books.google.com - The propagation of light in dispersive media is a subject of fundamental as well as practical importance. In recent years attention has focused in particular on how refractive index can vary with frequency in such a way that the group velocities of optical pulses can be much greater or much smaller than...https://books.google.com/books/about/Fast_Light_Slow_Light_and_Left_Handed_Li.html?id=kE8OUCvt7ecC&utm_source=gb-gplus-shareFast Light, Slow Light and Left-Handed Light
