High-precision hyperfine spectroscopy inM1-M1 double-resonance transitions on trappedPb+207

Optical pumping of the ground state of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}_{}^{+}{}_{}{}^{}$ ions, confined in a Paul ion trap on the weak 6${\mathit{P}}_{1/2\mathrm{-}}$6${\mathit{P}}_{3/2}$ M1 transition at λ=710 nm, and consequent magnetic-dipole transitions between the ground-state hyperfine Zeeman levels have resulted in an A factor of 12 968 180 601.61(0.22) Hz and linewidth of 0.5 Hz. The value includes corrections of Zeeman shifts from residual magnetic fields and second-order Doppler shifts in the several-eV-deep trap potential, while the ions were cooled by He buffer gas. Two M1 quanta have been applied simultaneously in a double-resonance experiment.