Magnetic lens, method for focussing charged particles and charged particle energy analyser

摘要

The invention provides a magnetic lens for generating a magnetic imaging field to focus charged particles emitted from a sample. The lens contains a central pole piece 114 and an outer pole piece 104 disposed about the central pole piece 114. The lens also contains at least one magnetic moveable element 116 for movement relative to at least one of the pole pieces 104, 114 whereby a focal length F of the lens is variable by said movement of the magnetic moveable element 116. This enables a zoom facility for changing the magnification of an image. The movement of the moveable element 116 preferably changes the magnetic circuit between the pole pieces 104,114. Also provided is a method of focusing charged particles emitted from a sample and a charged particle energy analyser, such as an imaging photoelectron spectroscopy system. Further embodiments show two magnetic movable elements which will allow three different magnifications to be produced by the same lens.