Multiple imaging by diffraction techniques

Zone plates with cells apodized by legendre profiles

By apodizing the cells of a zone plate and changing the opening ratio, it is possible to shape the relative power spectrum of its foci. We describe a novel procedure that leads to an analytical formula for shaping the focus power spectrum by using apodizers expressible as the Legendre series; these act on cells of arbitrary opening ratio. Our general result is used to design zone plates that have missing foci and to discuss a synthesis procedure using apodizers with various opening ratios. Our applications can also be used for shaping the power spectrum of 1-D gratings.

High efficiency multiple beam gratings

Diffraction gratings are used in many optical systems as beam splitters. In these applications the diffraction grating must (1) have high diffraction efficiency and (2) produce uniform intensities in the central block of diffracted beams. High diffraction efficiency is attained by making the grating a phase grating. In this paper we discuss in some detail the use of pulse width modulation (PWM) and pulse position modulation (PPM) to create grating structures that produce uniform central diffracted beams. By using these modulation techniques and proper phase relief for the grating, the diffraction grating can have a diffraction efficiency of 70% or more. Some examples of multiple beam diffraction gratings produced by using PWM and PPM are shown.