Multifocal diffractive elements

A method to compute diffractive elements focusing in a set of scaled lines located in different focal planes along the optical axis is considered. A phase nonlinearity is applied to the phase function of a focusator in a line. It is proved that the selection of the nonlinearity is reduced to the problem of the phase diffraction grating with preset energy distribution in the orders. Multifocal elements to focus in a set of scaled lines in a single plane are considered as well.