AC Stark Shift Cancellation in Hydrogen 2S-nS Spectroscopy

Hydrogen precision laser spectroscopy can provide a test of fundamental physics with the ability to determine constants such as the Rydberg constant and the proton charge radius. However, to rigorously test theory, multiple transitions need to be measured with a small fractional uncertainty. Unfortunately, many two-photon transitions require large laser intensities to acquire adequate signal-to-noise, resulting in significant AC Stark shifts. The AC Stark shift broadens the resonance in a beam style experiment and limits the fractional uncertainty with which the transition can be measured. Here, we present a method to mitigate the AC Stark shift in Hydrogen 2S-nS transitions through the addition of a laser with an opposite AC Stark shift coefficient to that of the spectroscopy laser. Simulations conducted using a density matrix model show that distortion of the lineshape due to the AC Stark shift can be significantly reduced with the addition of AC Stark shift cancelling radiation. In particular, our results show that resonance widths on the order of 50 kHz can be obtained and linecenter frequencies can be determined at the 100 Hz level with such a method.