A systematic analysis has been performed that predicts the existence of 36 cases in which 100% modulated, square-wave irradiance distributions can be generated in the Fresnel regime by simple binary-phase gratings. These types of distributions, referred to here as Lohmann images, have been previously predicted by researchers studying phase gratings known as Talbot array illuminators. Twenty of the cases are reported, to the best of my knowledge, for the first time. Sixteen of these new cases result in Lohmann images with twice the spatial frequency of the original grating. Experimental verifications of the theoretical predictions are presented.
Fabrication of diffractive optics with binary masks requires multiple photolithographic processes to produce high-efficiency elements. Alignment or etching errors at any stage of fabrication decrease the efficiency of the element. We developed an easily accessible procedure that reduces fabrication complexity and costs by using a single gray-scale mask. The gray-scale patterns are generated by commercial slide imagers and are then photoreduced onto low-contrast film plates. Multiple-level or continuous relief structures (kinoforms) may be constructed by use of the photoreduced gray-scale patterns as lithographic masks. Diffractive-optic lenses and blazed gratings were fabricated in photoresist with this procedure. First-order diffraction efficiencies as high as 85% were measured for the blazed gratings. The advantages and the limitations of this technique are discussed.
In the last 10 years, freeform optics has enabled compact and
high-performance imaging systems. This article begins with a brief
history of freeform optics, focusing on imaging systems, including
marketplace emergence. The development of this technology is motivated
by the clear opportunity to enable science across a wide range of
applications, spanning from extreme ultraviolet lithography to space
optics. Next, we define freeform optics and discuss concurrent
engineering that brings together design, fabrication, testing, and
assembly into one process. We then lay out the foundations of the
aberration theory for freeform optics and emerging design
methodologies. We describe fabrication methods, emphasizing
deterministic computer numerical control grinding, polishing, and
diamond machining. Next, we consider mid-spatial frequency errors that
inherently result from freeform fabrication techniques. We realize
that metrologies of freeform optics are simultaneously sparse in their
existence but diverse in their potential. Thus, we focus on metrology
techniques demonstrated for the measurement of freeform optics. We
conclude this review with an outlook on the future of freeform
optics.
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