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Measurement of the Optical Constants of Sand Samples Using Ellipsometry on Sand-Adhesive Composites
Jesse A Frantz1, Matthew B Hart1, Cobey L McGinnis1
1Optical Sciences Division, U.S. Naval Research Laboratory, Washington, District of Columbia, USA.
Applied Spectroscopy
|February 22, 2024
Summary
Accurate optical constants for sand particles are crucial for modeling light propagation. A new spectroscopic ellipsometry method effectively extracts these constants from particulate samples, enabling precise light scattering predictions.
Area of Science:
- Optical Physics
- Materials Science
- Geophysics
Background:
- Accurate optical constants of particulate matter are essential for modeling light propagation through suspensions like sand clouds.
- Existing methods for measuring these optical properties often lack high accuracy.
- Particulate materials present unique challenges for optical characterization.
Purpose of the Study:
- To present a novel method for accurately measuring the optical constants of particulate materials using spectroscopic ellipsometry (SE).
- To validate the method using known materials like silica and Arizona road dust.
- To apply the method to real-world sand samples and utilize the data for light scattering modeling.
Main Methods:
- Preparation of polished discs from an adhesive compound and then from a mixture of adhesive and sand.
- Spectroscopic ellipsometry (SE) measurements on the prepared discs.
- Application of the Bruggeman effective medium approximation to extract particulate optical constants from mixture data.
Main Results:
- The SE method successfully extracted optical constants for silica powder, showing good agreement with literature values.
- Optical constants were determined for Arizona road dust and desert sand samples.
- Light scattering models using the extracted data accurately predicted extinction coefficients and spectral properties, including the Christiansen feature.
Conclusions:
- The developed SE technique provides an accurate means to determine the optical constants of particulate materials.
- The extracted optical constants are suitable for input into rigorous light scattering models.
- This method advances the ability to model light propagation through various particulate media, such as sand clouds.
