A mirror for gravitons, built from magnetic fields and light

Graviton lasers have no obvious mirror: gravitons pass through ordinary matter without reflection. This paper proposes exploiting the Gertsenshtein effect — the conversion of gravitons into photons in an external magnetic field — to sidestep the problem. Gravitons would be converted to photons, reflected by conventional mirrors, then reconverted to gravitons before passing through a lasing medium, with the cycle repeating to build up an arbitrarily long effective path length. Three candidate lasing media are sketched, though the practical challenge of achieving sufficient conversion efficiency is left open.