T. Duvaut

Multiwavelength infrared pyrometry : optimization and computer simulations

Abstract We present here a preliminary study concerning a multi-wavelength pyrometry method. This technique may be useful for temperature measurements on materials of unknown, selective, rapidly varying emissivity. From a (simultaneous) measurement of the thermal emission at N wavelengths, a fitting procedure leads to the simultaneous identification of the temperature and the spectral emissivity. We present first a comprehensive discussion of the various parameters influencing the accuracy of the method. Then a number of simulated experiments are calculated in order to test the efficiency of various emissivity models and to estimate the robustness of the method. It appears that measurements in the (thermal) infrared spectral range may yield satisfying temperature measurements down to T = 600 K.

Site-selective upconversion excitation of Er3+:KYF4

A spectroscopic study of the green (4S3/2 4I15/2) and blue (2P3/2 4I11/2) emissions from Er3+:KYF4 induced by a red tunable laser excitation is realized at liquid nitrogen temperature, for two Er3+ concentrations: 0.1 and 5 at.%. The emission spectrum can only be accurately interpreted by considering that it is due to two sites, whose contributions are successfully isolated using a two-step absorption process via 4I13/2 for the green emission and a three-step absorption process via 4I13/2 and 4S3/2, for the blue emission. The excited-state energy transfer prevails over the excited-state absorption at high concentration (5 at.%).

Optical pyrometry measurement on oxidized Zircaloy-4 cladding

In order to improve the safety of nuclear power plant, loss-of-coolant accident experiments are implemented in research reactor. In this framework, we develop an optical pyrometry device to measure surface temperature (700-1200°C) of Zircaloy cladding without contact. The whole set-up of the simplified device (under air, without radiation) and the measurement procedure including data treatment based on bichromatic pyrometry are presented, as well as results for various temperature levels. Temperature retrieval based on the hypothesis of emissivity ratio equal to a constant, is scanned over a large wavelength range. A rather constant surface temperature is obtained on the spectral range of measurement, confirming the relevancy of emissivity hypothesis. Differences between this non-contact temperature measurement and a complementary thermocouple temperature measurement are also discussed.

Temperature sensor for scanning thermal microscopy based on photoluminescence of microcrystal

A new sensor is developed for measuring local temperatures. This sensor is based on a thermal-resistive probe and on photoluminescence of crystal. The final purpose is to develop a device calibrated in temperature and capable of acquiring images of local temperature at sub-micrometric scale. Indeed, the sensor temperature can be obtained in two distinct ways: one from the thermal probe parameters and the other from the green photoluminescence generated in the anti- Stokes mode by the Er ions directly excited by a red laser. The thermal probe is in Wollaston wire whose thermal-resistive element is in platinum/rhodium. Its temperature is estimated from the probe electrical characteristics and a modelling. A microcrystal of Cd0.7Sr0.3F2: Er3+(4%)-Yb3+(6%) about 25μm in diameter is glued at the probe extremity. This luminescent material has the particularity to give an emission spectrum with intensities sensitive to small temperature variations. The crystal temperature is estimated from the intensity measurements at 522, 540 and 549 nm by taking advantage of particular optical properties due to the crystalline nature of Cd0.7Sr0.3F2: Er3+-Yb3+. The temperature of probe microcrystal is then assessed as a function of electric current in the thermal probe by applying the Boltzmanns equations. The first results will be presented and discussed.