Fig. 6

Two dimensional ionization efficiency contour of natural erbium under Doppler free condition. The third excitation laser is tuned to 168Er resonance. The bandwidth and intensity of all excitation lasers are 100 MHz and 5 W/cm2 respectively. The weakly observed 15/2β17/2β19/2 hyperfine pathway of 167Er isotope is marked with *. Additional resonance of 162Er isotope is marked with #.