In 1968, H. Schwarz, while trying to modulate an electron beam with optical frequency, discovered that when a 50 keV electron beam was diffracted by a thin crystalline dielectric film illumnated with a laser, electrons produced a diffraction pattern on a non florescent target with the spots of the same color as the color of the laser light illuminating the crystal. It was noted the results of the experiment could not be explained by Quantum Mechanics. Does anyone know if this experiment has been repeated, or if a successful Quantum Mechanical explanation is availabe? H. Schwarz, Bull. Am. Phys. Soc. 13, 897 (1968).