Hollow-cathode lamp Excitation Process
The excitation process of the element of interest takes place through a few steps. First, the inert gas contained inside of the glass tube is ionized by a voltage. Ionization is the process by which neutral atoms are converted to charged species. This current allows for electrons to move to the anode and cathode. If the voltage applied is large enough, the ions of the inert gas gather enough energy to remove some of the metal atoms of interest from the surface of the cathode by striking the surface. The removal of these atoms produces a cloud around the cathode. The process of producing this cloud is called sputtering. Some of these metal atoms in the cloud have moved to an excited energy state and as they return to their ground state, they emit a specific radiation which is characteristic to the metal of interest.