An optical thermometer has been designed and developed at the "Laboratoire
d'optique Pierre-Michel Duffieux" (LOPMD, Pierre-Michel Duffieux
Optical Laboratory, CNRS-Université de Franche-Comté).
This thermometer, now in the final phase of characterization and miniaturization,
is designed to read the temperature of cryogenic liquids, such as
liquid nitrogen, oxygen or hydrogen, with a temperature range from
20K - 150K with a precision of 0.1K.
This
new generation of thermometer is based on the lifetime of the fluorescence
of a fluorophore composed of a calcium fluoride crystal doped with
a rare earth metal, Ytterbium. A simple law describes how the speed
at which fluorescence decays varies with temperature.
The
fluorophore immersed in the cryogenic fluid is excited by light from
a LED emitting at 370nm carried by a fiber-optic cable. Fluorescence
is captured by an array of fibers. The fluorophore is fixed to the
end of the fiber by a sol-gel procedure developed at the Ecole Nationale
Supérieure at Cachan.
In
its current configuration, the thermometer has a diameter of less
than two millimeters and the control unit is about the size of a box
of sugar cubes. Electricity consumption is about 1 Watt, and it can
easily be connected to computer network. Special attention has been
paid to its miniaturization and the reduction of its production cost.
