Photoelectric effect with a twist

Photons have fixed spin and unbounded orbital angular momentum (OAM). While the former is manifested in the polarization of light, the latter corresponds to the spatial phase distribution of its wavefront(1). The distinctive way in which the photon spin dictates the electron motion upon light-matter interaction is the basis for numerous well-established spectroscopies. By contrast, imprinting OAM on a matter wave, specifically on a propagating electron, is generally considered very challenging and the anticipated effect undetectable(2). In refs.(3,4), the authors provided evidence of OAM-dependent absorption of light by a bound electron. Here, we seek to observe an OAM-dependent dichroic photoelectric effect, using a sample of He atoms. Surprisingly, we find that the OAM of an optical field can be imprinted coherently onto a propagating electron wave. Our results reveal new aspects of light-matter interaction and point to a new kind of single-photon electron spectroscopy. The findings that the spatial distribution of an optical field with vortex phase profile can be imprinted coherently onto a propagating electron wave reveal new aspects of light-matter interactions and will help develop future single-photon electron spectroscopy.