Charged particle lens

A method of focusing a beam of charged particles towards a sample mounted at a sample position, comprising:

• providing a charged particle lens, comprising:
• a first pole piece, having a central aperture;
• a second pole piece, being electrically insulated from the first pole piece and having a central aperture, wherein the second pole piece is arranged to be aligned with the first pole piece such that a central axis of the charged particle lens extends through the central aperture of the first pole piece and the second pole piece, the central apertures of the first pole piece and the second pole piece for passing the beam of charged particles towards the sample;
• a lens coil arranged to generate a magnetic field at the first pole piece and at the second pole piece;
• and
• at least one voltage supply, arranged to apply a potential difference between the second pole piece and the sample mounted at the sample position to generate an electric field;
• wherein the method further comprises:
• generating the magnetic field and the electric field whilst passing the beam of charged particles through the central aperture of the first pole piece and the second pole piece towards the sample, the generated magnetic field and generated electric field for focusing the beam of charged particles towards the sample.