All-Optical Scheme for Generation of Isolated Attosecond Electron Pulses

We theoretically propose an all-optical scheme for generation of isolated electron pulses with subfemtosecond durations for ultrafast electron microscopy and diffraction. The scheme is based on simultaneous longitudinal and transverse momentum modulation of freely propagating electrons at two distinct frequencies via ponderomotive interaction with tailored light fields of three phase-controlled laser pulses in vacuum. After a drift distance, an attosecond electron pulse train is formed with the individual pulses displaced in the transverse direction. Spatial filtering of the electron beam by an aperture leads to isolation of an individual attosecond pulse with a duration of $<100\mathrm{as}$. Subfemtosecond isolated electron pulses will enable direct space-time imaging of attosecond electronic dynamics in atoms, molecules, and solids with atomic spatial resolution, allowing us to directly observe phenomena such as electron tunneling or electron-electron interaction in strong laser fields of few-cycle laser pulses.

Figure 1

(a) Layout of the proposed experimental setup for generation of isolated attosecond electron pulses. Three laser pulses at different frequencies ${\omega }_1$, ${\omega }_2$, and ${\omega }_3$ are intersected with a pulsed electron beam traveling in $z$ direction under angles $\alpha$, $\beta$, and $\gamma$. (b) The intensity distribution of the synchronous optical traveling waves copropagating with the electrons given by Eq. (4). Dashed and dotted lines indicate the maxima of the intensity modulation in the longitudinal and the transverse directions, respectively.

Figure 2

(a) Distribution of the transverse (${\beta }_x$, black points) and longitudinal (${\beta }_z$, red points) velocity components of the electrons immediately after the interaction with the three laser pulses. Black curve corresponds to the center of the ${\beta }_x$ distribution broadened due to electron beam divergence. (b) Spatial distribution of the electrons in the temporal focus after a drift distance of $f_t=1.55\mathrm{cm}$ downstream the interaction. The inset shows the detail of the central attosecond electron pulse.

Figure 3

Temporal profile of the electron density transmitted through an aperture with a diameter of $d=16\mu \mathrm{m}$ [indicated by dashed lines in Fig. 2]. Right inset shows the detail of the attosecond pulse with a duration of ${\tau }_{e,\mathrm{FWHM}}=90\mathrm{as}$. Left inset shows the energy spectrum of the central attosecond electron pulse.