{'fraction_non_alphanumeric': 0.019965277777777776, 'fraction_numerical': 0.006076388888888889, 'mean_word_length': 4.974093264248705, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Laser metrology for high stability optical bench characterization

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. 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. In answer to these requirements, SAGEIS-CSO has proposed a system consisting of a frequency stabilised laser, an optical coupler, two optical sensor heads named MOUSE I and a detection unit. The delivered information is a longitudinal displacement measurement between the sensor and its joint retroreflector. Verification of the resolution by tests has given a value of about 15 pm in a 15 Hz pass band. Displacement repeatability versus temperature has been checked before tests campaign and in the final configuration, giving a value between ±1.4 nm/K and ±1 nm/K. These excellent performances allowed the sensor to qualify the stability of the HSOB.