Ruby laser was the first man made laser, which was build by Theodore Maiman in 1960.

Ruby is a synthetic crystal of Aluminum Oxide (Al₂O₃), and is more familiar in daily life as a precious stone for jewel.

The chemical structure of Ruby is of Al₂O₃ (which is called Sapphire), with impurity of about 0.05% (by weight) of Chromium Ions (Cr⁺³).

The active ion is Cr⁺³, which replace Al atom in the crystal. This ion causes the red color of the crystal. The impurity ion of Cr⁺³ is responsible for the energy levels which participate in the process of lasing.