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Giant Isolated Attosecond Pulses from Two-Color Laser-Plasma Interactions
摘要： A new regime in the interaction of a two-color (ω; 2ω) laser with a nanometer-scale foil is identified, resulting in the emission of extremely intense, isolated attosecond pulses—even in the case of multicycle lasers. For foils irradiated by lasers exceeding the blow-out field strength (i.e., capable of fully separating electrons from the ion background), the addition of a second harmonic field results in the stabilization of the foil up to the blow-out intensity. This is then followed by a sharp transition to transparency that essentially occurs in a single optical cycle. During the transition cycle, a dense, nanometer-scale electron bunch is accelerated to relativistic velocities and emits a single, strong attosecond pulse with a peak intensity approaching that of the laser field.
关键词： two-color laser,laser-plasma interactions,attosecond pulses,coherent synchrotron emission
更新于2025-09-23 15:19:57
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Innovative education and training in high power laser plasmas (PowerLaPs) for plasma physics, high power laser matter interactions and high energy density physics: experimental diagnostics and simulations
摘要： The second and final year of the Erasmus Plus programme ‘Innovative Education and Training in high power laser plasmas’, otherwise known as PowerLaPs, is described. The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme, where teaching takes place in five separate institutes with a range of different aims and styles of delivery. The ‘in-class’ time is limited to 4 weeks a year, and the programme spans 2 years. PowerLaPs aims to train students from across Europe in theoretical, applied and laboratory skills relevant to the pursuit of research in laser plasma interaction physics and inertial confinement fusion. Lectures are intermingled with laboratory sessions and continuous assessment activities. The programme, which is led by workers from the Hellenic Mediterranean University and supported by co-workers from the Queen’s University Belfast, the University of Bordeaux, the Czech Technical University in Prague, Ecole Polytechnique, the University of Ioannina, the University of Salamanca and the University of York, has just finished its second and final year. Six Learning Teaching Training activities have been held at the Queen’s University Belfast, the University of Bordeaux, the Czech Technical University, the University of Salamanca and the Institute of Plasma Physics and Lasers of the Hellenic Mediterranean University. The last of these institutes hosted two 2-week-long Intensive Programmes, while the activities at the other four universities were each 5 days in length. In addition, a ‘Multiplier Event’ was held at the University of Ioannina, which will be briefly described. In this second year, the work has concentrated on training in both experimental diagnostics and simulation techniques appropriate to the study of plasma physics, high power laser matter interactions and high energy density physics. The nature of the programme will be described in detail, and some metrics relating to the activities carried out will be presented. In particular, this paper will focus on the overall assessment of the programme.
关键词： postgraduate education,laser plasma interactions
更新于2025-09-23 15:19:57
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Production of relativistic electrons at subrelativistic laser intensities
摘要： Relativistic electron temperatures were measured from kilojoule, subrelativistic laser-plasma interactions. Experiments show an order of magnitude higher temperatures than expected from a ponderomotive scaling, where temperatures of up to 2.2 MeV were generated using an intensity of 1 × 1018 W/cm2. Two-dimensional particle-in-cell simulations suggest that electrons gain superponderomotive energies by stochastic acceleration as they sample a large area of rapidly changing laser phase. We demonstrate that such high temperatures are possible from subrelativistic intensities by using lasers with long pulse durations and large spatial scales.
关键词： particle-in-cell simulations,relativistic electrons,stochastic acceleration,laser-plasma interactions,subrelativistic laser intensities
更新于2025-09-19 17:13:59
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Net energy gain in direct laser acceleration due to enhanced dephasing induced by an applied magnetic field
摘要： Even in the situation where an electron interacts with a single plane wave, the well-known dynamical adiabaticity can be broken when an applied magnetic field is present, which will act to increase the dephasing rate of the electron during the interaction. Here we demonstrate this for the case where there is a uniform static magnetic field which is oriented either parallel or perpendicular to the electric field of the incident plane wave, and perpendicular to the direction of its propagation. The described energy gain phenomenon has direct relevance to laser-plasma interactions that involve external magnetic fields generated by laser-driven capacitor coils.
关键词： net energy gain,direct laser acceleration,magnetic field,laser-plasma interactions,dephasing
更新于2025-09-19 17:13:59
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X-ray Spectroscopy Based Diagnostic of GigaGauss Magnetic Fields during Relativistic Laser-Plasma Interactions
摘要： GigaGauss (GG), and even multi-GG magnetic fields are expected to be developed during relativistic laser-plasma interactions. Sub-GG magnetic fields were previously measured by a method using the self-generated harmonics of the laser frequency, and the fact that the magnetized plasma is birefringent and/or optically active depending on the propagation direction of the electromagnetic wave. In the present short communication, we outline an idea for a method of measuring GG magnetic fields based on the phenomenon of Langmuir-wave-caused dips (L-dips) in X-ray line profiles. The L-dips were observed in several experimental spectroscopic studies of relativistic laser-plasma interactions. Ultrastrong magnetic fields affect the separation of the L-dips from one another, so that this relative shift can be used to measure such fields.
关键词： X-ray spectral line profiles,relativistic laser-plasma interactions,GigaGauss magnetic fields,Langmuir-wave-caused dips
更新于2025-09-16 10:30:52
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Intense attosecond pulses carrying orbital angular momentum using laser plasma interactions
摘要： Light beams with helical phase-fronts are known to carry orbital angular momentum (OAM) and provide an additional degree of freedom to beams of coherent light. While OAM beams can be readily derived from Gaussian laser beams with phase plates or gratings, this is far more challenging in the extreme ultra-violet (XUV), especially for the case of high XUV intensity. Here, we theoretically and numerically demonstrate that intense surface harmonics carrying OAM are naturally produced by the intrinsic dynamics of a relativistically intense circularly-polarized Gaussian beam (i.e. non-vortex) interacting with a target at normal incidence. Relativistic surface oscillations convert the laser pulses to intense XUV harmonic radiation via the well-known relativistic oscillating mirror mechanism. We show that the azimuthal and radial dependence of the harmonic generation process converts the spin angular momentum of the laser beam to orbital angular momentum resulting in an intense attosecond pulse (or pulse train) with OAM.
关键词： laser plasma interactions,orbital angular momentum,relativistic oscillating mirror,extreme ultra-violet,attosecond pulses
更新于2025-09-12 10:27:22
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Characterization of a 100 micrometer-scale cryogenically cooled gas jet for near-critical density laser-plasma experiments
摘要： We present the design and characterization of a thin, high density pulsed gas jet for use in the study of near critical laser plasma interactions with ultrashort Ti:sapphire laser pulses. The gas jet uses a range of capillary nozzles with inner diameters between 50 and 150 μm and is operated in the sonic regime. Cryogenic cooling of the gas valve body to ?160 ○C provides the necessary density enhancement for reaching overcritical plasma densities at λ = 800 nm (Ncr ≈ 1.7 × 1021 cm?3) using hydrogen gas at jet backing pressures below 1000 psi. Under certain conditions, fast expansion of the gas from a nozzle can lead to formation of clusters; here, we use our previously demonstrated all-optical method to estimate the cluster mean size and density. For the jets studied here, we find that cluster formation only begins at distances from the nozzle exit greater than a few times the nozzle orifice diameter.
关键词： laser-plasma interactions,cluster formation,gas jet,high density plasmas,cryogenic cooling
更新于2025-09-12 10:27:22
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Proton acceleration due to laser plasma interactions from mass-limited spherical targets
摘要： The proton acceleration processes involved in the interaction of an ultrashort circularly polarized laser with a near-critical density spherical target are investigated in this paper using three dimensional particles in cell simulations. Both the target size and the target density are varied to understand their influence on the accelerated beam of protons. The target is efficiently heated by relativistic transparency, and a complicated interplay is observed between the participating interaction processes. The electron heating and recirculations help in the formation of shocks which exert a further push to the protons accelerated by the electrostatic sheath formed due to the ponderomotive force. A maximum peak proton energy of about 40 MeV is observed, which is the result of the cumulative effects of various acceleration mechanisms. Electron jets are observed in the forward laser direction for the larger target size, which suppresses the energy of the proton beams.
关键词： spherical targets,laser plasma interactions,electrostatic sheath,electron heating,proton acceleration,relativistic transparency,ponderomotive force,shock formation
更新于2025-09-12 10:27:22
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Simulations of carbon ion acceleration by 10 PW laser pulses on ELI-NP
摘要： We present results of 2D particle-in-cell (PIC) simulations of carbon ion acceleration by 10 petawatt (PW) laser pulses, studying both circular polarized (CP) and linear polarized (LP) pulses. We carry out a thickness scanning of a solid carbon target to investigate the ideal thickness for carbon ion acceleration mechanisms using a 10 PW laser with an irradiance of 5 × 1022 W cm?2. The energy spectra of carbon ions and electrons and their temperature are studied. Additionally, for the carbon ions, their angular divergence is studied. It is shown that the ideal thickness for the carbon acceleration is 120 nm and the cutoff energy for carbon ions is 5 and 3 GeV for CP and LP pulses, respectively. The corresponding carbon ions temperature is ～1 and ～0.75 GeV. On the other hand, the energy cutoff for the electrons is ～500 MeV with LP and ～400 MeV with CP laser pulses. We report that the breakout afterburner mechanism is most likely causing the acceleration of carbon ions to such high energies for the optimal target thickness.
关键词： Laser–plasma interactions,particle acceleration,PIC simulations
更新于2025-09-11 14:15:04