Fig. 1. Sketch of laser resonance ionization and the corresponding schemes, including non-resonant ionization, resonant ionization, and field ionization

Fig. 2. Schematic of the two field ionization approaches(a) Electric field ionization, (b) Thermal ionization

Fig. 3. Comparison of the sensitivity and resolution achieved via different RIS techniques

Fig. 4. Schematic of the RADRIS experimental setup.The circle with a plus sign denotes the positive ion while that without a plus sign denotes the atom, and the series of reaction and detection processes is highlighted using the green arrows.

Fig. 5. Schematic of the CRIS experimental setup