Since the 1970s, the Janus laser, now part of the Jupiter Laser Facility (JLF), has served as an experimental proving ground to Lawrence Livermore National Laboratory's (LLNL) laser and fusion programs and the broader high-energy-density and laser science communities.
Today, JLF is not only home to Janus - one of the world's few hands-on laser platforms producing kilojoules of energy - but also Titan, a unique laser platform that combines high-energy pulses with long and extremely short pulse lengths, and COMET: a high repetition, standalone, compact multipulse terawatt laser system.
As one of the founding members of LaserNetUS - a constellation of laser facilities across North America - JLF is a prototype for the no-cost user facility model, operating on the idea that all researchers, regardless of their home institutions' laser capabilities, should have access to the brightest light available.
Former JLF director (now retired) Robert Cauble says, "My favorite part of my role was watching researchers and students come in and learn how to put experiments together, spending several weeks to set up, troubleshoot and acquire data. Seeing how driven they were to get results, thinking through the physics and technology in real time to reach a solution, was very rewarding."
To meet the growing demands of its user community, JLF underwent a four-year-long modernization effort before resuming normal operations in 2024. In its first year back, the facility hosted 65 users from 20 institutions and supported 15 experiments - each experimental campaign spans approximately four weeks, allowing time for assembly, troubleshooting and data collection.
Thanks to the hands-on support of the JLF Operations Team and LLNL's Physical and Life Sciences and National Ignition Facility and Photon Science (NIF&PS) organizations, JLF made several hundred small improvements and a number of large-scale renovations and new additions. Now, JLF offers enhanced energy and performance capabilities, higher shot rates and improved diagnostic instrumentation. In fact, many diagnostic tools currently used to capture valuable data from ignition experiments at NIF were originally developed at JLF, underscoring the synergistic and full-circle impact of this collaboration.
One new, notable addition to JLF is an advanced laser pulse-shaping technology known as STILETTO (Space-Time Induced Linearly Encoded Transcription for Temporal Optimization). STILETTO was coinvented by JLF and NIF&PS and made possible thanks to funding from LLNL's Laboratory Directed Research and Development program (21-ERD-034) and the Department of Energy's (DOE) Office of Fusion Energy Sciences (FES).
This new capability allows researchers to create highly customizable laser pulses with resolutions down to the picosecond (a trillionth of a second), generating over 1,000 independent temporal features (time-based attributes) over durations of up to 600 picoseconds. STILETTO's space-to-time mapping capabilities are analogous to a runner - in advance of their run - being able to precisely control and predict where their foot will land and with what intensity at each point in time. In a laser experiment, STILETTO can map where (spatially) and when (temporally) each feature of the laser pulse will occur.
With additional funding from the DOE's FES program, the facility was also able to add a third beamline in the laser bay dedicated to short-pulse operations in Titan. Now, with the dedicated short pulse and two long-pulse beamlines - one dedicated to Janus and the other switchable between Titan and Janus - the laser bay can shoot twice as often, more effectively serving simultaneous experiments in Titan and Janus.
The enhancements don't stop there, though. New, larger gratings were installed to improve the energy of Titan's short pulse by a factor of two (from 150 joules of energy to 300 joules), enabling close to a petawatt of power - about 1,000 times the capacity of the entire U.S. electrical grid - in 0.4 picoseconds.
For the user community, the new and improved facility will encourage researchers to stretch the realm of possibility and pursue novel experimental ideas at JLF.
Current JLF director Félicie Albert recounts just how vital JLF was to her early career at LLNL.
"One year, I prepared an experiment on Titan and all I got was noise with a hint of signal," she said. "The next year, I asked the JLF team if I could install a new parabolic mirror in Titan with a longer focal length, which required changes to the target chamber. Thanks to the JLF team's help, the experiment worked, and we got a good paper out of it. I love that part of JLF - how willing people are to help. It makes the long days of experiments worthwhile."
More than ever before, JLF is ready to address unique challenges and questions in high-energy-density and laser science at an international scale, train the next generation of researchers, and support larger laser facilities like NIF.
-Shelby Conn
