Yuqiong Li

The evaluation of phasemeter prototype performance for the space gravitational waves detection.

Heterodyne laser interferometry is considered as the most promising readout scheme for future space gravitational wave detection missions, in which the gravitational wave signals disguise as small phase variances within the heterodyne beat note. This makes the phasemeter, which extracts the phase information from the beat note, the key device to this system. In this paper, a prototype of phasemeter based on digital phase-locked loop technology is developed, and the major noise sources which may contribute to the noise spectra density are analyzed in detail. Two experiments are also carried out to evaluate the performance of the phasemeter prototype. The results show that the sensitivity is achieved 2π μrad/√Hz in the frequency range of 0.04 Hz-10 Hz. Due to the effect of thermal drift, the noise obviously increases with the frequencies down to 0.1 mHz.

Methodological demonstration of laser beam pointing control for space gravitational wave detection missions

In space laser interferometer gravitational wave (G.W.) detection missions, the stability of the laser beam pointing direction has to be kept at 10 nrad/√Hz. Otherwise, the beam pointing jitter noise will dominate the noise budget and make the detection of G.W. impossible. Disturbed by the residue non-conservative forces, the fluctuation of the laser beam pointing direction could be a few μrad/√Hz at frequencies from 0.1 mHz to 10 Hz. Therefore, the laser beam pointing control system is an essential requirement for those space G.W. detection missions. An on-ground test of such beam pointing control system is performed, where the Differential Wave-front Sensing technique is used to sense the beams pointing jitter. An active controlled steering mirror is employed to adjust the beam pointing direction to compensate the jitter. The experimental result shows that the pointing control system can be used for very large dynamic range up to 5 μrad. At the interested frequencies of space G.W. detection missions, between 1 mHz and 1 Hz, beam pointing stability of 6 nrad/√Hz is achieved.

Principle demonstration of fine pointing control system for inter-satellite laser communication

Due to high data rates and reliability, inter-satellite laser communication has developed rapidly in these days. However, the stability of the laser beam pointing is still a key technique which needs to be solved; otherwise, the beam pointing jitter noise would reduce the communication quality or, even worse, would make the inter-satellite laser communication impossible. For this purpose, a bench-top of the fine beam pointing control system has been built and tested for inter-satellite laser communication. The pointing offset of more than 100 μrad is produced by the steering mirror. With beam pointing control system turned on, the offset could be rapidly suppressed to lower than 100 nrad in less than 0.5 s. Moreover, the pointing stability can be kept at 40 nrad for yaw motion and 62 nrad for pitch motion, when the received beam jitter is set at 20 μrad.

The electrolytic polishing study of the stainless steel foil (SUS 304)

Flexible flat panel display (FPD) is considered to be one of the most optimal and flourishing display technologies in the 21st century, and the processing and exploitation of flexible substrate is one of the key techniques of flexible display. Until now there have been three choices of flexible substrate materials: (1) ultra-thin glass; (2) polymer materials; (3) metal foils. The flexible substrates of electroluminescence display must endure high-temperature annealing from 400°C to 700°C for doping activation, and have good flexibility and can obstruct oxygen and water penetration. Based on above considerations, to adopt the stainless steel foil for the FPD is the most suitable. In this paper, the electrolytic polishing process of stainless steel foil is investigated, and the results of the experiment show that the polishing time, current density, distance of cathode and anode panel, and other technical parameters affect the electrolytic polishing process, and then induce the best technical parameters. The surface roughness of stainless steel sheet decreases from 0.12μm to 0.044μm, but the dongas appear after the steel surface being polished. The dongas patterns are investigated, and this provides a more scientific basis for the experiments in the future.

A simulation of weak-light phase-locking for space laser interferometer

A simulation was investigated to better understand the impacts and effects of the additional technical noises on weak-light phase-locking for space laser interferometer. The result showed that the locking precision was limited by the phase readout noise when the laser frequency noise and clock jitter noise were removed, and this result was then confirmed by a benchtop experimental test. The required space laser interferometer noise floor was recovered from the simulation which proved the validity of the simulation program.