Is there a way we can see light at a microscopic scale? In other words, is there an experimentally feasible way to see the structure of photons?
Photons are simply quanta (very small pieces) of energy - they have no physical size, and no physical 'structure'. This video is a good introduction to our modern understanding of what light is.
light is made of photons, not of protons or anything else. And as an electromagnetic wave, it's structure is often the structure of its interaction with the matter (typically made of dielectrics and conducters).
Then, it all depends what you accept as "seeing":
- you can see it because it reach your captors (which are not exactly at the place of focus)
- you can see it through how it affects something else (secondary emissions or transformation, etc)
- in microscopy, you "see" by sending probes (usually photons, sometime electrons) which are modified in their transmission or by their reflection. I guess photons might slightly modify some electrons' flight, but probably not practical at usual energies.
Anyway it also depend what you expect to see: photons are traveling pretty fasts ! or due you want to see something like "the still surface of a fast river", like, steady caustics at some places due to the imperfect optics within the laser generator ?