Figure 17.

Plots of Δf/n and ΔΓ/n versus $n^2$ as motivated by Equation (46). The film thickness as derived from the offset in panel (A) is about 1.6 µm. The slope d(Δf/n)/d($n^2$) is almost constant, indicating that ${J_{\mathrm{f}}}^{\prime }$ only weakly depends on frequency. There is such a dependence on frequency in (B). The data were taken on a spin-cast film of polyisobutylene. Adapted from [81].