The energy level E 1 is known as ground state or lower energy state, the energy level E 2 is known as metastable state, and the energy level E 3 is known as pump state. Let us assume that initially most of the electrons are in the lower energy state E 1 and only a tiny number of electrons are in the excited states E 2 and E 3.
When light energy is supplied to the laser medium ruby , the electrons in the lower energy state or ground state E 1 gains enough energy and jumps into the pump state E 3. The lifetime of pump state E 3 is very small 10 -8 sec so the electrons in the pump state do not stay for long period.
After a short period, they fall into the metastable state E 2 by releasing radiationless energy. The lifetime of metastable state E 2 is 10 -3 sec which is much greater than the lifetime of pump state E 3. Therefore, the electrons reach E 2 much faster than they leave E 2. This results in an increase in the number of electrons in the metastable state E 2 and hence population inversion is achieved.
After some period, the electrons in the metastable state E 2 falls into the lower energy state E 1 by releasing energy in the form of photons. This is called spontaneous emission of radiation. When the emitted photon interacts with the electron in the metastable state, it forcefully makes that electron fall into the ground state E 1. As a result, two photons are emitted.
This is called stimulated emission of radiation. When these emitted photons again interacted with the metastable state electrons, then 4 photons are produced. Because of this continuous interaction with the electrons, millions of photons are produced. In an active medium ruby , a process called spontaneous emission produces light. The light produced within the laser medium will bounce back and forth between the two mirrors.
To construct the optical resonator cavity, the ends of the rods are polished such that they become flat and parallel to each other. Now one of the ends is coated with silver completely while the other one is partially silvered. Thus, the two silver-coated ends of the rod act as an optical resonator system. Thus, in ruby laser population inversion is achieved by using optical pumping. Ruby is a three energy level laser system. The schematic diagram of ruby laser can be drawn as: Construction of Ruby Laser The ruby lazer consists of a ruby rod.
Operation of Ruby Laser: When we switch on the circuit the R. Energy Level Diagram for Ruby Laser The above three level energy diagram show that in ruby lasers the absorption occurs in a rather broad range in the green part of the spectrum.
Advantages of Ruby Lasers From cost point of view, the ruby lasers are economical. Beam diameter of the ruby laser is comparatively less than CO 2 gas lasers. Output power of Ruby laser is not as less as in He-Ne gas lasers.
Since the ruby is in solid form therefore there is no chance of wasting material of active medium. Construction and function of ruby laser is self explanatory.
Disadvantages of Ruby Laser In ruby lasers no significant stimulated emission occurs, until at least half of the ground state electrons have been excited to the Meta stable state.
Efficiency of ruby laser is comparatively low. Optical cavity of ruby laser is short as compared to other lasers, which may be considered a disadvantage.
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