The Letts/Craven effect of generating muons from a material target with a 30 mW, 680 nm laser doesn’t agree with the Standard Model. A member of the Los Alamos National Laboratory research scientists repeated the procedure, obtaining similar findings. The parameters of creating the active material were not understood sufficiently well to reproduce once the batch was exhausted.
Holmlid and Olofson experiments a decade ago have found a route to recreate the muon production, a cascade of particle decay leading to muons created cheaply, in the sense of energy input to produce the muon. Norrønt Fusion Energy AS is furthering exploration into use of these particles to stimulate Deuterium fusion for heat production.
The direct energy extractable from initial meson generation by laser stimulation is relatively small, thus fusion serves to amplify that output.
https://www.tandfonline.com/doi/full/10.1080/15361055.2018.1546090
That's an excellent idea, the brute force approaches used to try to harness fusion seem remarkably unlikely to work.