Abstract
Improvements have been made in the Integrating Cavity Absorption Meter (ICAM). The ICAM is used to measure very small optical absorption coefficients (0.001m⁻¹), virtually independent of scattering effects. Optical absorption is measured by employing isotropic, homogeneous illumination of the sample; this eliminates the scattering problems associated with measuring the optical absorption of pure water. We optimize the early versions of the ICAM to enhance stability, sensitivity, and operational wavelength regions. The main part of this research work involves a complete reassembling of the optical components, innovations in the data acquisition/LabVIEW software, and instrument reconstruction associated with the new signal acquisition procedures. The integrating cavity assembly consists of two concentric and coaxial integrating cavities, that is, an integrating cavity within an integrating cavity. We use optical fibers to sample the irradiances in the inner cavity and outer cavity. And we use an extremely compact two-window double-channel light chopper to separate the signals proportional to the illumination in the two cavities. The negligible effects of elastic scattering result from the fact that this scattering does not remove any energy from the cavity combined with our uses of isotropic illumination. The latter is achieved by employing a high reflectivity (greater than 0.99) lambertian material to build the integrating cavity. We provide complete documentation of the apparatus, both the hardware and software components of the ICAM system, and present results for the absorption spectra of pure water between 380 and 750 nm.
Cui, Liqiu (2000). Improved integrating cavity absorption meter. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2000 -THESIS -C842.