Enhanced Backscattering of Light from Randomly Rough Diffusers. Appendix
IMPERIAL COLL OF SCIENCE AND TECHNOLOGY LONDON (UNITED KINGDOM) BLACKETT LAB
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An investigation into scattering of light by randomly rough diffusers is presented. Emphasis is placed on the phenomenon of enhanced backscattering, i.e. when the brightness of the incoherently scattered light peaks sharply in the direction of the illuminating source. Both experimental and theoretical aspects of the problem are addressed, comparing real measurements with numerical calculations. The experimental equipment employed for this study is able to take light measurements close to the backscatter direction enabling the backscatter peak, if present, to be observed. Measurements taken from a Lambertian reflectance standard barium sulfate exhibit strong backscatter enhancement. A method of fabricating Gaussian, randomly rough diffusers is described. Their surface profiles are characterized using a Talystep profilometer and an analysis is presented of finite-tip-size effects on the measured statistical parameters. A replication method is described which faithfully reproduces the random profile of a fabricated diffuser. A rigorous, one-dimensional analysis based on the Helmholtz-Kirchhoff integral equation is presented. Numerical calculations are critically compared with scattered light measurements from identical, metallic, and dielectric diffusers, examining the influence of the medium on the diffusers scattering properties. The effect of changing the radiation wavelength is also investigated.