Ruby laser construction and working
The Ruby laser was developed in 1960 by T.Maiman. It is made of a single-crystal of ruby rod. The dimensions are 10cm in length and 4.4 cm in Radius (8.8 cm diameter).
Ruby is nothing but a crystal of Aluminium oxide Al2O3. In this system, Al3+ ions are replaced by Cr3+ ions. Where Al is aluminium, and Cr is Chromium.
The end of the rod is parallel and flat. One end is the Ruby rod is fully silvered. Another end is semi-transparent and partially silvered.
The ruby is surrounded by a tube of Xenon Flash, to provide Photo energy to excite chromium ions to the upper energy level.
In Xenon Flash tube, flashes are produced that last for several milliseconds and with each flash few thousand joules are consumed.
Principle of Ruby Laser
The above diagram indicates an energy level diagram of chromium ions in a ruby laser that shows the excitation and decay of atoms.
The Chromium ions are in the grounded state E1 in the Normal state. When the ruby rod is illuminated by Xenon Flash, the 5500 Å Radiation (green colour) photons are absorbed by chromium ions pumped to the excited state E3.
The exited ion provides some energy to the crystal lattice and decays without giving radiation to the metastable state E2. As the state E2 has a longer lifetime (10-3 s), the number of ions increases in this stage.
In the stage between the states E2 and E1, the population inversion is achieved. When the excited ion in the metastable state E2 falls suddenly to the ground state E1, it emits a photon of wavelength 6943 Å.
This photon goes via the ruby rod and is reflected back and forth by the silvered ends til it stimulates other excited ions and makes them emit a fresh photon in phase with the stimulating photon.
Thus the reflections create more stimulated emission this is called amplification by stimulated emission.
This stimulated emission is laser beam producing. Finally, a laser beam of red light of wavelength 6943 Å comes out via the partially silvered end of the crystal.
Application of ruby laser
It is mainly used for research, Drilling holes in hard materials, and Tatoo removal, Due to its low power own output, it is used in Toys.
It is used in high-speed photography.
Drawbacks of the ruby laser
It is difficult to maintain the population inversion. Also, it requires a high power source. The output is not continuous, it gives output only for a few duration.
Ruby laser produces a low output, as a result, it has fewer applications. In some applications, water coolant is necessary for laser output stability.