On Precision Measurement of the Frequency of the 11S–23S Forbidden Transition of a Helium Atom

Abstract

The possibility is demonstrated of a precision frequency measurement for the 11S0−23S1 forbidden transition (at 62.6 nm) of a helium atom using the stimulated Raman scattering method. The 11S0 singlet state is the ground state of 4He, while the metastable 23S1 state has the lowest energy in the triplet part of the spectrum (4He*). The transition has a very small natural width, which allows us to consider it as a possible reference for creation of a frequency standard in the vacuum ultraviolet region.