Laser Principle

The term Laser is an acronym for "light amplification by stimulated emission of radiation". A laser is a device that emits light by optical amplification based on the stimulated emission of electromagnetic radiation. When an atom in a particular state absorbs a photon and jumps to a higher energy state, the photon is said to have stimulated the absorption. This implies, for an atom to change its energy state, it requires a photon. The work of A
Albert Einstein in 1917 the probability that an atom in its higher energy state will fall to a lower energy state and emit a photon is the sum of a spontaneous emission term and stimulated emission term. The stimulated emission term varies with the numbers of photon present in the excited atom.

The basic principle of laser is based on the idea illustrated in the diagram above. The diagram above shows the features of a gas laser. A gas laser is a laser in which an electric current is discharged through a gas, usually helium-neon gas mixture, to produce coherent light. The gas is contained inside a long quartz tube with plane mirrors at the adjacent ends. The power supply excites the helium atom to a higher energy level. The neon atom are respectively also excited by collision with the excited helium atom. This result in greater numbers of atom in higher energy level than the ground state (lowest energy state). Therefore, the excited atoms will tend to fall back to their ground state thereby emitting visible spectrum radiation. The photon are then multiplied by the reflections that occurs between the silvered mirrors in the end of the tube. This will eventually lead to a strong stimulated emission and a tremendous bust of light. The light pulse from a laser is monochromatic(having one colour throughout) because all photon the same energy and wavelength. Such photons are in coherent and intense.