Patent ID: 7041970

Claim:
A time of flight mass spectrometer having an ion source, a light source, a drift region and an electrostatic lens located in the drift region, said ion source including: a repelling plate to which a voltage can be applied to repel ions away from said plate, wherein the repelling plate is a sample plate on which the sample is deposited prior to ionization; and at least one extraction lens to which a voltage can be applied to accelerate ions towards said drift region, wherein an electric field defined by the repelling plate and the extraction lens is pulsable to extract ions from an extraction region between the repelling plate and the extraction lens, said extraction lens consisting of: an element having an aperture, said aperture extending through the element so as to form a through channel, such that, in use, ions may pass from one side of the element to the opposite side of the element by passing through said through channel; wherein said through channel has a length equal to or greater than 8/10 of the diameter of said aperture, wherein the paths taken by the ions as they are repelled from the repelling plate, have two distributions, spatial and angular, and the spatial distribution is focusable by one of the extraction lens and the electrostatic lens, and the angular distribution is focusable by the other of the extraction lens and the electrostatic lens, and wherein the electrostatic lens is located sufficiently far away from the extraction lens so that in use when ions repelled from the repelling plate pass through the lenses the focusing effect of the extraction lens on the ions is not significantly affected by the subsequent focusing of the ions by the electrostatic lens, wherein the light source is for directing light on to the sample plate through the aperture of the element.