title: Equilateral hyperbolic moiré zone plates with variable focus obtained by rotations.
abstract: We present equilateral hyperbolic zone plates with variable focal length, which are formed as moiré patterns by a mutual rotation of two identical basic grids. Among others, all principal zone plates, except of the spherical one, can be used as these basic transmittances. Three most important advantages of the proposed moiré zone plates are: a constant aperture of the created element during the mutual movement of basic grids, lack of aberrations due to their undesired mutual lateral displacements and high diffraction efficiency of the binary phase version. To obtain clearer moiré fringe pattern, a radial carrier frequency can be added additionally to the transmittances of basic grids. The destructive interference between both arms of the focal cross of the equilateral hyperbolic moiré zone plate can be obtained by a constant phase shift introduced in the transmittances of the basic grids. Potential applications of discussed elements are indicated, including the most promising one in the three-point alignment technique.
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Jaroszewicz
authors.forename: Andrzej
authors.initials: A
authors.lastname: Kołodziejczyk
authors.forename: Alejandro
authors.initials: A
authors.lastname: Mira
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Henao
authors.forename: Salvador
authors.initials: S
authors.lastname: Bará