The remarkable electronic properties of layered semiconducting transition metal dichalcogenides (... more The remarkable electronic properties of layered semiconducting transition metal dichalcogenides (TMDs) make them promising candidates for next-generation ultrathin, low-power, high-speed electronics. It has been suggested that electronics based upon ultra-thin TMDs may be appropriate for use in high radiation environments such as space. Here, we present the effects of irradiation by protons, iron, and silver ions at MeV-level energies on a WSe 2 /6H-SiC vertical heterostructure studied using XPS and UV-Vis-NIR spectroscopy. It was found that with 2 MeV protons, a fluence of 10 16 protons/cm 2 was necessary to induce a significant charge transfer from SiC to WSe 2 , where a reduction of valence band offset was observed. Simultaneously, a new absorption edge appeared at 1.1 eV below the conduction band of SiC. The irradiation with heavy ions at 10 16 ions/cm 2 converts WSe 2 into a mixture of WO x and Se-deficient WSe 2 . The valence band is also heavily altered due to oxidation and amorphization. However, these doses are in excess of the doses needed to damage TMD-based electronics due to defects generated in common dielectric and substrate materials. As such, the radiation stability of WSe 2 -based electronics is not expected to be limited by the radiation hardness of WSe 2 , but rather by the dielectric and substrate.
We present a design and preliminary performance of a compact, high-peak-power 5-µm pulsed laser s... more We present a design and preliminary performance of a compact, high-peak-power 5-µm pulsed laser source for pumping a dielectric photonic structure to produce an acceleration gradient of order GV/m in dielectric laser acceleration. The 5-µm laser source is based on two cascaded optical parametric amplifiers (OPA): a 2-µm BBO OPA with a mixed phase matching scheme is used as a pump source, and a type-I phase-matched ZGP OPA is designed to produce sub-mJ 5-µm laser pulses. Preliminary result of ∼53 µJ pulse energy at 5 µm is demonstrated using a two-stage optical parametric generator (OPG)/OPA scheme, and an improved OPA scheme with dispersion management for production of higher pulse energy at 5 µm is under development.
Bulletin of the American Physical Society, Nov 12, 2020
The ZEUS facility will include a repetitive dual-beamline 3 PW laser system, a 100 J programmable... more The ZEUS facility will include a repetitive dual-beamline 3 PW laser system, a 100 J programmable shape multi-ns pulse driver, three radiation shielded experimental areas and will provide unique new capabilities to explore nonlinear quantum electrodynamics, relativistic plasmas, particles acceleration, extreme laboratory astrophysics, basic plasma physics and nuclear photonics. Once completed, the ZEUS laser system will be the highest-power laser system in the US and will become a user facility for the US scientists and wider international research community.
Of particular interest to X-ray FEL light source facilities is Enhanced Self-Amplified Spontaneou... more Of particular interest to X-ray FEL light source facilities is Enhanced Self-Amplified Spontaneous Emission (ESASE) technique. Such a technique requires an ultrafast (20-50 fs) high peak power, high repetition rate reliable laser systems working in the mid-IR range of spectrum (2µm or more). The approach of this proposed work is to design a novel Ultrafast Mid-IR Laser System based on optical parametric chirped-pulse amplification (OPCPA). OPCPA is a technique ideally suited for production of ultrashort laser pulses at the center wavelength of 2 µm. Some of the key features of OPCPA are the wavelength agility, broad spectral bandwidth and negligible thermal load.
8th Int. Particle Accelerator Conf. (IPAC'17), Copenhagen, Denmark, 14â19 May, 2017, May 1, 2017
Direct laser acceleration (DLA) of an electron bunch can be achieved by utilizing the axial field... more Direct laser acceleration (DLA) of an electron bunch can be achieved by utilizing the axial field of a well-guided, radially polarized laser pulse in a density-modulated plasma waveguide. However, the ponderomotive force of a TWclass laser pulse excites a plasma wave that can generate a defocusing electrostatic field, which significantly deteriorates the transverse properties of the injected electron witness bunch. To improve the quality of the accelerated witness bunch, an additional leading electron bunch, termed a precursor, is introduced to generate ion-focusing force to effectively confine the trailing witness bunch. We conducted three-dimensional particle-in-cell simulations to investigate the effect of bunch charge, transverse size of the precursor, and the axial separation between the precursor and the witness bunch on the efficacy of DLA. Results indicate that the transverse properties of the witness bunch can be maintained and the overall DLA efficiency can be improved when a favorable ion-focusing force is provided by the precursor.
Conference on Lasers and Electro-Optics, May 5, 2019
Tritium detection poses a challenge because of the weak beta particle emission and absence of ion... more Tritium detection poses a challenge because of the weak beta particle emission and absence of ionizing radiation. We demonstrate the isotopic analysis of deuterated water via laser-induced breakdown spectroscopy as a modality for measuring tritium.
For over 40 years, physicists have considered possible uses for neutrino detectors in nuclear non... more For over 40 years, physicists have considered possible uses for neutrino detectors in nuclear nonproliferation, arms control, and fissile materials security. Neutrinos are an attractive fission signature because they readily pass through matter. The same property makes neutrinos challenging to detect in systems that would be practical for nuclear security applications. This colloquium presents a broad overview of several potential neutrino applications, including the near-field monitoring of known reactors, far-field monitoring of known or discovery of undeclared reactors, detection of reactor waste streams, and detection of nuclear explosions. We conclude that recent detector advances have made near-field monitoring feasible. Farther-field reactor detection and waste stream detection monitoring are possible in some cases with further research and development. Very long-range reactor monitoring and nuclear explosion detection do not appear feasible for the foreseeable future due to considerable physical and/or practical constraints.
In nuclear nonproliferation and safeguards, detecting and accurately characterizing special nucle... more In nuclear nonproliferation and safeguards, detecting and accurately characterizing special nuclear material remains one of the greatest challenges. Uranium enrichment determination is typically achieved by measuring the ratio of characteristic γ-ray emissions from 235 U and 238 U. Fission also produces β-delayed neutrons, which have been used in the past to determine uranium enrichment from the time dependence of the long-lived delayed neutron emission rate. Such measurements typically use moderated 3 He tube detectors. We demonstrate a new measurement technique that employs a fast neutron active interrogation probe and a scintillation detector to measure the enrichment of uranium using both the buildup and decay of β-delayed neutron emission. Instead of 3 He tubes, a capture-based heterogeneous composite detector consisting of scintillating Li-glass and polyvinyl toluene has been constructed and used, offering a prospect to scale delayed neutron measurements to larger detector sizes. Since the technique relies on the existing tabulated nuclear data, no calibration standards are required. It is shown that the buildup of delayed neutron emission can be used to distinguish between uranium samples and infer the uranium enrichment level, with accuracy that rivals the method that employs the time-dependent decay of delayed neutron emission.
Plants and other photosynthetic organisms have been suggested as potential pervasive biosensors f... more Plants and other photosynthetic organisms have been suggested as potential pervasive biosensors for nuclear nonproliferation monitoring. We demonstrate that ultrafast laser filament-induced fluorescence of chlorophyll in the green alga Chlamydomonas reinhardtii is a promising method for remote, in-field detection of stress from exposure to nuclear materials. This method holds an advantage over broad-area surveillance, such as solar-induced fluorescence monitoring, when targeting excitation of a specific plant would improve the detectability, for example when local biota density is low. After exposing C. reinhardtii to uranium, we find that the concentration of chlorophyll a, chlorophyll fluorescence lifetime, and carotenoid content increase. The increased fluorescence lifetime signifies a decrease in non-photochemical quenching. The simultaneous increase in carotenoid content implies oxidative stress, further confirmed by the production of radical oxygen species evidence in the steady-state absorption spectrum. This is potentially a unique signature of uranium, as previous work finds that heavy metal stress generally increases non-photochemical quenching. We identify the temporal profile of the chlorophyll fluorescence to be a distinguishing feature between uranium-exposed and unexposed algae. Discrimination of uranium-exposed samples is possible at a distance of ∼35 m with a single laser shot and a modest collection system, as determined through a combination of experiment and simulation of distance-scaled uncertainty in discriminating the temporal profiles. Illustrating the potential for remote detection, detection over 125 m would require 100 laser shots, commensurate with the detection time on the order of 1 s.
We present a novel chirped pulse ampifiation method which combiner optial parynctric amplrficatio... more We present a novel chirped pulse ampifiation method which combiner optial parynctric amplrfication and laser amplification. We have demonshated this hybrid CF' A concept with a combination of bebbuium b n t e a d sapphire. High-efficiency, mu16 tenwatt compatible amplification is achieved without gain nmwing and without elstrooptic modulators using a simple commercial pump laser.
Nuclear Instruments and Methods in Physics Research, 2023
Gamma-ray emission from special nuclear material (SNM) is relatively easy to shield from detectio... more Gamma-ray emission from special nuclear material (SNM) is relatively easy to shield from detection using modest amounts of high-Z material. In contrast, fast-neutrons are much more penetrating and can escape relatively thick high-Z shielding without losing significant energy. Furthermore, fast neutrons provide a clear and unambiguous signature of the presence of SNM with few competing natural background sources. The challenge of detecting fast neutrons is twofold. First, the neutron flux from SNM are only a fraction of the corresponding gamma-ray flux. Second, fast neutrons can be difficult to differentiate from gamma rays. The ability to discriminate gamma rays from neutrons combined with neutron imaging can yield large benefit to isolate the localized SNM neutron source from background. With the recent developments of pulse-shape-sensitive plastic scintillators that offer excellent gamma-ray/neutron discrimination, and arrays of silicon photomultipliers combined with highly scalable and fast positron-emission-tomography (PET) multi-channel readout systems, field-deployable neutron imagers suitable for SNM detection might now be within reach. In this paper, we present a characterization of the performance of a recently available commercial PET-scanner readout, including its sensitivity to pulse-shape differences between fast neutrons and gamma rays, energy and timing resolution, as well as linearity and dynamic range. We find that, while the pulse-shape discrimination is achievable with stilbene, further improvement of the readout is required to achieve it with the best available plastic scintillators. The time and energy resolution appear to be adequate for neutron imaging in some circumstances.
We report measurements of the structural response of a thin film of SrTiO3 (STO) under strong exc... more We report measurements of the structural response of a thin film of SrTiO3 (STO) under strong excitation with singlecycle terahertz (THz) fields using ultrafast x-rays. STO has a known soft phonon that is in close resonance with the central frequency of the THz driving field. For weak THz fields, we observe atomic motion which we associate with resonant phonon excitation. As we increase the THz field strength, we detect both a saturation in the soft mode excitation amplitude as well as the appearance of several new frequencies closely matched to known higher-frequency phonons in STO. Combining DFT calculations with measured x-ray diffraction measurements, we are able to extract the soft mode phonon potential.
The fiber-based, spatially and temporally shaped, picosecond UV laser system described here has b... more 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 μJ 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.
Bulletin of the American Physical Society, Oct 30, 2006
based systems offer a path to highbrightness high-energy (> 1 MeV) x-ray & gamma-ray sources due ... more based systems offer a path to highbrightness high-energy (> 1 MeV) x-ray & gamma-ray sources due to their favorable scaling with electron energy. LLNL is currently engaged in an effort to build such a device, dubbed the "Thomson-Radiated Extreme X-Ray" (T-REX) source. Presented here is an overview of the system design, which includes both a UVlaser-driven electron photoinjector and an intense scattering laser. Also shown are the results of detailed electron beam and gamma-ray generation modeling designed to optimize the brightness and flux of the gamma-ray beam, including UV drive laser profile effects, charge v. emittance tradeoffs, thermal emittance effects, and contributions of focusing geometry.
The remarkable electronic properties of layered semiconducting transition metal dichalcogenides (... more The remarkable electronic properties of layered semiconducting transition metal dichalcogenides (TMDs) make them promising candidates for next-generation ultrathin, low-power, high-speed electronics. It has been suggested that electronics based upon ultra-thin TMDs may be appropriate for use in high radiation environments such as space. Here, we present the effects of irradiation by protons, iron, and silver ions at MeV-level energies on a WSe 2 /6H-SiC vertical heterostructure studied using XPS and UV-Vis-NIR spectroscopy. It was found that with 2 MeV protons, a fluence of 10 16 protons/cm 2 was necessary to induce a significant charge transfer from SiC to WSe 2 , where a reduction of valence band offset was observed. Simultaneously, a new absorption edge appeared at 1.1 eV below the conduction band of SiC. The irradiation with heavy ions at 10 16 ions/cm 2 converts WSe 2 into a mixture of WO x and Se-deficient WSe 2 . The valence band is also heavily altered due to oxidation and amorphization. However, these doses are in excess of the doses needed to damage TMD-based electronics due to defects generated in common dielectric and substrate materials. As such, the radiation stability of WSe 2 -based electronics is not expected to be limited by the radiation hardness of WSe 2 , but rather by the dielectric and substrate.
We present a design and preliminary performance of a compact, high-peak-power 5-µm pulsed laser s... more We present a design and preliminary performance of a compact, high-peak-power 5-µm pulsed laser source for pumping a dielectric photonic structure to produce an acceleration gradient of order GV/m in dielectric laser acceleration. The 5-µm laser source is based on two cascaded optical parametric amplifiers (OPA): a 2-µm BBO OPA with a mixed phase matching scheme is used as a pump source, and a type-I phase-matched ZGP OPA is designed to produce sub-mJ 5-µm laser pulses. Preliminary result of ∼53 µJ pulse energy at 5 µm is demonstrated using a two-stage optical parametric generator (OPG)/OPA scheme, and an improved OPA scheme with dispersion management for production of higher pulse energy at 5 µm is under development.
Bulletin of the American Physical Society, Nov 12, 2020
The ZEUS facility will include a repetitive dual-beamline 3 PW laser system, a 100 J programmable... more The ZEUS facility will include a repetitive dual-beamline 3 PW laser system, a 100 J programmable shape multi-ns pulse driver, three radiation shielded experimental areas and will provide unique new capabilities to explore nonlinear quantum electrodynamics, relativistic plasmas, particles acceleration, extreme laboratory astrophysics, basic plasma physics and nuclear photonics. Once completed, the ZEUS laser system will be the highest-power laser system in the US and will become a user facility for the US scientists and wider international research community.
Of particular interest to X-ray FEL light source facilities is Enhanced Self-Amplified Spontaneou... more Of particular interest to X-ray FEL light source facilities is Enhanced Self-Amplified Spontaneous Emission (ESASE) technique. Such a technique requires an ultrafast (20-50 fs) high peak power, high repetition rate reliable laser systems working in the mid-IR range of spectrum (2µm or more). The approach of this proposed work is to design a novel Ultrafast Mid-IR Laser System based on optical parametric chirped-pulse amplification (OPCPA). OPCPA is a technique ideally suited for production of ultrashort laser pulses at the center wavelength of 2 µm. Some of the key features of OPCPA are the wavelength agility, broad spectral bandwidth and negligible thermal load.
8th Int. Particle Accelerator Conf. (IPAC'17), Copenhagen, Denmark, 14â19 May, 2017, May 1, 2017
Direct laser acceleration (DLA) of an electron bunch can be achieved by utilizing the axial field... more Direct laser acceleration (DLA) of an electron bunch can be achieved by utilizing the axial field of a well-guided, radially polarized laser pulse in a density-modulated plasma waveguide. However, the ponderomotive force of a TWclass laser pulse excites a plasma wave that can generate a defocusing electrostatic field, which significantly deteriorates the transverse properties of the injected electron witness bunch. To improve the quality of the accelerated witness bunch, an additional leading electron bunch, termed a precursor, is introduced to generate ion-focusing force to effectively confine the trailing witness bunch. We conducted three-dimensional particle-in-cell simulations to investigate the effect of bunch charge, transverse size of the precursor, and the axial separation between the precursor and the witness bunch on the efficacy of DLA. Results indicate that the transverse properties of the witness bunch can be maintained and the overall DLA efficiency can be improved when a favorable ion-focusing force is provided by the precursor.
Conference on Lasers and Electro-Optics, May 5, 2019
Tritium detection poses a challenge because of the weak beta particle emission and absence of ion... more Tritium detection poses a challenge because of the weak beta particle emission and absence of ionizing radiation. We demonstrate the isotopic analysis of deuterated water via laser-induced breakdown spectroscopy as a modality for measuring tritium.
For over 40 years, physicists have considered possible uses for neutrino detectors in nuclear non... more For over 40 years, physicists have considered possible uses for neutrino detectors in nuclear nonproliferation, arms control, and fissile materials security. Neutrinos are an attractive fission signature because they readily pass through matter. The same property makes neutrinos challenging to detect in systems that would be practical for nuclear security applications. This colloquium presents a broad overview of several potential neutrino applications, including the near-field monitoring of known reactors, far-field monitoring of known or discovery of undeclared reactors, detection of reactor waste streams, and detection of nuclear explosions. We conclude that recent detector advances have made near-field monitoring feasible. Farther-field reactor detection and waste stream detection monitoring are possible in some cases with further research and development. Very long-range reactor monitoring and nuclear explosion detection do not appear feasible for the foreseeable future due to considerable physical and/or practical constraints.
In nuclear nonproliferation and safeguards, detecting and accurately characterizing special nucle... more In nuclear nonproliferation and safeguards, detecting and accurately characterizing special nuclear material remains one of the greatest challenges. Uranium enrichment determination is typically achieved by measuring the ratio of characteristic γ-ray emissions from 235 U and 238 U. Fission also produces β-delayed neutrons, which have been used in the past to determine uranium enrichment from the time dependence of the long-lived delayed neutron emission rate. Such measurements typically use moderated 3 He tube detectors. We demonstrate a new measurement technique that employs a fast neutron active interrogation probe and a scintillation detector to measure the enrichment of uranium using both the buildup and decay of β-delayed neutron emission. Instead of 3 He tubes, a capture-based heterogeneous composite detector consisting of scintillating Li-glass and polyvinyl toluene has been constructed and used, offering a prospect to scale delayed neutron measurements to larger detector sizes. Since the technique relies on the existing tabulated nuclear data, no calibration standards are required. It is shown that the buildup of delayed neutron emission can be used to distinguish between uranium samples and infer the uranium enrichment level, with accuracy that rivals the method that employs the time-dependent decay of delayed neutron emission.
Plants and other photosynthetic organisms have been suggested as potential pervasive biosensors f... more Plants and other photosynthetic organisms have been suggested as potential pervasive biosensors for nuclear nonproliferation monitoring. We demonstrate that ultrafast laser filament-induced fluorescence of chlorophyll in the green alga Chlamydomonas reinhardtii is a promising method for remote, in-field detection of stress from exposure to nuclear materials. This method holds an advantage over broad-area surveillance, such as solar-induced fluorescence monitoring, when targeting excitation of a specific plant would improve the detectability, for example when local biota density is low. After exposing C. reinhardtii to uranium, we find that the concentration of chlorophyll a, chlorophyll fluorescence lifetime, and carotenoid content increase. The increased fluorescence lifetime signifies a decrease in non-photochemical quenching. The simultaneous increase in carotenoid content implies oxidative stress, further confirmed by the production of radical oxygen species evidence in the steady-state absorption spectrum. This is potentially a unique signature of uranium, as previous work finds that heavy metal stress generally increases non-photochemical quenching. We identify the temporal profile of the chlorophyll fluorescence to be a distinguishing feature between uranium-exposed and unexposed algae. Discrimination of uranium-exposed samples is possible at a distance of ∼35 m with a single laser shot and a modest collection system, as determined through a combination of experiment and simulation of distance-scaled uncertainty in discriminating the temporal profiles. Illustrating the potential for remote detection, detection over 125 m would require 100 laser shots, commensurate with the detection time on the order of 1 s.
We present a novel chirped pulse ampifiation method which combiner optial parynctric amplrficatio... more We present a novel chirped pulse ampifiation method which combiner optial parynctric amplrfication and laser amplification. We have demonshated this hybrid CF' A concept with a combination of bebbuium b n t e a d sapphire. High-efficiency, mu16 tenwatt compatible amplification is achieved without gain nmwing and without elstrooptic modulators using a simple commercial pump laser.
Nuclear Instruments and Methods in Physics Research, 2023
Gamma-ray emission from special nuclear material (SNM) is relatively easy to shield from detectio... more Gamma-ray emission from special nuclear material (SNM) is relatively easy to shield from detection using modest amounts of high-Z material. In contrast, fast-neutrons are much more penetrating and can escape relatively thick high-Z shielding without losing significant energy. Furthermore, fast neutrons provide a clear and unambiguous signature of the presence of SNM with few competing natural background sources. The challenge of detecting fast neutrons is twofold. First, the neutron flux from SNM are only a fraction of the corresponding gamma-ray flux. Second, fast neutrons can be difficult to differentiate from gamma rays. The ability to discriminate gamma rays from neutrons combined with neutron imaging can yield large benefit to isolate the localized SNM neutron source from background. With the recent developments of pulse-shape-sensitive plastic scintillators that offer excellent gamma-ray/neutron discrimination, and arrays of silicon photomultipliers combined with highly scalable and fast positron-emission-tomography (PET) multi-channel readout systems, field-deployable neutron imagers suitable for SNM detection might now be within reach. In this paper, we present a characterization of the performance of a recently available commercial PET-scanner readout, including its sensitivity to pulse-shape differences between fast neutrons and gamma rays, energy and timing resolution, as well as linearity and dynamic range. We find that, while the pulse-shape discrimination is achievable with stilbene, further improvement of the readout is required to achieve it with the best available plastic scintillators. The time and energy resolution appear to be adequate for neutron imaging in some circumstances.
We report measurements of the structural response of a thin film of SrTiO3 (STO) under strong exc... more We report measurements of the structural response of a thin film of SrTiO3 (STO) under strong excitation with singlecycle terahertz (THz) fields using ultrafast x-rays. STO has a known soft phonon that is in close resonance with the central frequency of the THz driving field. For weak THz fields, we observe atomic motion which we associate with resonant phonon excitation. As we increase the THz field strength, we detect both a saturation in the soft mode excitation amplitude as well as the appearance of several new frequencies closely matched to known higher-frequency phonons in STO. Combining DFT calculations with measured x-ray diffraction measurements, we are able to extract the soft mode phonon potential.
The fiber-based, spatially and temporally shaped, picosecond UV laser system described here has b... more 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 μJ 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.
Bulletin of the American Physical Society, Oct 30, 2006
based systems offer a path to highbrightness high-energy (> 1 MeV) x-ray & gamma-ray sources due ... more based systems offer a path to highbrightness high-energy (> 1 MeV) x-ray & gamma-ray sources due to their favorable scaling with electron energy. LLNL is currently engaged in an effort to build such a device, dubbed the "Thomson-Radiated Extreme X-Ray" (T-REX) source. Presented here is an overview of the system design, which includes both a UVlaser-driven electron photoinjector and an intense scattering laser. Also shown are the results of detailed electron beam and gamma-ray generation modeling designed to optimize the brightness and flux of the gamma-ray beam, including UV drive laser profile effects, charge v. emittance tradeoffs, thermal emittance effects, and contributions of focusing geometry.
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Papers by Igor Jovanovic