There are basically four types of lasers
1. Gas lasers
2. Solid lasers
3. Liquid lasers
4. Semi Conductor lasers
Gas lasers:- These lasers contain a mixture of helium and neon. This mixture is packed up into a glass tube. This packed mixture act as an active medium. The preassure inside the tube is maintained at 1 torr for helium and .1 torr for neon. The length of the glass tube is approx from .25m to 1m. Its diameter is nearly 1cm.
Two electrodes present in the tube are connected to a high voltage d.c. source. This circuit results in the generation of the discharge inside the tube. Further this discharge works like a pump. Two parallel mirrors are placed in front of each other. Both mirrors are present inside the tube. Only mirror M1 shows the complete reflection. The mirror M2 shows partial reflection.
When we pass the electric current through the tube, a continuous light wave will start flowing inside the tube with constant frequency. It is also known as coherent light waves. It will come out from the side of mirror M2.
Solid Lasers:- In this a ruby like crystal is used which acts as an active medium. It is basically cylindrical in shape. This crystal is surrounded by a xenon flash lamp T. This flash lamp is of helical shape. In this arrangement this lamp acts as a pumping arrangement. Both the ends E1 and E2 of the crystal are properly polished. Similar to the gas lasers, the surface M1 will do the complete reflection but on the other hand M2 will reflect partially. Whenever we will pass the current through the arrangement a laser beam of red color having large intensity will come out.
Liquid Lasers:- In liquid lasers organic dyes are used as active medium inside the glass tube. The complete circulation of dye is done in the tube with the help of a pump. From this organic dye laser light will emerge out.
Semi conductor Lasers:- In these lasers junction diodes are used. The doping of p-n junction diode is done. Both the acceptors and donors are doped. These are known as ILD(Injection Laser Diodes). Whenever the current is passed then the light modulation from the ILD can be seen. This is used in various electronic equipments.