We introduced a novel measurement methodology and associated observable in extreme ultraviolet (XUV) angle-resolved photoemission spectroscopy (ARPES), based on continuous modulation of the ionizing radiation polarization axis. Tracking the energy- and momentum-resolved amplitude and phase of the photoemission intensity modulation upon polarization axis rotation allows us to retrieve the circular dichroism in photoelectron angular distributions (CDAD) without using circular photons, providing direct insights into the phase of photoemission matrix elements. 

Polarization-modulated angle-resolved photoemission spectroscopy: Toward circular dichroism without circular photons and Bloch wave-function reconstruction, Michael Schüler, Tommaso Pincelli, Shuo Dong, Thomas P Devereaux, Martin Wolf, Laurenz Rettig, Ralph Ernstorfer, Samuel Beaulieu, Physical Review X 12 (1), 011019 (2022)