Fig. 4

The level scheme of ²⁵Mg⁺. The isotope ²⁵Mg⁺ used in this demonstration has a nuclear spin of I = 5/2. The resulting hyperfine structure denoted by (F,m) is calculated using the usual A and B factors taken from³⁸ for the ground state (A = −596.254376(54) MHz) and from³⁹ for the excited state (A = −18.89 MHz, B = 22.91 MHz). The lowest lying hyperfine level is 745.317970(68) MHz and 65.11 MHz below the hyperfine centroid for the 3s _1/2 and the 3p _3/2 states, respectively. The cycling transitions (thick arrows) are driven with either σ ⁺ or σ ⁻ polarization. The F = 2 ground state, that is populated by off resonant excitation, is kept unpopulated by repumper sidebands modulated on the laser (thin arrows)