Impact of analyzer angle and tube geometry on the iso-pathlength point in polarization-resolved measurements of scattering media

Optical polarization techniques provide valuable tools for non-invasive sensing of turbid biological media, yet multiple scattering induces depolarization and complicates signal interpretation. In this work, we investigate the effect of polarization on the iso-pathlength (IPL) point - a geometrical feature where detected intensity becomes independent of the scattering coefficient. Using linearly polarized illumination and analyzing the co-polarized and cross-polarized detected light, we observe a distinct polarization-dependent IPL shift. For a 10 mm tube, the IPL occurs at an azimuthal angle of 100.3 ∘ ,104.9 ∘ , and 111.7 ∘ for cross-polarized, unpolarized, and co-polarized detection, respectively. The IPL angle increases linearly with tube diameter, a trend confirmed by polarization-sensitive Monte Carlo simulations based on Stokes vector formalism.