The Laser Interferometer Space Antenna (LISA) is a large-scale space mission design to directly measure gravitational waves using laser interferometry techniques. The constellation of three spacecraft, each separated by 2:5 Gm, will follow a heliocentric orbit with a constant distance from Earth (~20°). Light exchanges between the spacecraft will be enabled by 300mm telescopes used to simultaneously transmit and receive. Each telescope is part of the interferometer, and each must meet tight requirements on its dimensional stability; below 1pm= pHz in the LISA band, μm-length stability over 10 years of mission duration, and below ppb backscatter of the transmitted light. Here, we present our progress in developing ground support equipment for the LISA telescope ground verification. We also report on recent experimental results of the dimensional stability for the telescope test structure; a key part of the ground support equipment, and simulations of the optical design and internal and external alignment tolerances of the test structure and the telescope within it.
Modern observatories including ultra-stable spectrographs, optical telescopes and gravitational wave observatories rely on ultra-stable structures to meet their science objectives. These structures must exhibit pm to nm level length stability over a few seconds to a few hours and m-level length stability over mission duration of several years in some cases. The use of ultra-low CTE glass substrates provide the required stability while being highly fragile, having limited adaptability while driving turnaround times longer. We characterized structures made using materials that can provide the required stability while improving on the adaptability, turnaround times, structural mass and strength. These include a compound structure made using ALLVAR Alloy, a metal with a negative CTE, a second structure made of HB-Cesic, a full-ULE structure and a metal-ULE hybrid structure. In this work, we present a comparative analysis of the measured length noise and the long-term length stability for these structures.
In this paper, we report on our study of UV-VIS absorption spectroscopy in suspended-core optical fibres (SCFs) filled with organic-dye solutions. We compare two different dye classes, the anionic dye - bromophenol blue sodium salt (BB) and cationic dye - oxazine 725 perchlorate (OX). While the results obtained with BB are in a good agreement with the spectra measured in a standard reference cuvette, those obtained with OX are different and reveal much stronger absorption of light than in cuvettes. This stronger absorption indicates accumulation of the dye molecules on the short section of the core close to the end of the fibre. This observation demonstrates difference in physicochemical properties of the two dye classes and is important for the development of chemical sensors based on SCFs.