A Letter from The Founders
September 10, 2026
Today, we announced a partnership with RTX to develop a relocatable, multi-kilojoule-class pulsed laser system for defense. RTX also announced an investment into Xcimer. Read the RTX-Xcimer news release.
We met each other 22 years ago as randomly assigned freshman roommates at MIT.
Back then, in 2004, neither of us imagined that more than two decades later we’d still be working together—let alone working on the same problem we first discussed in that dorm room: How can we make commercial fusion energy a reality?
In graduate school, we both worked at Los Alamos National Laboratory, where we learned about two Cold War programs that fundamentally changed how we thought about fusion.
The first was Halite-Centurion, a classified series of underground nuclear tests that demonstrated something fundamental: fusion fuel can ignite and produce high gain when driven with enough energy. Little known to most people, the physics of high-gain fusion were demonstrated 40 years ago. A review by the DOE and the national labs subsequently recommended a 10-megajoule laser to reproduce those conditions in the laboratory.
The second was the development of pulsed excimer lasers in the late 1970s and early 1980s under Cold War missile defense programs. Unlike the expensive glass lasers ultimately chosen for fusion, excimers generate intense ultraviolet light in a gas. In the late 1980s Los Alamos built Aurora, an excimer laser for fusion, pointing toward a potentially far less expensive route to the energy levels fusion would require.
Then the Cold War ended. Military excimer research dwindled, budgets shrank, and America ultimately chose one major path for laser fusion: Lawrence Livermore’s solid-state glass lasers. The National Ignition Facility, or NIF, was eventually built at roughly one-fifth the energy originally envisioned for the LMF, in part because its solid-state laser systems were so expensive.
By 2020, we were both working in other fields, but we saw that a nascent commercial fusion industry was being born. While we respected the dedication to science of some of these new companies, we observed that no one was pursuing the only approach to fusion that we thought could be made to work. And so in late 2021 we founded Xcimer, to pursue laser-inertial fusion.
In 2022, NIF achieved fusion ignition—the first laboratory demonstration that a fusion experiment could produce more energy than the laser delivered to the target. It was an extraordinary scientific achievement and an essential proof point for the field. NIF, and laser-inertial fusion, remains the only fusion approach experimentally demonstrated to exceed breakeven.
But the technology used on NIF, or derivatives of it, has no practical, economic path to scale to a commercial power plant. Fundamentally, it is constrained by the delicate, expensive glass optics and expensive laser diodes, which would require billions of dollars of supply chain investments and capital costs and even then result in a complex, expensive system unsuited for commercial operation.
The success of NIF—and its shortcomings—have validated the question Xcimer was founded upon:
What if the world has spent 40 years developing the wrong laser technology for laser fusion?
Building the Right Laser for Commercial Fusion
NIF confirmed one of the most important scientific questions of our time: fusion can produce more energy than the laser puts into the fuel.
But a scientific instrument and a commercial power plant have fundamentally different requirements. A power plant must operate repeatedly, economically and reliably for decades. The laser has to be efficient, affordable, manufacturable and capable of firing up to a shot per second.
That’s why we founded Xcimer.
Instead of simply scaling the NIF architecture, we designed a laser and power plant around the economics of commercial deployment:
- Gas lasers and gas optics instead of expensive, delicate laser glass and physical optics.
- Two beamlines instead of 192, each capable of delivering many megajoules.
- A fusion power plant built around a thick-liquid wall, designed for continuous operation for decades without replacing a conventional first wall.
Our laser architecture is no longer just a theory.
In 2023, we received the largest laser-fusion award in the Department of Energy’s Milestone-Based Fusion Development Program. In 2024, we began construction of our laser facility in Denver.
In February 2026, we published a white paper with the German laser company TRUMPF, comparing the costs and characteristics of our architecture with the conventional solid-state approach, validating our cost advantage.
In June 2026, we launched and began operations of Phoenix, now the world’s largest privately owned laser system, combining excimer amplification with our pulse-compression architecture at unprecedented energy levels. It is the physical embodiment of the idea that led us to start Xcimer: that a different laser architecture could make high-energy laser fusion practical at industrial scale.
Days later, the Department of Energy accepted our design report and roadmap for Athena, our commercial fusion power plant, following an extensive government review of our approach.
Those milestones show that Xcimer has moved from hypothesis to execution. We built the laser. We completed the first major facility. And we got a government-approved path to a commercial fusion power plant.
We’re optimizing our Athena laser-fusion power plants for the factors that really matter in the commercial economics of fusion—factors that most of the industry isn’t talking about:
- Low fuel inventory
- Low debris and waste production
- Low maintenance requirements and high availability (no need for downtime to replace the plasma-facing wall)
- High tritium breeding ratios
Another Lesson Learned in Los Alamos
Los Alamos taught us something else: great technologies rarely respect the boundaries between defense and civilian life.
The same laboratory created for the Manhattan Project now works at the frontier of computing, energy and space science. The Internet began as a defense project. Technologies developed for consumer applications now underpin national-security systems.
High-energy lasers are no different.
The excimer laser technology developed in Cold War defense programs was investigated for missile defense, the “Star Wars” programs, and anti-satellite applications. It was studied for inertial fusion, then commercialized at massive scale (but low energies) for semiconductor lithography. For 40 years, almost all CPUs and memory chips have been patterned with small excimer lasers, while the techniques and technologies for building large excimer lasers have been mostly set aside (other than the pioneering work at the Naval Research Laboratory on Nike and Electra).
We started Xcimer to bring large, high-energy excimer technology into the 21st century for commercial fusion energy—yet the world of defense was never far away. Inertial fusion itself, invented by the US nuclear weapons laboratories and classified until the early 1990s, has always had a closer connection to defense and national security work than magnetic fusion.
Similarly, our joint announcement today with RTX connects our technology back to its dual-use roots in America’s national labs.
The engineering challenges are remarkably similar across fusion and defense. Laser efficiency, pulsed power, beam quality, optics, manufacturing and cost all matter to both missions. Roughly 95% of the engineering underlying our energy and defense programs is shared. By developing for both markets, we can accelerate the technology, industrial base, supply chains and talent required to build the world’s largest and most advanced lasers, while bringing that same core capability to the grid and to next-generation defense.
A Different Way to Fund Fusion
There is another important consequence of building a company across both energy and defense—two of the largest and fastest growing sectors of the global economy.
Most fusion companies must finance the long road to their first power plant primarily through successive rounds of equity. Xcimer has a unique path.
The same factories, engineers and supply chains required for commercial fusion can generate substantial defense revenue years before our first fusion plant is commissioned. Directed energy, stockpile stewardship and nuclear-weapons-effects testing can accelerate the development of the industrial base fusion demands.
Our defense work is not a detour from our fusion mission; defense accelerates the industrialization that fusion requires.
The coming decade will determine who builds the industrial foundation for commercial fusion—and who builds the next generation of high-energy laser systems.
For us, it all comes back to the question we’ve been asking since we first drove through the Los Alamos security checkpoint in 2007:
What if the physics wasn’t the bottleneck?
What if the laser was?
We founded Xcimer to solve that challenge.
Conner Galloway
Co-founder, CEO & Chief Science Officer
Alexander Valys
Co-founder & President