A pulsed generator of electrically charged particles includes a vacuum chamber; wherein the vacuum chamber is configured to maintain an internal operating pressure between 10-6 mbar and atmospheric pressure; the vacuum chamber is configured to accommodate a photocathode and an anode, the photocathode and the anode being separated by an adjustable distance less than or equal to 30 mm; the vacuum chamber includes a window enabling pulsed light to reach firstly a rear face of the photocathode; the anode is arranged downstream of the photocathode and has an orifice suitable for the passage of electrically charged particles; the generator of electrically charged particles includes a system to apply a difference in potential between the photocathode and the anode, the voltage being configured to accelerate the charged particles.

An ion source for forming a plasma has a cathode with a cavity and a cathode surface defining a cathode step. A filament is disposed within the cavity, and a cathode shield has a cathode shield surface at least partially encircling the cathode surface. A cathode gap is defined between the cathode surface and the cathode shield surface, where the cathode gap defines a tortured path for limiting travel of the plasma through the gap. The cathode surface can have a stepped cylindrical surface defined by a first cathode diameter and a second cathode diameter, where the first cathode diameter and second cathode diameter differ from one another to define the cathode step. The stepped cylindrical surface can be an exterior surface or an interior surface. The first and second cathode diameters can be concentric or axially offset.

An ion source for forming a plasma has a cathode with a cavity and a cathode surface defining a cathode step. A filament is disposed within the cavity, and a cathode shield has a cathode shield surface at least partially encircling the cathode surface. A cathode gap is defined between the cathode surface and the cathode shield surface, where the cathode gap defines a tortured path for limiting travel of the plasma through the gap. The cathode surface can have a stepped cylindrical surface defined by a first cathode diameter and a second cathode diameter, where the first cathode diameter and second cathode diameter differ from one another to define the cathode step. The stepped cylindrical surface can be an exterior surface or an interior surface. The first and second cathode diameters can be concentric or axially offset.

In a secondary ion mass spectroscopic (SIMS) method, and a mass spectrometer for implementing the method, for depth-profiling analysis of alkali metals in a sample which comprises an insulating material or is an insulator. The sample is irradiated by an ion beam as an analysis beam for desorption of secondary ions from the uppermost layers, such that the surface of the sample is removed with the same or a further ion beam. The ion beam used for removal of the sample surface comprises essentially gas clusters or consists of gas clusters.

In a secondary ion mass spectroscopic (SIMS) method, and a mass spectrometer for implementing the method, for depth-profiling analysis of alkali metals in a sample which comprises an insulating material or is an insulator. The sample is irradiated by an ion beam as an analysis beam for desorption of secondary ions from the uppermost layers, such that the surface of the sample is removed with the same or a further ion beam. The ion beam used for removal of the sample surface comprises essentially gas clusters or consists of gas clusters.