Magnetic lens system
The magnetic lens system consists of a:
- Condenser lens
- Objective lens
- Scanning coils
The condenser lens controls the intensity of the electron beam reaching the specimen. The objective lens brings the electron beam into focus (de-magnifies) on the specimen.
Objective lens (OL) aperture
This aperture is used to reduce or exclude extraneous (scattered) electrons. An optimal aperture diameter should be selected for obtaining high resolution secondary electron images.
The beam is deflected in the x and y axes by a pair of scanning coils (or deflector plates). These are found below the condenser lens system and associated with the objective lens area. The deflection enables the movement of the beam, as lines of consecutive dwell-times for the beam spot, across a rectangular area of the sample surface. This is also called rastering.