Date of Award

3-24-2016

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Briana J. Singleton, PhD.

Abstract

This is the first published research focused on the impact of gamma and mixed gamma/neutron radiation on an actively lasing ytterbium-doped fiber laser. While the gain medium of the ytterbium-doped fiber laser was irradiated, the power was measured in-situ and the spectrum was recorded intermittently. Two radiation sources were used, a 60Co cell and a reactor. Three irradiation experiments were conducted per radiation source; pristine fibers were used for the first two experiments, and fibers from the second experiment were re-irradiated for the third experiment. The results indicate that as the total dose increased linearly with time, the laser experienced an exponential decay in power with a maximum power loss of 99.84% (at which time it was no longer lasing), and the lasing wavelength blueshifted up to 15 nm. The laser's initial power affects how much the radiation induced attenuation in the fiber. The laser, when exposed to 145 krad(Si), experienced less attenuation with a higher initial power than with a lower initial power. Power recovery experiments were conducted post-irradiation with the fiber laser off and actively lasing. Passively, the power recovered 100 and 550 µW in 18 and 90 hours respectively. Active recovery experienced the same 100 µW recovery in 9.3% of the time (10 min), and total power recovery of 12.6% and 4.4% for YDF1 and YDF2 respectively. The active recovery rate declined as the number of days following irradiation increased. This indicated a saturation of recovery after the less stable color centers were annealed. The active recovery rate for the re-irradiated fiber (gamma only) decreased 31% from the recovery rate just prior to re-irradiation.

AFIT Designator

AFIT-ENP-MS-16-M-079

DTIC Accession Number

AD1053917

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