Laboratory limit on the charge of photons by electric field deflection
  The deflection of a laser beam traveling through a modulated electric field is measured using phase-sensitive detection to place an upper bound on photon charge. An upper limit of $10^{-14}e$ is obtained. The experiment involves a number of experimental techniques that are commonly encountered in modern precision measurements and is suitable for both advanced undergraduate and beginning graduate students in physical science as a laboratory exercise. 
A. Hankins, C. Rackson, and W. J. Kim
physics.optics physics.class-ph