"Incoming photons" refers to the particles of light that are approaching or entering a particular place or surface, usually used when describing the flow or arrival of light in a specific context. Full definition
A gold electrode coated with nanoclusters of indium phosphide absorb incoming photons of light (that is the wavy line marked «hv» in the image). (treehugger.com)
Researchers have known for decades that if incoming photons have enough energy, they can liberate two or even three electrons. (sciencemag.org)
Einstein showed how electrons in particular elevated states could be stimulated by incoming photons to release photons identical to the incoming ones — the key insight that physicists Charles Townes and Arthur Schawlow built on 40 years later when they sketched out how cascades of such releases could very quickly accumulate to produce what we now know as a laser. (discovermagazine.com)