LASER stands for Light Amplification by Stimulated Emission of Radiation. It produces a highly coherent, directional, and monochromatic beam of light. The first LASER was developed by Theodore H. Maiman in 1960.
Interaction of Radiation with Matter:
Radiation interacts with matter in three main ways:
1. Induced Absorption
When a photon with energy E = h\nu strikes an atom in a lower energy state E_1 , the atom absorbs the photon and transitions to a higher energy state E_2 .
E = h\nu = E_2 - E_1
2. Spontaneous Emission
An atom in a higher energy state E_2 can spontaneously transition to a lower energy state E_1 , emitting a photon of energy:
This process is random and does not require an external photon.
3. Stimulated Emission
When a photon of energy h\nu interacts with an atom in an excited state E_2 , it can stimulate the emission of another photon that is identical (same phase, direction, and energy).
E = h\nu = E_2 - E_1
This process is the basis of LASER operation.