The ability to create a 62.6 nm frequency standard in helium using stimulated Raman scattering

The possibility of creating a frequency standard based on the $2^{3}S-1^{1}S$ (62.6 nm) forbidden transition of a helium atom using stimulated Raman scattering is shown. The $1^{1}S$ singlet state is the ground state, while the $2^{3}S$ metastable state (Не$^{*}$) has the lowest energy in the triplet part of the spectrum. The standard can be used to measure frequencies in the region of extreme ultraviolet and possibly X-ray radiation.