When energy is given to laser medium (solid, liquid or gas), then only a small fraction of laser medium shows lasing action. This part of laser medium is called active medium or active centre. Thus, due to this reason, the laser medium is also called the heart of a laser. For example, in case of ruby laser, Al2O3 is doped with Cr2O3. The laser is due to doped chromium ions. Thus Cr3+ ions are active centres. In He-Ne laser, laser is produced due to Ne atoms, therefore, Ne atoms are active centres.
Note: Dear students, next time, we will learn about optical pumping and its types.
Three main components of laser device are:
a) Active medium:
For example in ruby laser, the active medium is aluminum oxide doped with .05 percent of chromium ions.
In helium -neon laser it is the combination of helium and neon in the ratio of 10 :1.
b) Pumping source:
For example in ruby laser, the pumping source is optical pumping that is helical xenon flash tube.
In helium-neon laser, electrical pumping that is electric discharge is used for stimulated absorption.
c) Optical resonator system:
In most of the systems, it consists of system of two mirrors. On mirror is fully reflective and other is partially reflective.