A table-top ultrashort light source in the extreme ultraviolet for circular dichroism experiments

Circular dichroism in the extreme ultraviolet range is broadly used as a sensitive structural probe of matter, from the molecular photoionization of chiral species(1-3) to the magnetic properties of solids(4). Extending such techniques to the dynamical regime has been a long-standing quest of solid-state physics and physical chemistry, and was only achieved very recently(5) thanks to the development of femtosecond circular extreme ultraviolet sources. Only a few large facilities, such as femto-sliced synchrotrons(6,7) or free-electron lasers(8), are currently able to produce such pulses. Here, we propose a new compact and accessible alternative solution: resonant high-order harmonic generation of an elliptical laser pulse. We show that this process, based on a simple optical set-up, delivers bright, coherent, ultrashort, quasi-circular pulses in the extreme ultraviolet. We use this source to measure photoelectron circular dichroism on chiral molecules, opening the route to table-top time-resolved femtosecond and attosecond chiroptical experiments.