Abstract
Low noise, high power single-frequency lasers and amplifiers are key components of interferometric gravitational wave detectors. One way to increase the detector sensitivity is to increase the power injected into the interferometers. We developed a fiber amplifier engineering prototype with a pump power limited output power of 200 W at 1064 nm. No signs of stimulated Brillouin scattering are observed at 200 W. At the maximum output power the polarization extinction ratio is above 19 dB and the fractional power in the fundamental transverse mode (TEM 00) was measured to be 94.8 %. In addition, measurements of the frequency noise, relative power noise, and relative pointing noise were performed and demonstrate excellent low noise properties over the entire output power slope. In the context of single-frequency fiber amplifiers, the measured relative pointing noise below 100 Hz and the higher order mode content is, to the best of our knowledge, at 200 W the lowest ever measured. A long-term test of more than 695 h demonstrated stable operation without beam quality degradation. It is also the longest single-frequency fiber amplifier operation at 200 W ever reported.
Highlights
In 2016, the first direct observation of gravitational waves by interferometric gravitational wave detectors (GWD) was reported [1]
We developed a fiber amplifier engineering prototype with a pump power limited output power of 200 W at 1064 nm
Single-frequency fiber amplifiers are promising laser sources to address the challenging requirements of the next-generation GWDs
Summary
In 2016, the first direct observation of gravitational waves by interferometric gravitational wave detectors (GWD) was reported [1]. Current state-of-the-art GWDs, e.g., the advanced LIGO (aLIGO) detectors, use solid-state injection-locked Nd:YAG ring oscillators to achieve up to 200 W optical power [5] These solid-state lasers (SSL) fulfill the power and noise requirements but have disadvantages regarding usability, maintenance procedures and further power scaling. Fiber amplifiers enable very high output power levels and fulfill GWD requirements regarding low noise levels and exceptional beam quality (above 90 % TEM00-mode content). They produce low and well distributed heat load. In a first experimental step a fiber amplifier was built, which demonstrated excellent beam quality (94 % TEM00-mode content at 200 W), high polarization extinction ratio (PER) of >20 dB , and a maximum output power of 300 W [16] (approximately 250 W SBS-free). The performance of the engineering prototype is discussed within the remaining sections of this paper
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