Russell Burrows. In answer to your query, " How do I make a 70,000 watt laser?". Very carefully.

Three students asked to move a paraboidal mirror, salvaged from an old lighthouse, from one school to another on a sunny day in the winter were a little careless. The tarp covering the mirror was loose. So, when it arrived at the second school, they picked it up,uncovered, and one of them unintentionally walked through the focal point while it was facing South. It was about a meter and a half in diameter. Sunlight is ~ 1000 watts per square meter, concentrated to ~0.1 cm squared...young man walking not quite at focal point received a third degree burn. Your potential laser risk is enormously higher, should you tinker with them. That's why the lab signs......"Danger. Laser". Ciao. Pete.