 The primary ions are pulsed into short bursts of less than 10 ns (the time scale of secondary ion emission after impact is negligible (<10−12 s)).The primary beam is pulsed by a rapid deflection across a small aperture or by off-axis deflection, followed by a curved magnetic field to compress the pulse in space.There is very high accelerating fields at the sample (high extraction voltage and small (mm) extraction gaps) to reduce the initial energy spread of the secondary ions.