Types of Laser
Based on the type of active medium, Laser systems are broadly classified into the following categories.
S.NO TYPE OF LASER EXAMPLES
1. Solid State laser : Ruby Laser Nd:YAG laser
2. Gas laser : He-Ne Laser, CO2 Laser, Argon – ion laser
3. Liquid Laser : SeOCL2 Laser, Europium Chelate Laser
4. Dye laser : Rhodamine 6G laser, Coumarin dye laser
5. Semiconductor Laser : GaAs laser, GaAsP laser
Nd: YAG laser
Nd: YAG laser is a neodymium based laser. Nd stands for Neodymium (rare earth element) and YAG stands for Yttrium Aluminum Garnet ( Y3Al5 O12) . It is a four level solid state laser.
The active medium Nd: YAG rod is optically pumped by Krypton flash tubes. The Neodymium ions (Nd3+) are raised to excited levels. During the transition from meta stable state to ground state, a laser beam of wavelength 1.064μm is emitted.
The construction of Nd: YAG laser is as shown in the figure 2.17. A small amount of Yttrium ions (Y3+) is replaced by Neodymium (Nd3+) in the active element of Nd: YAG crystal.
This active element is cut into a cylindrical rod. The ends of the cylindrical rod are highly polished and they are made optically flat and parallel. This cylindrical rod (laser rod) and a pumping source (flash tube) are placed inside a highly (reflecting) elliptical reflector cavity.
The optical resonator is formed by using two external reflecting mirrors. One mirror (M1) is 100% reflecting while the other mirror (M2) is partially reflecting.
Figure 2.18 shows the energy level diagram for Nd: YAG laser. These energy levels are those of Neodymium (Nd3+) ions.
1. When the krypton flash lamp is switched on, by the absorption of light
radiation of wavelength 0.73μm and 0.8μm, the Neodymium(Nd3+) atoms are raised from ground level E0 to upper levels E3and E4 (Pump bands).
2. The Neodymium ions atoms make a transition from these energy levels E2 by non-radiative transition. E2 is a metastable state.
3. The Neodymium ions are collected in the level E2 and the population inversion is achieved between E2 and E1.
4. An ion makes a spontaneous transition from E2 to E1, emitting a photon of energy hγ. This emitted photon will trigger a chain of stimulated photons between E2 and E1.
5. The photons thus generated travel back and forth between two mirrors and grow in strength. After some time, the photon number multiplies more rapidly.
6. After enough strength is attained (condition for laser being satisfied),
an intense laser light of wavelength 1.06μm is emitted through the partial reflector. It corresponds to the transition from E2to E1.
1. Type: It is a four level solid state laser.
2. Active medium: The active medium is Nd: YAG laser.
3. Pumping method: Optical pumping is employed for pumping action.
4. Pumping source: Xenon or Krypton flash tube is used as pumping source.
5. Optical resonator: Two ends of Nd: YAG rod is polished with silver (one end is fully silvered and the other is partially silvered) are used as optical resonator.
6. Power output: The power output is approximately 70 watt.
7. Nature of output: The nature of output is pulsed or continuous beam of light.
8. Wavelength of the output: The wavelength of the output beam is 1.06μm(infra-red)
1. It has high energy output.
2. It has very high repetition rate operation
3. It is much easy to achieve population inversion.
The electron energy level structure of Nd3+ in YAG is complicated.
1. It finds many applications in range finders and illuminators.
2. It is widely used in engineering applications such as resistor, trimming scribing, micro machining operations as well as welding, drilling etc.
3. It finds many medical applications such as endoscopy, urology, neurosurgery, ENT, gynecology, dermatology, dental surgery and general surgery.
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