Fig. 1.

Model for the theoretical analysis. CW excitation light (S) injected at a source position, ${\mathbf{x}}_s$, propagates in a homogeneous semi-infinite medium, $\mathrm{\Omega }$ (green zigzag lines), and a detector (D) at a detection position, ${\mathbf{x}}_d$, measures fluorescence from a localized fluorescence target, T (solid orange zigzag lines), and homogeneous background emission (broken orange zigzag lines).