There are some pretty far out concepts here 300 GW for 30 minutes, that's the output of 300 nuclear power reactors or the energy equivalent of a 100 kT nuclear explosion. Focussed onto a sail that's 100's of atoms thick to generate an acceleration of 60000 g. I can imagine a sail that thin but I doubt it could withstand the forces exerted by the slightest inhomegenity in the beam, not to mention that the slightest speck of dust or deviation from near perfect reflectivity would vaporise it instantly.
Exciting idea though that we could even think about sending a probe to another star within the life span of current generations.