31:36

Calculation of Einsteins coefficient

27:57

Components of LASERs

27:38

Interaction of Light with matter

22:44

How Does a Laser Work? Quantum Nature of Light - [3]

28:28

Population inversion, 2-level system and 3-level system

26:56

LASER and its history

33:04

Spectroscopic Transitions

32:42

The Actual Reason Semiconductors Are Different From Conductors and Insulators.