A good mirror reflects more than 99% of incident light, effectively increasing the amount of power the laser needs to destroy the target by a factor of 100.
This isn’t the real concern, however. Fog, dust, clouds, and rain are quite common on the damp and dusty sphere we live on, and they would all strongly attenuate the beam power and greatly reduce the effective range.
A good mirror reflects more than 99% of incident light, effectively increasing the amount of power the laser needs to destroy the target by a factor of 100.
This isn’t the real concern, however. Fog, dust, clouds, and rain are quite common on the damp and dusty sphere we live on, and they would all strongly attenuate the beam power and greatly reduce the effective range.