Publications

Abstract not provided.

Fibers doped with rare-earth constituents such as Yb3+ and Er3+, as well as fibers co-doped with these species, form an essential part of many optical systems requiring amplification. This study consists of two separate investigations examining the effects of gamma-radiation-induced photodarkening on the behavior of rare-earth doped fibers. In one part of this study, a suite of previously irradiated rare-earth doped fibers was heated to an elevated temperature of 300°C and the transmittance monitored over an 8-hour period. Transmittance recoveries of ~10 - 20% were found for Er3+- doped fiber, while recoveries of ~5 - 15% and ~20% were found for Yb3+- and Yb3+/Er3+ co-doped fibers, respectively. In the other part of this study, an Yb3+-doped fiber was actively pumped by a laser diode during a gamma-radiation exposure to simulate the operation of an optical amplifier in a radiation environment. The response of the amplified signal was observed and monitored over time. A significant decrease in amplifier output was observed to result from the gamma-radiation exposure. © 2009 SPIE.

Rare-earth-doped fibers, such as Er3+- and Yb3+-doped aluminosilicates can be advantageous in space-based systems due to their stability, their high-bandwidth transmission properties and their lightweight, small-volume properties. In such environments the effect of ionizing-radiation on the optical transmission of these fibers is of paramount importance. For the present work, gamma-radiation experiments were conducted in which un-pumped Yb3+ and Er3+ doped sample fibers were irradiated with a Cobalt-60 source under different dose-rate and temperature conditions. In-situ spectral transmittance data over the near IR was monitored during the irradiations for total doses of up to tens of krad (Si). It was found that there was a dose-rate dependence in which higher rates resulted in more photodarkening. Higher temperatures were not found to significantly affect the rate of photodarkening at the dose rates used.

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Exposure of optical materials to transient-ionizing-radiation fields can give rise to transient and/or permanent photodarkening effects. In laser materials, such as YAG, such induced optical loss can result in significant degradation of the lasing characteristic of the material, making its selection for optical device applications in radiation environments unfeasible. In the present study, the effects of ionizing radiation on the optical response of undoped and 1.1% Nd-doped single-crystal and polycrystalline YAG have been investigated. In the undoped materials it is seen that both laser materials exhibit significant loss at the 1.06 ?m lasing wavelength following exposure to a 40 krad, 30 nsec pulse of gamma radiation. In the undoped single-crystal samples, the transmission loss is initially large but exhibits a rapid recovery. By contrast, the undoped polycrystalline YAG experiences an initial 100% loss in transmission, becoming totally opaque at 1.06 ?m following the radiation pulse. This loss is slow to recover and a large residual permanent photodarkening effect is observed. Nd-doping improves the optical response of the materials in that the radiation-induced optical loss is substantially smaller in both the polycrystalline and single-crystal YAG samples. Preliminary results on the radiation response of elevated-temperature samples will also be reported.