title: Method for more accurate transmittance measurements of low-angle scattering samples using an integrating sphere with an entry port beam diffuser.
abstract: For most integrating sphere measurements, the difference in light distribution between a specular reference beam and a diffused sample beam can result in significant errors. The problem becomes especially pronounced in integrating spheres that include a port for reflectance or diffuse transmittance measurements. The port is included in many standard spectrophotometers to facilitate a multipurpose instrument, however, absorption around the port edge can result in a detected signal that is too low. The absorption effect is especially apparent for low-angle scattering samples, because a significant portion of the light is scattered directly onto that edge. In this paper, a method for more accurate transmittance measurements of low-angle light-scattering samples is presented. The method uses a standard integrating sphere spectrophotometer, and the problem with increased absorption around the port edge is addressed by introducing a diffuser between the sample and the integrating sphere during both reference and sample scan. This reduces the discrepancy between the two scans and spreads the scattered light over a greater portion of the sphere wall. The problem with multiple reflections between the sample and diffuser is successfully addressed using a correction factor. The method is tested for two patterned glass samples with low-angle scattering and in both cases the transmittance accuracy is significantly improved.
authors.affiliation: Department of Engineering Sciences, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden. Annica.Nilsson@Angstrom.uu.se
authors.forename: Annica M
authors.initials: AM
authors.lastname: Nilsson
authors.forename: Andreas
authors.initials: A
authors.lastname: Jonsson
authors.forename: Jacob C
authors.initials: JC
authors.lastname: Jonsson
authors.forename: Arne
authors.initials: A
authors.lastname: Roos