Effects of diffraction efficiency on the modulation transfer function of diffractive lenses.

Diffractive lenses differ from conventional optical elements in that they can produce more than one image because of the presence of more than one diffraction order. These spurious, defocused images serve to lower the contrast of the desired image. We show that a quantity that we define as the integrated efficiency serves as a useful figure of merit to describe diffractive lenses. The integrated efficiency is shown to be the limiting value for the optical transfer function; in most cases it serves as an overall scale factor for the transfer function. We discuss both monochromatic and polychromatic applications of the integrated efficiency and provide examples to demonstrate its utility.