Abstract: A monoenergetic ion source for the generation of an ion beam is described with the ion energies which lie below 100 eV and also above 5 keV being capable of being freely selected so that the whole range of intermediate energies and independently of the selected ion current density with the aid of the operating parameters of the source. The ion current density is so freely adjustable independently of the ion energy. The ion source is provided with an optical beam focussing system and can in particular also be used to produce metal ions. This ion source also makes a special coating process possible which is likewise described here.