Tighter focus for ultrashort pulse vector light beams: change of the relative contribution of different field components to the focal spot upon pulse shortening

J Opt Soc Am A Opt Image Sci Vis. 2018 Jun 1;35(6):985-991. doi: 10.1364/JOSAA.35.000985.

Abstract

We investigate the focusing of Poisson-spectrum few cycle pulsed light beams for linear, circular, azimuthal, and radial input polarizations with and without a first-order vortex. It is shown that, for all the considered cases, the focal spot is tighter when compared to long pulses due to the increased blue frequency content in the ultrashort pulses spectrum. More significantly, we show, for what we believe is the first time, that upon pulse shortening different focused beam vector components associated with different Bessel functions J0 and J1 undergo a change in the relative weight of their respective contribution to the focal spot size. This effect is caused by the different spectral dependencies of J0 and J1 near the focus. This newly discovered property of broadband ultrashort pulses could be exploited in light-matter interactions advantageously.