Double pulsed time-of-flight mass spectrometer

Abstract

An improved method of operating a time-of-flight mass spectrometer. This method, which involves double pulsing, achieves an increase in the resolution of TOF mass spectrometers by compensating for the energy spread of the species extracted from the source and thus the time spread of ions of a specific mass arriving at a detector. According to this improved method, atoms (or molecules) for analysis are rapidly removed from a surface at a first well defined time. These atoms or molecules are then rapidly ionized at a location or region a distance, R, from the surface at a second well defined time after a selected time delay, T.sub.o. The resultant ions first move through a region of uniform electric field of a distance, S.sub.1, and then into a field-free region having a length, S.sub.2, Lastly, ions leaving the field-free region enter a short high energy accelerating region so as to impinge upon an ion detector. The output signal of the detector, as a function of arrival time, is an indication of the mass distribution of the ions and thus the analysis of the atoms or molecules. A proper choice of the uniform electric field and parameters R, S.sub. 1, S.sub.2 and T.sub.o provide compensation for the energy spread of ionized species and thus a reduction in time spread of ions at the detector. Certain special cases for enhanced resolution are described, as well as operation of the TOF according to the improved method to achieve atom enrichment of a specific mass.