A Fresnel zone plate of variable size can be formed as a moiré pattern between a suitable pair of identical grids. The focusing power may be varied over a considerable range by relative translation of the grids if their line shapes are determined by a combination of cubic and linear functions. Elliptical and hyperbolic patterns are also obtainable. If both grids are constructed in phase reversal form, the irradiance in the diffraction image due to the zone plate is enhanced substantially. The device may then be used with photoelectric detection to monitor the straightness of a continuous linear motion. A possible application to field widening in interference spectroscopy is also suggested.
© 1977 Optical Society of America
Original Manuscript: January 19, 1977
Published: September 1, 1977
J. M. Burch and D. C. Williams, "Varifocal moiré zone plates for straightness measurement," Appl. Opt. 16, 2445-2450 (1977)