Precision Wavelength Measurements and New Experimental Lamb Shifts in Helium

Abstract

Absolute wave numbers have been measured to 2-3 parts in ${10}^9$ for the $2{}_{}{}^3{}_{}{}^{}S\to 4{}_{}{}^3{}_{}{}^{}S, 5{}_{}{}^3{}_{}{}^{}S, 4{}_{}{}^3{}_{}{}^{}D, \mathrm{and} 5{}_{}{}^3{}_{}{}^{}D$ two-photon transitions and the $2{}_{}{}^3{}_{}{}^{}P\to 3{}_{}{}^3{}_{}{}^{}D$ one-photon transition in helium. With use of relativistic calculations, Lamb shift values for these energy levels are derived and compared to theory. With improvements of one to two orders of magnitude in the theoretical calculations, these measurements could provide a new value for the Rydberg constant with an accuracy of 2 parts in ${10}^9$.