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.
In most of the systems, it consists of system of two mirrors.
One mirror is fully reflective and other is partially reflective. I will explain this in detail in my next articles.