Hello everyone! I would like to ask you for help on this: 1. what are the differences between polariton, polaron and plasmon? 2. such as theoretical aspects I have to know to understand the functioning of a spaser? (spaser=surface plasmon amplification by stimulated emission of radiation) thanks for the help! p.s. if you have any books, articles or links to advise me, you would help me twice. see you soon!