Optical sensing techniques for temperature measurement.

Temperature is an important parameter that needs accurate measurement. Theoretical descriptions of the fluorescence ratio method, fluorescence lifetime sensing, and interferometric methods for temperature measurement are given. Fluorescence lifetime sensing calibration plots have been developed for temperature measurement from 20°C to 600°C using Er(3+)-doped glass, and from 20°C to 90°C using Sm(3+)-doped CaF(2). Lifetime sensing results of Pr(3+)-doped YAG and Ho(3+)-doped fluoride crystals for temperature measurement are also summarized. Mach-Zehnder interferometer measurements revealed that the passage of a 300 mW laser beam of 915 nm changed the temperature of the Yb(3+)-doped YAG crystal by 7.1°C. The interferometer technique is useful for measuring absolute temperature changes in laser cooling studies.