Reflectometers for Absolute and Relative Reflectance Measurements in the Mid-IR Region at Vacuum

Area of Science:

• Optics and Photonics
• Materials Science
• Metrology

Background:

• Accurate measurement of spectral diffuse reflectance is crucial for characterizing materials.
• Existing methods may lack precision or versatility for different sample types.
• Directional-hemispherical geometry is a standard for reflectance measurements.

Purpose of the Study:

• To develop and demonstrate spectral reflectometers for absolute and relative diffuse reflectance.
• To establish reliable spectral diffuse reflectance scales for various materials.
• To quantify the uncertainties associated with the developed measurement techniques.

Main Methods:

• Utilized an integrating sphere method coupled with a vacuum-based Fourier-transform infrared spectrometer.
• Employed the third Taylor method for absolute reflectance calibration using homemade reference plates.
• Performed relative reflectance measurements by comparing various samples (concrete, polystyrene, salt) against established standards.

Main Results:

• Successfully demonstrated spectral reflectometers for both absolute and relative diffuse reflectance measurements.
• Achieved spectral diffuse reflectance scales for diverse materials, including concrete, polystyrene, and salt plates.
• Quantified systematic uncertainties via ray-tracing simulations, yielding overall standard uncertainties of 2.18% (k=1) for absolute and 2.99% (k=1) for relative reflectance.

Conclusions:

• The developed spectral reflectometers offer accurate and reliable methods for diffuse reflectance characterization.
• The instruments establish robust spectral diffuse reflectance scales for scientific and industrial applications.
• The quantified uncertainties demonstrate the high precision of the measurement systems.