Electron macroparticles shown as grey dots and the longitudinal electric field shown as a colour density plot with the full pulse length 8 fs (3 cycles), peak intensity 1021 W/cm2: (a-b) at t/T = 11; (c-d) at t/T = 18; (e-f) at t/T = 25, where t is the simulation time and T is the laser period. The dashed-brown line shows the on-axis vertical electric field, which is due mostly to the laser pulse.
A paper recently published in Nature Scientific Reports led by Cristian Bonţoiu from our QUASAR Group, presents, for the first time, particle-in-cell (PIC) numerical results which demonstrate that it is theoretically possible to achieve laser wakefield acceleration in structured CNT targets with an 800 nm (infrared) laser pulse. Upon a suitable match of the laser pulse length and wavelength to the effective plasma density at complete ionization, electrons are self-injected and accelerated at TeV/m gradients with a total charge as high as 1 nC, contained within a bunch length as short as 5 fs.
It was found that due to the collective behaviour of the laser-target interaction, self-injection and acceleration does not depend on the exact arrangement of the CNT bundles and thus multiple choices can be made as long as the overall effective plasma density remains constant (~1020 cm-3). Moreover, a certain degree of misalignment and variation of the bundle diameter can be accepted while manufacturing the target.
Transverse view of two targets built with 25 nm-thick CNT bundles: (Left) 535 CNT bundles are distributed more uniformly in 30 shells; (Right) 546 CNT bundles distributed less uniformly in 9 shells. The black dashed line indicates the laser spot size.
If confirmed experimentally, the concept may have an impact on fundamental femtosecond research by delivering the shortest electron bunches ever produced in the laboratory with excellent potential to advance ultra-fast electron diffraction techniques beyond current limits. With further development, required to reduce the energy spread and divergence of the extracted electron bunches, it may also become a medium for compact light sources such as FELs or Compton γ-ray sources with promising implications across fields such as cell biology, surface chemistry, and condensed matter.
More information:
Cristian Bonţoiu, et al., 'Numerical study of self-injected electron acceleration in CNT structured targets driven by an 800 nm laser', Nature Sci Rep (2025) https://doi.org/10.1038/s41598-025-29386-4