Angle-dependent scattering of polarized light by polymer-dispersed liquid-crystal films

Abstract

Polymer-dispersed liquid crystal (PDLC) films are potentially useful for electronic displays, windows with electrically controllable light transmission, and other applications. PDLC film performance may depend strongly on the angular distribution of the light scattered by the films. We have measured the angular distributions of light scattered by both chemically cured and UV-cured PDLC films as a function of incident and scattered optical polarization. The measured angular dependences differ significantly from those produced by a collection of optically isotropic scatterers: off-diagonal elements of the amplitude scattering matrix are nonzero and comparable in magnitude to the diagonal elements. Furthermore, the scattered intensity for incident light polarized parallel to the scattering plane is not simply related to the scattered intensity for incident light polarized perpendicular to the scattering plane. Comparison of these results with a recent theory of light scattering from a nematic liquid-crystal droplet indicates that multiple scattering is important in PDLC films even in their on state. This multiple scattering is, at least in part, produced by total internal reflection at air-sample interfaces for certain scattering angles. From our polarization-dependent intensity measurements, we have computed the fractions of incident light scattered into the forward and backward hemispheres. The forward-scattered intensity is 2.5–4 times as large as the backscattered intensity for our samples.