Those theoretical studies suggest that using the CTLP with well-defined relative phases and timing can precisely control the injection of electrons into the plasma wake wave leading to boost the electron beam quality, which eventually translates to generation of ultrabright electron beams that are essential, for instance, to drive a desktop x-ray free-electron laser. In this scheme, electrons can potentially gain threefold higher energy as compared with the energy gain from a standard LWFA driven by an 800-nm wavelength laser pulse with equivalent power. ( 17) proposed using the CTLP in an all-optical dual-stage LWFA to enhance the electron bunch energy, where the leading FL laser pulse acts as an injector, whereas the subsequent SH laser pulse acts as an accelerator or booster. ( 16) proposed overlapping two relativistic laser pulses at the fundamental (FL 1ω) and third harmonic (3ω) inside a plasma the coherent interference of the two laser pulses can trigger an ionization injection of electrons only within a very short distance (because of the plasma dispersion), leading to the possibility of generating polychromatic narrow energy spread electron bunches. Such a method relies on exciting a large plasma wake wave by a relativistic midinfrared laser pulse while triggering the electron injection via the ionization of some inner-shell Kr ions ( 14, 15) using a properly delayed second harmonic (SH 2ω) intense laser pulse. ( 13) proposed using CTLP for generating low-emittance electron beams. Recently, the concept of a laser wakefield acceleration (LWFA) ( 12) driven by CTLP has been proposed via particle-in-cell (PIC) simulation studies, which can be briefly summarized as follows: In 2014, Yu et al. It is, therefore, clear that the application of two-color laser pulses in laser-matter interactions is receiving considerable attention. Furthermore, the two-color laser fields have also been applied to generate and control the above-threshold photoemission from nanotips ( 7), terahertz emission from air plasmas ( 8, 9), and high-order harmonic attosecond pulses from gases ( 10) and solid targets ( 11). For instance, by virtue of the synthesized laser field, manipulation of energy and angular distribution of the emitted electrons enabled investigations of the above-threshold ( 1, 2) and the dissociative ionization ( 3, 4) of atoms, dichroism in ionization ( 5), and the orientation of molecules ( 6). In recent years, schemes of copropagating two-color laser pulses (CTLP) have been extensively used to study and control microscopic dynamics of electrons on the femtosecond or attosecond time scales ( 1− 11).
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Therefore, our work confirms the merits of driving LPAs by two-color pulses and paves the way toward a downsizing of LPAs, making their potential applications in science and technology extremely attractive and affordable.
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Numerical simulations suggest that the trailing second harmonic relativistic laser pulse is capable of sustaining the acceleration structure for much longer distances after the preceding fundamental pulse is depleted in the plasma. Those results have been further confirmed in a practical application, where the electrons are used in a bremsstrahlung-based positron generation configuration, which led to a considerable boost in the positron energy as well. Here, we demonstrate the first LPA driven by CTLP where we observed substantial electron energy enhancements.
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Recently, there has been some theoretical work on the use of copropagating two-color laser pulses (CTLP) for LPA research. A typical laser-plasma accelerator (LPA) is driven by a single, ultrarelativistic laser pulse from terawatt- or petawatt-class lasers.