Fig. 4.

Retardance values $D$ for rafts of various radii $\alpha R$. The points indicate experimental data and the lines indicate theoretical results calculated with ${\alpha }_{\text{t}}=0.5$ and the parameter values in Table 1, corresponding to twist penetration depth $\lambda \sim 0.8\mathrm{\mu }\text{m}$ and chiral wavenumber difference $\mathrm{\Delta }q=0.5\mathrm{\mu }{\text{m}}^{-1}$. $\alpha$ is given by Eq. 5 and $R$ is adjusted to produce rafts of different radii. Experimental data and methods are reported in ref. 18.