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Nearly index-matched optical elements are described that have application to aspherical, diffractive, and hybrid refractive -diffractive elements. Owing to the small difference in index, tolerances on the interfacial surface profile are much looser than for conventional aspherical and diffractive elements. A condition on both the index and the dispersion is described that results in an achromatic phase, thereby allowing for diffractive elements with high efficiency over broad spectral bands. Properties of the elements are described and compared with those of conventional diffractive elements. Analytical results and experimental measurements with an inexpensive element with 40 waves of asphericity are presented.

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Well-characterized test conditions are essential for validating the engineering design of an adaptive optical system. A technique for fabricating high-resolution, well-characterized pseudo-random phase plates that addresses this need is described. Among other uses, these phase plates can be used to test adaptive optics systems under controlled conditions. Machining a surface whose relief height is proportional to the desired phase forms a pixellated phase plate. Using Lexitek's Near-Index-Match™ approach, a sandwich of two materials is formed that produces the desired phase. Phase plates with 20 micron pixels have been fabricated using a 4096x4096 pixel grid. Results are presented.

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