Can lasers be harmful?

We posed this question to Graham Hirst from the STFC Central Laser Facility...

Graeme - Well some do. It's not just true of laser light. In fact, you'll know that if you got one of those really, really powerful torches, you're warned not to put your hand directly in front of it, it will also be giving off a lot of heat. That really reflects the fact that heat - in the form of thermal radiation - and light are just the same sort of stuff. If you like, light goes blue, green, yellow, orange, red, infrared, heat. You can get lasers that work in the heat part of the spectrum as well. Some of them have very long wavelength indeed, cutting and welding lasers for instance will put out 10,000 watts of heat at the most powerful end.