Fractured Zone Plates for Spatial Separation of Frequencies

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Proceedings of the SPIE International Society of Optical Engineering

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Circle-to-point conversion has been used for collecting the output of an etalon where a suitable detector of equal area circular zones was not readily available. The output is converted to a line of points so that it may be read with a simple and readily available linear CCD detector. The purpose of this work was to determine the feasibility and practicality of making circle-to-point optical converters with up to 24 equal area annuli in a 24 mm diameter form factor. Each annulus redirects light into a focus and all foci lie in a straight line with equal spacing between them. The principal working wavelengths were 532 and 355 nm. The first approach was a step and repeat fabrication process using high resolution stepping stages to register 24 masks and a master HOE. The second method consisted of writing software that would generate the desired optic in the form of a single binary mark. An 8X photo reducer and a 4f optical processor were also used to improve performance. Both methods worked well and many samples of each were delivered with the goals being met. Work on the UV portion could not be completed on time but a simple RIE machine was configured and exposures into photo-resist were successfully made using a DCG hybrid master. The resist copies were etched with CF4 and O2 to make copies in fused silica. Further work will require an ion source to reduce losses in the UV HOEs by etching at an angle to the surface.

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