The first laser to be operated successfully was ruby laser. First demonstration of laser action using ruby crystal was given by T.H. Maiman in 1960. It is a solid state laser.
Ruby is a crystal of aluminium oxide (Al2O3) in which some of the aluminium ions (Al3+) are replaced by chromium ions (Cr3+). This is done by doping small amounts of chromium oxide (Cr2O3) in the melt of purified Al2O3.
These chromium ions give the crystal a pink or red color depending upon the concentration of chromium ions. Laser rods are prepared from a single crystal of pink ruby which contains 0.05% (by weight) chromium. Al2O3 does not participate in the laser action. It only acts as the host.
The ruby crystal is in the form of cylinder. Length of ruby crystal is usually 2 cm to 30 cm and diameter 0.5 cm to 2 cm. As very high temperature is produced during the operation of the laser, the rod is surrounded by liquid nitrogen to cool the apparatus.
Active medium or active center: Chromium ions act as active centers in ruby crystal. So it is the chromium ions that produce the laser.
Pumping source: A helical flash lamp filled with xenon is used as a pumping source. The ruby crystal is placed inside a xenon flash lamp. Thus, optical pumping is used to achieve population inversion in ruby laser.
Optical resonator system: The ends of ruby crystal are polished, grounded and made flat. The one of the ends is completely silvered while the other one is partially silvered to get the output. Thus the two polished ends act as optical resonator system.
Note: I will explain the working in next article. Meanwhile, try to make the construction diagram yourself. In case of problem, contact me.
Reference: This article is referred from my authored book “optics and lasers” having ISBN 81-272-2948-2. In case of any doubt, post in the comment section.