The Helium-Neon laser is also known as the He Ne laser. Actually, it is a sort of gas laser which consists of a capillary tube with a small bore and it is filled with a mixture of inert gases like helium and neon. The whole apparatus is energized by a DC electrical discharge.
A popular kind of laser
The first gas laser emitted infrared light but the helium neon laser which can operate at a visible wavelength is more popular. To improvise the device, many neon transitions were properly examined in order to get a neon transition with population inversion. The most popular choice of the visible spectrum that the Helium Neon laser uses is 633 nm. However, there are other ranges also which can be used in the manufacturing of this apparatus.
Mirror coatings
When a Helium Neon laser is made by using a wavelength of light other than 633 nm, mirror coatings at their maximum reflectance are used. Generally, red, orange, yellow and green transitions of the visible light are used to manufacture Helium Neon lasers. When these lasers make use of a visible transition other than 633 nm, they have lower gain and as a result of which they have not much output power and would cost you more. The most commonly known Helium Neon laser which is also the best operates at the wavelength of 632.8 nm and lies in the red part of the visible spectrum. This He Ne laser was manufactured at Bell telephone laboratories in 1962. Prior to that in 1960, the apparatus was successfully demonstrated.
The gain medium
The medium inside the He Ne laser is known as the gain medium which is a mixture of the inert gases helium and neon. These two gases are mixed in the ratio of 10:1 and were contained in a glass covering at a low pressure. A high voltage electric discharge which is passed through the mixture of inert gases filled between the two electrodes is the energy source or pump of the He Ne laser. To run the laser, a DC voltage of 3 to 20mA is needed.
The optical cavity
Moreover, the laser has an optical cavity which comprises of two concave mirrors or a plane and a concave mirror. Out of these two mirrors, one should have very high reflecting power and the other mirror called the output coupler mirror should allow only one per cent transmission.
The cavity length
Helium Neon lasers which are used commercially are small in size and their cavity length ranges from between 15 cm to 50 cm, although in order to achieve higher power sometimes the optical length goes up to one meter. However, the optical power ranges from between 0.5 to 50 mW. The widely used red He Ne laser has a wavelength of 633 nm. Lasing modes of the apparatus have a wavelength of around.001 nm.
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