Design optimization of fiber amplifiers exposed to high gamma-radiation doses

Abstract

I. INTRODUCTIONFiber lasers entered numerous applications due to their high efficiency and superior stability. Er-doped fiber lasers emitting around 1550 nm optical wavelength are capable to produce hundreds of Watts [1] and Millijoule pulse energy [2,3]. However, for space applications those lasers have to fulfill additional requirements set by the harsh environment, typically characterized by large temperature gradients, vibration and shock as well as different kinds of radiation. To meet those requirements, the realization of an all-fiber design and thus, an adjustment-free laser is most beneficial [4,5]. One of the most important aspects for long term operation in space is the influence of ionizing radiation, which typically leads to strong absorptions in active fibers [6,7]. As a result, radiation-resistant fibers are recommended [8,9]. Nevertheless, the performance of fiber amplifiers has to be considered including these radiation-induced absorption losses during mission lifetime.In this contribution, an experimental as well as a numerical study on an Er-doped single-clad fiber-based preamplifier system was conducted. Due to the low seed power and the high gain, the double-pass type setting is most sensitive to the influence of core-size, doping concentration and ionizing radiation. In section II, the performance of five different fibers is experimentally investigated and compared, followed by a numerical study on the impact of radiation-induced gain reduction in section III. The presented results can be conceived as a guideline how to design a low seed power high-gain preamplifier for use in space.