Precision measurements in helium at 58 nm: Ground state lamb shift and the 11 S-21 p transition isotope shift

Abstract

A source of narrow bandwidth (< 800 MHz) tunable laser radiation at 58.4 nm has been developed and is applied to record the 11S - 12P transition in 3He and 4He. From the 4He He transition frequency of 171134.8936(58)cm−1 a fivefold improved ground state Lamb shift of 1.3763(58)cm−1 is deduced, in good agreement with the theoretical value of 1.3755(10)cm−1 The measured 11S - 12P transition isotope shift of 263 410(7) MHz presents a more than 2 order of magnitude improvement over a previous value and agrees with a theoretical value of 263 411.26(11) MHz. © 1996 American Physical Society.