Hello everyone!
Let us learn types of interaction of an electromagnetic wave with matter.
There are three types of interactions.
{1} Induced Absorption : Induced absorption is the absorption of an incident photon by a system which takes place from lower energy state to higher energy state.
• The system that have two energy states are considered E1 and E2, where E2>E1.
• This system can be represented as,
ATOM + PHOTON => ATOM*
{2} Spontaneous Emission : Spontaneous emission is the emission of photon by the transition of a system from a higher energy state to a lower energy state but without the aid of any external energy.
•The system also have two energy states are considered E1 and E2, where E2>E1.
• This system can be represented as,
ATOM* => ATOM + PHOTON
{3} Stimulated Emission : Stimulated emission is the emission of a photon by the transition of a system from a higher energy state to a lower energy state but with the aid of an external energy.
•In this system the photon have same phase, frequency, direction with the incident photon.
It produce coherent beam of radiation.
• This system can be represented as,
ATOM* + PHOTON => ATOM + (PHOTON+PHOTON)