maybe old and stupid ones, they keep me wondering
I somehow have the impression this is a *forbidden* question; yet there were lots of speaking about "particle-wave duality". I think I can imagine photon as a particle - a particle is a small glass ball, for example (I did grew up in a village with glassworks, where such balls were produced). Point is very small ball (glass or metal, I did see Starman when I was a kid). But I have not seen the explicit formula, solution of Maxwell equations, called photon. Perhaps there is no such solution? I tend to imagine photon as a wavepacket; perhaps a soliton? In some of the calculations, photon was approximated by a plane wave. Yet in reality, the area where the electromagnetic field is strong is not infinitely wide. High intensity photon - as is the one from pulse laser - is compressed longitudinally, i.e. along the direction of propagation, while continuous laser feels to be on the other side - the coherence length is centimeters for He-Ne laser.
The size of hydrogen atom is around 1angstrom, that is 10^-10 m, 0.1nm. The ionization energy is 13.6 eV. This energy can be ... to the electron-proton system by a photon suitable hitting the atom. The wavelength
is defined as an energy required to give to one electron for the electron; but there is also certain field strength required to emit the electron from the metal.