A Difference between ASE and stimulated emission

[TheCanadian]

Is there any inherent difference between amplified spontaneous emission and stimulated emission? Is not stimulated emission simply the mechanism by which ASE occurs? Is stimulated emission just a broader term? I've read the two terms in literature and just wanted to ensure I understood the subtle differences between them.

 

[Zarqon]

They are both in principle stimulated emission yes, but the seeding photons are different. What you want in a laser is that all photons in the inverted population gets stimulated down into the specific narrow cavity mode that your mirrors define. However if a photon, for example, spontaneously decays into a mode other than the lasing one it also has a chance of causing further decay through the stimulated process. This is what is called ASE, and it's generally considered bad because it drains power from the narrow frequency mode you want your laser to have and puts it into the broadband (and also undirectional) ASE, essentially acting as noise around your main laser peak.