Recently, there have been some theoretical studies on the use of two-color intense laser pulses for the laser wakefield acceleration (LWFA) research. Here, we experimentally demonstrate a laser-plasma accelerator driven by relativistic copropagating two-color laser pulses (CTLP) in pure helium and in helium-nitrogen mixed gas targets where we observed significant enhancements in the energy spectra of the electron beams (Sci. Adv. 5. eaav7940, 2019). Such enhancement has been further confirmed in a real-application, where electrons from the CTLP-driven LWFA scheme are used in a bremsstrahlung-based positron beam generation configuration, which led to a significant boost in the positron beam energy as well. Numerical simulations suggested that the trailing second-harmonic relativistic laser pulse can sustain the acceleration structure (i.e., the plasma wave) for much longer distances after the preceding fundamental laser pulse is depleted in the plasma medium. Therefore, our experimental work confirms the advantage and robustness of the CTLP-driven LWFA scheme over the standard LWFA driven by a single-pulse of equivalent power. This paves the way towards a significant down-sizing of laser-plasma electron accelerators making their use in scientific and technological applications extremely attractive and affordable.
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