Lasers

Lasers Laser is light amplification via stimulated emission of radiation. Stimulated emission is key to the ability of the process to amplify light. Mainman was the first person to develop the first visible laser using a ruby.

See Mainman 1960

Emission and absorption of radiation

Two state system

Consider a simple two level system. There are two population of molecules (N1 and N2) at two possible energy levels (E1, E2). An atom on level E1 can be elevated to E2.

The absorption of a photon with the correct energy hnu (the difference between E1 and E2) results in a stimulated absorption and the system moves into the excited state. This leads to the emission of photon in a lifetime tau21. In spontaneous emission the emitted photon can have differing energies, polarization and phase than the stimulating photon.

In stimulated emission the absorbed photon causes the excited photon to emit light with specific characteristics.