  We recently performed experiments on the transfer of photon spin to electron
orbital angular momentum. For an interpretation of the experimental results we
used a classical electrodynamic model of the photon as a propagating
electromagnetic solitary wave which is developed in detail here. A linearly
polarized monochromatic photon is considered as a propagating solitary
electromagnetic wave of finite energy hf which carries an angular momentum
h/2pi with the frequency f and Plancks constant h. This model has, apart from
being a tool for an interpretation of our experimental results, far reaching
consequences of fundamental relevance and guides us to an outline to a unified
quantum theory of electromagnetism and gravitation including an explanation of
the electrodynamic origin of the quantized charge of an electron.
