Precision spectroscopy of highly excited states in hydrogen atom

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Joint German-Russian project aims at precise determination of the optical frequencies of the 2S-4P, 2S-6P and 2S-9P transitions in atomic hydrogen. In combination with previously measured 1S-2S frequency this allows to determine the proton charge radius and the Rydberg constant. A new value for the proton charge radius is of significant importance due to discrepancy between measurements in atomic hydrogen and recent Lamb shift measurement in muonic hydrogen. Solving this (proton charge radius puzzle) may result in more accurate value for the Rydberg constant. We plan to design new ultra-stable laser systems for excitation of the electric dipole transitions 2S-4P, 2S-6P and 2S-10P and measure transition frequencies with a target uncertainty of less than 3 kHz (spectral resolution of 1E12). To reach the desired uncertainty corresponding to 1E-4 of the line width we plan to extensively study excitation process and systematic effects such as Doppler effect, optical pumping, Stark shift and others. Along with absolute measurements of the number of transition frequencies (2S1/2-4P1/2, 3/2, 2S1/2-6P1/2,3/2, 2S1/2-9P1/2, 3/2), a detailed theoretical study of the line shape and contributions of systematic frequency shifts is planned.