a light beam itself which exceeds c? Perhaps, probable, I don't really know myself. But something which have mass like you and me would have difficulty going faster than c cos' of imaginary mass and all?
I've seen these experiments. A powerful pulse of some duration is sent through a filter that blocks most of the pulse. What comes out is a much shorther pulse, the beginning of which is later than the beginning of the input pulse, but the center of the much shorther pulse is before the center of the input pulse. The output pulse's time duration is completely within the time duration of the input pulse.
To me this is just the dyanamics of the medium. The speed of light is not exceeded.
This is very common, the error is to consider that the 2nd postulate of special relativity says that the speed of the light in the vacuum is the top speed. But this is not exactly correct. The 2nd postulate says:
The maximum speed of information transmission is the speed of the light in the vacuum.
In waves, the group velocity and phase velocity don't contains any information about the wave, so both can be greather than "c", and this complains with the 2nd postulate.