Protons have been accelerated to 132 MeV—nearly half the speed of light—using ultrathin, large-area suspended graphene targets in a breakthrough that could shrink the footprint of particle physics equipment.
Conquering the Destructive Laser Prepulse
Pushing protons to higher energies normally requires targets measuring just nanometers in thickness. Yet, standard ultrathin films are systematically destroyed by the weak prepulse that precedes a high-intensity laser’s main pulse.
To bypass this hardware limitation, an international team alongside researchers at the University of Osaka deployed large-area suspended graphene targets measuring only 4, 8, and 16 atomic layers thick. The material’s unique combination of extreme thinness and mechanical durability allowed it to withstand the initial prepulse completely intact until the primary laser strike arrived. Instead of relying on the ultra-short, ultra-intense laser pulses typical of these setups, the researchers utilized a 1.5-picosecond, moderate-intensity laser at Osaka’s Institute of Laser Engineering.
Surfing the Electrostatic Wave
This configuration sustained proton acceleration over several picoseconds through a propagating electrostatic wave moving inside the laser-generated plasma. Computer simulations confirmed that the particles continuously gain energy by riding a moving electrostatic wave, functioning much like surfing acceleration rather than taking a single, abrupt momentum kick.
AI Filters Millions of Microscope Scans
Because high-energy protons occur rarely and generate extremely faint detector signals, the team had to scan millions of individual microscope images to locate genuine ion impacts. To process this massive visual dataset efficiently, the researchers trained a convolutional neural network to isolate true high-energy proton signatures from ambient background noise.
A Compact Path for Medicine and Astrophysics
The machine learning model achieved 99.2% precision, establishing an automated workflow that the team considers vital for driving laser-driven ion acceleration toward even higher energy thresholds. Ultimately, this advance offers a more compact alternative to conventional radio-frequency particle accelerators for medicine and laboratory astrophysics.
