Figure 1.

Lens design. (a) Ion lenses are irreducibly bulky and the use of separate lenses for primary and secondary ions forces long working distances and low demagnification for primary ions (red) and/or low collection efficiency for secondary ions (blue). (b) A coaxial single lens design allows the shortest possible working distance and optimum primary ion demagnification together with high secondary ion collection efficiency. Secondary ions of opposite polarity to the primary ions are separated downstream by electrostatic deflection.