  Photon wave function is a controversial concept. Controversies stem from the
fact that photon wave functions can not have all the properties of the
Schroedinger wave functions of nonrelativistic wave mechanics. Insistence on
those properties that, owing to peculiarities of photon dynamics, cannot be
rendered, led some physicists to the extreme opinion that the photon wave
function does not exist. I reject such a fundamentalist point of view in favor
of a more pragmatic approach. In my view, the photon wave function exists as
long as it can be precisely defined and made useful.
