IR/DRS

Diffuse Reflection Spectroscpy

Diffuse reflection Spectroscopy

Diffuse Reflection Spectroscopy unlike the other reflection techniques is not based in a mirror like reflectance where the incident angle is equal to the reflected one, but for more complex sample surfaces that have a diffuse reflection in every direction. These complex spectra can be recorded with the aid of a high throughput illuminating system and especial optic systems to collect sufficient light for spectral analysis.

The technique has been done routinely in the UV-VIS region with integrating spheres, but Microptik develops also ellipsoids and paraboloids to collect the scattered radiation.

Even though this technique implies very complex optics for the collecting system with laborious and sometimes destructive sampling techniques, it can be used for certain applications in which the rest of the spectroscopy methods fail. Particularly effective when powders or rough surfaced samples are involved, two of the most important applications for which DRS are used, are to carry out catalysis studies and to follow chemical reactions such as coal oxidation.

Since DRS includes interaction of light in every conceivable way, the resulting spectra may exhibit typical features of transmission, external and/or internal reflection. One of the most characteristic and bothersome feature is the presence of reststrahlen (inverse) bands whose contrast can be reduced by sample grinding and dilution in non-absorbing powder such as KBr, KCl, Ge or Si. In addition, sample particle size, surface optical geometry and angle of illumination and observation affect incredibly the observed spectra so reproducibility and consistency in the preparation of the sample and the analysis conditions are vital. Further improvement of the spectra is achieved when low incident angles are employed.