I always have some interesting on the photon. after I read the oscillator expansion of the electromagnetic field in a finite volume, I find photon is more a mathematical concept in theoretical physics than real particle. not like electrons, number of photon is a representation of the energy level of a oscillator.by absorbing or emitting a photon the energy level of the oscillator will be changed. thereofre not like electron the wave function of a photon is meaningless because the position coordinate of the photon has no physical meaning. But of course we can discuss the energy and momentum of a photon.