Answer to Question #195180 in Quantum Mechanics for Barkat

Question

For laser action to occur, the medium used must have three energy levels. What must be the nature of these levels? Why is three the minimum number?

Answer 1

The material must have controlled purity ,size and shape and must have three energy levels.

The medium should have three or four Energy Levels  

1. Ground Energy Level

2. Met stable energy level

3. Excited energy level.

The material is pumped to level 3-- Excited state from Ground state --- Level 1 which comes down rapidly through Level 2 Through Spontaneous emission and again to level 1 by Stimulated emission from level 2 to level 1.

Where as For Four level Laser, The material is pumped to level 4 Excited level which will come down fast to level 3 Met stable and from level 3 to level 2 through Stimulated emission