Helium- Neon Laser
Helium-Neon laser is the first gas laser developed by Ali-Javan and his co-workers at Bell Telephone Laboratories, USA. The lasing medium is a mixture of Helium and Neon at ten torr pressure (1 torr is 1 mm of Hg pressure). Neon atoms are the laser-active centers, and Helium plays a significant role in the excitation of Neon. Electrical pumping helps the excitation process. A helium-neon laser demonstration. The glow running through the center of the tube is an electric discharge. This glowing plasma is the gain medium for the laser. Construction: A mixture of He and Ne (10:1 ratio) at low pressure is the lasing medium in a glass tube of 80 cm in length and 1 cm in diameter. The ends of the glass tube are closed by oblique quartz windows, making an angle α with the axis satisfying the relation tan α=n, the refractive index of quartz. It renders the output as plane polarized. Two spherical mirrors on both sides of the glass tube help the stable resonant cavity action. One mir