Optical porosimetry of weakly absorbing porous materials.

The physical porosity ${\Phi}$Φ of a porous material determines most of its properties. Although the optical porosity ${\Phi} _{\textrm {opt}}$Φ can be measured, relating this quantity to ${\Phi}$Φ remains a challenge. Here we derive relationships between the optical porosity, the effective refractive index $n_{\textrm {eff}}$n and the physical porosity of weakly absorbing porous media.