Gas, solid state, diode
The first type produced was a solid state laser. Solid state refers to any solid material like a glass rod. Diode lasers are very common because they are used to read compact disks and digital video disks in computers, CD players and DVD players. Before diode lasers, the most common type of laser may have been the helium-neon laser in which the active medium is a combination of the two gases helium and neon.