Precision spectroscopy of highly excited states in hydrogen atom

德俄联合项目旨在精确测定氢原子2S-4P、2S-6P和2S-9P跃迁的光学频率。结合先前测量的1S-2S频率，可以确定质子的电荷半径和里德伯常数。由于原子氢的测量值与最近介子氢的兰姆位移测量值之间的差异，一个新的质子电荷半径值具有重要意义。解决这个问题（质子电荷半径难题）可能会得到更精确的里德伯常数值。我们计划设计新的超稳定激光系统，用于激发2S-4P， 2S-6P和2S-10P的电偶极子跃迁，并测量目标不确定度小于3 kHz的跃迁频率（光谱分辨率为1E12）。为了达到所期望的线宽1E-4对应的不确定性，我们计划广泛研究激励过程和系统效应，如多普勒效应、光泵浦、斯塔克位移等。随着过渡频率（2S1/2-4P1/2, 3/2, 2S1/2-6P1/2,3/2, 2S1/2-9P1/2, 3/2）的绝对数量的测量，详细的理论研究的线形和贡献的系统频移计划。

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.