The mass spectrometer has a test material (9) mounted on a carrier (1) and positioned in front is an intermediate electrode (2) and a base electrode (3). In front of these are a front and centre electrodes (4,5) and a shield electrode (6). The pulsed laser (8) is focussed on the specimen and an ion stream (12) is generated. The process operates without a grating and depends upon specific sizes of orifices in the electrodes.
