Questions on Energy State Populations

1. What is a laser pump? What is its purpose?
2. How many different pumps are used in lasers?
3. What is meant by the word: "energy state population"?
4. In the absence of a pump which energy state will have the largest population? Why?
5. Aside from the ground state, which state will have the largest population? Why?
6. How can one change the natural order of energy state populations?
7. What is the lifetime of a transition?
8. What is the range of atomic lifetimes?
9. What are the differences between a spontaneous emission and a stimulated emission?
10. Do collisional excitations have stimulated and spontaneous transitions?
11. What is population inversion?
12. Why is stimulated emission important in a laser?