Measuring the absorption coefficient of optical materials with arbitrary shape or distribution within an integrating...

The absorption coefficient of a material is typically measured using transmittance through a homogeneous sample with flat optical faces and collimated illumination. This approach is limited when dealing with arbitrary shapes or inhomogeneous samples like granules, powders, or fibers. Prior research has shown that such configurations make traditional methods impractical. While integrating cavities offer a solution by providing a homogeneous and isotropic light field, no prior work had resolved how to adapt these principles for arbitrary geometries. This gap motivated the development of a new formal framework for absorption measurement. Existing methods lack the ability to handle complex spatial distributions and surface reflections accurately. The need for a generalizable method has remained unmet in the field of optical spectroscopy. This paper addresses the limitations of classical transmittance techniques and proposes a new radiometric approach. It introduces a novel concept to better describe absorption in complex samples.

This study aims to develop a new method for measuring the absorption coefficient of optical materials with arbitrary shapes or spatial distributions. The authors propose to use an integrating sphere setup to overcome the limitations of traditional transmittance measurements. The goal is to provide a generalizable framework applicable to a wide range of sample formats. The study introduces a new radiometric concept called the optical form factor to describe absorption. The motivation stems from the inability of classical methods to handle inhomogeneous or irregularly shaped samples. The authors seek to expand the range of materials that can be analyzed using quantitative absorption spectroscopy. This approach is intended to be simple yet robust enough for practical use. The study also includes validation with PMMA samples of various forms.

The authors revisit the use of an integrating cavity to measure absorption. They base their approach on simple radiometric laws and principles. A new concept, the optical form factor, is introduced to describe absorption. The study includes a rigorous treatment of several regular forms. Surface reflection and full absorption ranges are considered in the model. An integrating sphere setup is modeled and improved for reliable measurements. The method is tested with samples of PMMA in different formats. The integration of radiometric principles allows for general conclusions about arbitrary shapes.

The study introduces a new formal basis for absorption measurement using an integrating sphere. The optical form factor concept is validated through rigorous treatment of regular forms. The model accounts for surface reflections and full absorption ranges. An improved integrating sphere setup is developed for reliable measurements. The method is tested with PMMA samples in various formats. The absorption coefficient of PMMA varies by nearly three orders of magnitude. The range explored is 380–1650 nm. The results demonstrate the method's applicability to arbitrary shapes and distributions.

The authors conclude that their new formal basis allows for reliable absorption measurements of arbitrary shapes. The optical form factor concept provides a generalizable framework for absorption spectroscopy. The method is validated using PMMA samples in different formats. The integrating sphere setup is shown to be effective for inhomogeneous samples. The approach expands the range of materials that can be analyzed. The study confirms the method's applicability from weak to highly absorbing materials. The results support the use of radiometric principles in absorption measurement. The method is proposed as a practical alternative to traditional transmittance techniques.