| CPC H01J 37/3177 (2013.01) [H01J 37/145 (2013.01); H01J 37/28 (2013.01); H01J 2237/0453 (2013.01)] | 21 Claims |

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16. A non-transitory computer readable medium storing a set of instructions that is executable by one or more processors of a multi-beam apparatus having first and second aperture arrays to cause the multi-beam apparatus to perform operations comprising:
activating a charged-particle source to generate a primary charged-particle beam; and
adjusting a position of a plane of a condenser lens along a primary optical axis in relation to the first aperture array and the second aperture array, wherein:
the first aperture array is configured to generate a plurality of primary beamlets from the primary charged-particle beam using a first plurality of apertures,
a portion of charged particles of a primary beamlet of the plurality of primary beamlets forms a corresponding probing beamlet,
the first plurality of apertures includes a plurality of off-axis apertures configured to generate a plurality of off-axis beamlets, and
the plurality of off-axis apertures includes apertures of various sizes disposed along a curved path.
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