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High-Power Laser Pulse Recirculation for Inverse Compton Scattering-Produced Gamma-Rays

Description: Inverse Compton scattering of high-power laser pulses on relativistic electron bunches represents an attractive method for high-brightness, quasi-monoenergetic {gamma}-ray production. The efficiency of {gamma}-ray generation via inverse Compton scattering is severely constrained by the small Thomson scattering cross section. Furthermore, repetition rates of high-energy short-pulse lasers are poorly matched with those available from electron accelerators, resulting in low repetition rates for generated {gamma}-rays. Laser recirculation has been proposed as a method to address those limitations, but has been limited to only small pulse energies and peak powers. Here we propose and experimentally demonstrate an alternative method for laser pulse recirculation that is uniquely capable of recirculating short pulses with energies exceeding 1 J. Inverse Compton scattering of recirculated Joule-level laser pulses has a potential to produce unprecedented peak and average {gamma}-ray brightness in the next generation of sources.
Date: April 17, 2007
Creator: Jovanovic, I; Shverdin, M; Gibson, D & Brown, C
Partner: UNT Libraries Government Documents Department

System Modeling of kJ-class Petawatt Lasers at LLNL

Description: Advanced Radiographic Capability (ARC) project at the National Ignition Facility (NIF) is designed to produce energetic, ultrafast x-rays in the range of 70-100 keV for backlighting NIF targets. The chirped pulse amplification (CPA) laser system will deliver kilo-Joule pulses at an adjustable pulse duration from 1 ps to 50 ps. System complexity requires sophisticated simulation and modeling tools for design, performance prediction, and comprehension of experimental results. We provide a brief overview of ARC, present our main modeling tools, and describe important performance predictions. The laser system (Fig. 1) consists of an all-fiber front end, including chirped-fiber Bragg grating (CFBG) stretchers. The beam after the final fiber amplifier is split into two apertures and spatially shaped. The split beam first seeds a regenerative amplifier and is then amplified in a multi-pass Nd:glass amplifier. Next, the preamplified chirped pulse is split in time into four identical replicas and injected into one NIF Quad. At the output of the NIF beamline, each of the eight amplified pulses is compressed in an individual, folded, four-grating compressor. Compressor grating pairs have slightly different groove densities to enable compact folding geometry and eliminate adjacent beam cross-talk. Pulse duration is adjustable with a small, rack-mounted compressor in the front-end. We use non-sequential ray-tracing software, FRED for design and layout of the optical system. Currently, our FRED model includes all of the optical components from the output of the fiber front end to the target center (Fig. 2). CAD designed opto-mechanical components are imported into our FRED model to provide a complete system description. In addition to incoherent ray tracing and scattering analysis, FRED uses Gaussian beam decomposition to model coherent beam propagation. Neglecting nonlinear effects, we can obtain a nearly complete frequency domain description of the ARC beam at different stages in the system. We employ ...
Date: April 14, 2010
Creator: Shverdin, M Y; Rushford, M; Henesian, M A; Boley, C; Haefner, C; Heebner, J E et al.
Partner: UNT Libraries Government Documents Department

GAMMA-RAY COMPTON LIGHT SOURCE DEVELOPMENT AT LLNL

Description: A new class of tunable, monochromatic {gamma}-ray sources capable of operating at high peak and average brightness is currently being developed at LLNL for nuclear photoscience and applications. These novel systems are based on Compton scattering of laser photons by a high brightness relativistic electron beam produced by an rf photoinjector. A prototype, capable of producing > 10{sup 8} 0.7 MeV photons in a single shot, with a fractional bandwidth of 1%, and a repetition rate of 10 Hz, is currently under construction at LLNL; this system will be used to perform nuclear resonance fluorescence experiments. A new symmetrized S-band rf gun, using a Mg photocathode, will produce up to 1 nC of charge in an 8 ps bunch, with a normalized emittance modeled at 0.8 mm.mrad; electrons are subsequently accelerated up to 120 MeV to interact with a 500 mJ, 10 ps, 355 nm laser pulse and generate {gamma}-rays. The laser front end is a fiber-based system, using corrugated-fiber Bragg gratings for stretching, and drives both the frequency-quadrupled photocathode illumination laser and the Nd:YAG interaction laser. Two new technologies are used in the laser: a hyper-Michelson temporal pulse stacker capable of producing 8 ps square UV pulses, and a hyper-dispersion compressor for the interaction laser. Other key technologies, basic scaling laws, and recent experimental results will also be presented, along with an overview of future research and development directions.
Date: August 15, 2007
Creator: Hartemann, F V; Anderson, S G; Gibson, D J; Hagmann, C A; Johnson, M S; Jovanovic, I et al.
Partner: UNT Libraries Government Documents Department

Fiber-Based, Spatially and Temporally Shaped Picosecond UV Laser for Advanced RF Gun Applications

Description: The fiber-based, spatially and temporally shaped, picosecond UV laser system described here has been specifically designed for advanced rf gun applications, with a special emphasis on the production of high-brightness electron beams for free-electron lasers and Compton scattering light sources. The laser pulse can be shaped to a flat-top in both space and time with a duration of 10 ps at full width of half-maximum (FWHM) and rise and fall times under 1 ps. The expected pulse energy is 50 {micro}J at 261.75 nm and the spot size diameter of the beam at the photocathode is 2 mm. A fiber oscillator and amplifier system generates a chirped pump pulse at 1047 nm; stretching is achieved in a chirped fiber Bragg grating. A single multi-layer dielectric grating based compressor recompresses the input pulse to 250 fs FWHM and a two stage harmonic converter frequency quadruples the beam. Temporal shaping is achieved with a Michelson-based ultrafast pulse stacking device with nearly 100% throughput. Spatial shaping is achieved by truncating the beam at the 20% energy level with an iris and relay-imaging the resulting beam profile onto the photocathode. The integration of the system, as well as preliminary laser measurements will be presented.
Date: June 8, 2007
Creator: Shverdin, M Y; Anderson, S G; Betts, S M; Gibson, D J; Hartemann, F V; Hernandez, J E et al.
Partner: UNT Libraries Government Documents Department

Optimal Design of a Tunable Thomson-Scattering Based Gamma-Ray Source

Description: Thomson-Scattering based systems offer a path to high-brightness high-energy (> 1 MeV) x-ray and {gamma}-ray sources due to their favorable scaling with electron energy. LLNL is currently engaged in an effort to optimize such a device, dubbed the ''Thomson-Radiated Extreme X-Ray'' (T-REX) source, targeting up to 680 keV photon energy. Such a system requires precise design of the interaction between a high-intensity laser pulse and a high-brightness electron beam. Presented here are the optimal design parameters for such an interaction, including factors such as the collision angle, focal spot size, optimal bunch charge, and laser energy. These parameters were chosen based on extensive modeling using PARMELA and in-house, well-benchmarked scattering simulation codes.
Date: June 7, 2007
Creator: Gibson, D J; Anderson, S G; Betts, S M; Hartemann, F V; Jovanovic, I; McNabb, D P et al.
Partner: UNT Libraries Government Documents Department

COMMISSIONING OF A HIGH-BRIGHTNESS PHOTOINJECTOR FOR COMPTON SCATTERING X-RAY SOURCES

Description: Compton scattering of intense laser pulses with ultrarelativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV energies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free-electron lasers and laser and plasma based advanced accelerators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scattering experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emittance diagnostic development, results of sputtered magnesium photo-cathode experiments, and UV laser pulse shaping are discussed. Initial operation of the photoinjector is described.
Date: June 21, 2007
Creator: Anderson, S G; Gibson, D J; Hartemann, F V; Messerly, M; Shverdin, M; Siders, C W et al.
Partner: UNT Libraries Government Documents Department

High Power Picosecond Laser Pulse Recirculation

Description: We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering based light sources. We demonstrate up to 36x average power enhancement of frequency doubled sub-millijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses.
Date: April 12, 2010
Creator: Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J et al.
Partner: UNT Libraries Government Documents Department

High Power Picosecond Laser Pulse Recirculation

Description: We propose a novel high peak power ultrashort laser pulse re-circulation technique suitable for gamma-ray generation in Compton-backscattering sources. The two primary obstacles to higher average brightness and conversion efficiency of laser pulse energy to gamma-rays are the relatively small Compton scattering cross-section and the typically low repetition rates of Joule-class interaction lasers (10 Hz). Only a very small fraction (10{sup -10}) of the available laser photons is converted to gamma-rays, while the bulk is discarded. To significantly reduce the average power requirements of the laser and increase the overall system efficiency, we can re-circulate laser light for repeated interactions.
Date: April 23, 2007
Creator: Shverdin, M; Jovanovic, I; Gibson, D; Hartemann, F; Brown, C; Anderson, S et al.
Partner: UNT Libraries Government Documents Department

Techniques and use of a tunable, laser-based, MeV-Class Compton scattering light source

Description: A Compton scattering {gamma}-ray source, capable of producing photons with energies ranging from 0.1 MeV to 0.9 MeV has been commissioned and characterized, and then used to perform nuclear resonance fluorescence (NRF) experiments. The key source parameters are the size (0.01 mm{sup 2}), horizontal and vertical divergence (6 x 10 mrad{sup 2}), duration (10 ps), spectrum and intensity (10{sup 5} photons/shot). These parameters are summarized by the peak brightness, 1.5 x 10{sup 15} photons/mm{sup 2}/mrad{sup 2}/s/0.1%bandwidth, measured at 478 keV. Additional measurements of the flux as a function of the timing difference between the drive laser pulse and the relativistic photoelectron bunch, {gamma}-ray beam profile, and background evaluations are presented. These results are systematically compared to theoretical models and computer simulations. NRF measurements performed on {sup 7}Li in LiH demonstrate the potential of Compton scattering photon sources to accurately detect isotopes in situ.
Date: June 30, 2009
Creator: Albert, F; Anderson, S G; Gibson, D J; Hagmann, C A; Johnson, M S; Messerly, M et al.
Partner: UNT Libraries Government Documents Department

Design and Operation of a tunable MeV-level Compton-scattering-based (gamma-ray) source

Description: A mono-energetic gamma-ray (MEGa-ray) source based on Compton-scattering, targeting nuclear physics applications such as nuclear resonance fluorescence, has been constructed and commissioned at Lawrence Livermore National Laboratory. In this paper, the overall architecture of the system, as well as some of the critical design decisions made in the development of the source, are discussed. The performances of the two laser systems (one for electron production, one for scattering), the electron photoinjector, and the linear accelerator are also detailed, and initial {gamma}-ray results are presented.
Date: July 7, 2009
Creator: Gibson, D J; Albert, F; Anderson, S G; Betts, S M; Messerly, M J; Phan, H H et al.
Partner: UNT Libraries Government Documents Department

Advanced Compton scattering light source R&D at LLNL

Description: We report the design and current status of a monoenergetic laser-based Compton scattering 0.5-2.5 MeV {gamma}-ray source. Previous nuclear resonance fluorescence results and future linac and laser developments for the source are presented. At MeV photon energies relevant for nuclear processes, Compton scattering light sources are attractive because of their relative compactness and improved brightness above 100 keV, compared to typical 4th generation synchrotrons. Recent progress in accelerator physics and laser technology have enabled the development of a new class of tunable Mono-Energetic Gamma-Ray (MEGa-Ray) light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A new precision, tunable gamma-ray source driven by a compact, high-gradient X-band linac is currently under development and construction at LLNL. High-brightness, relativistic electron bunches produced by an X-band linac designed in collaboration with SLAC will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable {gamma}-rays in the 0.5-2.5 MeV photon energy range via Compton scattering. Based on the success of the previous Thomson-Radiated Extreme X-rays (T-REX) Compton scattering source at LLNL, the source will be used to excite nuclear resonance fluorescence lines in various isotopes; applications include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. After a brief presentation of successful nuclear resonance fluorescence (NRF) experiments done with T-REX, the new source design, key parameters, and current status are presented.
Date: February 16, 2010
Creator: Albert, F; Anderson, S G; Anderson, G; Betts, S M; Chu, T S; Gibson, D J et al.
Partner: UNT Libraries Government Documents Department

Possibilities for Nuclear Photo-Science with Intense Lasers

Description: The interaction of intense laser light with relativistic electrons can produce unique sources of high-energy x rays and gamma rays via Thomson scattering. ''Thomson-Radiated Extreme X-ray'' (T-REX) sources with peak photon brightness (photons per unit time per unit bandwidth per unit solid angle per unit area) that exceed that available from world's largest synchrotrons by more than 15 orders of magnitude are possible from optimally designed systems. Such sources offer the potential for development of ''nuclear photo-science'' applications in which the primary photon-atom interaction is with the nucleons and not the valence electrons. Applications include isotope-specific detection and imaging of materials, inverse density radiography, transmutation of nuclear waste and fundamental studies of nuclear structure. Because Thomson scattering cross sections are small, < 1 barn, the output from a T-REX source is optimized when the laser spot size and the electron spot size are minimized and when the electron and laser pulse durations are similar and short compared to the transit time through the focal region. The principle limitation to increased x-ray or gamma-ray brightness is ability to focus the electron beam. The effects of space charge on electron beam focus decrease approximately linearly with electron beam energy. For this reason, T-REX brightness increases rapidly as a function of the electron beam energy. As illustrated in Figure 1, above 100 keV these sources are unique in their ability to produce bright, narrow-beam, tunable, narrow-band gamma rays. New, intense, short-pulse, laser technologies for advanced T-REX sources are currently being developed at LLNL. The construction of a {approx}1 MeV-class machine with this technology is underway and will be used to excite nuclear resonance fluorescence in variety of materials. Nuclear resonance fluorescent spectra are unique signatures of each isotope and provide an ideal mechanism for identification of nuclear materials. With TREX it is possible ...
Date: June 26, 2006
Creator: Barty, C J; Hartemann, F V; McNabb, D P; Messerly, M; Siders, C; Anderson, S et al.
Partner: UNT Libraries Government Documents Department

High-energy Picosecond Laser Pulse Recirculation for Compton Scattering

Description: Frequency upconversion of laser-generated photons by inverse Compton scattering for applications such as nuclear spectroscopy and gamma-gamma collider concepts on the future ILC would benefit from an increase of average source brightness. The primary obstacle to higher average brightness is the relatively small Thomson scattering cross section. It has been proposed that this limitation can be partially overcome by use of laser pulse recirculation. The traditional approach to laser recirculation entails resonant coupling of low-energy pulse train to a cavity through a partially reflective mirror. Here we present an alternative, passive approach that is akin to 'burst-mode' operation and does not require interferometric alignment accuracy. Injection of a short and energetic laser pulse is achieved by placing a thin frequency converter, such as a nonlinear optical crystal, into the cavity in the path of the incident laser pulse. This method leads to the increase of x-ray/gamma-ray energy proportional to the increase in photon energy in frequency conversion. Furthermore, frequency tunability can be achieved by utilizing parametric amplifier in place of the frequency converter.
Date: June 12, 2007
Creator: Jovanovic, I; Anderson, S G; Betts, S M; Brown, C; Gibson, D J; Hartemann, F V et al.
Partner: UNT Libraries Government Documents Department

Development of diagnostics for high-energy petawatt pulses

Description: Applications accessed by high energy petawatt (HEPW) lasers require complete, single-shot characterization of pulse spatial, temporal, and energy characteristics. We describe techniques that enable single-shot characterization of the temporal shape and pulse contrast of HEPW pulses with >10{sup 8} dynamic range over a ns-temporal window. Approaches to measure pulse durations that span two orders of magnitude will be discussed. Finally, we describe a novel implementation of spectrally dispersed two-beam interferometry for measurement of the phase difference between two HEPW pulses. This technique can be applied to dispersion and B-integral measurements in a HEPW system, as well as to achieve precise timing of nanosecond pulses. Lastly, spectrally dispersed interferometry represents an ideal technique to enable coherent addition of HEPW pulses for production of ultrahigh intensities.
Date: June 15, 2006
Creator: Jovanovic, I; Hernandez, J; Appel, G; Barker, D; Betts, S; Brewer, W et al.
Partner: UNT Libraries Government Documents Department

Ultrabright Laser-based MeV-class Light Source

Description: We report first light from a novel, new source of 10-ps 0.776-MeV gamma-ray pulses known as T-REX (Thomson-Radiated Extreme X-rays). The MeV-class radiation produced by TREX is unique in the world with respect to its brightness, spectral purity, tunability, pulse duration and laser-like beam character. With T-REX, one can use photons to efficiently probe and excite the isotope-dependent resonant structure of atomic nucleus. This ability will be enabling to an entirely new class of isotope-specific, high resolution imaging and detection capabilities.
Date: April 2, 2008
Creator: Albert, F; Anderson, G; Anderson, S; Bayramian, A; Berry, B; Betts, S et al.
Partner: UNT Libraries Government Documents Department

LASER TECHNOLOGY FOR PRECISION MONOENERGETIC GAMMA-RAY SOURCE R&D AT LLNL

Description: Generation of mono-energetic, high brightness gamma-rays requires state of the art lasers to both produce a low emittance electron beam in the linac and high intensity, narrow linewidth laser photons for scattering with the relativistic electrons. Here, we overview the laser systems for the 3rd generation Monoenergetic Gamma-ray Source (MEGa-ray) currently under construction at Lawrence Livermore National Lab (LLNL). We also describe a method for increasing the efficiency of laser Compton scattering through laser pulse recirculation. The fiber-based photoinjector laser will produce 50 {micro}J temporally and spatially shaped UV pulses at 120 Hz to generate a low emittance electron beam in the X-band RF photoinjector. The interaction laser generates high intensity photons that focus into the interaction region and scatter off the accelerated electrons. This system utilizes chirped pulse amplification and commercial diode pumped solid state Nd:YAG amplifiers to produce 0.5 J, 10 ps, 120 Hz pulses at 1064 nm and up to 0.2 J after frequency doubling. A single passively mode-locked Ytterbium fiber oscillator seeds both laser systems and provides a timing synch with the linac.
Date: April 20, 2010
Creator: Shverdin, M Y; Bayramian, A; Albert, F; Anderson, S G; Betts, S M; Chu, T S et al.
Partner: UNT Libraries Government Documents Department

OVERVIEW OF MONO-ENERGETIC GAMMA-RAY SOURCES & APPLICATIONS

Description: Recent progress in accelerator physics and laser technology have enabled the development of a new class of tunable gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A precision, tunable Mono-Energetic Gamma-ray (MEGa-ray) source driven by a compact, high-gradient X-band linac is currently under development and construction at LLNL. High-brightness, relativistic electron bunches produced by an X-band linac designed in collaboration with SLAC NAL will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable {gamma}-rays in the 0.5-2.5 MeV photon energy range via Compton scattering. This MEGa-ray source will be used to excite nuclear resonance fluorescence in various isotopes. Applications include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status are presented, along with important applications, including nuclear resonance fluorescence. In conclusion, we have optimized the design of a high brightness Compton scattering gamma-ray source, specifically designed for NRF applications. Two different parameters sets have been considered: one where the number of photons scattered in a single shot reaches approximately 7.5 x 10{sup 8}, with a focal spot size around 8 {micro}m; in the second set, the spectral brightness is optimized by using a 20 {micro}m spot size, with 0.2% relative bandwidth.
Date: May 18, 2010
Creator: Hartemann, F V; Albert, F; Anderson, G G; Anderson, S G; Bayramian, A J; Betts, S M et al.
Partner: UNT Libraries Government Documents Department