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A diffraction-limited geodesic lens was demonstrated in a polyurethane film-glass substrate waveguide structure. The lens has an aspherical depression and a rounded edge. The measured focal length remained at 10 mm up to 92% of the aperture. Diffraction-limited focal spot size was measured for an input beam width of 2 mm. For larger input beamwidth, the spot size measurement was limited by the optical resolution of the detection system.
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Chen et al. (1978) studied this question.
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