SKEDSOFT

Introduction:

Principle and production: Under normal circumstances when light interacts with matter, electrons in the matter may absorb the light energy and go to the higher energy level and come back to the ground state by emitting the light of the same frequency. But in any given situation the number of electrons in the ground state is more than that in the excited state. The Laser is based on the principle of light amplification by stimulated emission of radiation. This is achieved by having excess concentration of electrons in the higher energy states and stimulating the system by radiation to bring about the de-excitation process.

Induced absorption, spontaneous emission and stimulated emission:

An atom in the ground state may absorb a photon of suitable energy and go to an excited state. This is known as the induced absorption and the process is represented by the following equation.

atom photon → atom∗

An atom which is already in an excited state will be unstable and it falls back to the ground state by emitting a photon of appropriate energy. This is know as the spontaneous emission and the process is represented by the following equation

atom∗→atom photon

An atom which is already in an excited state will emit a photon on its own while making its transition to the ground state. But by passing a photon of just right energy we can stimulate the excited atom to emit a photon of the same phase, energy and directed in the same direction as that of the introduced one. This is known as the stimulated emission and the process is represented by the following equation.

atom∗ photon → atom photon photon