Bidirectional reflectance distribution function of gold-plated sandpaper.

Area of Science:

• Optical Engineering
• Materials Science
• Spectroscopy

Background:

• Standard reference reflectors are crucial for accurate measurements in the infrared (IR) spectrum.
• Traditional Lambertian reflectors have limitations in certain IR applications.
• Investigating novel materials like gold-plated sandpaper for improved reflectivity.

Purpose of the Study:

• To evaluate gold-plated sandpaper as a Lambertian standard reference reflector for the IR spectrum.
• To determine the optimal sandpaper grit sizes and materials for different IR wavelengths.
• To compare the performance of gold-plated sandpaper with existing IR reflectors.

Main Methods:

• Studied various grit sizes (3-400 microm) and materials (silicon carbide, aluminum oxide) of gold-plated sandpaper.
• Measured scattering using three laser wavelengths (0.6328, 3.39, 10.6 microm) at multiple angles of incidence (0-60 degrees).
• Analyzed the correlation between surface roughness, particle density (filling factor), and Lambertian behavior.

Main Results:

• Identified optimal sandpaper: 9-microm Al2O3 for 0.6328/3.39 microm and 600-grit Armak Co. for 10.6 microm radiation.
• Found particle density (filling factor) is more critical for Lambertian approximation than grit size.
• Achieved good Lambertian approximations at small angles of incidence, but performance degraded at 60 degrees.

Conclusions:

• Gold-plated sandpaper, specifically optimized grit sizes, can serve as a Lambertian reference reflector in the IR spectrum.
• Particle packing density significantly influences the degree of Lambertian behavior.
• The effectiveness of sandpaper reflectors is angle-dependent, performing best at lower incidence angles.