Distributed crystal fiber sensing for extreme environments

Distributed sensing of temperature can be achieved by using time-correlated two-photon excited fluorescence (TPF). To assess the extension of this technique to single-crystal fibers for high-temperature applications, various aspects are considered including the two-photon absorption cross-section (delta), dopant density, and the geometry of single crystal fibers. By comparing the fluorescence yield for two-photon excitation with that for single-photon excitation of the same transition, delta for ruby was measured over the 0.8-1.2 mu m range with maximum room temperature values of 5.9 x 10(-3) GM for e-polarization and 4.6 x 10(-3) GM for o-polarization at 840 nm. It is shown that values of this magnitude are adequate for a practical TPF-based crystal fiber sensor to be realized.