For designing relativistic rocket engines, there's no point in using lasers to accelerate ions to close to the speed of light. You can just use the laser direct

For designing relativistic rocket engines, there's no point in using lasers to accelerate ions to close to the speed of light. You can just use the laser directly -- the other stuff is extraneous. A relativistic electron has no more momentum than a photon of the same energy. https://en.wikipedia.org/wiki/Photon_rocket https://en.wikipedia.org/wiki/Photon_rocket