955. How do you make lasers that burn?
Lasers use excited atoms or atom-like systems to amplify light. Putting mirrors around such excited atoms or atom-like systems allows them to amplify their own light until the laser is emitted vast numbers of identical light particles or "photons." To burn something with laser light, there must be a great many excited atoms or atom-like systems and they must be very efficient at amplifying light. Probably the easiest to build powerful laser is a carbon dioxide laser. This laser uses an electric discharge in a mixture of nitrogen and carbon dioxide gas to produce excited carbon dioxide molecules. These molecules amplify infrared light at a wavelength of 10.2 microns extremely efficiently, so that a laser consuming about 1000 watts of electric power can emit approximately 100 watts of infrared light. That's enough power to burn things very quickly. Even more powerful carbon dioxide lasers are used in industry to cut and machine metals, including thick steel plates. But while they are surprisingly simple to build and operate, given the right components, carbon dioxide lasers require dangerous high voltage power supplies. There were many physics graduate students electrocuted in the 1960's while tinkering with homemade carbon dioxide lasers.