RUBY LASER

The construction of a ruby laser is shown in fig1. It consists of a pink rod, which is a crystal of aluminum oxide doped with 50% chromium oxide and 4 cm in length. Its ends are optically flat and one is fully and other is partly silvered. A coiled flash tube (Xenon lamp) surrounds the rod. When flash of light takes place, green and yellow light is absorbed by chromium ions and thus they are excited to higher energy states while the red is allowed to pass through. This red light suffers successive reflections at the silvered ends. Excited atoms jump to a common metastable state giving energy to the crystal. Energy in metastable state is equal to the energy of red light which is already present. Thus, the ions return to the ground state with the stimulated emission of red radiations. Since large number of chromium atoms are present in metastable state, thus stimulated emission is continuously amplified and hence an intense coherent beam of light leaked out into air through partly silvered end. This laser is an example of solid state laser.

                                    Fig1.

Ruby is aluminium oxide which contains a few chromium atoms. The energy level diagram of Cr ions which produce the laser action is shown in fig2. The optical pumping results when incident photons of wavelength 5,500 A raise the chromium ions from energy level E1 to E3. They then return to their ground state in two stages. From energy level E3 the ions decay the metastable state E2 producing of population inversion. Atoms remain an intermediate (metastable) state of excitation for about 3 milliseconds. When during this period, the metastable state is exposed to ruby red light (photon) of wavelength 6943 A stimulated emission of radiation results, producing a strong coherent laser beam.

                                     Fig2.