Questions on Semiconductor & Solid-state lasers

1. What does the shell-model of the atom describe?
2. How is the shell-model related to the energy-level model of the atom?
3. What is the valence electron in an atom? 
4. How can two neutral atoms form a bound molecule? Give an example of this.
5. Describe what a crystal is.
6. What are energy bands? How are they similar to and different from the energy levels/shell model?
7. What is the valence band in a crystal?
8. What are the differences in the energy band configurations between conductors, insulators, and semiconductors?
9. What is a p-n junction? What is a transistor?
10. What kind of transition leads to the production of light in a semiconductor p-n junction?
11. Describe what a semiconductor laser is and how it operates.
12. Give a few examples of the uses and advantages of semiconductor lasers.
13. What are some of the output wavelengths and powers of semiconductor lasers?
14. In what ways are the transitions in solid-state lasers different from atomic ones?
15. What is ruby? What is its color and what species of atom is involved in lasing in a ruby laser?
16. How are ruby lasers made to laser, i.e. please explain their pump, medium, and laser cavity?
17. What is the color of ruby laser light? Is its output cw or pulsed? Why?
18. What is Q-switching and what is its function?
19. What are ruby lasers used for?
20. What are the required properties of the host crystal in solid-state lasers?
21. What is a YAG laser? What is the host and what is its lasing species in the YAG?
22. What is the typical output wavelength of a YAG laser? 
23. What are some of the advantages of YAG lasers? Some of its applications?
24. What is a Ti:sapphire laser? How is it different from a ruby laser in make-up and in operation?