Towards high precision frequency comb spectroscopy in the extreme ultraviolet - Gil Porat

High precision spectroscopy of few-electron atoms and ions is strongly motivated by the need to test fundamental theory (e.g. quantum electrodynamics) in simple systems, amenable to precise calculation for comparison with experimental measurement. Additionally, transitions from the ground state are most susceptible to nuclear structure effects (e.g. charge radius), making them appealing as tools for testing nuclear structure theory. The frequencies of transitions from the ground state in many such systems reside in the extreme ultraviolet range of the electromagnetic spectrum (XUV, wavelengths of 10~120 nm). However, spectroscopic resolution in the XUV is severely limited by the availability of appropriate sources of XUV radiation, e.g. lasers. In this talk I will explain how precision XUV spectroscopy of helium could be used to address the open problems of the proton radius puzzle and the helium isotope charge radius difference discrepancy. Furthermore, I will discuss our experimental method of generating an XUV frequency comb laser, and our progress in scaling up the power of this laser in order to enable the highest spectroscopic precision in the XUV to date.