Ruby Laser

The first working laser was built in 1960 by Maiman, using a ruby crystal and so called the Ruby laser.

Ruby belongs to the family of gems consisting of Al₂O₃ with various types of impurities. For example pink Ruby contains 0.05% Cr atoms. The schematic diagram of ruby laser can be drawn as:

Construction of Ruby Laser

The ruby lazer consists of a ruby rod . which is made of chromium doped ruby material. At the opposite ends of this rod there are two silver polished mirrors. Whose one is fully polished and other is partially polished. A spring is attached to the rod with fully polished end for adjustment of wave length of the lazer light. Around the ruby rod a flash light is kept for the pump input. The whole assembly is kept in the glass tube. Around the neck of the glass tube the R.F source and switching control is designed in order to switch on and off the flash light for desired intervals.

Operation of Ruby Laser:

When we switch on the circuit the R.F operates. As a result the flash of light is obtained around the ruby rod. this flash causes the electrons within ruby rod to move from lower energy band towards higher energy band. The population inversion take place at high energy band and electrons starts back to travel towards the lower energy band. During this movement the electron emits the laser light . This emitted light travels between the two mirrors where cross reflection takes place of this light. The stimulated lazer light now escapes from partially polished mirror in shape of laser beam.

The spring attached with the fully polished mirror is used to adjust the wave length equal to λ/2 of lazer light for optimum lazer beam. The switching control of the R.F source is used to switch on and off the flash light so that excessive heat should not be generated due to very high frequency of the movement of the electron.

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. This makes raise the electrons from ground state E₁ to the band of level E₃ higher than E₁. At E₃ these excited levels are highly unstable and so the electrons decays rapidly to the level of E₂. This transition occurs with energy difference (E₁ – E₂) given up as heat (radiation less transmission). The level E₂ is very important for stimulated emission process and is known as Meta stable state. Electrons in this level have an average life time of about 5m.s before they fall to ground state. After this the population inversion can be established between E₂ and E₁. The population inversion is obtained by optical pumping of the ruby rod with a flash lamp. A common type of the flash lamp is a glass tube wrapped around the ruby rod and filled with xenon gas. When the flash lamp intensity becomes large enough to create population inversion, then stimulated emission from the Meta stable level to the ground level occurs which result in the laser output. Once the population inversion begins, the Meta stable level is depopulated very quickly. Thus the laser output consists of an intense spike lasting from a few Nano sec to µsec. after stimulated emission spike, population inversion builds up again and a 2^nd spike results. This process continues as long as the flash lamp intensity is enough to create the population inversion.

Advantages of Ruby Lasers

From cost point of view, the ruby lasers are economical.
Beam diameter of the ruby laser is comparatively less than CO₂ 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.

Applications of ruby Laser

Due to low output power they are class-I lasers and so may used as toys for children’s.
It can be used in schools, colleges, universities for science programs.
It can be used as decoration piece & artistic display.

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