The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation.


1. MONOCHROMATICITY: Made of only one colour.


when an electron in the excited level E2 is induced(stimulated) by a photon of energy (e2-e1), the electron moves to lower energy level e1 emitting another hoton of energy E2-E1. This process is called Stimulated emission

    Spontaneous emission

When an electron in excited level E2 false spontaneously to lower energy level E1 after its life time, a hoton is emitted. The energy of the emitted hoton is given by E2-E1=h.

Both stimulated and stimulating photons are in phase with each other.
Stimulated emission of radiation results in amplification of lights.

    Conditions For Lasing:-

1. Suitable active medium
2. Creation of population inversion
3. Proper optical feedback


    Population inversion

For light amplification by stimulated emission of radiation the population of excited state must be greater than the population of lower energy state. This condition is called population inversion.

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