Fig. 3.

Spatial-frequency space with $k_z$-axis antiparallel to ${\mathbf{k}}_i$. (a) Cross section of $T_{\mathrm{\Delta }{\mathbf{k}}_{\mathbf{s}}}$, $T_{k\mathrm{NA}}$, and their interception, $T_{3\text{-}\mathrm{D}}$; (b) PSD of the RI fluctuation (blue) and $T_{3\text{-}\mathrm{D}}$ (gray) when the sample can be considered infinite (i.e., the LSs of internal organization are much smaller than sample thickness $L$); and (c) when the sample is finite. Reproduced with permission from Ref. 19, courtesy of Phys. Rev. Lett.