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A reflectron is also sometimes called an ion mirror because it reverses the trajectory of an ion. The purpose of the reflectron is to minimize the spread of kinetic energy of ions with the same mass to charge ratio.
In the diagram below, the ions which are 3 different masses (M1, M2, and M3) are initially all in one packet at the bottom right of the figure.
As they traverse the flight tube, they are separated by their masses and you can see distinct packets of them in the middle right of the diagram.
In the reflectron, the ions are turned around. A higher energy ion will travel further in the reflectron than a lower energy ion of the same mass, so the kinetic energy spread of ions is decreased and thus the resolution of the instrument improves.
The flight path is twice as long when the reflectron is used, which also improves resolution so the packets of ions are much smaller and more spread out before they hit the detector (middle left). Higher resolution allows the instrument to discriminate ions of similar but not identical mass to charge ratio.
Reflectron as it sits in the instrument
View down the reflectron (path that ions take)
Last Updated: 02/25/2020