A robust method for producing half-cycle-few-cycle pulses in mid-infrared to extreme ultraviolet spectral ranges is proposed. It is based on coherent undulator radiation of relativistic ultrathin electron layers, which are produced by microbunching of ultrashort electron bunches by a TW power laser in a modulator undulator. According to our numerical calculations it is possible to generate as short as 10 nm long electron layers in a single-period modulator undulator having an undulator parameter of only K = 0.25 and which is significantly shorter than the resonant period length. By using these electron layers the production of carrier-envelope-phase stable pulses with up to a few nJ energy and down to 30 nm wavelength and 70 as duration is predicted.PACS numbers: 41.60. Cr, 41.50.+h, 41.75.Ht Waveform-controlled few-cycle laser pulses enabled the generation of isolated attosecond pulses and their application to the study of electron dynamics in atoms, molecules, and solids [1]. Intense waveform-controlled extreme ultraviolet (EUV)/X-ray attosecond pulses could enable precision time-resolved studies of core-electron processes by using e.g. pump-probe techniques [2]. Examples are time-resolved imaging of isomerisation dynamics, nonlinear inner-shell interactions, or multiphoton processes of core electrons. EUV pump-EUV probe experiments can be carried out at free-electron lasers (FELs) [3,4]; however, the temporal resolution is limited to the fs regime and the stochastic pulse shape is disadvantageous.The shortest electromagnetic pulses reported to date, down to a duration of only 67 as, were generated by high-order harmonic generation (HHG) in gas targets [5,6]. Isolated single-cycle 130-as pulses were generated by HHG using driving pulses with a modulated polarization state [7]. One drawback of gas HHG is the relatively low EUV pulse energy due to the ionization depletion of the medium. The use of long focal length for the IR driving field, or using strong THz fields for HHG enhancement [8] were proposed to increase the EUV pulse energy. The generation of half-cycle 50-as EUV pulses with up to 0.1 mJ energy is predicted by coherent Thomson backscattering from a laser-driven relativistic ultrathin electron layer by irradiating a double-foil target with intense few-cycle laser pulses at oblique incidence [9,10]. Various schemes, such as the longitudinal space charge amplifier [11,12], or two-color enhanced self-amplified spontaneous emission (SASE) [13,14] were proposed for attosecond pulse generation at FELs. However, the realization of these technically challenging schemes has yet to be demonstrated and precise waveform control is difficult.In this Letter we propose a robust method for producing waveform-controlled pulses down to half-cycle durations in the mid-infrared (MIR) to the EUV spectral ranges. The method is based on coherent undulator radiation emitted by relativistic ultrathin electron layers, which are produced by microbunching of a picosecond electron bunch obtained from microwave electron inject...
Research at modern light sources continues to improve our knowledge of the natural world, from the subtle workings of life to matter under extreme conditions. Free-electron lasers, for instance, have enabled the characterization of biomolecular structures with sub-ångström spatial resolution, and paved the way to controlling the molecular functions. On the other hand, attosecond temporal resolution is necessary to broaden our scope of the ultrafast world. Here we discuss attosecond pulse generation beyond present capabilities. Furthermore, we review three recently proposed methods of generating attosecond x-ray pulses. These novel methods exploit the coherent radiation of microbunched electrons in undulators and the tailoring of the emitted wavefronts. The computed pulse energy outperforms pre-existing technologies by three orders of magnitude. Specifically, our simulations of the proposed Soft X-Ray Laser (SXL) at MAX IV (Lund, Sweden) show that a pulse duration of 50-100 attoseconds and a pulse energy up to 5 microjoules is feasible with the novel methods. In addition, the methods feature pulse shape control, enable the incorporation of orbital angular momentum, and can be used in combination with modern compact free-electron laser setups.
We investigate the acceleration of a proton beam driven by intense tera-hertz (THz) laser field from a near critical density hydrogen plasma. Two-dimension-in-space and three-dimension-in-velocity particle-in-cell simulation results show that a relatively long wavelength and an intense THz laser can be employed for proton acceleration to high energies from near critical density plasmas. We adopt here the electromagnetic field in a long wavelength (0.33 THz) regime in contrast to the optical and/or near infrared wavelength regime, which offers distinct advantages due to their long wavelength (λ=350 μm), such as the λ2 scaling of the electron ponderomotive energy. Simulation study delineates the evolution of THz laser field in a near critical plasma reflecting the enhancement in the electric field of laser, which can be of high relevance for staged or post ion acceleration.
The acceleration of single electrons and electron bunches by focused THz pulse pairs has been investigated by numerical simulations. The effect of the choice of the beam waist radius, the carrier-envelope phase, and the propagation direction of the THz pulses on the energy of the accelerated electrons was investigated. The acceleration of electron bunches from rest up to 150 keV was predicted using single-cycle THz pulses with 1 mJ energy and a central frequency in the 0.1 THz to 3.0 THz range. The post-acceleration of electrons by pairs of focused THz pulses has also been proposed.
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