Ok say we have two identical lasers firing beams perpendicular to each other such that the beams intersect at some point. A semisilvered mirror is placed at this intersection, at 45 degrees to both of the laser beams, so that each beam is split into two beams of half the intensity, one going in the same direction as the original beam and one perpendicular to it. Say that one of the lasers is placed so that, at the point of intersection, one of the beams has a phase shift of half a wavelength relative to the other. I would expect the two beams to exactly cancel each other out from destructive interference, but this would be an example of energy being destroyed, would it not? Where is the error in my thinking? Thank you very much.