Sample (usually smooth mirror like

Sample (usually smooth mirror like surface material)

In external reflectance, incident radiation is focused onto the sample and two forms of reflection
can occur – diffuse and specular. Energy from the incident beam that penetrates one or more
particles is reflected in all directions and this component of light is called diffuse reflectance.
On a rough or irregular surface material, such as a powder, specularly reflected light is a minor
contributor to the overall signal. Therefore Specac accessories are optimised to increase
collection of the diffuse reflectance component and decrease the specular component. Collection
of the diffusely scattered light can be made directly from a sample or by using an abrasive
sampling pad for intractable samples. Many samples will give diffusely reflected spectra including
powders, fibers or matt surfaced samples such as textiles.
There are two types of Specac diffuse reflectance accessories, the Minidiff Plus and the Selector.
Specifically, the Selector has an “off axis” optical design to select for diffusely reflected light. It
can also be extended in its capabilities for the study of samples at elevated temperatures and
pressurised conditions by using with its complementary Environmental Chamber accessory.