Manufacture of a hollow corner cube retroreflector for next generation of lunar laser ranging

Lunar laser ranging has made significant contributions to the study of gravitational physics and the Earth-Moon system. The best results for fundamental gravitational experiments have been achieved using lunar laser ranging data accumulated so far. However, corner cube retroreflector arrays placed on the Moon currently set a limit on the laser-ranging precision, which is approximately several centimeters for a single photon received. To achieve millimeter precision, next generation of lunar laser ranging using a single hollow retroreflector with a large aperture has been proposed. We developed a prototype hollow retroreflector with a 100-mm aperture using silicate bonding together with a new fabrication method. Dihedral angle offsets of 0.5′′, 0.8′′and 1.9′′were realized, which partly come close to meeting the requirements(offset of 0.6′′for each dihedral angle) for lunar laser ranging. Fluctuation of the wavefront is approximately 1.038λ at 633 nm. A thermal cycle test ranging from -40℃ to +75℃ was carried out for 18.5 periods(approximately 5 d). After this test, the dihedral angle offsets were measured to be 0.39′′, 1.00′′and 2.06′′. The results indicate the potential application of our method for manufacturing a hollow retroreflector with a large aperture to realize lunar laser ranging.

Ultraprecision intersatellite laser interferometry

Precision measurement tools are compulsory to reduce measurement errors or machining errors in the processes of calibration and manufacturing.The laser interferometer is one of the most important measurement tools invented in the 20th century.Today,it is commonly used in ultraprecision machining and manufacturing,ultraprecision positioning control,and many noncontact optical sensing technologies.So far,the state-of-the-art laser interferometers are the ground-based gravitational-wave detectors,e.g.the Laser Interferometer Gravitational-wave Observatory(LIGO).The LIGO has reached the measurement quantum limit,and some quantum technologies with squeezed light are currently being tested in order to further decompress the noise level.In this paper,we focus on the laser interferometry developed for space-based gravitational-wave detection.The basic working principle and the current status of the key technologies of intersatellite laser interferometry are introduced and discussed in detail.The launch and operation of these large-scale,gravitational-wave detectors based on space-based laser interferometry is proposed for the 2030s.