Engineering Physics

10.7 Ruby laser

Ruby laser is a solid state pulsed, three-level laser. It consists of a cylindrical-shaped ruby crystal rod of length varying from 2 to 20 cms and diameter varying from 0.1 to 2 cms. The end faces of the rod are highly flat and parallel. One of the faces is highly silvered and the other face is partially silvered so that it transmits 10 to 25% of incident light and reflects the rest so as to make the rod-resonant cavity. Basically, ruby crystal is aluminium oxide [Al₂O₃] doped with 0.05 to 0.5% of chromium atoms. These chromium atoms serve as activators. Due to the presence of 0.05% of chromium, the ruby crystal appears in pink colour. The ruby crystal is placed along the axis of a helical Xenon or Krypton flash lamp of high intensity. ...