US-based laser start-up Xcimer Energy has activated Phoenix, a 38-metre-long prototype system that stands as the world’s largest privately owned laser. Housed in a 74,000-square-foot facility in Denver, Colorado, the system serves as a foundational proof of concept for affordable, industrial-scale inertial fusion energy (IFE).
In 2022, the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) demonstrated net energy gain from fusion, and in 2025 produced 8.6 megajoules of fusion energy from 2 megajoules of laser input. While NIF proved that laser fusion works using a complex, 192-beam solid-state glass laser architecture, the system is too expensive and high-maintenance for grid scale electricity generation. Xcimer Energy is approaching the problem with a radically simplified system.
Phoenix utilises a Krypton Fluoride (KrF) excimer laser core. This design dramatically lowers overall costs and resists thermal stress far better than solid-state alternatives. Instead of nearly 200 beamlines, Xcimer’s operational architecture is built around just two beamlines, massively reducing engineering complexity. The technology successfully leverages Stimulated Brillouin Scattering (SBS). This technique compresses a microsecond-long gas laser pulse into the hyper-fast nanosecond timescales needed to ignite a fusion fuel target.
“NIF proved laser fusion physics works,” said Xcimer co-founder and President Alexander Valys. “Our thesis is that commercial laser fusion becomes possible only if the laser system itself becomes dramatically simpler, cheaper, and more manufacturable.”
Building Phoenix forced the company to source and restore specialised, Cold War-era knowledge regarding electron-beam-pumped excimer lasers, an area of high-energy physics the US had nearly lost. “We had to rebuild an industrial capability the United States largely abandoned after the Cold War, restoring specialized supply chains, recruiting many of the last engineers with direct experience in these systems, and transferring that knowledge to a new generation,” said Conner Galloway, co-founder and CEO of Xcimer. “Phoenix represents both a technical milestone and the reindustrialisation of high-energy excimer lasers in America.”
Xcimer spent four years assembling one of the world’s deepest concentrations of fusion and laser expertise, recruiting engineers, physicists, pulsed-power specialists, and technicians from national laboratories, the National Ignition Facility (NIF), commercial aerospace, the US Navy, and past government excimer laser efforts. The US Naval Research Laboratory, which built and operated the only two remaining large-scale KrF excimer laser systems in the United States, preserved critical technical knowledge that helped bridge the gap between earlier government programs and today’s renewed commercial efforts.
Phoenix currently operates at pulse energies over 1 kilojoule. While this is a milestone for gas optic technology, commercial grid fusion will require hitting targets with greater than 12 megajoules of energy. Xcimer is navigating a multi-phase development timeline to get to achieve this:
- Phoenix (2026): Active demonstration of core tech and integrated SBS pulse compression at Denver laser bay;
- Anvil (2028): Commercial-scale excimer amplifier delivering 200 kilojoules on target in a complete two-sided beamline;
- Vulcan (early 2030s): 4–12 megajoule laser system targeting wall-plug breakeven and supporting high-energy-density and national-security applications – Xcimer expects to select a Vulcan site this year.
- Athena (mid-2030s): Commercial-scale laser fusion power plant designed for continuous grid-scale electricity generation aiming for an output of roughly 400 MWe.
Excimer was founded in 2022 by engineering partners Conner Galloway (CEO & Chief Science Officer) and Alexander Valys (President & CTO). The founders were originally undergraduate roommates at the Massachusetts Institute of Technology (MIT). Before launching Xcimer, both worked at LANL. Galloway has specialised in radiation hydrodynamics and laser architectures since 2009, while Valys brings a background in building early-stage tech startups. With headquarters in Denver, Colorado and satellite offices in Redwood City, California, the company now has a team of more than 150 specialists.
Xcimer has secured more than $150m in total funding through a combination of venture capital and selective federal grants. In 2022, the company raised an initial $2.5m seed round to establish core engineering concepts. In 2024, a Series A round secured $100m. The round was led by the venture firm Hedosophia, with participation from prominent climate tech funds including Bill Gates’ Breakthrough Energy Ventures, Chris Sacca’s Lowercarbon Capital, Prelude Ventures, Gigascale Capital, Starlight Ventures, and the Emerson Collective.
In 2023, Xcimer was selected for a $9m award from the Department of Energy’s (DOE’s) Milestone-Based Fusion Development Program, a highly competitive public-private partnership programme designed to expedite the path towards putting fusion energy on the power grid. DOE has created three inertial fusion energy hubs in the Inertial Fusion Energy Science & Technology Accelerated Research (IFE-STAR) initiative, consisting of public and private organisations and government research labs. Xcimer is a member of all three hubs.
