Science of Laser

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 Science of Laser

P.K.Ghatak, MD

No.35

Atoms of all substances are in constant motion, vibrate, and rotate.

The nucleus of an atom is made up of Protons and Neutrons. Electrons move around the nucleus in several circular orbits(currently considered in the form of a cloud). Electrons with low energy circle close to the nucleus and electrons with high energy in the distal orbits. Elections remain in their own orbits, unless they are disturbed by an energy that makes them either gain energy and move to an outer circle, or lose energy and move to an inward circle. Those electrons that gained energy returned to the initial state after a time. The excess energy is emitted as electromagnetic radiation. That emitted radiation has different wavelengths, moves in different directions, and is unpredictable. To produce Laser light, all the photons must be the same wavelength, travel in the same direction and the same color. This is achieved by Stimulated Emission.

Stimulated Emission:

Stimulated emission occurs when electrons, in an excited state, interact with a photon (light particle) and emit a second photon with the same energy, frequency, color, and move in the same direction as the incident photon. The produced photons then stimulate further and excite more atoms, leading to a cascade and amplification.

Population Inversion:

Population inversion occurs when more electrons exist in an excited/higher energy state compared to those in a resting state. Only those electrons in an excited state can be used to produce photons by stimulated emission.

Mechanism of Laser Production:

A laser is created when electrons of glass, crystal, or gas absorb energy and reach an excited state and then the excess energy is released as a laser.

The energy source is heat, electricity, or light. A vacuum tube equipped with a highly reflective mirror at one end and a semi-silver mirror (allows some light to pass and the rest to be reflected back) at the other end. The source material is enclosed inside the tube

By switching on the energy source, the electrons inside the tube gain energy and emit excess energy as photons of the same wavelengths as the energy source;  and move back and forth by the reflecting mirrors, making more and more electrons in the excited state and population inversion occurs. This process generates a Laser of uniform wavelengths that travel in the same direction and of the same color.

Types of Lasers.

Lasers are of 5 main types: Gas, Solid state, Fibers, Liquid or Dye, and Semiconductor lasers.

The medical lasers are also several. The main medical lasers are:

 Carbon dioxide Laser, used in cutting and destroying tissues and tumors.

Nd: YAG laser is used where deeper penetration of tissues is required.

Excimer Laser. Used in LASIK corneal surgery.

Diode Laser. Used in Dental surgery and also as a hair removal agent.


This part is lifted from my other blog. Medical matters: Archive

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