Electron vs. Photon's electrical potential

Hi guys,

After reading a paper about electron scattering, I became very interested. So if an electron is travelling in empty space, the electron's potential (according to the paper) is supposedly:

http://www.flickr.com/photos/31694672@N07/
(I used flickr and Glui to post this equation)

In the equation, the high-lighted part is an associated Legendre's function, μ is cos θ, and I was not sure what ω would be.

Anyhow, I was wondering what the potential would look like for a PHOTON, travelling in empty space (instead of an electron).


(Un-necessary background information: I was reading a paper about how an Electron is scattered by a dielectric hemisphere. The theoretical space was divided into 3 parts: 1. before the electron hits the hemisphere, 2. when the electron is within the hemisphere or passing right by the hemisphere, and 3. after the electron passes by the hemisphere. The paper presented the potential for 1, 2, and 3. I wanted to focus on part 1 for now, being the topic of the paragraphs above.)



Thank you for reading,

Z. Zheng