Karr and Trebes reply: Due to length constraints, we omitted discussion of many significant directed-energy efforts, including the Joint High Power Solid State Laser (JHPSSL) program. We regret any misunderstanding resulting from the briefness of our article. It was never our intention to slight the accomplishments of the JHPSSL program, its contractors, or the many other directed-energy-weapons achievements of other contractors.
We are happy to set the record straight. John Boness is correct. The JHPSSL program had two competing contractors: Textron Defense Systems and Northrop Grumman. Both contractors built electrically pumped solid-state lasers. The architecture of both JHPSSL lasers was a coherent phased array of solid-state media pumped by laser diodes and lasing in a “zigzag” geometry. Each demonstrated 100 kW average power with good beam quality in 2009–10. It was a great achievement by both contractor teams, and it motivated the high-energy-laser community to focus additional effort on electrically pumped solid-state lasers. We noted the achievement and included references to work by Textron Defense Systems and Northrop Grumman1–3 in our initial manuscript. We deleted discussion of the JHPSSL in later revisions, shortening the article and focusing it on current developments. Despite its success, the JHPSSL architecture was not used in any subsequent US Department of Defense high-energy-laser program.
The Defense Advanced Research Projects Agency (DARPA) in 2004 funded General Atomics for its distributed-gain laser—a laser architecture that promised better scaling to higher power, lower specific volume, and lower specific mass than the JHPSSL architecture. The exact power achieved by the DARPA program has not been publicly released; we can say that by 2015 it achieved “100 kW class power.” We stand by our statement that General Atomics’ solid-state, distributed-gain laser in 2015 had “the highest average power ever achieved in an electrically pumped laser.” General Atomics further advanced its distributed-gain laser under the DOD’s High Energy Laser Scaling Initiative (HELSI). In 2023 a General Atomics distributed-gain laser achieved average power greater than 300 kW.
In 2022 under the HELSI program, nLIGHT and Lockheed Martin also demonstrated 300 kW average power high-energy lasers with diode-pumped fiber lasers—coherently and spectrally combined, respectively. Northrop Grumman is under contract to achieve a similar milestone. As part of the Solid-State Laser Technology Maturation program, in 2019 the US Navy installed Northrop Grumman’s Laser Weapon System Demonstrator—a 150 kW average power diode-pumped fiber laser weapon—on the USS Portland, where it stayed until 2023. It is the highest average power directed-energy weapon ever deployed by the US.
