The laser is a raycast and two textured lines (one for the laser and one for the glow). On every frame, the line's points are set to the raycast origin and collision point, unless it hits a mirror, in which case the raycast and line handling function will get called recursively.
I noticed that in the last level but didn't have much time to mess with the camera to fix it. All of the mirrors are on screen when you start the level though, only the two at the top are hidden by the camera when you step down.