LLNL Hosts Workshop to Shape the Future of Diode-Pumped Laser Technology

The laser system that drove Lawrence Livermore National Laboratory (LLNL)’s historic achievement of fusion ignition at the National Ignition Facility (NIF) is fired by flashlamp technology. A future inertial fusion energy facility, however, will likely be driven by a much more efficient diode-pumped solid-state laser (DPSSL) system.

To help stimulate the development of next-generation DPSSL technology, LLNL recently hosted a workshop to assemble the world’s top experts in that specialized field.

The High-Energy-Class Diode-Pumped Solid-State Laser (HEC-DPSSL) workshop drew about 75 participants representing 28 institutes, research groups, and companies involved in DPSSL system and component R&D. The attendees came from the United States, the United Kingdom, Germany, France, the Czech Republic, Lithuania, and Japan.

“Given the current momentum around inertial fusion energy and recent promising developments in DPSSL technology, this was the ideal opportunity to gather the community for a series of detailed technical discussions,” said LLNL laser physicist Issa Tamer, who co-organized the workshop. “There are many new concepts, but also challenges, for this type of technology, so bringing everyone together in one room allows us to learn from each other directly and move forward towards a common vision.”

The invitation-only workshop, held March 25 to March 27 at Garré Vineyard & Winery event center in Livermore, also marked the first time the Lab hosted a HEC-DPSSL gathering since September 2012, and the third time overall since the workshops began in 2001.

Since 2012, the development of high peak- and average-power pulsed lasers generally shifted away from the U.S., such that the last HEC-DPSSL workshop held in South Korea in 2019 had no U.S. representation, said Tamer, a scientist within the NIF and Photon Science Directorate Advanced Photon Technologies (APT) program. The following HEC-DPSSL meeting, originally scheduled in China, was cancelled due to the COVID-19 pandemic.

Last year, HEC-DPSSL organizers approached the Lab about hosting a HEC-DPPSL restart. With the 2022 ignition achievement and LLNL’s work on high-energy diode-pumped systems like the Big Aperture Thulium (BAT) laser, the L3-High-Repetition-Rate Advanced Petawatt Laser System (L3-HAPLS), and a major high-power laser upgrade to SLAC National Accelerator Laboratory’s Linac Coherent Light Source, this year’s HEC-DPSSL provided the chance to “reinsert the U.S. into this discussion and be a part of the community again,” Tamer said.

“We were able to demonstrate in front of the entire community that the Laboratory is a leading institution for high-energy, high-power laser research and development, and also a valuable partner for future collaborations on large-scale laser programs,” he said.

The HEC-DPSSL workshop was partially supported by the U.S. Department of Energy’s Office of Science Fusion Energy Sciences program. Additionally, the workshop was sponsored by Amplitude Laser, Northrop Grumman Cutting Edge Optronics, Coherent, Leonardo Electronics U.S., Hamamatsu Photonics, and Thales. Other participants represented institutions including Friedrich Schiller University Jena, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), HiLASE Centre, Rutherford Appleton Laboratory, Colorado State University, and more.

Light-emitting diodes (LEDs) have become commonplace for a wide variety of applications, such as energy-efficient home lighting and traffic lights. The workshop reviewed developments on a different class of diodes that can be used in high-energy laser systems.

NIF was designed and constructed over 20 years ago as a key element of the NNSA’s science-based Stockpile Stewardship Program mission to maintain the reliability, security, and safety of the U.S. nuclear deterrent without full-scale testing. At that time, LLNL selected a cost-efficient system using flashlamps to energize the neodymium-doped glass that amplifies the laser beams (see “Amplifiers”).

While the photons with the desired laser color head to the Target Chamber, photons of the other colors are absorbed and heat up the glass, which takes hours to cool down—one of the reasons the world’s most energetic laser system needs hours to reset between experiments.

“With diodes, you pick the color you need, the wavelength you need,” said Tammy Ma, who leads LLNL’s Inertial Fusion Energy (IFE) Institutional Initiative. “You only energize the glass with that one color. So, when the laser comes through, it’s only interacting with the colors it needs. You don’t leave a lot of extra, unusable energy behind in the glass.”

Such a system could fire at a much higher rate—about 10 times per second—with greater energy efficiency.

“That is the fundamental advance of going from the NIF architecture to this diode-pumped laser system,” Ma said. “And that’s why we need those lasers for IFE.”

Scientists hope developments of HEC-DPSSL systems will enable new experimental capabilities at a quicker pace. From a technology standpoint, the faster the HEC-DPSSL community innovates, “the faster everyone else has to move to keep up,” she said.

One of the major challenges, however, is further developing HEC-DPSSL systems and then ramping up production for what, at least for now, is a niche industry.

“If you put all of the diode vendors in the world together right now, we don’t have enough of these high-power diodes to build one power plant yet,” she said.

Sessions at HEC-DPSSL included technical discussions on IFE requirements for high-power diodes and laser systems, remaining science and technology gaps, and the challenges of scaling up manufacturing. The workshop provided a glimpse into the breakthroughs in laser fusion research, offering a mix of optimism and realism about its future potential, especially as momentum builds for both national security and energy security needs.

The workshop also touched on recent advancements made on systems like the LLNL-designed L3-HAPLS laser at the ELI Beamlines facility in the Czech Republic, and the thulium-doped yttrium lithium fluoride (Tm:YLF) BAT laser, which is at the center of new research into extreme ultraviolet lithography.

The workshop differed from a larger scientific conference, where past research is presented, said Joachim Hein, a senior scientist at the Friedrich Schiller University Institute of Optics and Quantum Electronics.

“We wanted a view into the future, into 10 years or 20 years from now, and not what was done in the past,” said Hein, who first initiated the HEC-DPSSL workshop series and was the only audience member to attend all meetings since 2001.

Scientist Daniel Albach, representing the HZDR research center’s Petawatt Energy-Efficient Laser for Optical Plasma Experiments (PEnELOPE) project in Germany, enjoyed the interpersonal, face-to-face nature of HEC-DPSSL.

“It is a very unique workshop where people can interact openly,” said Albach, whose research center is set to host the next HEC-DPSSL in Dresden in 2027. “You cannot trade secrets, obviously, that’s not possible. But it’s a very nice type of workshop for exchanges and to … start new collaborations.”

Tamer and LLNL colleague Salma Helwa were the event’s main organizers, with technical program and organizational support from Ma, Jeff Bude, Bob Deri, Jim McCarrick, Tom Spinka, and Jeff Wisoff.

LLNL speakers and session chairs included Tamer, Spinka, Jean-Michel Di Nicola, Will Fenwick, Zbynek Hubka, Jack Kotovsky, Emily Link, Tammy Ma, and Brendan Reagan.

The Lab’s logistics and operations support team included Mary Harrington, Andrea Seiwald, Amy Chen, David Alyea, Deborah Bradford, Cortlan Casey, Jesse Davis, Nicolle Dunn, Freshta Esmatyar, Rachel Ghilarducci, Donald Harrison, Stephanie Lahman, Aarti Mani, Katie Mathisen, Pam Newcomb, Mary Orrett, AJ Salacies, and James Wickboldt.

More Information:

“LLNL Selected to Lead Next-Gen Extreme Ultraviolet Lithography Research,” NIF & Photon Science News, December 23, 2024

“Machine Learning Optimizes High-Power Laser Experiments,” NIF & Photon Science News, May 20, 2024

“LLNL Constructing High-Power Laser for New Experimental Facility at SLAC,” NIF & Photon Science News, March 9, 2022

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