Optics: What is phase matching, and mode locking

[bfusco]

Homework Statement

The other day in lecture my professor mentioned the words mode locking and phase matching (same as velocity matching apparently) while on the topics of lasers. However, i can't find anything that can provide a simple explanation of what they are. Is there anyone who would know how to explain in simple terms what they are? Thank you in advance

 

[Simon Bridge]

That will be because there is no "simple explanation" of what they are, whatever that means.
You should start from a picture of what you are doing and what happens normally - i.e. when the phases are not matched etc.

It sounds to me like you missed a lecture.