around a laser generating system. In this configuration the laser shines light on a probe sail accelerating it outwards which is then reflected back through the Fresnel lens to be reflected off a larger more massive reflector probe going in the other direction. The laser light is reflected back and forth many times improving the force transmitted but importantly allows the large lens to remain in a more stable position as it is not greatly influenced by the laser lights momentum.

An optical cavity allows greater re-use of photons, but