Fig. 3.

$L_1$ , $L_2$ and $L_T$ in a two-layered medium vs. $\rho$ for different thicknesses of layer 1. (a) to (c): ${\mu }_{a,1}=$ 0.0067 ${\mathrm{mm}}^{-1}<{\mu }_{a,2}=$ 0.0125 ${\mathrm{mm}}^{-1}$ ; (d) to (f): ${\mu }_{a,1}=$ 0.0125 ${\mathrm{mm}}^{-1}>{\mu }_{a,2}=$ 0.0067 ${\mathrm{mm}}^{-1}$ . ${\mu }_s^{\mathrm{\prime }}=$ 1 ${\mathrm{mm}}^{-1}$ (for all layers).