A multi-reflecting ion optical device includes electrostatic field generating means configured to generate electrostatic field defined by a superposition of first and second distributions of electrostatic potential ΦEF, ΦLS. The first distribution ΦEF subjects ions to energy focusing in a flight direction and the second distribution ΦLS subjects ions to stability in one lateral direction, to stability in another lateral direction for the duration of at least a finite number of oscillations in the one lateral direction and to subject ions to energy focusing in the one lateral direction for a predetermined energy range.