Browsing by Subject "Laser"
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Item Beam diagnostics for the Texas Petawatt Laser Wakefield Acceleration Project(2009-12) Bedacht, Stefan; Downer, Michael Coffin; Fink, ManfredAn overview of the beam diagnostics for the laser wakefield acceleration project at the Texas Petawatt Laser facility is presented. In this experiment, short and intense laser pulses of 165 fs and up to 190 J will be used to accelerate electrons up to the GeV energy range using laser wakefield acceleration. The density variation of the plasma generated in a helium gas cell will be measured with different optical detection systems such as frequency domain holography. Spectra of the transmitted laser beam and optical transition radiation will yield information about the energy transfer to the plasma and the energy of the electrons, respectively. In addition, a calorimeter will measure accelerated electron energies. Prior to the final experiment, preliminary frequency shift measurements and simulations on optical transition radiation were performed.Item Characteristics of foamed asphalt binders for warm mix asphalt applications(2014-08) Arega, Zelalem Alebel; Bhasin, Amit; Li, Wei, doctor of mechanical engineering; Prozzi, Jorge A; Zhang, Zhanmin; Juenger, Maria GAn increase in environmental awareness and energy concerns had recently prompted efforts to make pavement construction cheaper and more environmentally friendly. Warm mix asphalt (WMA) is an asphalt mixture production technology that promises to reduce production costs and greenhouse gas emissions. Foamed asphalt binder is increasingly being used to produce WMA. This dissertation addresses several issues related to the use of foamed asphalt binder for WMA applications. The first objective of the research presented in this dissertation is to develop a method and metrics to precisely quantify the characteristics of asphalt binder foams. Laboratory measurements were obtained using the newly developed method to evaluate the extent and stability of foams produced using different asphalt binders at different water contents and laboratory foaming devices. Results demonstrate that the method developed is promising in terms of its ability to provide a detailed history of the behavior of foamed asphalt binder as the foam collapses. In addition, results indicate that the method is sensitive to distinguish between foaming characteristics of different asphalt binders as well as different water contents and foaming devices. The second objective of this study was to relate intrinsic properties of the asphalt binder to its foaming characteristics. A physical model was developed for expansion of asphalt binder foam based on foam physics and fluid mechanics of micro-droplets. The model relates foamant water and asphalt binder mixing efficiency with the surface tension of the asphalt binder. The model can be used to predict which binder can be effectively foamed and used, and whether any chemical modification to the binder is necessary to achieve the same. Results indicate that only a small percentage of water is effective in foaming the asphalt binder. The last objective of this research was to evaluate the influence of foaming on asphalt binder residues and mixture workability and coatability. The influence of foaming process on the rheological properties of asphalt binder residue was investigated. In addition, the significance of foamed asphalt binder characteristics on mixture workability and coatability was evaluated. Results from this last part of the study can be used to optimize binder foaming such that the resulting mixture is coated and compacted without compromising performance.Item Chirped pulse raman amplifier(2009-12) Grigsby, Franklin Bhogaraju; Downer, Michael C., 1954-; Frommhold, Lothar W.; Becker, Michael F.; Keto, John W.; Sitz, Greg O.All modern terawatt- and petawatt-class laser systems are based on the principle of chirped-pulse amplification (CPA). In this work, a compact subsystem that shifts a micro-joule portion of the chirped pulse energy to a new wavelength outside its original bandwidth, then amplifies it to millijoule energy without adding pump lasers, and without compromising the output of the fundamental CPA system in any significant way, has been developed and integrated into a standard terawatt-class CPA system. In this chirped pulse Raman amplifier sub-system, a 30 mJ portion of a chirped 800 nm fundamental pulse within the CPA system was split into two unequal portions, each of which impinged on a Raman-active barium nitrate, or Ba(NO3)2, crystal of length 5 cm. The weaker portion created a weak (15 J) first Stokes pulse (873 nm) by Stimulated Raman Scattering (SRS) in the first crystal, which then seeded a non-collinear four-wave-mixing process driven by the stronger portion of the split-off CPA pulse in the second crystal. The latter process amplified the first Stokes seed pulse to several millijoules with excellent beam quality. A study of Raman gain as a function of time delay between pump and Stokes pulse in the second crystal revealed a sharply peaked narrow interval ( 3 ps FWHM) of high gain and a wider interval ( 50 ps) of low gain. The amplified, chirped first Stokes pulse was successfully compressed to 100 fs duration using a grating pair of different line density than in the main CPA system, based on a comprehensive dispersion analysis of the optical path of the first Stokes pulse. The possibility of generating higher-order Stokes and anti-Stokes sidebands of the CPA pulse is also demonstrated. Further amplification of the sideband pulse by conventional methods, using an additional pump laser, appears straightforward. The chirped pulse Raman amplifier provides temporally synchronized fundamental and Raman sideband pulses for performing two-color, high-intensity laser experiments, some of which are briefly discussed. It can be integrated into any standard CPA system, and provides significant new versatility for high-intensity laser sources.Item The effect of laser contrast and target thickness on laser-plasma interactions at the Texas Petawatt(2014-12) Meadows, Alexander Ross; Hegelich, Bjorn ManuelA two-year experimental campaign is described during which diamond-like carbon and plastic targets with thicknesses from 20 nanometers to 15 micrometers were irradiated by the Texas Petawatt Laser. Target composition and thickness were varied to modify the specifics of the laser-matter interaction. Plasma mirrors were selectively implemented to affect the contrast of the laser system and provide additional control of the physical processes under investigation. A number of particle diagnostics were implemented to measure the distribution of laser accelerated ions and electrons. In addition, optical diagnostics were fielded to measure the intensity profile of the laser and measure the density of the target pre-plasma. The results of these experiments suggest that the Texas Petawatt laser pulse has pre-pulse and pedestal features with intensities at least 10⁻⁸ of the main pulse. Micronscale targets were able to survive these features and maintain a relatively sharp density gradient until the arrival of the main laser pulse, allowing for ion acceleration. Electron spectra measured in this configuration show an average temperature of 10 MeV, with no v angular dependence out to at least 60 degrees. By contrast, interferometric plasma density measurements and a lack of any observable ion acceleration suggest that nanoscale targets were destroyed well before the main pulse. In this case, the peak of the laser pulse interacted with a cloud of plasma between 10⁻³ and 10⁻² of critical density. The contrast improvement offered by the implementation of plasma mirrors was seen to increase the maximum energy of laser accelerated protons from targets thicker than 1 micrometer. In addition, the plasma mirrors allowed nanoscale targets to survive pre-pulse and pedestal features and support the production of ion beams. Proton spectra show that ions were accelerated to greater maximum energies from nanoscale targets than from more traditional micron-scale targets. This effect can be attributed to a reduction in the target pre-plasma scale length upon the introduction of plasma mirrors. These results indicate that the manipulation of target properties and laser contrast can significantly affect the interaction between an ultrahigh intensity laser and a target.Item An electrostatic approach for producing nanoparticulate membranes using laser ablation of microparticle aerosols(2011-08) Davis, Claire Elisabeth; Kovar, Desiderio; Becker, Michael F.The Laser Ablation of Microparticle Aerosols (LAMA) process produces nanoparticles by ablating microparticles that are entrained in an aerosol. Two of the main advantages of this process are that the particles produced are charged (preventing agglomeration) and bare (without a capping layer). Two different techniques are possible to collect the nanoparticles. In this work, the charged state of the particles formed was utilized to collect them electrostatically. This approach has the additional advantage that particles can be selected according to their size. The focus here was a particular application for gas separation. The nanoparticles produced were directly collected in a polymeric liquid, which was then irradiated with ultraviolet light to form a rubbery film. These membranes were tested for olefin/paraffin gas separation, a challenge that finds many applications, notably in the petroleum industry.Item Experimental studies of laser driven proton acceleration from ultrashort and highly intense laser pulse interaction with overdense plasma(2014-12) Kuk, Donghoon; Ditmire, Todd R.The generation of high current multi-MeV protons and ions by irradiation of short pulse high intense laser on an ultra-thin target has been observed and subjected great interest in recent. When ultra-thin overdense target is irradiated by focused ultraintense laser pulse, hot electrons are generated by various mechanisms and they generate energetic ion beams. In TNSA, a quasi-electrostatic field is produced on the target rear surface when the the laser pulse interacts with overdense target, driving hot electrons go torward the target rear surface. However, this mechanism results in a range of field gradients leading to a broad proton energy distribution typically. To overcome the issue, an alternative accelration mechanism has been presented to achieve the quasi-monoenergetic proton acceleration and the mechanism is called Radiation Pressure Acceleration. In the RPA, the radiation pressure push electrons into the target smoothly and setting up an electrostatic field by the laser pressure. In this thesis, we study two alternative experimental methods for the quasi-monoenergetic proton acceleration and find experimental feasibility of the presented methods from other research groups.Item Fire retardant polyamide 11 nanocomposites/elastomer blends for selective laser sintering(2016-05) Ortiz, Rogelio; Bourell, David Lee; Koo, Joseph H.Additive manufacturing (AM) had previously been used solely for prototyping and visualization purposes, but in recent years, this technique has shifted to the idea of producing end-use parts. This has already been successfully done in some areas via selective laser sintering (SLS). Unfortunately, current polymeric materials for processing via SLS do not meet the requirements of the majority of commercial applications. Hence, this thesis presents efforts to develop a multifunctional polyamide 11 (PA11) polymer with enhanced thermal, mechanical, and flammability properties for SLS through the use of nanotechnology.Item High resolution retinal imaging to evaluate laser and light safety in the retina for near and long term health effects(2012-12) Pocock, Ginger Madeleine; Snodderly, D. Max; Rylander, H. Grady (Henry Grady), 1948-; Markey, Mia K.; Milner, Tom E.; Oliver, Jeffrey W.The purpose of this research was to investigate detect and monitor laser-tissue interactions at threshold and potentially sub-threshold levels of injury. High resolution imaging modalities can provide a deeper understanding of candidate biomarkers disease and injury at the molecular, cellular, and tissue-levels which can be used to identify and diagnose early stages disease and damage. In addition, multi-scale and multi-modal imaging have also been used to identify inherent biomarkers of retinal disease and injury. Monitoring tissue changes can be mapped back to biological changes at the cellular and sub-cellular level. Diseases often alter tissue on the ultra-structural level yet retinal clinical diagnosis often monitor changes in tissue at the organ level. If injury and disease is detected and diagnosed during an “early” stage of development, treatments and drug interventions may prevent further spread of the pathology. Non-invasive imaging is expected to be a valuable tool for in vivo medical research as well as for the diagnosis and management of disease. In addition to developing new imaging tools and techniques to image the retina, the identification of inherent biomarkers of disease and health using diagnostic methods are almost equally as important. Using the inherent optical properties of retinal tissue, we can non- invasively quantify differences in the absorption and reflection of light to gauge the risk for visual disability or worse yet irreversible vision loss as a result of retinal disease and chronic light exposure. The research presented with in this dissertation is three separate studies aimed at identifying light injury and potential biomarkers indicating the risk of light mediated development of disease.Item Hydrodynamic instabilities of radiative blast waves(2013-12) Kim, In Tai; Ditmire, Todd R.We present the results from a series of experimental investigations into the hydrodynamic instabilities that occur in radiative blast waves. In particular, we examine the Vishniac instability in which the perturbation modes oscillate in time and, for certain mode numbers and polytropic index of the medium, can exhibit a growth in their amplitudes. Experiments were conducted on the GHOST laser laboratory in which a source of atomic clusters was irradiated by a 1J-2J, 115fs laser pulse to produce cylindrical blast waves. The thrust of this thesis falls into two categories. First, we analyze the effects radiative cooling has on the evolution of blast waves such as the lowering of the effective polytropic index and consequently the lowering of their deceleration parameter. Radiation from the blast wave surface results in a preheated ionization precursor in the upstream material and is indicated by a gradual decline in the electron density profile of the blast wave rather than a sharp jump. This mechanism, if strong enough, can also create a secondary shock wave to form ahead of the main blast wave. The second set of experiments investigates the temporal evolution of longitudinal perturbations induced on the blast waves by use of a transverse interferometric beam that modifies the cluster medium prior to the onset of the main pump beam. These perturbations are analyzed and compared to theory set forth in Vishniac's mechanism for oscillatory instabilities and their growth rate.Item Isochoric heating of copper to Warm Dense Matter state using protons produced through laser solid-laser interactions(2013-05) Feldman, Samuel Henry; Ditmire, Todd R.This thesis examines the equation of state of copper at Warm Dense Matter states, between 1-100 eV and .1-10 times solid density. Protons accelerated off a thin metal foil irradiated with a high intensity laser beam flash heat solid density copper to between 5-10 eV before significant expansion occurs. The measured temperature and expansion are compared against simulations using various equations of states. The production and characterization of the laser system and proton beam used to heat the matter is also presented.Item Laser and waterjet cutting for theatrical costumes(2016-05) Collings, Justin Shaw; Glavan, James; Mickey, Susan EAs a costume technician, I am interested in ways we can incorporate new and different technologies into our craft. The use of laser cutting technology has become increasingly prevalent in the fashion industry to create one of a kind fabrics and embellishments on garments. I am interested in how we can use laser cutting to create costumes. For my thesis project, I will create three historically based costume pieces using a laser cutter and a waterjet cutting machine. The projects will be one: a jeweled metal crown inspired by the ducal crown of France, Italy, Spain, and Portugal as illustrated in Heralischer Atlas, by Hugo Gerhard Stroh; two, a 16th Century leather breastplate with laser cut and etched leather embellishments; and finally a re-creation on an early 20th century Edwardian lace collar and yoke.Item Laser line scanning processing system for wrinkling in nation during coating(2011-05) Doblar, Peter Anthony; Beaman, Joseph J.; Wood, KristinOne of the major limiting factors in fuel cell production is the time and effort that are required in the ink coating process of the Nafion film that is at the heart of what makes a fuel cell work. The principle reason that this issued has not been tackled by the industry at large is the inherent difficulties that arise. First and foremost is the rapid and extensive expansion of the material upon contact with the liquid ink causing the Nafion film to wrinkle while being processed. In the drive to help mitigate this issue it must be understood by what conditions and severity that wrinkling occurs. The method chosen to detect this was to develop a laser profile scanner to record and output the severity of any wrinkles present in the film. This thesis showcases and explains the laser scanning system designed specifically for this problem and material.Item Study of picosecond-scale electron dynamics in laser-produced plasmas with and without an external magnetic field(2013-12) McCormick, Matthew Warren; Ditmire, ToddThe interaction of ultra-short laser pulses and cluster targets can be used to explore a number of interesting phenomena, ranging from nuclear fusion to astrophysical blast waves. In our experiments, we focused on exploring very fast plasma dynamics of a plasma created by ionizing clusters and monomer gas. By using a 115 fs laser pulse, we can even study sub-picosecond plasma dynamics. In addition, we also wanted to impose an external magnetic field on these plasmas to study how the plasma evolution would change. The results of this work produced two significant results. First, a new, extremely fast ionization mechanism, with velocities as high as 0.5 c, was discovered which allows for significant plasma expansion on a picosecond time-scale. Experimental studies measured the velocity of the ionization wave, while particle-in-cell simulations helped explain the source and longevity of the wave. It was also observed that this ionization wave was not affected by the external magnetic field. Second, the external field was shown to inhibit plasma expansion on a time-scale of tens of picoseconds, which seems to be one of the first demonstrations of magnetic confinement on such a fast time-scale. Simple 1D simulations tell us that the field appears to slow electron heat transport in the plasma as well as inhibiting collisional ionization of electrons expanding into the surrounding gas. The inhibition of plasma expansion by the field on this time-scale may provide some evidence that magnetic confinement of a fusion plasma created by exploding clusters could improve the fusion yield by slowing heat loss as well as possibly electrostatically confining the hot ions.Item Terawatt Raman laser system for two-color laser plasma interactions(2014-08) Sanders, James Christopher; Downer, Michael CoffinIn some high-field laser-plasma experiments, it is advantageous to accompany the main high-energy (~1 J) laser with a second high-energy pulse (~0.1 J) which has been frequency-shifted by ~10-20%. Such a pulse-pair would have a low walk-off velocity while remaining spectrally distinct for use in two-color pump-probe experiments. Moreover, by shifting the second pulse by ~plasma frequency, it is theoretically possible to exercise some amount of control over a variety of laser-plasma instabilities, including forward Raman scattering, electromagnetic cascading, and relativistic self-focusing. Alternatively, the two pulses may be counter-propagated so that the collide in the plasma and create a slowly-propagating beatwave which can be used to inject electrons into a laser wakefield accelerator. The design, characeterization, and performance of a hybrid chirped-pulse Raman amplifier (CPRA)/Ti-Sapphire amplifier are reported and discussed. This hybrid system allows for the generation of a high-energy (>200 mJ), broadband (15-20 nm bandwidth FWHM), short duration (>100 fs duration) laser sideband. When amplified and compressed, the Raman beam's power exceeds 1 TW. This sideband is combined with the primary laser system to create a bi-color terawatt laser system which is capable of performing two-color high-field experiments. This two-color capability can be added to any commercial terawatt laser system without compromising the energy, duration or beam quality of the primary system. Preliminary two-color laser-plasma experiments are also discussed.Item Tunable quasi-monoenergetic compton x-ray source from laser-plasma accelerator(2015-05) Tsai, Hai-En; Downer, Michael Coffin; Ditmire, Todd; Keto, John; Breizman, Boris; Ben-Yakar, AdelaThis work present an in-depth experimental study of the parameters necessary to optimize a tunable, quasi-monoenergetic, efficient, low background Compton backscattering (CBS) x-ray source that is based on the self-aligned combination of a laser-plasma accelerator (LPA) and a plasma mirror (PM). The main findings are: (1) an LPA driven in the blowout regime by 30 TW, 30 fs laser pulses produces not only a high-quality, tunable, quasi-monoenergetic electron beam, but also a high-quality, relativistically intense (a₀ ~ 1) spent drive pulse that remains stable in profile and intensity over the LPA tuning range. (2) A thin plastic film near the gas jet exit retro-reflects the spent drive pulse efficiently into oncoming electrons to produce CBS x-rays without detectable bremsstrahlung background. Meanwhile anomalous far-field divergence of the retro-reflected light demonstrates relativistic "denting" of the PM. Exploiting these optimized LPA and PM conditions, we demonstrate quasi-monoenergetic (50% FWHM energy spread), tunable (75 to 200 KeV) CBS x-rays, characteristics previously achieved only on more powerful laser systems by CBS of a split-off, counter-propagating pulse. Moreover, laser-to-x-ray photon conversion efficiency ( ~ 6x10⁻¹²) exceeds that of any previous LPA-based quasi-monoenergetic Compton source. Particle-in-cell simulations agree well with the measurements.Item Two-color high intensity laser plasma interaction phenomena, and status of experiments on the UT³ laser system(2014-05) Jolly, Spencer Windhorst; Downer, Michael CoffinWe report the status of two-color high intensity laser-plasma interaction experiments on the UT³ laser system at the University of Texas at Austin. After an outline of the experimental apparatus, an overview of the motivating theoretical work, and a characterization of the performance of our Chirped Pulse Raman Amplification system (CPRA) we report the status of our most recent experiment. We have attempted to seed the growth of the Raman Forward Scattering (RFS) instability in order to produce electrons at lower driving pulse power than is conventionally needed. We have been unsuccessful, and provide reasons why and recommendations for future modifications to the experimental apparatus. The most significant conclusion is that the CPRA system as it is now is not appropriate for this experiment because the observed RFS spectrum is at higher wavelength than our system. Possible future changes include either amplifying a separate barium nitrate sideband at 938 nm through the CPRA system or using a different Raman active medium after the main 800 nm UT³ pulse is compressed. The feasibility study of these possible modifications is not yet complete.