In the Airborne Laser system, the laser beam is directed from the nose of a Boeing airplane towards the target. In this system, the angle of laser beam with respect to airplane body can be changed at the nose of the plane.
What kind of material can deflect such high energy beam? Can a missile get protected from the laser by deflecting the light, if the same material is coated around the missile body?
The ABL beam director system is, or at least was, available in schematic form somewhere on the LockheedMartin website.
To answer your specific question: the mirrors in the system are highly developed to withstand high-energy laser beams without damage. The coatings are quite specialized and the substrates are designed for efficient heat-sinking. Even so, there are sensors to correct not only atmospheric-induced beam aberrations but aberrations due to the internal optics, platform (i.e. the aircraft) vibrations, and so on.
