Abstract

The proton charge radius deduced from muonic hydrogen spectroscopy has disrupted the test of quantum electrodynamics calculations from hydrogen spectroscopy. To improve the spectroscopy of hydrogen, we have developed a powerful continuous wave (cw) laser source at 205 nm (15 mW) and realized the two-photon spectroscopy of the 1S-3S transition with a statistical relative uncertainty of 7.5×10⁻¹³. Currently, depending on the pressure dependence of the velocity distribution used to calculate the 2nd order Doppler effect, two values of the proton charge radius can be extracted from our experiment in agreement either with muonic hydrogen or hydrogen spectroscopy.

© 2015 Optical Society of America