Design of terahertz metamaterial absorbers with switchable absorption functions utilizing thermal and electrical dual-modulation strategies.

This work demonstrates a dual-functional tunable terahertz metamaterial absorber based on thermally controllable vanadium dioxide (VO2) and electrically tunable graphene. The switchable absorption functions could be obtained in the same metamaterial, which consists of alternating stacked cross-cut graphene disks (CGDs) and VO2 square rings (VSRs) separated by an ultra-thin dielectric film placed on a continuous gold mirror. The metallic state of VSRs is the dominant factor for the broadband absorption function, resulting in a broadband absorption of 4.746 THz. Based on this, the Fermi energy level of CGDs increases to 0.7 eV, which could broaden the absorption bandwidth to 5.398 THz. When the VSRs are in the insulating state, CGDs dominate the absorption, and the suggested device switches to the dual-band absorption function. These two absorption peaks appear to be larger than 97% and their frequencies could be dynamically controlled by the Fermi energy level of CGDs. In addition to the excellent absorption characteristics of dynamic switching of two different functions, polarization insensitivity and large-angle tolerance are also advantages of this work, which could provide new insights and guidance for the study of dynamically tunable metamaterial absorbers.

Multi-optimization for thermal deformation of gravitational wave telescope based on CFRP characteristics.

Gravitational wave telescope place extremely high demands on structural thermal deformation, making material selection a critical issue. Carbon fiber reinforced polymer (CFRP) is an ideal choice for the support structure of telescope due to its low coefficient of thermal expansion (CTE) and designable properties. However, current research on the optimization of the CTE of CFRP is scarce, and conventional methods struggle to find layups that meet the requirements. In this paper, an unconventional layup optimization method is proposed to solve this problem. Initially defining the characteristics of the telescope structure and using different layup material for the main and side support rods to minimize thermal deformation. Subsequently, the NSGA-II algorithm is used to optimize the layups which are divided into conventional and unconventional layups. Specimens are then produced from these results and tested to assess the impact of processing errors on practical applications. The results demonstrate that the optimized CFRP meet the CTE requirements and, when applied to the structure, significantly reduces the thermal deformation in the eccentric direction compared to conventional designs. Additionally, a numerical analysis evaluates the effect of ply orientation errors on the performance of unconventional layups, discussing the method's limitations within these contexts.

Research on High-Stability Composite Control Methods for Telescope Pointing Systems under Multiple Disturbances.

During the operation of space gravitational wave detectors, the constellation configuration formed by three satellites gradually deviates from the ideal 60° angle due to the periodic variations in orbits. To ensure the stability of inter-satellite laser links, active compensation of the breathing angle variation within the constellation plane is achieved by rotating the optical subassembly through the telescope pointing mechanism. This paper proposes a high-performance robust composite control method designed to enhance the robust stability, disturbance rejection, and tracking performance of the telescope pointing system. Specifically, based on the dynamic model of the telescope pointing mechanism and the disturbance noise model, an H∞ controller has been designed to ensure system stability and disturbance rejection capabilities. Meanwhile, employing the method of an H∞ norm optimized disturbance observer (HODOB) enhances the nonlinear friction rejection ability of the telescope pointing system. The simulation results indicate that, compared to the traditional disturbance observer (DOB) design, utilizing the HODOB method can enhance the tracking accuracy and pointing stability of the telescope pointing system by an order of magnitude. Furthermore, the proposed composite control method improves the overall system performance, ensuring that the stability of the telescope pointing system meets the 10 nrad/Hz1/2 @0.1 mHz~1 Hz requirement specified for the TianQin mission.

Optimized design of a gravitational wave telescope system based on pupil aberration.

The telescope is vital for accurate gravitational wave detection in the TianQin project. It must meet criteria like a geometric tilt-to-length (TTL) coupling noise c o e f f i c i e n t≤0.02√2n m/µr a d and wavefront R M S≤λ/30. Analyzing the pupil aberration's impact on geometric TTL noise, we devised an optimization method using the chief ray spot diagram's standard deviation. Implementing this in Zemax with a ZPL macro, we designed an optical system meeting TianQin's requirements. The system has a maximum geometric TTL noise coefficient of 0.0250 nm/µrad over the science FOV and a wavefront RMS of 0.0111λ, confirming the method's feasibility.

Analysis of alignment requirements for off-axis resonant cavity based on coupling efficiency.

The optical path length stability of the off-axis four-reflection telescope is one of the key technical indicators for the TianQin gravitational wave detection system. In the MHz observation band, the telescope must exhibit an optical path length stability of 0.4p m/H z 1/2. As a feasible solution, the optical path length stability measurement of the off-axis four-reflection telescope based on the Pound-Drever-Hall (PDH) technique imposes stringent requirements on the alignment of the off-axis resonant cavity (ORC). Taking the off-axis two-reflection prototype as the research object, we propose a Monte Carlo analysis-based method for ORC alignment precision analysis. By considering misalignment as an intermediate function, we establish a relationship between the coupling efficiency of the ORC and the wavefront aberration of the telescope. The research results show that by considering the combined effects of multiple misalignment couplings of the primary and secondary mirrors, when the detected telescope wavefront aberration is better than 0.068λ (λ=1064n m) with a probability of 98%, the ORC coupling efficiency can achieve greater than 40% with a probability of 97.13%, which can be used as the main reference indicator for system misalignment analysis. This method simplifies the alignment difficulty of the target under test and can provide alignment reference for subsequent resonant cavities with internal off-axis telescopes.