Spatiotemporal evolutions of ultrashort vortex pulses generated by spiral multi-pinhole plate.

We use the spiral multi-pinhole plate to generate ultrashort vortex pulses and study their spatiotemporal evolutions involving intensity, phase, orbital angular momentum, and energy current. In the experiment, a Mach-Zehnder-type interferometer is employed to perform the investigation of ultrashort vortices. Combining the experimental results and the theoretical analyses, we discuss the spatiotemporal evolutions of ultrashort vortex pulses in femtosecond regime. The results show that the distribution of orbital angular momentum in the cross-section of the vortex pulse is maintained almost invariable in the pulse duration, while both the intensity and the energy current obey a Gaussian-like distribution. With time evolution, the phase contour lines of such vortex pulses rotate around the propagation axis.