B.W. Noel

Fiber Optic Pulsed Laser Delivery For Remote Measurements

The results of a research program on the delivery of high-peak-power laser light via fiber optics are presented. We discuss the influence of the host medium and the optical signals on the choice of fiber materials, complemented by a consideration of the measurement environments effects on the quality of the data. We pay close attention to the choice of input/output beam/fiber coupling optics, nonlinear processes in the core, measurement system noise, and baseline drifts. Useful discussions of pulsed laser damage to optical fibers and data for optimization of a given fiber optic laser beam delivery system are given. As an example, details are given of the optical and instrumentational aspects of a particular fiber optic system developed for remote sensing of pressures and temperatures of UF6 gas in an operating advanced gas centrifuge.

Fiber sensor design for turbine engines

Determination of blade temperatures in the high-speed and turbulent environment of a turbine engine is difficult using standard pyrometry techniques because of the presence of high- temperature flame and the reflective nature of the inspection surfaces. A technique utilizing thermographic phosphor compounds bonded to engine vanes and turbine blades is presented that mitigates the negative effects of blackbody radiation while potentially allowing near real- time acquisition of blade temperature information. Specialized single and dual fiber-optic probes were designed to interrogate both fixed and rotating surfaces by delivering ultraviolet light from a quadrupled Nd:YAG (266 nm) laser to phosphor coatings consisting of Y2O3:Eu, YVO4, and YAG:Tb ceramic compounds. This technique utilizes the temperature- dependent fluorescent emission of a ceramic phosphor coating to discern the temperature of the interrogated surface. By using these methods, surface temperature measurements to 1200 degree(s)C are achievable in the combustion environment.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Evaluating thermographic phosphors in an operating turbine engine

The results of a field test in a commercial turbine engine showed that we can remotely measure the temperature of engine components in operating engines using thermographic phosphors. The remote-measurement method exploits the temperature dependence of the characteristic decay time of the laser-induced fluorescence of thermographic phosphors. This paper summarizes recent work leading up to and including a successful test of the thermographic-phosphor method in an operating turbine engine.Copyright

Laser‐induced breakdown of UF6 and its application to flow diagnostics

Breakdown of gaseous UF6 can be produced with relatively low fluence (approximately 106 W/cm2) near‐uv pulsed laser light. A broad spectrum is produced consisting of hundred of atomic (U1 and U11) lines. Following breakdown, particles are formed from the dissociation/ionization products and the sample volume remains ionized for a long time. This sample volume is elevated in temperature, and a shock wave is produced. Other pertinent details are presented. A schlieren technique is described for observing the motion, hence velocity, of the temperature defect and shock wave. Also given is a flow visualization method based on imaging a long‐lived emission component with a gated (≥10‐ns) image intensifier system. These and other methods are prospective ways to perform flow diagnostics in gas centrifuges.

Phosphor Thermometry of Gas Turbine Surfaces

This paper describes a nondestructive method for thermometry applicable to ceramic surfaces and coatings. To date our primary application has been to turbine engine and air vehicle surfaces. This method makes use of thermally sensitive phosphors many of which, as it turns out, are also ceramics. These materials fluoresce when suitably illuminated by ultraviolet light. The fluorescence intensity and decay time are well-behaved functions of temperature and therefore serve as reliable indicators of the temperature of the substrate to which the fluorescing material is attached. It is a non- contact method in that the light delivery and collection optics can be remotely located. A range of phosphor materials have been tested and any temperature ranging from 8 to 1900 K can be measured by selection of the appropriate phosphor. Turbine blades, vanes, thermal barrier coatings, and panels are examples of surfaces which have been diagnosed to date in either engine or engine-simulation facilities. A variety of coating methods are used, including electron-beam deposition, radio-frequency sputtering, and curing with inorganic binders. This paper summarizes the results to date and status of this technology.