Diffuse reflecting material for integrating cavity spectroscopy, including ring-down spectroscopy

We report the development of a diffuse reflecting material with measured reflectivity values as high as 0.99919 at 532 nm and 0.99686 at 266 nm. This material is a high-purity fumed silica, or quartz powder, with particle sizes on the order of 40 nm. We demonstrate that this material can be used to produce surfaces with nearly Lambertian behavior, which in turn can be used to form the inner walls of high-reflectivity integrating cavities. Light reflecting off such a surface penetrates into the material. This means there will be an effective "wall time" for each reflection off the walls in an integrating cavity. We measure this wall time and show that it can be on the order of several picoseconds. Finally, we introduce a technique for absorption spectroscopy in an integrating cavity based on cavity ring-down spectroscopy. We call this technique integrating cavity ring-down spectroscopy.