With the rapid iteration of ultra-intense femtosecond laser technology, laser intensities have entered the relativistic regime (> 10¹⁸ W/cm²). Under such extreme physical conditions, matter is completely ionized into plasma, and extremely lightweight electrons can be directly accelerated by the laser's electric field-a process known as Direct Laser Acceleration (DLA). This process serves as the fundamental basis for many frontier fields, including advanced accelerators, high-energy radiation sources, and attosecond science.
However, traditional DLA technology has long been plagued by a core challenge: it primarily relies on the longitudinal ponderomotive force of Gaussian lasers for driving. Yet, the transverse ponderomotive force of a Gaussian laser exhibits a Gaussian distribution, which inevitably pushes electrons outward. This severely hinders stable electron acceleration and has become a "bottleneck" problem in the field.
To overcome this challenge, the SIOM research team innovatively expanded structured laser fields into electron acceleration experiments. They utilized the unique hollow intensity distribution and intrinsic orbital angular momentum of Laguerre-Gaussian (LG) lasers to precisely manipulate electrons. Experimental results show that left-handed circularly polarized LG lasers possess a unique longitudinal electric field on the optical axis. Combined with the transverse focusing effect, this successfully forms a stable "vacuum bubble" acceleration structure. This structure is similar to the plasma bubbles in classical wakefield acceleration, providing an ideal environment for stable and highly efficient electron acceleration.
This achievement not only fills the gap in the experimental verification of relativistic LG laser-driven DLA but also significantly enhances the stability and collimation of the electron beam. Furthermore, the acceleration gradient in the LG laser field is directly proportional to the laser intensity and is independent of the subsequent complex plasma environment. This unique characteristic opens up a completely new path for creating micrometer-scale compact acceleration structures, potentially turning the concept of "compact accelerators" into a reality. With further optimization in the future, this technology is expected to be widely applied in ultrafast physics, materials science, and medical imaging, driving leapfrog development across multiple disciplines.
