Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
Hexagon
A hexagonal quasi-monolithic optical bench has been built to demonstrate critical technologies in LISA on the ground.
A hexagonal quasi-monolithic optical bench consists of three fiber injectors and six beam splitters. The three beams are first split by beam splitters right after the fiber injectors. Then, they interfere pairwise at combining beam splitters and end up with three optical beatnotes. Their phases are extracted via photoreceivers and phasemeters and enable an optical three-signal test in order to demonstrate their precision and linearity over a high dynamic range.
A hexagonal quasi-monolithic optical bench consists of three fiber injectors and six beam splitters. The three beams are first split by beam splitters right after the fiber injectors. Then, they interfere pairwise at combining beam splitters and end up with three optical beatnotes. Their phases are extracted via photoreceivers and phasemeters and enable an optical three-signal test in order to demonstrate their precision and linearity over a high dynamic range.
This setup generates three optical beat notes pairwise from three beam sources phase-locked to each other and conceptually acts as a miniature scale LISA. With this ultra-stable testbed, essential devices like phasemeters and photoreceivers can be tested at required pico-meter precisions [1]. Furthermore, the experiment is used to test elements of the LISA data analysis pipeline such as Kalman filtering, time-delay interferometry ranging, interpolation, and others.
The latest demonstration of clock synchronization with this setup reached nano-second accuracy and verified specific noise coupling mechanisms, e.g. interpolation errors and aliasing effects, stemming from LISA data analysis [2]. To incorporate ranging into this experiment, we are currently finalizing the design of the so-called delay-locked loop on our phasemeter.
Finally, due to the central role the Hexagon plays in testing core technology for LISA, an improved second version of the Hexagon has been designed and is now ready to be constructed, not only for redundancy purposes but also to be able to run two test campaigns in parallel.
Literature
1.
Schwarze, T. S.; Fernández Barranco, G.; Penkert, D.; Kaufer, M.; Gerberding, O.; Heinzel, G.: Picometer-Stable Hexagonal Optical Bench to Verify LISA Phase Extraction Linearity and Precision. Physical Review Letters 122 (8), 081104 (2019)
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