Short electron bunch generation using single-cycle ultrafast electron guns

We introduce a solution for producing ultrashort ($\sim \mathrm{fs}$) high charge ($\sim \mathrm{pC}$) from ultracompact guns utilizing single-cycle THz pulses. We show that the readily available THz pulses with energies as low as $20\mu \mathrm{J}$ are sufficient to generate multi-10 keV electron bunches. Moreover, it is demonstrated that THz energies of 2 mJ are sufficient to generate relativistic electron bunches with higher than 2 MeV energy. The high acceleration gradients possible in the structures provide 30 fs electron bunches at 30 keV energy and 45 fs bunches at 2 MeV energy. These structures will underpin future devices for strong field THz physics in general and miniaturized electron guns, in which the high fields combined with the short pulse duration enable electron beams with ultrahigh brightness.

Figure 1

Temporal signature of a single cycle pulse considered as the excitation in this paper.

Figure 2

(a) Schematic illustration of the planar single cycle THz gun, (b) Energy of an electron released at the instant with $E_z=50\mathrm{MV}/\mathrm{m}$ versus the traveled distance, (c) Snapshots of the accelerating field ($E_z$) profile over two half-space cuts of the gun at $t_1=22\mathrm{ps}$, $t_2=27\mathrm{ps}$, and $t_3=33\mathrm{ps}$.

Figure 3

(a) Schematic illustration of the low energy ultrafast electron gun, (b) Energy of the accelerated electron versus the traveled distance, and (c) Snapshots of ($E_z$) profile over two half-space cuts of the gun. Note the change in the color map scaling for different snapshots.

Figure 4

Acceleration of 1 pC photoemitted bunch in the high energy THz gun: (a) bunch charge, (b) size, and (c) energy in terms of travelled path and (d) shape, (e) transverse phase space, and (f) longitudinal phase-space $100\mu \mathrm{m}$ from gun exit are depicted (red dots: output particles; blue dots: trapped particles).

Figure 5

Results of the sensitivity study for the horn gun. The legend on the left of the plot introduces the studied parameters.

Figure 6

Schematic illustration of the high-energy ultrafast gun concept.

Figure 7

(a) Schematic illustration of the optimized ultrafast electron gun, (b) electron energy $E_e(z)$ versus the traveled distance and position of the electron superposed on the accelerating field map $E_z(z,t)$ as the subset, and (c) snapshots of the field profile at four different instants labeled in (b).

Figure 8

Acceleration of 1 pC photoemitted bunch in the high energy THz gun: (a) bunch charge, (b) size, and (c) energy in terms of traveled path and (d) shape, (e) transverse phase space, and (f) longitudinal phase-space 3 mm from gun exit are depicted (red dots: output particles; blue dots: trapped particles).

Figure 9

Sensitivity of the multilayer gun to variations in (a) layer thicknesses and (b) length of quartz inclusions.