Why don't combat aircraft have rear-facing *laser* weapons? This question is similar, but only talks about guns. I don't mean a laser that is going to destroy the plane, but why aren't rear-mounted, rear-firing lasers that can blind a pilot a thing? Most of the concerns about weight and relative velocities from the other question disappear with a lighter-weight laser that is firing light.
Such weapons are not used by countries that abide by the Geneva Convention:


  It is prohibited to employ laser weapons specifically designed, as their sole combat function or as one of their combat functions, to cause permanent blindness to unenhanced vision, that is to the naked eye or to the eye with corrective eyesight devices.


For the U.S.A., page 45 of Navy Shipboard Lasers for Surface, Air, and Missile Defense says: