| dc.description.abstract | 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. | en |
