The HSOB GAIA: a cryogenic high stability cesic optical bench for missions requiring sub-nanometric optical stability

Laser metrology for high stability optical bench characterization

“…The very good performance of SAGEIS-CSO laser metrologic system has allowed the HSOB tests to be brought to a successful conclusion [1]. This test campaign has also formed a good basis to understand the technical limitations of this system when dedicated to the measurements of sub-nanometric displacements.…”

“…measuring arm output (2) measuring arm input (3) injection point (1) interferometric area single-mode waveguide output single-mode waveguides (6) curved reference guide reference photometric arm (5) measuring photometric arm (4) : junction measuring arm output (2) measuring arm input (3) injection point (1) interferometric area single-mode waveguide output single-mode waveguides (6) curved reference guide reference photometric arm (5) measuring photometric arm (4) : junction a straight input waveguide, in which we inject the optical beam coming from a single-mode fibre; a splitting junction, dividing this beam into two arms: the measuring one (straight) and the reference one (curved). This junction can be an asymmetric Y-junction or a directional coupler; a return straight waveguide, in which we collect the measuring beam coming back from the corner cube; a loop, allowing to drive the reference beam into an area where it interferes with the measuring beam.…”

“…-Run 1: thermal expansion of arm -Y -Run 2: thermal expansion of arm +Y -Run 3: thermal expansion of arm -Y Comparison between results of run 1 to run 2, run 2 to run 3 gave the wanted information on the thermal behaviour of the CeSiC optical bench (see results in [1]).…”

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In the framework of activities dedicated to the GAIA mission, Alcatel Alénia Space has developed a High Stability Optical Bench (HSOB) made with CeSiC. A key criterion was the stability of its geometry, requiring it to be confirmed by tests [1]. The idea was to use a metrologic system able to work in a primary vacuum environment with sub-nanometric resolution and reproducibility compliant with the expected performances of the bench.

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Laser-dilatometer calibration using a single-crystal silicon sample

“…This material combination was proved to offer the needed dimensional stability at the nanometer level at room temperature. [7] The Global Astrometric Interferometer for Astrophysics [8] (GAIA) mission is another example where dimensional stability is critical: its mirrors and support are made of silicon carbide structures and need stabilities at the picometer and picoradian level in a cold environment [9,10] (%100 K). The future spaceborne gravitational wave detector, LISA, will also require extremely stable optical assemblies such as optical benches and telescopes.…”