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DIRECTED
ENERGY
PROFESSIONAL
SOCIETY
Abstract: 25-Symp-097
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UNCLASSIFIED, PUBLIC RELEASE
In-situ spectroscopic thermometry of gas-filled hollow-core fiber for applications to high-energy lasers
Hollow-core optical fibers (HCF) are promising candidates for high-energy laser (HEL) beam delivery, owing to factors including an inherently high threshold for optical nonlinearities, reduced scattering, and high-power handling capabilities. Additionally, novel mid-IR laser sources using gas-filled HCF, where heating occurs as a direct result of the quantum defect, have been explored. Although scattering and absorption within the HCF is low, heating may still occur when guiding multi-kW class HELs, which can have deleterious effects on power throughput and damage the fiber. In this work, we present an in-situ, spectroscopic temperature diagnostic, in which acetylene is introduced to the HCF to function as a temperature probe. Leveraging the broadband (>30nm), high-resolution (~100 MHz), and rapid acquisition technique of dual-comb spectroscopy (DCS), we measure the absorption spectrum of an acetylene rovibrational band within the HCF. From the measured absorption spectrum, the temperature of the gas and therefore the HCF can be extracted. We will describe ongoing efforts to develop this diagnostic as well as the data analysis methods employed to accurately estimate the temperature from the absorption spectrum.
UNCLASSIFIED, PUBLIC RELEASE
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