Thermo-optic and photoelastic effects on fiber optic interferometry during pulsed plasma radiation

Le résumé fourni par la source

Radiation-induced refractive index change in fiber optic materials presents challenges for photonic Doppler velocimetry and other high-resolution interferometric techniques at fusion research facilities such as the Z Machine (Sandia National Laboratories). Signal pollution, including phase shifts and artificial resonances, has been observed in many radiation-producing experiments yet remains largely unexplained. We use radiation, thermal, and mechanical simulation to show that these noise sources originate from a combination of the thermo-optic effect and cyclical photoelastic compression of the fiber core and cladding, dynamically altering the refractive index of the fiber. In contrast, thermal dilation and elongation of the waveguide are shown to be insignificant. By simulating the evolution of refractive index along the waveguide, the interferometric phase shifts observed in several experiments are successfully reproduced. Analytical approximations based on shock compression of silica also support the findings. The identification of these effects may allow for their mitigation in designing diagnostics for plasma-generating facilities.

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