We have had attosecond and zeptosecond time scale for photon pulses, but now comes yoctosecond! I'm not all that up on these various terminology, and I had to go look up what yoctosecond is. It is 10^-24 second. A new paper published in PRL this week talks about the possibility of producing photon pulses of that time scale from heavy-ion collisions such as from the one at RHIC.
What comes after yoctosecond?
 A. Ipp et al., Phys. Rev. Lett. v.103, p.152301 (2009).
Edit : There's a coverage of this work in APS Physics. You might even get free access to the paper!