Supercontinuum-laser diffuse reflectance spectroscopy in conjunction with an extended Kubelka-Munk model-a methodology for determination of temperature-dependent quantum efficiency in highly scattering and fluorescent media.

Temperature-dependent diffuse reflectance measurements on Cr-doped α-alumina monoliths have been performed using supercontinuum-laser illumination and CO2-laser heating. These measurements have been interpreted using an extended Kubelka-Munk (K-M) model describing diffuse-light propagation in highly scattering and fluorescent media to assess the temperature dependence of fluorescence quantum efficiency. Analysis of experimental results has provided a qualitative understanding of the temperature-dependent conditions for model applicability and also suggests methods for using supercontinuum-laser diffuse reflectance spectroscopy for detection of unknown fluorescent dopants.

Experimental characterization and physics-based modeling of the temperature-dependent diffuse reflectance of plasma-sprayed Nd2Zr2O7 in the near to short-wave infrared.

Supercontinuum-laser illumination in conjunction with CO2-laser heating has been implemented to measure the near to short-wave infrared (970-1660 nm) diffuse reflectance of plasma-sprayed Nd2Zr2O7 as a function of temperature. Owing to the broadband nature of this experimental technique, the diffuse reflectance of plasma-sprayed Nd2Zr2O7 has been measured at many wavelengths and has been shown to decrease with increasing temperature. A physics-based model for diffuse reflectance predicated on the crystal/electronic band structure of highly scattering semiconductor materials has been constructed to interpret the results of these measurements. Baseline materials characterization has also been performed to assist in the development of crystal/electronic band structure-optical property relationships that could be useful for the design of next-generation environmental barrier coatings. This characterization has included ambient and non-ambient x-ray diffraction as well as room-temperature, integrating-sphere diffuse reflectance spectroscopy.

Temperature-dependent diffuse reflectance spectroscopy of plasma-sprayed Cr-doped α-alumina using supercontinuum laser illumination and CO2 laser heating.

This study presents results for the high-temperature (up to 1550 K) optical properties of polycrystalline Cr-doped α-alumina materials. Diffuse reflectance spectra in the wavelength range of 510-840 nm are presented as a function of temperature to illustrate changes to the optical behavior of these materials including a previously unreported thermally activated splitting of the U-band absorption (A24→T24) in octahedrally coordinated Cr3+. Measurements were made using a unique laser-based approach for high-temperature solid-state spectroscopy, involving front-side supercontinuum laser illumination and back-side CO2 laser heating. This approach required development of samples that could withstand related thermal stresses, and measurements were made on plasma-sprayed, Cr-doped α-alumina monoliths. Measured spectra are interpreted, in part, using published optical spectra for ruby; agreement between results here with those obtained using more traditional methods serves to validate the measurement methods used for this work.

Lidar measurements of solid rocket propellant fire particle plumes.

This paper presents the first, to our knowledge, direct measurement of aerosol produced by an aluminized solid rocket propellant (SRP) fire on the ground. Such fires produce aluminum oxide particles small enough to loft high into the atmosphere and disperse over a wide area. These results can be applied to spacecraft launchpad accidents that expose spacecraft to such fires; during these fires, there is concern that some of the plutonium from the spacecraft power system will be carried with the aerosols. Accident-related lofting of this material would be the net result of many contributing processes that are currently being evaluated. To resolve the complexity of fire processes, a self-consistent model of the ground-level and upper-level parts of the plume was determined by merging ground-level optical measurements of the fire with lidar measurements of the aerosol plume at height during a series of SRP fire tests that simulated propellant fire accident scenarios. On the basis of the measurements and model results, the Johns Hopkins University Applied Physics Laboratory (JHU/APL) team was able to estimate the amount of aluminum oxide (alumina) lofted into the atmosphere above the fire. The quantification of this ratio is critical for a complete understanding of accident scenarios, because contaminants are transported through the plume. This paper provides an estimate for the mass of alumina lofted into the air.