When a high-powered laser fires, causing photons to impact electrons at a tremendous velocity, it is possible for matter -- a positron-electron pair -- to be created by the impact, as was demonstrated in a Stanford experiment in 1997. When such matter is created with a sufficiently high energy, it in turn can emit photons that move fast enough that they create their own matter. This cascade effect can have as much energy as the laser itself does, and result in the destruction of the laser.