Very very powerful lasers—not like the Spyder III, but actual building-sized lasers used for science—might be reaching their physical ceiling for intensity. Going beyond a certain point means they can destroy themselves.
It all comes down to the fact that light and matter are interchangeable (mass-energy equivalence!), and at high enough energies, that laser light can create matter. And then...
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.
What this means in terms of laser weapons and high-powered (Death Star, planet-exploding) lasers is unclear. Maybe it's time to make the switch to phasers, eh? Make it so, science. [Physics Buzz via Pop Sci]