28 June 2019
Vol 364, Issue 6447

About The Cover

Cover image expansion

COVER Illustration of a pair of time-delayed vortex laser pulses (red) being coherently up-converted into extreme ultraviolet (EUV) vortex pulses (cyan) that possess self-torque. This property manifests as a smooth, temporal increase in orbital angular momentum (OAM) (represented by the frequency of spatial twists in the EUV beam), progressing from low OAM (top right) to high OAM (bottom left). See eaaw9486.
Image: Chris Bickel/Science