My guess is that for some definition of "emerged", the three microsecond-long (3000 ns-long) pulse emerged 62 ns early. Most of the results like this involve s

My guess is that for some definition of "emerged", the three microsecond-long (3000 ns-long) pulse emerged 62 ns early. Most of the results like this involve some sort of anomalous dispersion and careful definition of the term "emerge". Relevant keywords you're looking for if you delve into the work are "group velocity" and "phase velocity". TL;DR: Details. They'll matter in this case.