Yeah, the lasers need a clear line of site as light doesn’t obviously bend, so things like rain and clouds can get in the way and reduce the power of the laser when it hits the target, at what level it becomes useless I’m not sure, it might be a case that if conditions aren’t optimal the laser just takes longer to burn through but it does still work. I wonder what happens if the missile or drone is covered in a reflective material, will the laser just bounce off?
The laser uses infrared light, which interacts with materials quite differently. Like every laser, it will refract depending on atmospheric conditions, some components in the air will absorb a fraction, etc., but the object it hits will heat up. Heating is a function of the ratio of surface absorptivity and emissivity (alpha/epsilon). For IR light, finding materials that have low alpha/epsilon are few and far between; these are usually (classified) white paints, which are not mechanically stable. If you shoot a rocket with such paint, it will likely have the paint stripped in the first few meters at high speed. There is not much protection from an IR laser.