I think the idea is to achieve extreme energy densities and a high degree of control, with many practical benefits over a particle accelerator. This old article

I think the idea is to achieve extreme energy densities and a high degree of control, with many practical benefits over a particle accelerator. This old article describes some of the stuff they were doing with a petawatt laser [0]. Essentially, they used it for microscale imaging and also generating extremely high energy electrons. There is also 'photofission' where gamma rays cause nuclear fission to occur [1]. There is some additional detail in this article [2]. They seem to be saying that obviously photon-electron interactions are incredibly useful in science, and a gamma ray laser would be just as useful but for photon-nuclear interactions. Finally of course, a gamma ray laser would be a useful space weapon. For example, at [1] they could penetrate 6 inches of lead. It isn't clear how you could reliably stop a high energy gamma laser, as it would degrade even very dense shielding at the same time as generating showers of ultra high energy electrons, neutrons and protons. [0] https://web.archive.org/web/20080614224504/http://newton.ex.ac.uk/aip/physnews.401.html#3 https://web.archive.org/web/20080614224504/http://newton.ex.... [1] https://en.wikipedia.org/wiki/Photofission https://en.wikipedia.org/wiki/Photofission [2] https://spie.org/news/3681-nuclear-photonics-with-laser-based-gamma-rays#B4 https://spie.org/news/3681-nuclear-photonics-with-laser-base...