FIGURE 4.

Contrast inversion curve as a function of Δf for the central (▴) and right lateral (•) peaks of a Gaussian ruffle. Using Eqs. 7a and 7b to fit these data, we obtained h₀Δn = (0.0161 ± 0.0002) μm for the central peak and h₀ = (0.31 ± 0.02) μm, Δn = (0.051 ± 0.005) for the right lateral peak. Since both curves belong to the same structure, we can use the value of h₀ obtained from the fit on the lateral peak to obtain Δn = (0.052 ± 0.005) for the central peak. For this ruffle, w = 0.4 μm. The distance between the central and the lateral peaks was 0.7 μm.