Technique for measuring the reflectance of irregular, submillimeter-sized samples

Area of Science:

• Spectroscopy
• Optical Physics
• Materials Science

Background:

• Accurate optical characterization of small, irregular samples is crucial for understanding material properties.
• Existing techniques often struggle with sample size limitations and complex scattering effects.

Purpose of the Study:

• To develop and validate a versatile technique for measuring the near-normal incidence reflectance of submillimeter-sized, irregular samples.
• To cover a broad spectral range from the far-infrared to the visible spectrum.
• To enable measurements at cryogenic temperatures (10–300 K).

Main Methods:

• Utilized a modified Michelson interferometer or grating spectrometer.
• Employed nonreflecting cones for sample and reference mirror mounting.
• Implemented in situ gold or aluminum evaporation for scattering correction.
• Applied Mie theory to estimate and correct for diffraction effects.
• Interchanged sample and reference positions using a 90° rotation with mechanical stops.

Main Results:

• The technique successfully measures reflectance from 40 cm(-1) to 40000 cm(-1) between 10 K and 300 K.
• Scattering and diffraction effects were corrected, allowing for accurate measurements.
• Calculations indicate that the ratio of backscattered intensities approximates specular reflectance for samples ~1 mm in diameter.

Conclusions:

• The developed technique offers a reliable method for characterizing the optical properties of small, irregular samples.
• The approach is suitable for a wide range of materials and experimental conditions.
• This method enhances the ability to study material behavior across different spectral regions and temperatures.