In regular laser, we need:
- stimulating photon => this makes the output light coherent
- ways to make inversion population
- resonant cavity
in the pictures about semiconductor laser, I do not see any incoming photon. I checked it in the book Solid state devices by Banerjee and in the internet. Does semiconductor laser need stimulating photon to produce coherent light?
if it does, what is used to produce that stimulating photon?
if it does not, how is a coherent light output produced?