fixed aperture

An aperture with a certain size fixed at an appropriate position. It includes various apertures: An fixed aperture is placed below the condenser lens to cut unnecessary beams from the electron source. A fixed aperture made of tantalum is inserted into the illumination system to cut X-rays excited in the column for achieving high-accuracy analysis. A fixed aperture is inserted at the entrance of the intermediate lens system of the imaging system to cut reflection electrons in the column. A fixed aperture is inserted below the projector lens to enable differential pumping between the camera chamber and the column part.

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