The theoretical intensity profile of a phase shift and absorption Fresnel lens in a thin-film waveguide has been calculated. An experimental lens has been constructed with F=5 and a focal length=4 mm using CeO deposited on a BaO waveguide. A 3-dB spot size (full width half-maximum) of 3 μm was obtained compared to a diffraction-limited spot size of 2 μm from theory. Efficiency is approximately 25% and a variation of less than 3 dB in peak intensity is observed over incident angles of up to ±15° from normal.
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Ashley et al. (1978) studied this question.
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