Coherence is also quantifiable - e.g. how many coherent photons travel into a certain direction within a time interval. A resonator increases that amount by man

Coherence is also quantifiable - e.g. how many coherent photons travel into a certain direction within a time interval. A resonator increases that amount by many magnitudes. Edit: I mean this in terms of a maximum norm. You get a smaller maximum amount of mutually coherent photons without an optical resonator.