Introduction of Population Inversion for BTech 1 Year Physics Students:
We use Population Inversion to Achieve Amplification
Metastable states, where the lifetime of the atoms are of the order of milliseconds.
More number of atoms should stay at metastable state and less number in the lower state. In such a situation we say population inversion has taken place. To attain this the metastable state should continuously get atoms and atoms must be removed from the lower states. Such a process is named as ‘pumping’.
The emitted photons should stay longer in the system so that they can interact with the system to release large number of photons. This can be achieved by keeping parallel mirrors, which reflect light back to the system.
The photons have to be made highly directional, which can be achieved by throwing out the photons at random directions through the sides of the laser and only those parallel to the axis of the cylinder is amplified.