Development of the concept of the phase focusing of electrons

An analysis is made of the phase focusing typical of the one-dimensional infinitely thin electron fluxes of the O-type devices. It is proposed that this type of focusing be treated as phase focusing in time. The characteristic features of phase focusing are examined for two-dimensional electron fluxes where this process tends to become spatial-temporal. A particular case of the focusing of a wide ribbon electron flux modulated by a traveling wave field is discussed.