Question

(a) What does the term population inversion refer to with respect to a laser and (b) why is population inversion required for light amplification to occur?

Answer 1

The questions are from photochemistry chapter. Let explain the answers step by step. The concept is very easy to understand.

a . The population inversion is a term which come from statistical mechanics and it says that the population (it may be electrons,atom etc) of higher energy state is greater than the lower energy state.

If you understand the energy state where the lower energy state called ground state and the high energy state is called excited state. Practically the lower energy state is more populated because of the stability and excited states are less populated.So when we say population inversion it means the higher energy state the much more populated then ground state.  

The mechanism of leser is a continuous emmision of light. So when we excited some electron to the higher energy state it came back to the ground state and it emissions light. It is very quick. So when it comes for the laser the emission must be continuous for the time being. So when the the excited state get more populated its take more time to come to the ground state and it shows continuous emission. This is why the population inversion is most important in laser.  

  

B. Light amplification is general phenomenon of leser.which means we increase the intensity of light.and the same concept of population inversion needed to amplify the light.if I show the diagram then you can understand better .This is level 1 leser

I hope you understood .If you have have any questions then ask me .Thank you

o E oo & ooooo oo EL 0000000000 0000000 ground stale. F.00000006 easier Normal population population inversion.

Level13 Ny population R (fast, radiation less transition) Level 2 I Ne polulation Pump un (slow, laser transition) transition ground Level 1 state Ni population level 1 leser.