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Evolution of the contrast profile for a Gaussian ruffle as a function of the position x and the defocusing distance Δf, according to Eq. 5. As Δf varies from positive to negative values, the contrast profile is gradually inverted, so that positions showing positive contrast (light regions) swap to negative contrast (dark regions) and vice versa. For this example, we used h0 = 0.5 μm, w = 0.4 μm, and Δn = 0.05.
