The history says, that during the defense of Syracuze, citizen Archimedes used "mirrors" to direct the sunlight at the enemy ships and burned them. Physicists usually say that this is impossible since the sunlight would not have enough temperature to burn ships. Those who believe this possible, still say that it would be unlikely. It would be extremely difficult to make concave mirrors that would act as lenses and focus the sunrays at a specific distance. They believe however that if such focused rays would reach the ship at the "focused" distance, the ship would probably catch fire.
Oh boy, they are all wrong. As usuall, i have to explain things like to children...
The "mirrors" are NOT concave! and NOT "lenses"! The "mirrors" are MIRRORS! Imagine 20 big mirrors, which direct sunrays to 1 big mirror. If the temperature was then 25 degrees Celsius, each mirror would direct the rays with temperature of 25 degrees to the BIG MIRROR. Conservation of energy law would apply. The big mirror would therefore receive 25 degrees from each mirror. That would be 20 mirrors * 25 degrees. The BIG MIRROR would receive 500 degrees Celsius. That is temperature of fire. If you direct that mirror at a ship... this would be equivalent to applying a fire to it. I think that was the first laser.
PAWEL KOLASA