The L4 ATON Kilojoule laser at the Extreme Light Infrastructure (ELI) - ELI Beamlines Facility achieved a peak power exceeding 5 PW. The demonstration showed that the L4 can be operated safely and reliably at this energy level which is key for scaling up to higher power and preparing for scientific experiments. During a test campaign in September, the flagship L4 ATON system demonstrated a laser performance of 786 J energy compressed to 154 fs, corresponding to a peak power of 5.1 PW. This currently represents the highest pulse energy achieved worldwide at the multi-petawatt power level. “This accomplishment is about more than figures,” said Allen Weeks, director general of ELI ERIC. “It demonstrates the maturity of ELI’s technology and establishing ELI as a world-leading facility that enables scientists to carry out groundbreaking experiments in high-intensity laser research.” A test campaign last month demonstrated that the L4 ATON laser at ELI Beamlines can safely operate at a peak power exceeding 5 PW. Courtesy of ELI. The L4 ATON laser system was developed by a consortium of international partners made up of National Energetics from the U.S., EKSPLA, from Lithuania, and the ELI Beamlines Facility team. L4 ATON combines optical parametric chirped pulse amplification (OPCPA) with a kilojoule-class, liquid-cooled glass amplifier, allowing operation at a repetition rate of one shot per minute, an order of magnitude higher than other lasers of comparable energy. Installed in 2018, a series of upgrades led by ELI Beamlines’ laser and engineering teams introduced innovations in amplifier cooling, laser diagnostics, control systems, and adaptive optics. The upgrades significantly improve beam quality, stability, and reliability which have gradually built unique in-house expertise in the design, alignment, and operation of high-energy, high-repetition-rate laser systems. A vacuum compressor system was constructed for the final femtosecond pulse compression. The system reaches 18 m in length. Courtesy of ELI. The 18-m-long vacuum compressor system was constructed for the final femtosecond pulse compression. Working in cooperation with Lawrence Livermore National Laboratory, new multilayer dielectric diffraction gratings were developed. These gratings are a key innovation enabling operation at extremely high energy densities on optical components. Since 2021, the L4 ATON laser has been serving scientific experiments within the Plasma Physics Platform (P3). A commissioning campaign in December will integrate the system with new experimental setups, paving the way for external user experiments beginning in 2027 under the ELI User Programme. Researchers from Lawrence Livermore National Laboratory assisted in the development of new multilayer dielectric diffraction gratings. Courtesy of ELI. With its high stability and ability to repeat experiments at one-minute intervals, L4 ATON opens new possibilities for studies in laser-driven particle acceleration, extreme-state physics, and strong-field quantum electrodynamics, as well as for further progress in laser-driven fusion research. The ELI team is analyzing performance data to increase power toward 10 PW in 2026. This next step will expand the facility’s experimental reach even further, solidifying ELI’s position among the world’s leading research facilities for high-intensity laser science.