go From the basics of laser like absorption, spontaneous emission and stimulated emission with basic picture of diagram is explained. Then after the transition probability is explained in these three process with simple examples. Relationship of Einstein’s coefficients and information through that in normal way in terms of frequency of radiation and explained. Why spontaneous emission dominates over the stimulated emission in general. Then after population inversion explained with the help by taking of regional cities example.
http://www.tentaclefilms.com/?yutie=opzioni-digitali-con-la-banca&776=aa What are two energy level, three and four energy level schemes and how to get an idea about the excited and meta stable states. The lasers Ruby, He-Ne and Semiconductor are explained with basic physical concepts.