How To Build A Laser On The Cheap Start with an inexpensive 808-nanometer (nm) infrared laser . Focus its
light through a pair of lenses  onto a crystalline semiconductor  that re-emits light at either 920nm (when making blue) or 1060nm (when making green). Halve the resulting wavelength by sending it through a second crystal  to produce visible blue (460nm) or visible green (530nm) laser light as it exits the output coupler .
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.