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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Cavity-Enhanced Noncollinear High-Harmonic Generation
摘要： The generation of extreme-ultraviolet (XUV) attosecond pulse trains (APTs) by the process of high harmonic generation (HHG) has enabled the investigation of electronic dynamics in atoms, molecules and solids. Enhancing the pulse energy impinging on the target gas by usually one to two orders of magnitude by means of an external, passive resonator (enhancement cavity, EC) permits efficient HHG at repetition rates exceeding 10 MHz, enabling applications in XUV precision spectroscopy and space-charge-limited regimes of photoelectron or coincidence spectroscopy.
关键词： attosecond pulse trains,high harmonic generation,extreme-ultraviolet,XUV precision spectroscopy,enhancement cavity
更新于2025-09-16 10:30:52
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Ultrahigh brightness attosecond electron beams from intense X-ray laser driven plasma photocathode
摘要： The emerging intense attosecond X-ray lasers can extend the Laser Wakefield Acceleration mechanism to higher plasma densities in which the acceleration gradients are greatly enhanced. Here we present simulation results of high quality electron acceleration driven by intense attosecond X-ray laser pulses in liquid methane. Ultrahigh brightness electron beams can be generated with 5-dimensional beam brightness over 1020 A · m?2 · rad?2. The pulse duration of the electron bunch can be shorter than 20 as. Such unique electron sources can benefit research areas requiring crucial spatial and temporal resolutions.
关键词： attosecond X-ray lasers,ultrahigh brightness electron beams,liquid methane,Laser Wakefield Acceleration,5-dimensional beam brightness
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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Attosecond Pulse Amplification in a Plasma-Based X-Ray Laser Dressed by an Infrared Laser Field
摘要： High-harmonic generation (HHG) of laser radiation has led to attosecond pulse formation which offers unprecedented temporal resolution in observing and controlling electron and nuclear dynamics. But the energy of attosecond pulses remains quite small, especially for photon energies exceeding 100 eV, which limits their practical applications. We propose a method for amplification of attosecond pulses in the active medium of a plasma-based x-ray laser dressed by a replica of the laser field used for HHG. The experimental implementation is suggested in hydrogenlike C5t x-ray laser at 3.4 nm wavelength in the “water window” range.
关键词： attosecond pulse amplification,infrared laser field,plasma-based x-ray laser,high-harmonic generation,water window
更新于2025-09-12 10:27:22
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Attosecond pulse generation by relativistic flying mirrors in laser-plasma interaction: Effect of plasma density and driver amplitude on the generated pulse
摘要： The generation of high-intensity attosecond pulses by the interaction of two counterpropagating short laser pulses with underdense plasma is investigated. By using parallel fully kinetic particles in cell simulation, which shows the formation of relativistic ?ying mirrors in the wake wave of the intense driver laser pulse and the focusing re?ection of the weak source pulse, it is demonstrated that intense attosecond pulses can be produced under the optimized conditions of plasma density and driver laser amplitude according to the relativistic similarity theory. In addition, it is shown that the frequency of the source pulse is upshifted by a factor from 10 to 80 corresponding to a re?ected radiation wavelength from 20 to 164 nm which lies in the extreme ultraviolet region, while most of the energy lies around a frequency upshift of 20, in agreement with the measured Lorentz factor. The intensity of the main attosecond pulse is two orders higher than the source pulse intensity.
关键词： plasma density,driver amplitude,attosecond pulse generation,relativistic flying mirrors,laser-plasma interaction
更新于2025-09-12 10:27:22
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Topological strong-field physics on sub-laser-cycle timescale
摘要： The sub-laser-cycle timescale of the electronic response to strong fields enables attosecond dynamical imaging in atoms, molecules and solids, with optical tunnelling and high-harmonic generation the hallmarks of attosecond optical spectroscopy. Topological insulators are intimately linked with electron dynamics, as manifested via the chiral edge currents, but it is unclear if and how topology leaves its mark on optical tunnelling and sub-cycle electronic response. Here, we identify distinct bulk topological effects on directionality and timing of currents arising during electron injection into conduction bands. We show that electrons tunnel differently in trivial and topological insulators, for the same band structure, and identify the key role of the Berry curvature in this process. These effects map onto topologically dependent attosecond delays and helicities of emitted harmonics that record the phase diagram of the system. Our findings create new roadmaps in studies of topological systems, building on the ubiquitous properties of the sub-laser-cycle strong-field response—a unique mark of attosecond science.
关键词： high-harmonic generation,attosecond science,Berry curvature,topological insulators,strong-field physics
更新于2025-09-12 10:27:22
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Behavioral study of high-order harmonics and attosecond pulse generation via bichromatic driving laser fields
摘要： High-order harmonics intensity and subsequently attosecond pulses which are generated after the interaction of some two color femtosecond pulses with helium ions are studied in this paper. Cutoff frequency in the high-order harmonics' intensity spectrum, maximum ionization probability, attosecond pulse intensity and duration in this research are investigated versus the frequency spacing of the two color driving pulse elements (δω). It is seen that the cutoff frequency decays exponentially by δω, whereas generation of the most powerful and shortest attosecond pulses as well as the maximum ionization probability occurs around the value of δω = 0 (i.e., for the single color pulses). However, the longest attosecond pulses are generated for the case of δω = 0.8 ω0 (in which ω0 is the frequency of the fundamental pulse). Finally, the most isolated attosecond pulses are generated for the case in which δω = 1.25 ω0.
关键词： Attosecond,helium ion,two color,High order harmonic generation
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - High Efficiency, High Energy Few-Cycle Driver at 1-μm
摘要： The recent development of high repetition rate lasers based on ytterbium-doped fiber amplifiers (YDFA), has paved the way to increase the repetition rate (>100 kHz) of coherent extreme ultra violet (XUV) sources generated by high harmonic generation (HHG). High repetition rate HHG driver comes with several advantages, such as increased photon flux [1], reduction of the acquisition time in coincidence experiments to study molecular dynamics such as COLTRIMS, and the possibility to study the electronic structure of matter via photoemission spectroscopy and microscopy, where low doses are needed to avoid space-charge effects [2]. Up to now, the overall majority of HHG studies and applications has been restricted to the low repetition rates of Ti:sapphire lasers. Commonly, Ti:sapphire lasers delivers 20 fs pulses at a central wavelength λ = 800 nm, with pulse energies up to hundreds of mJ. However, the average power of these laser systems cannot easily be scaled beyond 10 W, restricting HHG at low repetition rates (up to 10 kHz). Currently, the most mature and powerful ultrafast source technology is undoubtedly ytterbium-based systems, with average power levels beyond 1 kW [3] and numerous industrial applications. However, the long pulse duration of around >200 fs delivered by YDFA sources limits their relevance to this application field. Therefore, nonlinear compression setups have been used successfully to reduce the pulse duration and obtain XUV photon flux among the highest ever reported for HHG-based sources [1]. However, to reach sub-3 cycles regime (< 10 fs at 1030 nm), which is typically required in combination with gating techniques to obtain isolated attosecond pulses, two stages of compression must usually be implemented [4]. This reduces the energy efficiency of the systems dedicated to attosecond physics to typically less than 30% of the overall YDA energy. Here, we demonstrate a two-cycle-source based on a high-energy femtosecond YDFA followed by a hybrid two-stage nonlinear compression setup. The association of a multipass cell-based stage and large-diameter capillary stage provides a compression factor of 48 with an overall transmission of 61%. This source is, to the best of our knowledge, the most efficient few cycle, high energy and high repetition rate laser demonstrated to date. It is very compact with an overall footprint of 1.8 m × 1.0 m and provides a stable train of few-cycle pulses at a central wavelength of 1030 nm that has been continuously characterized over more than 8h. The delivered 6.8 fs (see Fig. 1) 140 μJ pulses at 150 kHz repetition rate, corresponding to 21 W average power, are ideally suited to drive high-photon flux XUV sources [5] through HHG. The described laser system is robust, compact, and power efficient, making it an ideal driver laser for application-ready high flux XUV and attosecond sources.
关键词： attosecond pulses,high harmonic generation,ytterbium-doped fiber amplifiers,extreme ultra violet,high repetition rate lasers
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Polarization-Resolved High Harmonic Spectroscopy of Interlocked Attosecond Bursts
摘要： High-harmonic spectroscopy is an important tool for investigation of nonlinear atom-laser interaction. Polarization-resolved high harmonic spectroscopy is becoming a promising method for exploring chiral quantities, in particular as numerous techniques have been demonstrated experimentally for generating bright and applicable high-order harmonics with highly helical polarization. In this context, a simple direct mapping (ideally, analytical formula) between the harmonics polarization and time-domain description of the HHG process would be very useful. Here, we present an analytic mapping between ellipticities of the high harmonics and variables of an interlocked pair of attosecond pulse trains - relative emission directions, relative delay, and their ellipticities – in a new scheme for generation of bright helically polarized high harmonics. In this scheme, HHG is driven by a two-color pulse, a fundamental frequency and its second harmonic, where the two colors are slightly elliptically polarized with opposite helicity and perpendicular ellipse major axes. In the time domain, the HHG emission consists of a pair of nearly linearly polarized attosecond pulse trains (APTs), yet with very different polarization axes. The ellipticities of the harmonics vary from linear to circular by tweaking the ellipticity of the pump. We discovered that the underlying mechanism for this ultra-sensitive polarization knob is dominantly induced by phase shifts between the pair of interlocked APTs. The ellipticity of the attosecond bursts and their relative emission angles play a secondary, yet still easily measured, role. Obtaining an analytic formula for the ellipticities of the high harmonics as a function of the APTs variables allow us to probe the APTs by ellipticity-resolved high harmonic spectroscopy. We demonstrate this approach experimentally.
关键词： High-harmonic spectroscopy,attosecond pulse trains,helical polarization,polarization-resolved,two-color pulse
更新于2025-09-12 10:27:22
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Net Acceleration and Direct Measurement of Attosecond Electron Pulses in a Silicon Dielectric Laser Accelerator
摘要： Net acceleration of attosecond-scale electron pulses is critical to the development of on-chip accelerators. We demonstrate a silicon-based laser-driven two-stage accelerator as an injector stage prototype for a Dielectric Laser Accelerator (DLA). The first stage converts a 57-keV (500 (cid:1) 100)-fs (FWHM) electron pulse into a pulse train of 700 (cid:1) 200 as (FWHM) microbunches. The second stage harnesses the tunability of dual-drive DLA to perform both a net acceleration and a streaking measurement. In the acceleration mode, the second stage increases the net energy of the electron pulse by 200 eV over 12.25 μm. In the deflection mode, the microbunch temporal profile is analyzed by a direct streaking measurement with 200 as resolution. This work provides a demonstration of a novel, on-chip method to access the attosecond regime, opening new paths towards attosecond science using DLA.
关键词： electron pulses,streaking measurement,attosecond,silicon dielectric laser accelerator,net acceleration
更新于2025-09-12 10:27:22