digital Shadowgraphy system for small caliber projectile target interaction studies
Optical Engineering, 2014Co-Authors: Ramesh C Kalonia, Dharam P Chhachhia, Phun Phun Bajpai, Manjit Singh, Ipsita Biswas, Mohinder S YadavAbstract:High-speed optical Shadowgraphy plays an important role in study of various phenomena including projectile-target interaction for small caliber projectile. Present work reports design, development, and imple- mentation of a multiple laser-based high-speed digital Shadowgraphy system to study the behavior of a small caliber projectile in flight as well as the projectile-target interaction. System is based on Cranz- Schardin technique. Low power digitally modulated laser diodes along with low-resolution CMOS cameras in global shuttering mode are used to record good quality digital shadowgraphs. The system can record 11 shadowgraphs at a maximum frame rate of 1 million∕s and is able to capture even minute details of fragments in the form of shockwaves. Operation of the system, image recording and analysis are fully computer controlled. The design and system description inclusive ultra-short pulse generator and opto-electronic triggering unit are presented and experimental results are discussed.©2014 Societyof Photo-Optical InstrumentationEngineers (SPIE)(DOI:10.1117/1 .OE.53.3.034104)
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multiple laser flash Shadowgraphy system for terminal studies of small caliber projectiles
Optical Engineering, 2010Co-Authors: Ramesh C Kalonia, Manjit Singh, Gautam Mitra, Ganga Sharan Singh, R K Varma, Manpreet Singh, V S Sethi, Mohinder S YadavAbstract:A multiple-laser flash Shadowgraphy system has been innovatively designed and developed to study the terminal effects of projectiles. The system has been designed based on modulated laser diodes operated at low voltage and current. In order to study the ballistics effects of small arms, an exposure time of the order of a few hundreds ns and a delay time of the order of a few tens of μs are needed. An ultrashort pulse generator has been developed to provide the exposure and delay time pulses. The developed system has been integrated with a field lens assembly and camera assembly. To record the shadowgraphs, a target is placed near the center of the field lens and a bullet is fired from a fixed gun. The system is described, and experimental results and conclusions are reported.
James Shawstewart - One of the best experts on this subject based on the ideXlab platform.
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comparison of 193nm and 308nm laser liquid printing by Shadowgraphy imaging
Applied Surface Science, 2013Co-Authors: A Pallapapavlu, Thomas Lippert, Alexander Wokaun, James Shawstewart, Thomas Mattle, Valentina Dinca, M DinescuAbstract:Over the last years laser-induced forward transfer has emerged as a versatile and powerful tool for engineering surfaces with active compounds. Soft, easily damageable materials can be transferred using a triazene polymer as a sacrificial layer which acts as a pressure generator and at the same time protects the material from direct laser irradiation. To understand and optimize the transfer process of biomolecules in liquid solution by using an intermediate triazene polymer photosensitive layer, Shadowgraphy imaging is carried out. Two laser systems i.e. an ArF laser operating at 193 nm and a XeCl laser operating at 308 nm are applied for the transfer. Solutions with 50% v/v glycerol concentration are prepared and the influence of the triazene polymer sacrificial layer thickness (60 nm) on the deposits is studied. The Shadowgraphy images reveal a pronounced difference between laser-induced forward transfer using 193 nm or 308 nm, i.e. very different shapes of the ejected liquid.
A.j. Taylor - One of the best experts on this subject based on the ideXlab platform.
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Electromagnetically‐Driven Cylindrical 2‐D Shockwave Profile Measurements in Water with Laser Shadowgraphy
AIP Conference Proceedings, 2004Co-Authors: George Rodriguez, J.p. Roberts, A.j. TaylorAbstract:Experiments performed at the Los Alamos National Laboratory’s Atlas 23 MJ z‐pinch capacitor bank facility allows for experimental characterization of electro‐magnetically driven cylindrical shockwave implosions. Time resolved laser Shadowgraphy is used to dynamically image an Atlas generated liner‐target radial shock implosion in water with 2‐D imaging detail that provides benchmark results for numerical hydro‐code validation efforts at Los Alamos. Theoretical interest in these shock experiments arises since the shock propagation velocity is modified as shock‐strengthening effects are predicted to occur as material flow approaches the region of on‐axis convergence. Our laser shadowgraph measurements capture eight separate image frames of shockwave motion in the water with an overall spatial and temporal resolution of ±0.25 mm and 10 ns, respectively. Imaging of the shockwave radial shape and position inside the water volume allows for quantitative comparison with numerical simulations. A linear fit to the...
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high speed laser Shadowgraphy for electromagnetically driven cylindrical implosions
Review of Scientific Instruments, 2001Co-Authors: G. Rodriguez, J.p. Roberts, J.a. Echave, A.j. TaylorAbstract:A laser Shadowgraphy system for high-speed imaging of a convergent cylindrical shockwave generated by an electromagnetically driven solid density liner implosion in Lucite is described. The laser Shadowgraphy system utilizes an advanced high-energy, long-pulse, frequency-doubled Nd:YAG laser for target illumination and a fast framing camera for multiple frame imaging of the shockwave as it radially converges and transits the Lucite. The time window resolution is 10 ns as determined by the fastest exposure time capable with the camera. Two on-axis symmetric implosions and two off-axis asymmetric implosion experiments were fielded at the Air Force Research Laboratory’s Shiva Star 4.2 MJ capacitor bank z-pinch facility. For each experimental shot, the Shadowgraphy system captured several frames of shadowgraph images as the shockwave moved through the Lucite. Analysis of the shockwave shadowgraph image shapes is done by fitting each shadowgraph image to a generic elliptical fit function and plotting the resultant two-dimensional image fits for comparison. For the on-axis symmetric implosion shots, a radial trajectory plot is extracted and a radial shock velocity is calculated. The Lucite shock speed is seen to increase monotonically from an initial velocity of 7.9 mm/μs to a near final velocity of 13.4 mm/μs as convergence effects dominate the shock speed calculated at small radii.
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Development and fielding of high-speed laser Shadowgraphy for electro-magnetically driven cylindrical implosions
PPPS-2001 Pulsed Power Plasma Science 2001. 28th IEEE International Conference on Plasma Science and 13th IEEE International Pulsed Power Conference. , 2001Co-Authors: J.p. Roberts, G. Rodriguez, J.a. Echave, A.j. TaylorAbstract:A laser Shadowgraphy system for high-speed imaging of a convergent cylindrical shockwave generated by an electro-magnetically driven solid density liner implosion in Lucite is described. The laser Shadowgraphy system utilizes an advanced high-energy, long-pulse, frequency-doubled Nd:YAG laser for target illumination and a fast framing camera for multiple frame imaging of the shockwave as it radially converges and transits the Lucite. The time window resolution is 10 ns as determined by the fastest exposure time capable with the camera. Two on-axis symmetric implosions and two off-axis antisymmetric implosion experiments were fielded at the Air Force Research Laboratory's Shiva Star 4.2 MJ capacitor bank z-pinch facility. For each experimental shot, the Shadowgraphy system captured several frames of shadowgraph images as the shockwave moved through the Lucite. Analysis of the shockwave shadowgraph image shapes is done by fitting each shadowgraph image to a generic elliptical fit function and plotting the resultant 2-D image fits for comparison. For the on-axis symmetric implosion shots, a radial shock velocity is calculated. The Lucite shock speed is seen to increase monotonically from an initial velocity of 7.9 mm//spl mu/s to a near final velocity of 13.4 mm//spl mu/s as convergence effects dominate the shock speed calculated at small radii.
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Development and fielding of high speed laser Shadowgraphy for electro-magnetically driven cylindrical implosions
IEEE Conference Record - Abstracts. PPPS-2001 Pulsed Power Plasma Science 2001. 28th IEEE International Conference on Plasma Science and 13th IEEE Int, 2001Co-Authors: G. Rodriguez, J.p. Roberts, A.j. Taylor, J.a. EchaveAbstract:Summary form only given. Experimental characterization of a converging shockwave in a cylindrical geometry provides fundamental benchmarks used in the modeling of hydrodynamic phenomena from solid density implosions. A high-speed laser Shadowgraphy system for detailed imaging of a cylindrical convergent shockwave provides diagnosis where multiple sampling of the shock front position and radial shape are desired. We present the development of an advanced laser Shadowgraphy system: a novel laser source, the fiber optic delivery system, double-pass target imaging, and fast frame camera image acquisition, recently fielded on a set of hydrodynamic implosion experiments. Labeled the Near Term Liner Experiments (NTLX), an experimental series of four shots were conducted at the Shiva Star Pulsed Power Facility in Albuquerque, NM for the High Energy Density Hydrodynamics Program at Los Alamos National Laboratory.