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Articles 1 - 19 of 19
Full-Text Articles in Physics
Detailed Characterization Of A Khz-Rate Laser-Driven Fusion At A Thin Liquid Sheet With A Neutron Detection Suite, Benjamin M. Knight, Connor Gautam, Colton R. Stoner, Bryan V. Egner, Joseph R. Smith, Christopher M. Orban, Juan J. Manfredi, Kyle Frische, Michael L. Dexter, Enam A. Chowdury, Anil K. Patniak
Detailed Characterization Of A Khz-Rate Laser-Driven Fusion At A Thin Liquid Sheet With A Neutron Detection Suite, Benjamin M. Knight, Connor Gautam, Colton R. Stoner, Bryan V. Egner, Joseph R. Smith, Christopher M. Orban, Juan J. Manfredi, Kyle Frische, Michael L. Dexter, Enam A. Chowdury, Anil K. Patniak
Faculty Publications
We present detailed characterization of laser driven fusion and neutron production (∼105/second) employing 8 mJ, 40fs laser pulses on a thin (< 1 µm) D2O liquid sheet employing a measurement suite. At relativistic intensity (∼5×1018W/cm2) and high repetition-rate (1 kHz), the system produces consistent D-D fusion, allowing for consistent neutron generation. Evidence of D-D fusion neutron production is verified b y a measurement suite with three independent detection systems: an EJ-309 organic scintillator with pulse-shape discrimination, a 3He proportional counter, and a set of 36 bubble detectors. Time-of-flight analysis of the scintillator data shows …
Numerical Simulation Of Steady-State Thermal Blooming With Natural Convection, Jeremiah S. Lane, Justin Cook, Martin Richardson, Benjamin F. Akers
Numerical Simulation Of Steady-State Thermal Blooming With Natural Convection, Jeremiah S. Lane, Justin Cook, Martin Richardson, Benjamin F. Akers
Faculty Publications
This work investigates steady-state thermal blooming of a high-energy laser in the presence of laser-driven convection. While thermal blooming has historically been simulated with prescribed fluid velocities, the model introduced here solves for the fluid dynamics along the propagation path using a Boussinesq approximation to the incompressible Navier–Stokes equations. The resultant temperature fluctuations were coupled to refractive index fluctuations, and the beam propagation was modeled using the paraxial wave equation. Fixed-point methods were used to solve the fluid equations as well as to couple the beam propagation to the steady-state flow. The simulated results are discussed relative to recent experimental …
The Behavior Of Partially Coherent Twisted Space-Time Beams In Atmospheric Turbulence, Milo W. Hyde Iv
The Behavior Of Partially Coherent Twisted Space-Time Beams In Atmospheric Turbulence, Milo W. Hyde Iv
Faculty Publications
We study how atmospheric turbulence affects twisted space-time beams, which are non-stationary random optical fields whose space and time dimensions are coupled with a stochastic twist. Applying the extended Huygens–Fresnel principle, we derive the mutual coherence function of a twisted space-time beam after propagating a distance z through atmospheric turbulence of arbitrary strength. We specialize the result to derive the ensemble-averaged irradiance and discuss how turbulence affects the beam’s spatial size, pulse width, and space-time twist. Lastly, we generate, in simulation, twisted space-time beam field realizations and propagate them through atmospheric phase screens to validate our analysis.
Particle-In-Cell Simulations Of Ion Dynamics In A Pinched-Beam Diode, Jesse C. Foster, John W. Mcclory, S. B. B. Swanekamp, D. D. Hinshelwood, A. S. Richardson, Paul E. Adamson, J. W. Schumer, R. W. James, P. F. Ottinger, D. Mosher
Particle-In-Cell Simulations Of Ion Dynamics In A Pinched-Beam Diode, Jesse C. Foster, John W. Mcclory, S. B. B. Swanekamp, D. D. Hinshelwood, A. S. Richardson, Paul E. Adamson, J. W. Schumer, R. W. James, P. F. Ottinger, D. Mosher
Faculty Publications
article-in-cell simulations of a 1.6 MV, 800 kA, and 50 ns pinched-beam diode have been completed with emphasis placed on the quality of the ion beams produced. Simulations show the formation of multiple regions in the electron beam flow characterized by locally high charge and current density (“hot spots”). As ions flow through the electron-space-charge cloud, these hot spots electrostatically attract ions to produce a non-uniform ion current distribution. The length of the cavity extending beyond the anode-to-cathode gap (i.e., behind the cathode tip) influences both the number and amplitude of hot spots. A longer cavity length increases the number …
Spatiotemporal Non-Uniformly Correlated Beams, Milo W. Hyde Iv
Spatiotemporal Non-Uniformly Correlated Beams, Milo W. Hyde Iv
Faculty Publications
We present a new partially coherent source with spatiotemporal coupling. The stochastic light, which we call a spatiotemporal (ST) non-uniformly correlated (NUC) beam, combines space and time in an inhomogeneous (shift- or space-variant) correlation function. This results in a source that self-focuses at a controllable location in space-time, making these beams potentially useful in applications such as optical trapping, optical tweezing, and particle manipulation. We begin by developing the mutual coherence function for an ST NUC beam. We then examine its free-space propagation characteristics by deriving an expression for the mean intensity at any plane z ≥ 0. To validate …
The Impact Of Laser Control On The Porosity And Microstructure Of Selective Laser Melted Nickel Superalloy 718, Travis E. Shelton, Gregory R. Cobb, Carl R. Hartsfield, Benjamin M. Doane, Cayla C. Eckley, Ryan A. Kemnitz
The Impact Of Laser Control On The Porosity And Microstructure Of Selective Laser Melted Nickel Superalloy 718, Travis E. Shelton, Gregory R. Cobb, Carl R. Hartsfield, Benjamin M. Doane, Cayla C. Eckley, Ryan A. Kemnitz
Faculty Publications
Additively manufacturing high performance metals by laser processing represents an exciting opportunity to exploit localized properties by varying input parameters throughout the process. This work explores the solidification and microstructural properties of selectively laser melted (SLM) Inconel 718 (IN718) using unique processing parameters. By employing traditional pulsed laser physics techniques, samples were manufactured with a continuous wave laser to study a potential ubiquitous approach. While the overall power density was controlled, the power, speed, and hatch spacing were varied. The porosity and grain sizes of the samples were characterized by optical and scanning electron microscopes. The influence of processing parameters …
Multi-Gaussian Random Variables For Modeling Optical Phenomena, Olga Korotkova, Milo W. Hyde Iv
Multi-Gaussian Random Variables For Modeling Optical Phenomena, Olga Korotkova, Milo W. Hyde Iv
Faculty Publications
A generalization of the classic Gaussian random variable to the family of multi-Gaussian (MG) random variables characterized by shape parameter M > 0, in addition to the mean and the standard deviation, is introduced. The probability density function (PDF) of the MG family members is an alternating series of Gaussian functions with suitably chosen heights and widths. In particular, for integer values of M, the series has a finite number of terms and leads to flattened profiles, while reducing to the classic Gaussian PDF for M = 1. For non-integer, positive values of M, a convergent infinite series of …
Generating Electromagnetic Nonuniformly Correlated Beams, Milo W. Hyde Iv, Xifeng Xiao, David G. Voelz
Generating Electromagnetic Nonuniformly Correlated Beams, Milo W. Hyde Iv, Xifeng Xiao, David G. Voelz
Faculty Publications
We develop a method to generate electromagnetic nonuniformly correlated (ENUC) sources from vector Gaussian Schell-model (GSM) beams. Having spatially varying correlation properties, ENUC sources are more difficult to synthesize than their Schell-model counterparts (which can be generated by filtering circular complex Gaussian random numbers) and, in past work, have only been realized using Cholesky decomposition—a computationally intensive procedure. Here we transform electromagnetic GSM field instances directly into ENUC instances, thereby avoiding computing Cholesky factors resulting in significant savings in time and computing resources. We validate our method by generating (via simulation) an ENUC beam with desired parameters. We find the …
Effect Of Ar(3p54p; 2p)+M -> Ar(3p54s; 1s)+M Branching Ratio On Optically Pumped Rare Gas Laser Performance, Daniel J. Emmons Ii, David E. Weeks
Effect Of Ar(3p54p; 2p)+M -> Ar(3p54s; 1s)+M Branching Ratio On Optically Pumped Rare Gas Laser Performance, Daniel J. Emmons Ii, David E. Weeks
Faculty Publications
Optically pumped rare gas laser performance is analyzed as a function of the Ar(3p54p; 2p) + M → Ar(3p54s; 1s) + M branching ratios. Due to the uncertainty in the branching ratios, a sensitivity study is performed to determine the effect on output and absorbed pump laser intensities. The analysis is performed using a radio frequency dielectric barrier discharge as the source of metastable production for a variety of Argon in Helium mixtures over pressures ranging from 200 to 500 Torr. Peak output laser intensities show a factor of 7 increase as the branching ratio is …
Measurement Of Electron Density And Temperature From Laser-Induced Nitrogen Plasma At Elevated Pressure (1–6 Bar), Ashwin P. Rao [*], Mark Gragston, Anil K. Patnaik, Paul S. Hsu, Michael B. Shattan
Measurement Of Electron Density And Temperature From Laser-Induced Nitrogen Plasma At Elevated Pressure (1–6 Bar), Ashwin P. Rao [*], Mark Gragston, Anil K. Patnaik, Paul S. Hsu, Michael B. Shattan
Faculty Publications
Laser-induced plasmas experience Stark broadening and shifts of spectral lines carrying spectral signatures of plasma properties. In this paper, we report time-resolved Stark broadening measurements of a nitrogen triplet emission line at 1–6 bar ambient pressure in a pure nitrogen cell. Electron densities are calculated using the Stark broadening for different pressure conditions, which are shown to linearly increase with pressure. Additionally, using a Boltzmann fit for the triplet, the electron temperature is calculated and shown to decrease with increasing pressure. The rate of plasma cooling is observed to increase with pressure. The reported Stark broadening based plasma diagnostics in …
Plasma Spectroscopy Of Titanium Monoxide For Characterization Of Laser Ablation, Todd A. Van Woerkom, Glen P. Perram, Christian G. Parigger, Brian D. Dolasinski, Charles D. Phelps, Patrick A. Berry
Plasma Spectroscopy Of Titanium Monoxide For Characterization Of Laser Ablation, Todd A. Van Woerkom, Glen P. Perram, Christian G. Parigger, Brian D. Dolasinski, Charles D. Phelps, Patrick A. Berry
Faculty Publications
Ablation of titanium wafers in air is accomplished with 60 µs pulsed, 2.94 µm laser radiation. Titanium monoxide spectra are measured in the wavelength range of 500 nm to 750 nm, and molecular signatures include bands of the C3 Δ → X3 Δ α, B3 Π → X3 Δ γ', and A3 Φ → X3 Δ γ transitions. The spatially and temporally averaged spectra appear to be in qualitative agreement with previous temporally resolved studies that employed shorter wavelengths and shorter pulse durations than utilized in this work. The background signals in the current study are possibly due to particulate …
Experimental Study: Underwater Propagation Of Super-Gaussian And Multi-Gaussian Schell-Model Partially Coherent Beams With Varying Degrees Of Spatial Coherence, Svetlana Avramov-Zamurovic, Charles L. Nelson, Milo W. Hyde Iv
Experimental Study: Underwater Propagation Of Super-Gaussian And Multi-Gaussian Schell-Model Partially Coherent Beams With Varying Degrees Of Spatial Coherence, Svetlana Avramov-Zamurovic, Charles L. Nelson, Milo W. Hyde Iv
Faculty Publications
We report on experiments where super-Gaussian and flat-top, multi-Gaussian Schell-model spatially partially coherent beams, with varying degrees of spatial coherence, were propagated underwater. Two scenarios were explored—calm and mechanically agitated water. The main objective of our study was the experimental comparison of the scintillation statistics. For a similar degree of coherence widths, the results show a potentially improved performance of scintillation index for the multi-Gaussian Schell-model beams as compared to the super-Gaussian beams. It should be noted that the presented results pertain only to the given experimental scenarios and further investigation is necessary to determine the scope of the findings.
Laser-Induced Plasma Analysis For Surrogate Nuclear Debris, Michael B. Shattan, John Auxier, A. C. Stowe, Christian G. Parigger
Laser-Induced Plasma Analysis For Surrogate Nuclear Debris, Michael B. Shattan, John Auxier, A. C. Stowe, Christian G. Parigger
Faculty Publications
This work identifies analytical lines in laser-induced plasma for chemical analyses of major elements found in surrogate nuclear debris. These lines are evaluated for interferences and signal strength to insure they would be useful to measure relative concentrations. Compact, portable instruments are employed and can be included as part of a mobile nuclear forensics laboratory for field screening of nuclear debris and contamination. The average plasma temperature is measured using the well-established Boltzmann plot technique, and plasma's average electron density is determined using empirical formulae based on Stark broadening of the H-alpha line. These measurements suggest existence of partial local …
Target-Based Coherent Beam Combining Of An Optical Phased Array Fed By A Broadband Laser Source, Milo W. Hyde Iv, Jack E. Mccrae, Glenn A. Tyler
Target-Based Coherent Beam Combining Of An Optical Phased Array Fed By A Broadband Laser Source, Milo W. Hyde Iv, Jack E. Mccrae, Glenn A. Tyler
Faculty Publications
The target-based phasing of an optical phased array (OPA) fed by a broadband master oscillator laser source is investigated. The specific scenario examined here considers an OPA phasing through atmospheric turbulence on a rough curved object. An analytical expression for the detected or received intensity is derived. Gleaned from this expression are the conditions under which target-based phasing is possible. A detailed OPA wave optics simulation is performed to validate the theoretical findings. Key aspects of the simulation set-up as well as the results are thoroughly discussed.
Kinetics Of High Pressure Argon-Helium Pulsed Gas Discharge, Daniel J. Emmons, David E. Weeks
Kinetics Of High Pressure Argon-Helium Pulsed Gas Discharge, Daniel J. Emmons, David E. Weeks
Faculty Publications
Simulations of a pulsed direct current discharge are performed for a 7% argon in helium mixture at a pressure of 270 Torr using both zero- and one-dimensional models. Kinetics of species relevant to the operation of an optically pumped rare-gas laser are analyzed throughout the pulse duration to identify key reaction pathways. Time dependent densities, electron temperatures, current densities, and reduced electric fields in the positive column are analyzed over a single 20 μs pulse, showing temporal agreement between the two models. Through the use of a robust reaction rate package, radiation trapping is determined to play a key role …
Reflective Inverse Diffusion, Kenneth W. Burgi, Jessica Ullom, Michael A. Marciniak, Mark E. Oxley
Reflective Inverse Diffusion, Kenneth W. Burgi, Jessica Ullom, Michael A. Marciniak, Mark E. Oxley
Faculty Publications
Phase front modulation was previously used to refocus light after transmission through scattering media. This process has been adapted here to work in reflection. A liquid crystal spatial light modulator is used to conjugate the phase scattering properties of diffuse reflectors to produce a converging phase front just after reflection. The resultant focused spot had intensity enhancement values between 13 and 122 depending on the type of reflector. The intensity enhancement of more specular materials was greater in the specular region, while diffuse reflector materials achieved a greater enhancement in non-specular regions, facilitating non-mechanical steering of the focused spot. Scalar …
Ir Nonlinear Absorption Leading To Laser-Induced Damage In Ge & Gasb, Torrey J. Wagner, Matthew J. Bohn, Ronald A. Coutu Jr., L. P. Gonzales, J. M. Murray, K. L. Schepler, S. Guha
Ir Nonlinear Absorption Leading To Laser-Induced Damage In Ge & Gasb, Torrey J. Wagner, Matthew J. Bohn, Ronald A. Coutu Jr., L. P. Gonzales, J. M. Murray, K. L. Schepler, S. Guha
Faculty Publications
Using a simultaneous fitting technique to extract nonlinear absorption coefficients from data at two pulse widths, we measure two-photon and free-carrier absorption coefficients for Ge and GaSb at 2.05 and 2.5 μm for the first time. Results agreed well with published theory. Single-shot damage thresholds were also measured at 2.5 μm and agreed well with modeled thresholds using experimentally determined parameters including nonlinear absorption coefficients and temperature dependent linear absorption. The damage threshold for a single-layer Al2O3 anti-reflective coating on Ge was 55% or 35% lower than the uncoated threshold for ps or ns pulses, respectively. Wavelength-dependant …
Energy Scaling Of Nanosecond Gain-Switched Cr2+:Znse Lasers, Vladimir V. Fedorov, Igor S. Moskalev, M. S. Mirov, S. B. Mirov, Torrey J. Wagner, Matthew J. Bohn, Patrick A. Berry, K. L. Schepler
Energy Scaling Of Nanosecond Gain-Switched Cr2+:Znse Lasers, Vladimir V. Fedorov, Igor S. Moskalev, M. S. Mirov, S. B. Mirov, Torrey J. Wagner, Matthew J. Bohn, Patrick A. Berry, K. L. Schepler
Faculty Publications
In this paper, we report record nanosecond output energies of gain-switched CrZnSe lasers pumped by Q-switched CrTmHoYAG 100 ns at 2.096 microns and Raman shifted NdYAG lasers 7 ns at 1.906 microns. In these experiments we used Brewster cut CrZnSe gain elements with a chromium concentration of 8x1018cm-3. Under CrTmHoYAG pumping, the first CrZnSe laser demonstrated 3.1 mJ of output energy, 52 slope efficiency and 110 nm linewidth centered at a wavelength of 2.47 microns. Maximum output energy of the second CrZnSe laser reached 10.1 mJ under H2 Raman shifted NdYAG laser pumping. The slope …
Use Of A Continuous Wave Raman Fiber Laser In Graded-Index Multimode Fiber For Srs Beam Combination, Nathan B. Terry, Kevin T. Engel, Thomas G. Alley, Timothy H. Russell
Use Of A Continuous Wave Raman Fiber Laser In Graded-Index Multimode Fiber For Srs Beam Combination, Nathan B. Terry, Kevin T. Engel, Thomas G. Alley, Timothy H. Russell
Faculty Publications
We report using a Raman fiber laser (RFL) based on a multimode graded-index fiber as a novel method for beam combination of two continuous wave pump beams. Due to stimulated Raman scattering, the RFL generates a Stokes beam which can be up to 300% brighter than the pump beams. Up to 5.8 W of Stokes power is generated with an optical conversion efficiency of 56%.