Fabrication of ruby sensor probe for the fiber-optic thermometer using fluorescence decay

Ruby single crystals have been grown successfully from the melt droplet on the sapphire crystal fibers as the sensor head directly coupled with optical fiber for the thermometer applications using fluorescence decay. In this fabrication process, droplets of slurry of ruby powders are formed on the end of the sapphire crystal fiber and are dried, sintered, and then melted and solidified in a floating-zone furnace. The photoluminescence (PL) lifetime of the ruby sensor head varies from τ=3.8 to 2.5 ms with the Cr 3+ concentrations from 0.07 to 1.0 at. %. The ruby crystal with a Cr 3+ concentration of 0.35 at. % is found to be the most suitable sensor head having the longest PL lifetime. The temperature coefficient of the fiber-optic thermometer equipment using the directly coupled ruby sensor head with a Cr 3+ concentration of 0.35 at. % is −12.4 μs/K.