Analytical Evaluation and Correction of Port Loss Error in Integrating Sphere Reflectometers

Published

November 1, 2003

Author(s)

A Prokhorov, Sergey Mekhontsev, Leonard Hanssen

Abstract

Incomplete hemispherical irradiation of the sample (or collection of radiation, in the reverse geometry) in an integrating sphere reflectometer is unavoidable due to sample viewing (or illumination) requirements. This means that one measures with nearly hemispherical irradiation and obtains a quantity that is not identical to the hemispherical/directional (or directional/hemispherical) reflectance factor (HDR) of the sample. The assumption that this quantity is identifical to the HDR can lead to error in the measurement result, which is not generally corrected for.The error, a.k.a. port loss error, is minimal for comparative measurements of samples with similar reflective properties, but can easily amount to several percent for a diffuse vs. specular comparison and could be even higher for samples that exhibit strong forward scattering. Few papers in the literature have dealt with this issue, perhaps due to the existence of other larger sources of error.Our approach to this problem has three elements: (1) establish a definition and set of equations that quantify the error due to incomplete irradiation of the sample due to the presence of the viewing port (port loss uncertainty); (2) develop algorithms and computer models to predict port loss effects for a specular-diffuse sphere coating and specular-diffuse (or more general bi-directional reflectance distribution function (BRDF)) sample; (3) design a technique and instrumentation to allow routine direct measurements of port loss to correct the error; using reference standards such as an Al mirror and a polytetraflouroethylene (PTFE).

Proceedings Title

Optical Diagnostic Methods for Inorganic Materials, Conference | 3rd | Optical Diagnostic Methods for Inorganic Materials III | SPIE

Conference Dates

August 6-7, 2003

Conference Location

Undefined

Conference Title

Proceedings of SPIE--the International Society for Optical Engineering

Pub Type

Conferences

Keywords

BRDF, integrating sphere, reflectance, uncertainty

Citation

Prokhorov, A. , Mekhontsev, S. and Hanssen, L. (2003), Analytical Evaluation and Correction of Port Loss Error in Integrating Sphere Reflectometers, Optical Diagnostic Methods for Inorganic Materials, Conference | 3rd | Optical Diagnostic Methods for Inorganic Materials III | SPIE, Undefined (Accessed April 18, 2024)