This proposes a linear e+e- collider with beam energies of about 250 GeV. Now if you shine a laser light on these electron beams, then the back-scattered photo

This proposes a linear e+e- collider with beam energies of about 250 GeV. Now if you shine a laser light on these electron beams, then the back-scattered photons will carry ~80% of the electrons' energy. So you'll have 200 GeV photons. And, since photons do not repel from each other, you can focus them much better - meaning that you might achieve even higher luminosities, despite conversion losses. This is the idea of a Photon Linear Collider (PLC), that a bunch of my profs came up with in 1981: https://inspirehep.net/literature/166246 https://inspirehep.net/literature/166246