That is true that photons are photons, the trick is getting them to be coherent in the first place. Optical lasers use stimulated emission in some form. I presu

That is true that photons are photons, the trick is getting them to be coherent in the first place. Optical lasers use stimulated emission in some form. I presume that positronium from the article is able to somehow also undergo stimulated emission in the form of the particles anihilating and making 511 kev photons. The distinction between that and how HIGS works is that HIGS is effectively bouncing laser light off a fast moving mirror made of electrons, which actually destroys the coherence, even though the resulting gamma rays are still very similar.