Fabrication of diffractive optical elements with binary transmission lithographic masks was used in Chapters 6 and 7 to demonstrate a number of principles. However, there are other techniques that have been developed for fabrication of diffractive microstructures. As previously noted, these techniques fall into three main categories: lithographic methods, direct machining, and replication. In this chapter we present a survey of other techniques used to make diffractive optics. Additional overviews of the history and techniques of modern micro-optics fabrication can be found in several references.
In addition to the binary mask method discussed in Chapter 7, other lithographic techniques are commonly used for fabrication of surface relief structures. These techniques differ from those used in creating binary optics primarily in the method used to expose the pattern on the photoresist. Some of the methods use a different etching procedure as well. We now consider several additional lithographic techniques for fabrication of diffractive optical elements, including direct writing, interferometric exposure, gray-scale lithography, and near-field holography (NFH).
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