28 November 2007 Rays propagation in optical tunnel
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Optical tunnels are widespread in mircolithographic illumination systems. It reshapes the rays and illuminates masks with dose-and-directional uniformity. Rays were focused the input end, reflected by the walls of the optical tunnel and lapped over the output end. According to rays reflecting by walls, optical tunnel was expanded along the reflecting walls. The approaches of rays' propagation in the optical tunnel were given. It indicates the luminance of the source is important for the optical tunnel performance; the defect of small inclination between bottom and top walls are neglectable for the uniformity of the output end. The taper of tunnel leads to the dissimilar of rays NA between output end and input end. The relation of the NA was given. The indications were confirmed by the simulations. When a collimated beam was focused on the input end, simulations show that the dropping of nonuniformity was unsmooth as the optical tunnel length increasing. When the luminance turned to a Gaussian distribution, the uniformity improved greatly. The uniformity of the output will be insensitivity with a fitting luminance. The nonuniformity would be less than 0.7% when the radius diminished less than the half. The edges' defect degrade the uniformity greatly both confirmed by the simulations and experiments. It shows that optical tunnels with sharp edges are excellent optical integrators with fitting luminance sources.
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Zhijie Liao, Zhijie Liao, Tingwen Xing, Tingwen Xing, } "Rays propagation in optical tunnel", Proc. SPIE 6834, Optical Design and Testing III, 68340A (28 November 2007); doi: 10.1117/12.756633; https://doi.org/10.1117/12.756633

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