SUMMARY

The scattering of light in a turbid medium has been studied in various areas including colorimetry, atmosphere science, astrophysics, and photometry. Polytetrafluoroethylene (PTFE) is a highly scattering material and has been regarded to have optical properties similar to biological tissues. While many studies have measured the bidirectional reflectance distribution function (BRDF) of a thick PTFE slab, little is known in regards to its scattering coefficient and scattering phase function. In the present study, the ranges of the scattering coefficient, absorption coefficient, and the asymmetric parameter of the Henyey-Greenstein scattering phase function are assessed for sintered semitransparent PTFE films whose thicknesses range from 0.11 mm to 10 mm. The BRDF and bidirectional transmittance distribution function (BTDF) of these samples were measured using a laser scatterometer at a wavelength of 635 nm. The directional-hemispherical reflectance and transmittance were obtained by integrating the BRDF and BTDF over the corresponding hemisphere. The scattering coefficient of PTFE is estimated to exceed 1200 (1/cm) which is nearly 10 times greater than that of typical biological tissures. On the other hand, the absorption coefficient should be less than 0.01 (1/cm). A Monte Carlo simulation was employed to predict the BRDF and BTDF of PTFE films, then the calculations were compared with measurements at various incidence angles. The result and approach used in this study are beneficial to the understanding of light scattering in a highly scattering, little absorbing medium, such as PTFE. It is also important for future research of light scattering in biological media for disease diagnostics and laser medicine.