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Thermodynamics

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Laser

Recent researches in solid state physics have revealed a new device called ‘Laser’ which means ‘Light Amplification by Stimulated Emission of Radiation’. Towns and Schawlow in 1958 worked on the principle of Laser. The principle of a laser is similar to that of ‘Masser’ which means Micro wave Amplification by Stimulated Emission of Radiation. Due to this reason laser is also called ‘Optical Maser’.

Laser works on the principle of quantum theory of radiation. When an electron in an orbit absorbs energy, it goes to an orbit of higher energy level. When the electron jumps back to a stable orbit, it emits radiations in the form of electro-magnetic waves. The energy of each photon = hv.

Laser consists of a ruby rod surrounded by a flash tube. One end of the ruby is highly silvered and the other end is semi-transparent. The flash tube is called the pump and it surrounds the ruby rod in the form of a spiral show in fig.

Synthetic ruby consists of a crystal of AIO (aluminium oxide) in which a few of the aluminium atoms are replaced by chromium atoms. Chromium atoms have the property of absorbing green light. The electrons are excited to higher energy levels. When the electrons jump back to their original levels, red light is emitted. This is the reason why the ruby has natural red colour. The excited electrons are highly unstable in the higher energy levels and tend to give up their extra energy. When these electrons in the excited state are exposed to the radiations of the same frequency which they are about to emit, the emission process is triggered instantaneously. These radiations are exactly in phase with the exposed radiations and reinforce with one another.

These radiations are allowed to pass back and forth millions of times in the ruby with the help of the mirror at the two ends. A chain reaction is started and a powerful coherent beam of red light is obtained. This powerful beam of red light emerges out of the semi-transparent mirror at one end. Recently, a solid state injection laser has been invented. This laser can be turned on and off as desired.

Uses: Laser has a number of practical applications. It is useful in surgery, radar, welding microscopic wires and vaporizing any known material. A focused laser beam has helped in the study of the moon’s surface. It will provide a very handy communication because of its large band width. It can accommodate 80 million television channels. It is hoped that laser will be a useful tool in the study of distant planets.