Question

The condition for achieving laser action are
(i) the system must be in a state of population inversion
(ii) the excited state of the system should be in metastable state
(iii) the atom should be in lower energy state
(iv) no conditions required

• A. (i) and (ii)
• B. (ii) and (iii)
• C. (iii) and (iv)
• D. (i), (ii), (iii),(iv)

Answer 1

The correct option is A (i) and (ii)

Laser is light amplification by stimulated emission radiation.

For stimulated emission to take place, there should be more no. of atoms in the higher energy state than ground state. This non-equilibrium between the energy states is referred as population inversion. This is important for laser action to take place.

The population inversion occurs only in between the metastable state and lower state. Metastable state is a higher state but with a lifetime of ${10}^{-5}$ to ${10}^{-6}s$. It is a short lived state but longer lifetime than an ordinary excited state and shorter lifetime than ground state.