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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Investigations on electrical properties and correlations to electron and X-ray energies of pyroelectric LiTaO<inf>3</inf> and LiNbO<inf>3</inf>
摘要： The electrical properties of pyroelectric Lithium Tantalate (LiTaO3) and Lithium Niobate (LiNbO3) were investigated and compared to accessible X-ray energies by using the pyroelectric effect to generate X-rays. The capacitances of different crystals of varying sizes were measured and the resulting permittivities were calculated. A vacuum setup enabled a correlation to the maximum X-ray energies at a variable pressure. The presented results provide an overview of fundamental material properties and the effect on the generated difference of potential.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray spectrum,permittivity,X-ray energy,electron acceleration,electron emission,capacitance,Lithium Tantalate
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Self-focusing of electrons emitted by rectangular pyroelectric crystals: A study on geometrical conditions for optimized X-ray intensities
摘要： Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high energy and intensity. These pyroelectric X-ray sources may be used in XRF applications due to particular advantages. This report deals with systematic studies on the behavior of these crystals enabling an optimization of X-ray intensity. Furthermore, the focusing of electrons emitted by rectangular pyroelectric crystals has been studied.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray intensity,X-ray spectrum,focusing,electron acceleration,electron emission,Lithium Tantalate
更新于2025-09-23 15:21:21
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Electron acceleration up to MeV level under nonlinear interaction of subterawatt femtosecond laser chirped pulses with Kr clusters
摘要： The acceleration of electrons to MeV energies from a Kr cluster jet irradiated by a relativistic (6 × 1018 W cm?2) femtosecond laser pulse is studied. For the first time, the action of transform-limited laser pulse effects on the generation of hot electrons with an effective temperature (Thot) of around 150 keV is experimentally demonstrated. The particles were accelerated in the plasma channel formed under self-focusing of the laser beam. Introducing a linear positive chirp together with pulse elongation from 50–~120 fs results in substantially enhanced hot electrons flux with a growth of Thot up to 300 keV and a maximal energy of over 2 MeV. The observed effect may be related to the strongly nonlinear propagation of the pulse through plasma, accompanied by more favorable conditions for efficient particles energy gain and pulse nonlinear compression.
关键词： femtosecond laser,nonlinear phenomena,krypton,clusters,laser-driven electron acceleration
更新于2025-09-23 15:21:01
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Optimization of PBG-Waveguides for Terahertz-Driven Electron Acceleration
摘要： The properties of 2-D photonic bandgap dielectric structures, also called photonic crystals, are numerically investigated to assist the design of waveguides for terahertz (THz)-driven linear electron acceleration. Given the broadband nature of the driving pulses in THz acceleration regimes, one design aim is to maximize the photonic bandgap width to allow propagation of the relevant frequencies within the photonic crystal linear defect waveguide. The proposed design is optimized to provide the best compromise between effective acceleration bandwidth and strong beam–wave interaction at the synchronism central frequency. Considerations on achieved acceleration bandwidth, accelerating voltage, and surface magnetic field are given to compare the proposed geometry to one of the main counterparts in the literature—the dielectric-lined waveguide.
关键词： Photonic crystals,terahertz (THz) electron acceleration,photonic-bandgap waveguides (PBG-Ws)
更新于2025-09-23 15:21:01
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Laser-heated capillary discharge plasma waveguides for electron acceleration to 8 GeV
摘要： A plasma channel created by the combination of a capillary discharge and inverse Bremsstrahlung laser heating enabled the generation of electron bunches with energy up to 7.8 GeV in a laser-driven plasma accelerator. The capillary discharge created an initial plasma channel and was used to tune the plasma temperature, which optimized laser heating. Although optimized colder initial plasma temperatures reduced the ionization degree, subsequent ionization from the heater pulse created a fully ionized plasma on-axis. The heater pulse duration was chosen to be longer than the hydrodynamic timescale of ~1 ns, such that later temporal slices were more efficiently guided by the channel created by the front of the pulse. Simulations are presented which show that this thermal self-guiding of the heater pulse enabled channel formation over 20 cm. The post-heated channel had lower on-axis density and increased focusing strength compared to relying on the discharge alone, which allowed for guiding of relativistically intense laser pulses with a peak power of 0.85 PW and wakefield acceleration over 15 diffraction lengths. Electrons were injected into the wake in multiple buckets and times, leading to several electron bunches with different peak energies. To create single electron bunches with low energy spread, experiments using localized ionization injection inside a capillary discharge waveguide were performed. A single injected bunch with energy 1.6 GeV, charge 38 pC, divergence 1 mrad, and relative energy spread below 2% full-width half-maximum was produced in a 3.3 cm-long capillary discharge waveguide. This development shows promise for mitigation of energy spread and future high efficiency staged acceleration experiments.
关键词： capillary discharge,inverse Bremsstrahlung laser heating,electron acceleration,laser-driven plasma accelerator,plasma channel
更新于2025-09-23 15:21:01
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Tomographic reconstruction algorithms for structured gas density profiles of the targets for laser wakefield acceleration
摘要： The output of a laser wakefield accelerator strongly depends on the gas target density profile. In this work we focus on the reconstruction of the 3D density profiles from tomographic measurements. We compare analytical and iterative methods, and we propose a new one, FARM, which is tailored for the reconstruction of gas targets for laser wakefield acceleration. Several methods are tested on both simplified and realistic geometries. The algorithms are evaluated in terms of the quality of the density profile reconstruction, the number of projections needed, and the computation time required.
关键词： interferometry,tomography,laser wakefield acceleration,density profile,gas target,laser plasma acceleration,tomographic reconstruction,laser electron acceleration
更新于2025-09-23 15:19:57
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Effect of a tightly focused chirped Gaussian laser pulse on electron acceleration in helical undulator
摘要： The chirped-pulse inverse free electron laser (CIFEL) interaction has been investigated by considering a tightly focused chirped Gaussian laser pulse and a helical undulator in vacuum. We consider the more realistic description of a laser, i.e., seventh-order calculation in the spatial term and first-order calculation in the temporal term. Numerical calculations show that better electron acceleration can be achieved using a tightly focused chirped Gaussian laser pulse in the CIFEL scheme. The investigation shows that a 10 MeV electron can be accelerated up to a few giga-electron volts energy with the present available laser parameters.
关键词： CIFEL,tightly focused chirped Gaussian laser pulse,helical undulator,electron acceleration,chirped-pulse inverse free electron laser
更新于2025-09-23 15:19:57
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Interference microscopy study of the preplasma formed on an iron target surface exposed to high-power femtosecond laser pulses
摘要： The characteristic scale of spread of the plasma formed on the surface of a bulk iron target irradiated by a femtosecond laser pulse with an intensity of 1016 W cm–2 is measured by time-resolved interference microscopy using femtosecond pulses emitted by a Cr : forsterite laser system with an intensity contrast of 107. The chosen technique is demonstrated to be efficient in such measurements. It is shown experimentally that, as a result of laser pulse impact, the displacement of a plasma layer with a density exceeding critical does not exceed 30 nm.
关键词： interference microscopy,femtosecond pulse,electron acceleration mechanisms,hot electrons
更新于2025-09-23 15:19:57
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Generation of gamma radiation by a subterawatt ultrashort laser pulse: optimisation of preplasma and pulse duration
摘要： We report an experimental and numerical study of the acceleration of electrons in a plasma interacting with a subterawatt laser pulse (intensity of ~3 × 10^18 W cm^–2 at a pulse duration of 50 fs). A preplasma layer on the surface of a molybdenum target is formed by an additional laser pulse with a duration of 8 ns and an intensity of ~2 × 10^12 W cm^–2. It is shown that an increase in the laser pulse duration to 1700 fs at a constant energy (and a proportional decrease in intensity) leads to an increase in the yield of bremsstrahlung γ-radiation by more than an order of magnitude when the nanosecond pulse is ahead of the femtosecond one by 15 – 25 ns. Interferometry data and results of diagnostics of optical and γ-radiation of a plasma demonstrate that the collisional ionisation of atoms by electrons oscillating in the field of such a laser pulse plays an essential role in the formation of electron density profile. The sensitivity of the described effect to the level of amplified spontaneous emission is determined, despite the nanosecond pulse impact. Numerical simulations show that at a large pulse duration, the acceleration of electrons is stipulated by the beaking of plasma waves excited during stimulated Raman scattering of laser radiation.
关键词： preplasma,subrelativistic intensity,amplified spontaneous emission,laser plasma,contrast,electron acceleration,collisional ionisation
更新于2025-09-23 15:19:57
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Electron Acceleration in Direct Laser-Solid Interactions Far Beyond the Ponderomotive Limit
摘要： In laser-solid interactions, electrons may be generated and subsequently accelerated to energies of the order of magnitude of the ponderomotive limit, with the underlying process dominated by direct laser acceleration. The breaking of this limit, realized here by a radially polarized laser pulse incident upon a wire target, can be associated with several novel effects. Three-dimensional particle-in-cell simulations show that a relativistic intense laser pulse can extract electrons from the wire and inject them into the accelerating field. Antidephasing, resulting from collective plasma effects, is shown here to enhance the accelerated electron energy by 2 orders of magnitude compared to the ponderomotive limit. It is demonstrated that ultrashort radially polarized pulses produce superponderomotive electrons more efficiently than pulses of the linear and circular polarization varieties.
关键词： laser-solid interactions,ponderomotive limit,antidephasing acceleration,radially polarized laser pulse,electron acceleration
更新于2025-09-19 17:13:59