Vishwa Bandhu Pathak

A compact source of high-energy femtosecond photons stands as a transformative tool across diverse fields, attainable through betatron radiation generated in the laser wakefield acceleration process. The concurrent pursuit of photon energy and flux confronts a critical challenge, arising from the intrinsic discrepancy between the acceleration and radiation processes. To address this, we demonstrate a hybrid betatron scheme, driven by multi-petawatt laser pulses, using a two-stage gas medium to decouple acceleration from radiation. A low-density medium enables efficient acceleration, followed by a high-density plasma that markedly enhances betatron flux and photon energy. It yields gamma-ray pulses with a brilliance of ~5×10²⁴ photons∙s⁻¹∙mm⁻²∙mrad⁻²∙0.1%-BW at 180 keV, applied to radiography of a complex metallic structure. Particle-in-cell simulations confirm that the dense radiator stage efficiently converts high-energy electrons into high-brightness gamma rays. These results establish a simple, scalable route to compact, ultrabright betatron gamma-ray sources, opening new opportunities in photon-driven science and technology.

A direct acceleration scheme to generate high-energy, high-charge electron beams with an intense few-cycle Laguerre–Gaussian (LG) laser pulse was investigated using three-dimensional particle-in-cell simulations. In this scheme, an intense LG laser pulse was irradiated onto a solid density plasma slab. When the laser pulse is reflected, electrons on the target front surface are injected into the longitudinal electric field of the laser and accelerated further. We found that the carrier-envelope phase (CEP) of the few-cycle laser pulse plays a key role in the electron injection and acceleration process. Using a three-cycle LG laser pulse with a 0 = 2 and an appropriate CEP, an about 60 pC electron beam could be obtained at a maximum energy of 16 MeV. In comparison, when a laser pulse with mismatched CEP was used, a total of 4 pC electron beam with a maximum energy of 3.5 MeV was obtained. Linear scaling of electron energy to the laser strength was shown up to a 0 = 100 at which a quasi-monoenergetic electron beam of 850 MeV energy with a charge equal to 600 pC could be obtained. These results demonstrate that high-energy electron beams can be stably generated through direct laser acceleration using a CEP-controlled intense few-cycle LG laser pulse.

Laser wakefield electron acceleration (LWFA) is an emerging technology for the next generation of electron accelerators. As intense laser technology has rapidly developed, LWFA has overcome its limitations and has proven its possibilities to facilitate compact high-energy electron beams. Since high-power lasers reach peak power beyond petawatts (PW), LWFA has a new chance to explore the multi-GeV energy regime. In this article, we review the recent development of multi-GeV electron acceleration with PW lasers and discuss the limitations and perspectives of the LWFA with high-power lasers.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

We investigate the effect of laser polarization on spatial and momentum distribution of back-reflected e ⁻ e ⁺ pairs from the collision of an intense laser pulse ( I = 5 × 10 ²² W cm ⁻² ) with a counter-propagating 5 GeV electron beam. During the pair production, a significant amount of particles (10 ⁶ –10 ⁷ ) are ejected in the opposite direction of the incoming electron beam (back-reflected), they are trapped by and co-propagate with the laser beam, gaining energy up to the GeV level. From our multi-dimensional particle-in-cell studies, we observe that laser polarization affects the angular distribution of these particles: a linearly polarized pulse produces two transversely separated particle jets, while a circular one leads to the formation of a radially symmetric cone-shaped emission. The results presented here add insights for future experiments performed at multi-PW laser facilities.