It is quite possible that the laser will be reflected, BUT! It could destroy the mirror because the temperature is too high, and a mirror is a fragile thing.
As for why diamonds are relevant, I don't understand. They are transparent.
Bow down and hear our cry,
Our earthly rulers falter,
Our people drift and die,
The walls of gold entomb us,
The swords of scorn divide,
Take not thy thunder from us,
Take away our pride.
G.K. Chesterton: English Hymnal