Excimer and Nd:YAG laser-based systems incorporating air-cooled fiber-optic probes for turbine engine high-temperature fluorescence intensity imaging and fluorescence decay lifetime thermometry measurements

Abstract In this work, a description for a pulsed Nd:YAG laser-based system operating at 266 nm (generated by passing the 1.064 μm fundamental wavelength through two non-linear KD*P crystals ) for non-contact high-temperature 1-D thermographic phosphors fluorescence intensity and decay lifetime measurements is provided. Also, the article provides a description for a pulsed XeCl excimer laser-based system operating at 308 nm (XeCl) for non-contact high-temperature 2-D thermographic phosphor fluorescence intensity measurements. Both laser systems incorporate air-cooled fiber-optic probes for delivering the excitation laser energy to an engine part coated with thermographic phosphor (Y 2 O 3 :Eu or YAG:Tb). Furthermore, the air-cooled probe used with the Nd:YAG laser measurement system incorporates nine 1000 μm core diameter fibers for guiding the emitted fluorescence radiation to the photomultiplier detection system. Whereas, the air-cooled probe used with the excimer laser-based system incorporates a coherent fiber-optic bundle endoscope for imaging the engine parts. The honeycomb pattern (pixelation effect) imposed on images captured by the CCD camera (12 × 13.7 μm pixel size) coupled to the endoscope eyepiece is removed by applying digital high-frequency spatial filter to the image 2-D Fourier transform. Moreover, fluorescence decay lifetime and intensity measurements collected from Y 2 O 3 :Eu and YAG:Tb phosphors as a function of temperature are discussed.