<title>High-efficiency replicated diffractive optics</title>

Abstract

Diffractive optics technology offers optical system designers new degrees of freedom that can be used to optimize the performance of optical systems. The zone spacing of a diffractive lens can be chosen to impart focusing power as well as aspheric correction to the emerging wavefront. The surface (or blaze) profile within a given zone determines the diffraction efficiency of the element, or in other words, determines how the incident energy is distributed among the various diffraction orders. Unless the zone profile is generated with high fidelity, incident energy will be distributed into extraneous diffraction orders, which generally reduces the optical system performance. Several diffractive optical components have been fabricated using replication techniques that provide high-efficiency and accurate wavefront generation. Typical minimum efficiency measurements at the design wavelength for diffractive zone spacings greater than 10 jim are 95% or above. For minimum zone features as small as 5 jim, the measured efficiency is greater than 85% at the design wavelength. The integrated diffraction efficiency, which is a weighted measure of the efficiency across the clear aperture, is typically 2-3% more than the efficiency measurement at the minimum feature.During the past several years the interest in diffractive optics technology has increased significantly. There has been a relatively steady progression of technical developments from early papers1 that first mentioned the potential benefits of diffractive elements to readily available commercial optical design software packages that provide the ability to easily incorporate diffractive elements in optical system designs. A very important detail that is not modeled in the commercially available lens design software is the impact of non-unity diffraction efficiency.2 Typically, phase coefficients or the Sweat model are used to design diffractive surfaces.3 However, as mentioned above, a designer unfamiliar with diffractive optics technology may not be aware of the potential system performance losses due to energy propagating in spurious diffraction orders.Section 2 provides a brief review of degradation in optical system performance due to non-unity diffraction efficiency. Specific examples of measured MTFs of diffractive elements with different integrated diffraction efficiency values are presented. The requirements to fabricate high fidelity zone structures are discussed in Section 3. In addition, specific examples of measured zone structures are presented to demonstrate the fidelity of the master fabrication and replication techniques. Imaging effects of non-unity diffraction efficiencyA rather strange characteristic of diffractive optical elements (DOEs) is that a diffraction-limited spot can be obtained in an optical system that has rather poor imaging properties. This phenomenon is due to Fakils is currently employed with PSC, Webster, NY. 50 ISPIE Vol. 2600 0-8194-1964-8/95/$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/22/2016 Terms ...

Template-Directed Preparation of Macroporous Polymers with Oriented and Crystalline Arrays of Voids

“…The aim of this work is to develop a versatile templating strategy for creating macroporous polymer films appropriate for quantitative comparison with standard models of diffractive optics. We chose to work with polymers, rather than inorganic matrices, because such materials may extend the use of diffractive optics into applications that require light-weight and/or low-cost materials. − In addition, the polymer-curing process involves much less volume shrinkage than the corresponding precursor decomposition used to make inorganic systems . This allows for the formation of large area (∼1 cm 2 ) samples which can be cast as films on optical substrates.…”