Progress towards precision measurements of 2S-nS two photon transitions in atomic hydrogen

Precision spectroscopy of atomic hydrogen is important for tests of fundamental physics and the determination of fundamental constants such as the Rydberg constant and proton charge radius. We will discuss progress towards absolute frequency measurements of 2S-nS two photon transitions. Current measurements of such transitions have been limited by significant ac and dc Stark shifts of the resonance. Here, both effects are mitigated through active cancellation techniques. We will present preliminary results of achievable statistical uncertainties and characterization of systematic effects including the dc Stark effect and second order Doppler shift.