Fig. 3.

$E[{|\tilde{I}|}^2(z)]$ is obtained by FDTD. Sample thickness $2\mu \mathrm{m}$, exponential functional form of RI spatial distribution with correlation length (a) $l_c=20\mathrm{nm}$ (exemplifying a case when ${\tilde{\mathrm{\Sigma }}}_R^2\gg {\tilde{\mathrm{\Sigma }}}_L^2$) and (b) $l_c=250\mathrm{nm}$ (exemplifying a case when ${\tilde{\mathrm{\Sigma }}}_R^2<{\tilde{\mathrm{\Sigma }}}_L^2$). On each curve, the depth $L$ at which ${\tilde{\mathrm{\Sigma }}}_L^2$ is evaluated shown by red circles, and depth $L/2$ is used for ${\tilde{\mathrm{\Sigma }}}_R^2$ evaluation by green dots. The shape of $E[{|\tilde{I}|}^2(z)]$ changes with $l_c$ due to the difference in the functional forms of ${\tilde{\mathrm{\Sigma }}}_R^2(l_c)$ and ${\tilde{\mathrm{\Sigma }}}_L^2(l_c)$.