An electrostatic lens is a lens that transports
electrons emitted from a sample to an electron analyser .
The recent development of electron spectroscopy makes it possible
to reveal the electronic structures of molecules.
Although this is mainly accomplished by electron analysers,
electrostatic lenses also play a significant role
in the development of electron spectroscopy.
Since electron spectroscopy detects several physical phenomena
from the electrons emitted from samples,
it is necessary to transport the electrons to the electron analyser.
Electrostatic lenses satisfy the general properties of lenses.
Systems of electrostatic lenses can be designed in the same way
as optical lenses,
so electrostatic lenses easily magnify or converge
the electron trajectories.
There are several types of electrostatic lenses:
cylinder lenses ,
aperture lenses ,
and quadrupole lenses .
As an example, the principle of the cylinder lenses is explained.
A cylinder lens consists of several cylinders
whose sides are thin walls.
Each cylinder lines up parallel to the optical axis
into which electrons enter.
There are small gaps put between the cylinders.
When each cylinder has a different voltage,
the gap between the cylinders works as a lens.
The magnification is able to be changed
by choosing different voltage combinations.
Although the magnification of two cylinder lenses can be changed,
the focal point is also changed by this operation.
Three cylinder lenses achieve the change of the magnification
while holding the object and image positions
because there are two gaps that work as lenses.
Although the voltages have to change
depending on the electron kinetic energy,
the voltage ratio is kept constant
when the optical parameters are not changed.