Comparison of methods for generation of absolute reflectance-factor values for bidirectional reflectance-distribution...

Area of Science:

• Spectrophotometry
• Materials Science
• Optical Engineering

Background:

• Current spectrophotometric standards lack calibration for many geometries and broad spectral ranges.
• Existing methods are limited by Commission Internationale de l'Eclairage (CIE) recommendations, often restricted to visible wavelengths.

Purpose of the Study:

• To develop and validate new procedures for calibrating spectral bidirectional reflectance factor.
• To extend calibration capabilities to a broader spectral range (400 nm to 2500 nm) and nearly all illumination/viewing geometries.

Main Methods:

• Two distinct methods were employed to determine the absolute bidirectional reflectance factor of a sintered polytetrafluoroethylene (PTFE) sample.
• Calibration utilized a 45/0 reflectance standard from the National Institute of Standards and Technology (NIST) and a traceable directional, hemispherical reflectance factor standard.

Main Results:

• The bidirectional reflectance factor of the PTFE sample was determined for nearly all geometries between 400 nm and 2500 nm.
• Results from the two calibration methods showed excellent agreement, with reflectance factor values differing by less than 0.01.
• The calibrated PTFE sample serves as a reliable transfer standard for future measurements.

Conclusions:

• The developed methods successfully extend the calibration of spectrophotometric standards to broader spectral ranges and geometries.
• The sintered PTFE sample is validated as a robust transfer standard for accurate bidirectional reflectance factor measurements.
• These advancements enable more comprehensive and precise optical characterization of materials.