A helium-neon laser is a laser that uses a mixture of helium and neon as its active medium. Helium-neon lasers are often used in laboratory experiments and optics. It has a working wavelength of 632.8 nanometers, located in the red part of the visible spectrum.
The working medium of a helium-neon laser is a mixture of helium and neon in the ratio 5:1, which is in a glass flask under low pressure (usually about 300 Pascal). Pumping energy is supplied from two electric spark gaps with a voltage of about 1000 V, located at the ends of the flask. The resonator of this laser typically consists of two mirrors - a fully opaque on one side of a flask and the other one that transmits around 1% of incident radiation on the output side of the device.
A glowing ray in the center is not actually a laser beam. It is the electrical discharge, which generates a glow, just as it is in neon lights. The beam is projected on the screen to the right in the form of a glowing red dot.
The bandwidth that maintains the effect of radiation amplification by the laser working medium is quite narrow, and is about 1.5 GHz. It is explained by the presence of Doppler broadening. This property makes helium-neon lasers good sources of radiation to be used in holography, spectroscopy, and also in devices for bar-code reading.
Helium-neon lasers are compact. Typical size of the chamber is from 15 cm to 0.5 m, and their output power ranges from 1 to 100 mW.