Comparison Study of Radiation-Resistant Polarization-Maintaining PANDA Fibers With Undoped- and N-Doped-Silica Core

For the first time, radiation-induced absorption (RIA) of light is compared in two types of polarization-maintaining PANDA fibers having 1) undoped-silica core and F-doped-silica cladding, or 2) N-doped-silica core and undoped-silica cladding. RIA at λ = 1.55 μm is compared under γ-irradiation and post-irradiation recovery at room temperature (RT) and −60 °C. The post-irradiation RIA decay at RT is used to extrapolate RIA to the postulated end of the PANDA space mission (15 years) with the help of the "n th -order kinetic" model. The RIA extrapolation values for both PANDA types are found to be comparable. RIA spectra are measured in the PANDAs in the spectral range ∼0.5-4 eV in the process of both γ-irradiation and recovery; then the spectra are deconvolved into Gaussians components. The RIA spectra of both PANDA types are found to be composed of inherent and strain-assisted self-trapped holes (STHs), some undoped PANDAs demonstrating, in addition, a long-wavelength RIA tail affecting λ = 1.55 μm. No N-related color centers are revealed. Finally, RIA at λ = 1.55 μm is compared upon pulsed-X-ray irradiation. Undoped PANDAs are found to feature much smaller RIA at RT at post-pulse times larger than ∼40-1000 μs, whereas at smaller times, an N-doped PANDA proved to be superior. At −60 °C and at t > 1 ms, both PANDA types demonstrate approximately equal RIAs. Thus, the experiments showed that the two PANDA types are quite comparable, each type having its own advantages and disadvantages.