The fundamental physics of laser operation are similar for all media capable of laser operation, whether gases, insulators, or semiconductors. However, the operating details are vastly different in the various materials.

The early lasers were made using special solid-state materials or gases confined within glass envelopes. For example, important gas lasers use helium-neon or argon gas mixtures enclosed in a large glass tube 10 centimeters or more long. These are obviously bulky but useful as light sources when certain emission colors or high power are required – but not for the major applications that awaited semiconductor lasers.

The basic attraction of semiconductor lasers is their high atomic density, which makes possible laser operation in a volume which is ten million times smaller than in a gas. The idea of using semiconductors was discussed theoretically in the 1950s, but it took until 1962 for a laser diode device to be demonstrated.

In semiconductors, lasing is possible only in certain classes of materials endowed with special natural properties – direct bandgap semiconductors. Lasing occurs as a result of a highly complex interactive process between very high densities of electrons and holes confined within a region where the intense radiation released by their recombination is also confined.

Laser emission has been obtained in semiconductor laser diodes in a spectral region ranging from the blue to the far-infrared.