A New Diffuse Reflecting Material with Applications Including Integrating Cavity Ring-Down Spectroscopy

Abstract

We report the development of a new diffuse reflecting material with measured diffuse reflectivity values as high as 0.9992 at 532 nm, and 0.9969 at 266 nm. These values are, to the author’s best knowledge, the highest diffuse reflectivity values ever produced. The material is a high-purity fumed silica, or quartz powder. We demonstrate the application of this new material to several areas of integrating cavity enhanced spectroscopy, including absorption, Raman, and fluorescence spectroscopy. In addition, we demonstrate a new spectroscopic technique based on cavity ring-down spectroscopy using an integrating cavity made of our new diffuse reflector. This technique, which we call integrating cavity ring-down spectroscopy (ICRDS), has tremendous potential for sensitive absorption measurements of low-absorbing samples, even when there is strong scattering. Results for measurements of the absorption coefficient of retinal pigment epithelium cells using this ICRDS technique are also presented. Finally, we discuss the importance of the “wall-time” when considering the temporal response of an integrating cavity. Light reflecting off the inner wall of an integrating cavity actually penetrates into the diffuse reflecting material. Therefore, the light spends some time inside the cavity wall. We measure this wall-time via two independent methods, and show that it can be on the order of several picoseconds.