external source ---> excites atoms to short-lived energy level ---> spontaneous emission to metastable level ----> large population at metastable --->population inversion between metastable and lower laser level ----> stimulated emission (photons spontaneous emitted in the population inversion area) ----> laser.
hulala. quiz for laser this morning. wish me luck!
LASER - Light Amplification by Stimulated Emission of Radiation
LOSER - not that loser okay..but Light Oscillation by Stimulated Emission by Radiation
aja aja !