Differences in reflectivity values

Is one angle vertical and the other horizontal?

No - they are both horizontal 

1. Angular Resolution:

   • The UMA provides the ability to move the detector and the sample independently of each other, allowing multi-modal measurements without moving the sample.
   • The angular resolution for setting the sample angle is 0.02°. When you measure in increments of 10 degrees or 2 degrees, you’re effectively rounding the sample angle to the nearest multiple of those increments. This rounding can lead to slight variations in the measured reflectivity.

2. Sample Surface Characteristics:

   • Reflectance measurements are sensitive to the surface properties of the sample. Even small variations in surface roughness, microstructure, or contaminants can affect the reflectivity.
   • At different angles, the sample surface interacts with light differently. For example, at shallow angles, surface imperfections may scatter light more effectively, affecting the measured reflectance.

3. Wavelength Dependency:

   • The wavelength range you’re scanning (200 nm to 2500 nm) plays a role. Different materials exhibit varying reflectance behavior across this range.
   • Some materials may have strong absorption or interference effects at specific wavelengths, leading to fluctuations in reflectivity.

4. Polarization Effects:

   • The UMA uses wire grid polarizers to ensure high polarization accuracy. However, polarization can impact reflectance.
   • Depending on the sample’s anisotropic properties, the reflectivity may vary with polarization direction.

5. Instrument Stability and Baseline:

   • Although you mention using the same baseline, small instrument drifts or variations can occur over time.
   • Ensure that the instrument is well-calibrated and stable during measurements.

6. Environmental Factors:

   • Even within a 24-hour window, environmental conditions (temperature, humidity, etc.) can subtly affect measurements.
   • Changes in ambient light or vibrations may contribute to variations.

7. Measurement Precision:

   • The Cary UMA provides unprecedented data quality in terms of accuracy and precision. However, no measurement system is entirely free from noise.
   • Variations in the sample setup, alignment, or handling can introduce minor discrepancies.

It may be sample related. We ordered reference mirrors and will attempt analysis using those