Applications of Fumed Silica Integrating Cavities
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Integrating cavities have been used in radiometric and photometric measurements since their creation by Frederick Ulbricht in 1900. Modern commercial integrating cavities use Spectralon, a PTFE-based diffuse reflector with a reflectivity > 97.5% from 350-1600 nm, as a diffuse reflector. However, Spectralon’s reflectivity diminishes in the ultraviolet which limits the potential for short wavelength experiments. The high reflectivity of a recently characterized diffuse reflector, fumed silica, in the UV, as well as the VIS-NIR, has improved the sensitivity of integrating cavity based measurements. With the increased ultraviolet reflectivity, measurements of the optical absorption coefficient of pure water were performed using an improved version of the Integrating Cavity Absorption Meter (ICAM), the ICAM-II. The ICAM-II replaces Spectralon of the inner and outer cavity from the original ICAM with fumed silica powder. The fumed silica diffuse reflector, along with increased volume in the sample region, extended the optical pathlength by a factor of 2.5 at 532 nm and much more in the UV at 250 nm. Scattering independent measurements of the absorption coefficient of pure water from 250-550 nm were made with this instrument. Furthermore, the increased reflectivity of fumed silica, the new scattering-independent integrating cavity ring-down spectroscopy technique can be applied to measuring the absorption coefficient of highly scattering media. ICRDS measurements were made of various biological cells and tissues. The results from these measurements were compared with the well-established Inverse Adding-Doubling (IAD) technique.
Mason, John David (2016). Applications of Fumed Silica Integrating Cavities. Doctoral dissertation, Texas A & M University. Available electronically from