The value of diffuse reflectance as an infrared or near-infrared spectroscopic sampling procedure has been limited by the low efficiency of accessories designed for it. In terms of signal-to-noise ratio, these average 2–6% for integrating spheres and 10–12% for various ellipsoidal mirror arrangements. Much better performances, up to 37% efficiency, can be obtained by optimizing a concentric confocal ellipsoidal mirror arrangement by using a very large central opening in the amular collector mirror, and adapting the throughput of the detector to the geometry of the collected beam.
