The Experts below are selected from a list of 70629 Experts worldwide ranked by ideXlab platform
A. J. Taylor - One of the best experts on this subject based on the ideXlab platform.
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scaling of terahertz radiation via optical rectification in electro optic crystals
Applied Physics Letters, 1995Co-Authors: Timothy J Carrig, A. J. Taylor, George Rodriguez, T S Clement, Kevin R StewartAbstract:We report on the scalability of generating terahertz radiation by optical rectification with the electro‐optic materials LiNbO3, LiTaO3, and dimethyl amino 4‐N‐methylstilbazolium tosylate (DAST). A Ti:sapphire laser system, producing 215 fs, 20 mJ pulses at 810 nm, was used for the experiment. Using LiNbO3 and LiTaO3, the peak of the generated terahertz electric field was found to scale linearly with increasing optical Fluence for Fluences up to 60 mJ/cm2, while with DAST the peak field scaled sublinearly in this Fluence range.
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scaling of terahertz radiation from large aperture biased photoconductors
Journal of The Optical Society of America B-optical Physics, 1994Co-Authors: P K Benicewicz, J P Roberts, A. J. TaylorAbstract:We present a theoretical and experimental investigation into the generation of subpicosecond pulses of terahertz radiation from large-aperture biased photoconductors with 1.5-eV photon excitation. A model that describes the far-field radiation from the optically excited, biased photoconductor is developed. The peak of the radiated electric field as well as waveforms are presented as a function of optical excitation Fluence and pulse width. The dependence of the terahertz radiation from biased InP and GaAs emitters on the applied bias field and on incident optical Fluence for bias fields as high as 12 kV/cm and for optical Fluences of 0.01–1.0 mJ/cm2 is presented. For a given level of optical excitation the radiated electric field is predicted by theory to scale linearly with the applied bias field. This prediction is verified experimentally, with radiated-field strengths as high as 1.23 ± 0.13 kV/cm being demonstrated. The radiated electric field also exhibits the monotonic saturation behavior predicted by theory, and saturation Fluences of 0.058 ± 0.015 and 0.018 ± 0.008 mJ/cm2 are obtained for InP and GaAs emitters, respectively.
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scaling of terahertz radiation from large aperture biased inp photoconductors
Optics Letters, 1993Co-Authors: P K Benicewicz, A. J. TaylorAbstract:We present, for biased InP emitters, the dependence of the generated terahertz radiation on bias field and optical Fluence for optical Fluences of 0.01–1.0 mJ/cm2 and bias fields as high as 12 kV/cm. The radiated electric field scales linearly with the bias field up to 12 kV/cm and exhibits monotonic saturation behavior, radiating half the maximum field at an excitation Fluence of 0.058 mJ/cm2.
Ted A Laurence - One of the best experts on this subject based on the ideXlab platform.
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high Fluence laser damage precursors and their mitigation in fused silica
Optics Express, 2014Co-Authors: J D Bude, Philip E Miller, Salmaan H Baxamusa, Nan Shen, Ted A Laurence, William A Steele, Tayyab I Suratwala, Lana Wong, W Carr, David A CrossAbstract:The use of any optical material is limited at high Fluences by laser-induced damage to optical surfaces. In many optical materials, the damage results from a series of sources which initiate at a large range of Fluences and intensities. Much progress has been made recently eliminating silica surface damage due to fracture-related precursors at relatively low Fluences (i.e., less than 10 J/cm2, when damaged by 355 nm, 5 ns pulses). At higher Fluence, most materials are limited by other classes of damage precursors which exhibit a strong threshold behavior and high areal density (>105 cm−2); we refer to these collectively as high Fluence precursors. Here, we show that a variety of nominally transparent materials in trace quantities can act as surface damage precursors. We show that by minimizing the presence of precipitates during chemical processing, we can reduce damage density in silica at high Fluence by more than 100 times while shifting the Fluence onset of observable damage by about 7 J/cm2. A better understanding of the complex chemistry and physics of cleaning, rinsing, and drying will likely lead to even further improvements in the damage performance of silica and potentially other optical materials.
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extracting the distribution of laser damage precursors on fused silica surfaces for 351 nm 3 ns laser pulses at high Fluences 20 150 j cm 2
Optics Express, 2012Co-Authors: Ted A Laurence, Nan Shen, Jeff D Bude, Michael D FeitAbstract:Surface laser damage limits the lifetime of optics for systems guiding high Fluence pulses, particularly damage in silica optics used for inertial confinement fusion-class lasers (nanosecond-scale high energy pulses at 355 nm/3.5 eV). The density of damage precursors at low Fluence has been measured using large beams (1-3 cm); higher Fluences cannot be measured easily since the high density of resulting damage initiation sites results in clustering. We developed automated experiments and analysis that allow us to damage test thousands of sites with small beams (10-30 µm), and automatically image the test sites to determine if laser damage occurred. We developed an analysis method that provides a rigorous connection between these small beam damage test results of damage probability versus laser pulse energy and the large beam damage results of damage precursor densities versus Fluence. We find that for uncoated and coated fused silica samples, the distribution of precursors nearly flattens at very high Fluences, up to 150 J/cm2, providing important constraints on the physical distribution and nature of these precursors.
Costas P Grigoropoulos - One of the best experts on this subject based on the ideXlab platform.
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time resolved emission and scattering imaging of plume dynamics and nanoparticle ejection in femtosecond laser ablation of silver thin films
Applied Physics Letters, 2020Co-Authors: Minok Park, Jinhong Jeun, Gyoowan Han, Costas P GrigoropoulosAbstract:Time-resolved emission and scattering imaging are employed to analyze the ablation mechanisms of silver thin films induced by femtosecond laser irradiation of Gaussian intensity profile under different laser Fluences and gas background pressures. At Fluences near the ablation threshold, nanoparticles (NPs) of 40 nm–100 nm in size are ejected in the vertical direction from the target sample. The average ejection speed of these NPs increases with the laser Fluence and also as the background gas pressure drops from ambient atmospheric to ∼10−5 Torr. At higher Fluences, a plume is formed at the center of the laser beam and NPs are released in oblique trajectories from the peripheral area of the laser-irradiated spot.
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efficiency of silicon micromachining by femtosecond laser pulses in ambient air
Journal of Applied Physics, 2006Co-Authors: David J Hwang, Costas P Grigoropoulos, Tae Y ChoiAbstract:Femtosecond lasers have proven to be effective tools for precise micromachining. Taking advantage of the reduced heat diffusion and the sharp ablation threshold at comparatively low energy densities, subdiffraction limit sized craters have been machined on silicon wafers by single near infrared Ti:sapphire laser pulses using a high numerical aperture objective lens. Two different ablation regimes have been identified by varying the laser Fluence. While two-photon absorption dominates in the low Fluence regime, electronic diffusion is a major energy transport mechanism at higher laser Fluences. Time-resolved pump-and-probe side-view imaging has been performed to investigate the energy coupling to the target specimen over a wide range of Fluences (up to around 1000J∕cm2) at lateral beam dimensions of the order of micrometers. The decrease of the ablation efficiency in the high Fluence regime (>10J∕cm2) is attributed to the strong interaction of the laser pulse with the laser-induced plasma.
Nan Shen - One of the best experts on this subject based on the ideXlab platform.
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high Fluence laser damage precursors and their mitigation in fused silica
Optics Express, 2014Co-Authors: J D Bude, Philip E Miller, Salmaan H Baxamusa, Nan Shen, Ted A Laurence, William A Steele, Tayyab I Suratwala, Lana Wong, W Carr, David A CrossAbstract:The use of any optical material is limited at high Fluences by laser-induced damage to optical surfaces. In many optical materials, the damage results from a series of sources which initiate at a large range of Fluences and intensities. Much progress has been made recently eliminating silica surface damage due to fracture-related precursors at relatively low Fluences (i.e., less than 10 J/cm2, when damaged by 355 nm, 5 ns pulses). At higher Fluence, most materials are limited by other classes of damage precursors which exhibit a strong threshold behavior and high areal density (>105 cm−2); we refer to these collectively as high Fluence precursors. Here, we show that a variety of nominally transparent materials in trace quantities can act as surface damage precursors. We show that by minimizing the presence of precipitates during chemical processing, we can reduce damage density in silica at high Fluence by more than 100 times while shifting the Fluence onset of observable damage by about 7 J/cm2. A better understanding of the complex chemistry and physics of cleaning, rinsing, and drying will likely lead to even further improvements in the damage performance of silica and potentially other optical materials.
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extracting the distribution of laser damage precursors on fused silica surfaces for 351 nm 3 ns laser pulses at high Fluences 20 150 j cm 2
Optics Express, 2012Co-Authors: Ted A Laurence, Nan Shen, Jeff D Bude, Michael D FeitAbstract:Surface laser damage limits the lifetime of optics for systems guiding high Fluence pulses, particularly damage in silica optics used for inertial confinement fusion-class lasers (nanosecond-scale high energy pulses at 355 nm/3.5 eV). The density of damage precursors at low Fluence has been measured using large beams (1-3 cm); higher Fluences cannot be measured easily since the high density of resulting damage initiation sites results in clustering. We developed automated experiments and analysis that allow us to damage test thousands of sites with small beams (10-30 µm), and automatically image the test sites to determine if laser damage occurred. We developed an analysis method that provides a rigorous connection between these small beam damage test results of damage probability versus laser pulse energy and the large beam damage results of damage precursor densities versus Fluence. We find that for uncoated and coated fused silica samples, the distribution of precursors nearly flattens at very high Fluences, up to 150 J/cm2, providing important constraints on the physical distribution and nature of these precursors.
Alexander Lawerenz - One of the best experts on this subject based on the ideXlab platform.
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ultra short pulsed laser ablation of silicon nitride layers investigation near threshold Fluence
Applied Surface Science, 2013Co-Authors: Gerrit Heinrich, Markus Wollgarten, Mario Bahr, Alexander LawerenzAbstract:Abstract In this work, silicon nitride (SiNx) layers, deposited on a planar silicon wafer are locally irradiated by ultra short laser pulses with Fluences near the threshold Fluence. The irradiated areas are investigated by SEM and TEM in order to analyze the laser inFluence to silicon and to the SiNx layer. Thereby, a lift-off process is observed for this SiNx layer. The silicon absorbs the laser pulse energy. For low Fluences, crystalline silicon is disordered below the SiNx layer. For high Fluences, silicon evaporates below the SiNx layer and bulge the SiNx layer. If the pressure within the bulge is high enough, the SiNx layer will break down due to high mechanical stress.