Question

Draw the diagram of a Helium-Neon laser tube and label the parts.

Answer 1

Hint:First draw the diagram of a He-Ne laser tube and label the parts of it. Then discuss how the laser tube works. From the diagram explain its various parts and their purpose.

Complete step by step solution:

Fig: Helium-Neon laser tube diagram

It is a type of gas laser whose gain medium is consists of a mixture of $85\% $ helium and $15\% $ neon inside of a small electrical discharge which operates at a wavelength of $6328\;\mathop {\text{A}}\limits^{\text{o}} $, in the red part of the visible spectrum.
There is a tube which consists of a gas envelope with a narrow capillary tube through the centre; this is where mainly the lasing action takes place. The main work of the capillary tube is to direct the electrical discharge through its small bore to produce huge current densities in the gas. There is a large metallic cathode and smaller anode. The current is directed from cathode to anode. There is a high reflecting mirror in the anode end. The gas mixture of low-pressure helium and neon is contained in the plasma tube.
In a He-Ne laser tube laser light is produced by the atomic transitions within the Ne atom. When the pumping source provides the energy to the He-Ne gas mixture then the He atoms achieve an excited state. Now when the He atoms move through the tube; they collide with Ne atoms. So, when the He atoms collide with the Ne atoms some energy is transferred into the Ne atoms and they reach a meta-stable phase. When a sufficient number of Ne atoms reach the meta-stable phase population inversion takes place and lasing takes place.

Note:As we know that, the Helium-Neon laser tube is a low power device, due to which the output power is low, and we have to suppress the other wavelength to obtain the single wavelength of the laser light.