| 摘要 |
In a first aspect there is provided an extraction lens for a TOF mass spectrometer ion source, said lens including 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; characterised in that said through channel has a length equal to or greater than 8/10 of the diameter of said aperture. This provides an extraction lens which leads to improved extraction and spatial focussing of ions. In addition, as the length of the through channel formed by the aperture is at least equal to 8/10 of its diameter, field penetration through the extraction lens aperture into the region in front of the sample plate is kept at a low level and ions are not prematurely extracted. The aperture can thus be made larger than would otherwise be possible. A larger aperture is advantageous because compared to a smaller aperture, it does not become quickly contaminated with material sputtered from the sample. It is also easier to direct a laser or other light source through a larger aperture. This is useful when it is desired to direct a light beam onto the sample plate, along a path at a small angle to or substantially coincident with the spectrometer's ion-optical axis.
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