THE  RUBY LASER-A PULSED LASER     It is the first working laser developed by maiman in 1960. it is a solid stat  laser and makes use of the three  level  scheme of population inversion . It consists of three essential parts:     1. The working material: the working material is a ruby crystal which belongs to a family of gems. actually it is aluminium oxide (Al₂O₃) doped with 0.05% chromium oxide (Cr₂O₃).Thus some of the aluminium atom in the crystal lattice are replaced by    Cr++ion which give ruby a pink colour.     The resonant cavity: It is a specially prepared ruby cylinder in which light intensity can be build up by multiple reflection. For this purpose a ruby laser 20 to 30 cm. and 0.5 to 2 cm in diameter  is grown. the crystal is cut polished, so that the ends are flat and parallel, with the end planes perpendicular to the axis  of rod.     2.The optical pumping system: The optical pumping is done by an external source. in general ,a helical ...