Fig. 2. (IMAGE)

Ultrafast Science

Fig. 2.

Caption

Fig. 2. Optimal generation of a single RES with a waveform-controlled laser driver. (A) The longitudinal velocity of the ejected electron beam, averaged over the bunch ⟨훽x⟩ as

a function of P and Δ휙. (B) The waveform-dependent maximum energy of accelerated electrons in the bunch represented by the acquired cutoff energy 휀c in ( P, Δ휙 ) space.

The dashed encircled region in (A) and (B) denotes the parameter space, in which a single RES is produced and accelerated. The density profiles of the electron beam after

traveling 5휆L to the location of the detector ( x=11휆L ) are plotted for 2 optimal waveforms of the drive laser (C) P = 0.4 with Δ휙 = 0 and (D) P = 0.6 with Δ휙 = −휋 ∕ 3, in which

a single electron beam with an attosecond duration is emitted. (E) shows the spatiotemporal evolution of the thin foil electron density (red to yellow colormap) and the drive

pulse field (green to violet colormap) for a single-color Gaussian driver. (F) The space-time evolution of the laser field and electron density in the single-RES regime driven

by a combination of in-phase frequencies ( 1휔+2휔 ) with an energy ratio P = 0.4. The time axis denotes the simulation time (see Fig. 1B and C) during the interaction of the

drive beam. The dashed lines in (E) and (F) mark the trajectories of the representative electrons that are subject to the normalized drive field Bz . Panels (G) and (H) show the

temporal variation of the longitudinal and transverse components of the velocity of the representative electrons (black curve the 1휔 field and magenta for the 1휔 + 2휔

field). The temporal evolution of (I) bunch peak density and (J) thickness during the interaction with a counterpropagating source pulse with the RES generated by the 2-color

Gaussian driver beam (with P = 0.4 and Δ휙 = 0). The FWHM of the bunch is calculated by fitting a Gaussian function on the electron density profile. A greater longitudinal

velocity of the RES during the interaction phase results in a larger compression of the AP in the case of a synthesized pulse.

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Ultrafast Science

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