Low loss coatings for the VIRGO large mirrors

présentée par L. PinardThe goal of the VIRGO program is to build a giant Michelson type interferometer (3 kilometer long arms) to detect gravitational waves. Large optical components (350 mm in diameter), having extremely low loss at 1064 nm, are needed. Today, the Ion beam Sputtering is the only deposition technique able to produce optical components with such performances. Consequently, a large ion beam sputtering deposition system was built to coat large optics up to 700 mm in diameter. The performances of this coater are described in term of layer uniformity on large scale and optical losses (absorption and scattering characterization). The VIRGO interferometer needs six main mirrors. The first set was ready in June 2002 and its installation is in progress on the VIRGO site (Italy). The optical performances of this first set are discussed. The requirements at 1064 nm are all satisfied. Indeed, the absorption level is close to 1 ppm (part per million), the scattering is lower than 5 ppm and the R.M.S. wavefront of these optics is lower than 8 nm on 150 mm in diameter. Finally, some solutions are proposed to further improve these performances, especially the absorption level (lower than 0.1 ppm) and the mechanical quality factor Q of the mirrors (thermal noise reduction)

The World Federation of Democratic Youth and Bruno Bernini's encounter with Mao's China

This paper examines the role played by adult-led youth groups in providing avenues for early encounters between Italian and Chinese Communists in the '50s. In particular, it focuses on the links built up within international organisations linked to the Soviet-sponsored peace movement at a time when direct exchange between the Italian and Chinese Communist parties had yet to start. Relying on a large variety of primary and secondary sources, some of which have never been used before, I provide evidence of how participation in Soviet-led international organisations made early political contacts and interactions possible. The focus is on Bruno Bernini, whose personal experience in China is examined within the context of the World Federation of Democratic Youth's policies and initiatives in the early and mid-'50s