How to Use Reflectance Spectroscopy to Study Solid Samples

Reflectance spectroscopy is a powerful method to analyze diverse types of materials and environments. It works by measuring the light that bounces off the surface of a solid sample, while the rest of the light is either absorbed, scattered, or passed through. This interaction gives information about the composition of the sample.

In this article, we will explain some of the basic principles of reflectance spectroscopy, describe the common components and procedures of a spectrometer system, and show an example application where reflectance spectroscopy is used to check the quality of a product.

Specular and Diffuse Reflectance

The way light reflects from the surface depends on how smooth or rough it is. Surfaces that are exceptionally smooth or shiny, like mirrors, optical parts, thin films, and some metals, have specular reflectance, which means the light reflects in the same direction as it came from (Figure 1). Surfaces that are rough or matte, like paper, powders, and grains, have diffuse reflectance, which means the light reflects in all directions (Figure 1). Some surfaces, like plastic beads, have both specular and diffuse reflectance, which is called total reflectance.

It is important to know the difference in reflectance types of the samples that need to be analyzed, because it affects how to set up the best spectral system to measure them.