Development of a compact sapphire fiber thermometer probe using fluorescent decay

A new constructed fiber thermometer probe using fluorescent decay is presented. The fluorescent material in the probe is substituted for by using a compact sapphire fiber, in which the end part is doped with some fluorescent dopant. The sapphire fiber is coupled with the normal silica fiber for signal transmission. Because the sapphire fiber is of enough length, the coupling can be made at a place away from the severe environment. Then the performance of the probe can be assured by the excellent physical properties of the sapphire fiber if only the doped end is ideally combined with the fiber itself. The sapphire fiber with Cr3+ doping in the end was grown using laser heated pedestal growth (LHPG) apparatus. Two kinds of doping methods were compared to achieve an ideally combined sapphire fiber. Using a high bright green LED as the stimulating light source, the fluorescence of the fiber with only end doped was measured using an optical multi-channel analyzer. The fluorescence at the wavelength of 694 nm can be clearly detected. Temperature dependance of the fluorescent decay is being determined between the temperature of 20 to 450 degrees Celsius, on which the temperature can be measured.