Large Mirror Research Articles

Dynamic Characteristics, Analysis, and Measurement of a Large Optical Mirror Processing System

Dynamic Characteristics, Analysis, and Measurement of a Large Optical Mirror Processing System

Analytical study of the beam quality of a diode-pumped alkali laser with unstable resonator

Analytical model of Cs diode-pumped alkali laser with unstable confocal resonator is reported. Two of the parameters characterizing the quality of the output beam were studied: the axial luminous intensity in the far field and the power in the bucket (PIB). The far-field axial light intensity and PIB were compared with their values for a truncated Gaussian reference beam whose aperture was limited by the aperture of the large resonator mirror and 99% of the Gaussian beam energy passed through the aperture of this mirror. For large values of the unstable resonator magnification factor m > 5, the far-field axial light intensity is approximately 40% larger than that of the Gaussian reference beam. Analysis of the PIB curves showed that for large m > 5, the values of the integrated fractional encircled power within a sufficiently large diffraction angles for the unstable resonator exceed its values for the reference Gaussian beam.

Structural Analysis Technique and Its Validation for Large Range Mirror Refocusing System for Spaceborne Deployable Telescopes

Large aperture deployable telescopes with numerous onboard instruments are popular in the space industry for astronomy. Scientific data in various wavelength bands, from 0.6µ to 28µ, is provided by these instruments and is crucial for deep space exploration. The deployment mechanisms handle the alignment and functionality at the telescope level only. At instrument level, there is always a need for a refocusing system which can cater individual need of instrument for focusing independent to other instruments nearby. In this paper, we present a structural analysis technique for such a type of large range mirror refocusing mechanism, similar to the Near Infrared Spectrograph (NIRSpec) payload of the James Webb Space Telescope (JWST). The method relies on geometric non-linearity for large deflection, in which the structure's stiffness matrix changes as a function of loading. We have designed, analyzed structurally, and tested a 4mm range slider crank based compliant mechanism. The outcomes of linear and non-linear static analysis, computed numerically, have been compared. There are noticeable significant variations in one direction between the two analyses' results. The results are validated using appropriately designed and realized test setups, like measurements of displacement, changes in focus and image position of the optical system.

AlScN-based quasi-static multi-degree-of-freedom piezoelectric MEMS micromirror with large mirror plate and high fill factor

A quasi-static multi-degree-of-freedom piezoelectric MEMS micromirror with large mirror plate and high fill factor based on AlScN is presented. It consists of two individual components, namely the mirror plate and the actuator. They are fabricated separately and vertically assembled together to form the final combination. In current case, a square mirror plate with side length of 5 mm is used. The actuator is designed into a gimbal-less structure, which involves a central connection platform with a mounting hole and four groups of piezoelectric actuators that are connected to the platform's corners via serpentine springs. This configuration provides multi-degree-of-freedom driving capabilities, allowing tip-tilt-piston mirror movement. The piezoelectric actuator is composed of three-stage cantilever-type actuation units that are connected in series, and they are intentionally arranged into S-shape so as to be completely hidden beneath the mirror plate. Moreover, the driving performance is further improved by optimizing the electrode coverage region on each actuation unit. As a result, not only large displacement but also nearly 100 % fill factor as well as high optical utilization efficiency can be achieved. From experimental results, the as-fabricated MEMS micromirror demonstrates static mechanical tilt angles of approximately ±2.2° about two orthogonal axes and piston vertical movement of ±54.9 μm within ±50 VDC driving voltage range with excellent linearity. Given the large mirror size, high fill factor and multi-degree-of-freedom motion advantages, the proposed micromirror could be found application perspective in light field shaping, free space optical communication and projection lithography areas.

High fidelity adaptive mirror simulations with reduced order models

In the design process of large adaptive mirrors numerical simulations represent the first step to evaluate the system design compliance in terms of performance, stability and robustness. For the next generation of Extremely Large Telescopes increased system dimensions and bandwidths lead to the need of modeling not only the deformable mirror alone, but also all the system supporting structure or even the full telescope. The capability to perform the simulations with an acceptable amount of time and computational resources is highly dependent on finding appropriate methods to reduce the size of the resulting dynamic models. In this paper we present a framework developed together with the company Microgate to create a reduced order structural model of a large adaptive mirror as a preprocessing step to the control system simulations. The reduced dynamic model is then combined with the remaining system components allowing to simulate the full adaptive mirror in a computationally efficient way. We analyze the feasibility of our reduced models for Microgate’s prototype of the adaptive mirror of the Giant Magellan Telescope.

The development of a low-temperature terahertz scanning tunneling microscope based on a cryogen-free scheme.

We have developed a cryogen-free, low-temperature terahertz scanning tunneling microscope (THz-STM). This system utilizes a continuous-flow cryogen-free cooler to achieve low temperatures of ∼25K. Meanwhile, an ultra-small ultra-high vacuum chamber results in the reduction of the distance from sample to viewport to only 4cm. NA = 0.6 can be achieved while placing the entire optical component, including a large parabolic mirror, outside the vacuum chamber. Thus, the convenience of optical coupling is much improved without compromising the performance of STM. Based on this, we introduced THz pulses into the tunnel junction and constructed the THz-STM, achieving atomic-level spatial resolution in THz-driven current imaging and sub-picosecond (sub-ps) time resolution in autocorrelation signals during pump-probe measurements. Experimental data from various representative samples are presented to showcase the performance of the instrument, establishing it as an ideal platform for studying non-equilibrium dynamic processes at nanoscale.

Development of a large stroke 3-DOF piezoelectric steering mirror for optical system

The steering mirrors and the focusing mechanisms are the key components of the optical system. Traditional steering mirrors driven by voice coil actuator or piezoelectric stack actuator have the disadvantages of short stroke, self-locking difficulty and poor structural reliability. These defects limit the performance of the steering mirrors and make it difficult to be compatible with the focusing mechanism. As a result, additional focusing devices are required in the optical system, which significantly increases the complexity of the system. To simplify the optical system, a large stroke three-degree-of-freedom (3-DOF) piezoelectric steering mirror (PSM) which can realize both light path adjustment and focus adjustment is proposed in this study. Two rotational degrees of freedom of the PSM are used to adjust the light path, and a translational degree of freedom is used to adjust the focus. The screwed-typed piezoelectric actuators (STPAs) are designed to drive the PSM by exciting the travelling wave. The feasibility of the operating principle and reliability of the proposed PSM have been verified by finite element simulation. A prototype of the PSM is fabricated and tested. The experimental results show that the PSM achieves rotational degrees of freedom around the x-axis, y-axis and translational degree of freedom along the z-axis with maximum ranges of ±0.17 rad, ±0.17 rad, and ±10 mm, respectively, meeting the application requirements of the optical systems. The resolutions of the two rotary motions of the PSM are 28 μrad, and 21 μrad, respectively, and that of the translational motion is 0.5 μm. Finally, the position adjustment and focusing operations of the image are demonstrated to validate the potential application of PSM in optical systems.

Towards robotic on-orbit assembly of large space telescopes: Mission architectures, concepts, and analyses

Imaging systems larger than the James Webb Space Telescope will enable unprecedented astronomy in the future. Larger aperture space-based imagers will also support next-generation Earth Observation missions for national security and disaster monitoring. However, launching and operating such large telescopes in the poses several practical challenges. A key challenge is that mirrors with apertures larger than 3 m cannot be monolithically manufactured so a segmented design is utilized to achieve primary mirror apertures. Even if larger mirrors could be made, it would be impossible to stow them in fairings of most existing and future launch vehicles. Folded-wing designs to deploy segmented primary mirrors, as done with the James Webb Space Telescope, are one approach to overcoming this volumetric challenge but inappropriate for 25 m apertures considered in this study. This paper presents the concept of operations and mission architectures/analysis for on-orbit assembly of a 25 m aperture telescope operating in the visible waveband of the electromagnetic spectrum capable of 1 m spatial resolution from geostationary orbit. Further, a technology demonstration roadmap towards maturing the robotic assembly technology stack is then presented as precursors to the 25 m imaging system.

Large-range high-precision macroscopic common phase detection of segmented mirrors based on white light dynamic Twyman-Green interferometer

Segmented mirrors (SMs) provide a solution for the construction of the next generation of extremely large telescopes. The large-range, high-precision detection of piston error between mirror segments is a must-be solved problem in the application of SMs. This paper proposes a large-range high-precision macroscopic co-phase detection method of SMs based on white light dynamic Twyman-Green interferometer. By adopting a white light interferometry in the macroscopic co-phase detection, the probability of the occurring of the 2π ambiguity anomalies can be reduced. A piston error calculation model for SMs was established through Zernike fitting analysis, which improved the detection accuracy. A white light Twyman-Green interferometer with Kohler illumination was experimentally constructed. Based on the scanning of the reference mirror, an efficient detection of the piston error was achieved simultaneously with large range and high precision. Through the new method, the piston error of two planar mirrors was compensated from 38.9344 μm in coarse co-phase stage to 3.6 nm in fine co-phase stage. The method shows great potential for efficient co-phase adjustment of large primary segmented mirrors.

Efficient full-aperture mirror polishing method with variable orbital radius in computer-controlled optical surfacing

Optical systems in astronomy have extremely high requirements on the full-aperture surface precision and fabrication efficiency of aspherical mirrors. However, the current full-aperture optics fabrication method suffers from both fabrication and computation inefficiency. The former is caused by the isolated polishing strategy for the inner and edge regions of the mirror with different tools, while the latter is caused by the global computation strategy for the two regions. In this paper, a full-aperture mirror polishing method with the reversed strategy is proposed to solve this problem. Firstly, the dwell time of inner/edge regions are respectively calculated by the deconvolution method and the linear equations method based on the space-variant tool influence function. Therefore, both the computation cost and the edge polishing error can be reduced. Then, a fused tool path is developed to achieve variable orbital radius in the inner/edge region so the full aperture can be polished in one round. Simulations and experiments using a SiC aspherical mirror and large segmented mirrors demonstrate that the surface error can converge quickly in the full aperture. As a consequence, the full-aperture fabrication accuracy and efficiency can be greatly improved through the proposed method.

Expected Impact of Glints from Space Debris in the LSST

We examine the simple model put forth in a recent note by Loeb regarding the brightness of space debris in the size range of 1–10 cm and their impact on the Rubin Observatory Legacy Survey of Space and Time (LSST) transient object searches. Their main conclusion was that “image contamination by untracked space debris might pose a bigger challenge [than large commercial satellite constellations in Low-Earth orbit].” Following corrections and improvements to this model, we calculate the apparent brightness of tumbling low-Earth orbit (LEO) debris of various sizes, and we briefly discuss the likely impact and potential mitigations of glints from space debris in LSST. We find the majority of the difference in predicted signal-to-noise ratio (S/N), about a factor of 6, arises from the defocus of LEO objects due to the large Simonyi Survey Telescope primary mirror and finite range of the debris. The largest change from the Loeb estimates is that 1–10 cm debris in LEO pose no threat to LSST transient object alert generation because their S/N for detection will be much lower than estimated by Loeb due to defocus. We find that only tumbling LEO debris larger than 10 cm or with significantly greater reflectivity, which give 1 ms glints, might be detected with high confidence (S/N > 5). We estimate that only one in five LSST exposures low on the sky during twilight might be affected. More slowly tumbling objects of larger size can give flares in brightness that are easily detected; however, these will not be cataloged by the LSST Science Pipelines because of the resulting long streak.

Refocusing beams of a satellite mirror antenna with moderate deformations of its reflector

Multibeam hybrid reflector antenna (MBHRA) is part of high-performance satellite communication systems. It provides high gain thanks to its large mirror and the use of antenna array to form enough beams covering the working area. Therefore, it is crucial to maintain the needed beams configuration to provide clients with high quality signal. The location of the beams may change because the reflector profile changes under the changeable thermal flux from the Sun, which is not stationary due to orbital motion of the satellite. Although the appearing distortions of the reflector profile are a priori small, but they cause beams to displace from their assigned positions in up to their width of tenth of a degree. Consequently, the level of the signal in coverage areas goes down. Modern MBHRA form their beams with clusters, i.e. groups of elements of the antenna array. Typically, cluster consists out of seven elements: one in the center and others at the vertices of a perfect hexagon. The fact that several antenna elements form a beam opens up the possibility of electronically controlling the beams by adjusting the amplitudes and phases of the exciting distribution, or more precisely, the weighting coefficients of the clusters. To determine which amplitudes and phases to apply, it is necessary to know the current state of the reflector, characterized by either its geometry or its electrodynamic equivalent, such as the best-fit paraboloid (BFP). Laser measurement and photogrammetry are popular solutions for that. A useful alternative to them is reconstruction of the BFP from the signals received by the MBHRA antenna array from a ground-based radio beacon. Emphasizing the dependence of these signals on the state of the reflector, we call them the “signal imprint” of the reflector. The possibility to implement a single ground beacon is due approximation the reflector profile as an equivalent best-fit paraboloid. BFP is uniquely defined by six parameters: change of the focal length, turns in two orthogonal planes and shift of the apex in space {ΔF; αz; αy; Δx; Δy; Δz}. Since some of the parameters are highly correlated in terms of their influence on the signal imprint, the re-construction problem becomes more complicated. So a question whether the set of parameters is overloaded arises reasonably. Maybe it is possible to get rid of some parameters. We considered two options to reduce the number of parameters: focal displacement + turns {ΔF; αz; αy} and apex shift {Δx; Δy; Δz}. Statistical modelling confirms the possibility to reduce the number of sought-for BFP parameters down to the mentioned three instead of six. If the maximum of the focal spot does not shift outside the cluster, then reducing the number of the sought-for BFP parameters to three causes a very small decrease in the gain of beams compared to using the full set of parameters. For the above options, the decrease in gain is 0.03 dB or 0.25 dB. It is interesting to note that in the turns option {ΔF; αz; αy} there is a better correspondence to the reflector surface compared to the displacement option {Δx; Δy; Δz}, but worse matching of the signal imprint, and as a consequence a greater loss in gain. This is due to the higher sensitivity of the beam orientation to the mirror rotations than to the vertex displacement.

Gravity unloading of a very large spaceborne monolithic SiC mirror.

We formulated a gravity unloading strategy for a monolithic silicon carbide (SiC) mirror with a Φ3m aperture in space. Employing the finite element analysis (FEA) technique, a rapid solution analytical approach for determining optimal support forces during gravity unloading is introduced. This method demonstrates enhanced efficiency and accuracy compared to conventional approaches. A quantitative evaluation methodology for the gravity release error, grounded in the minimum-energy mode, is delineated. The adverse impacts could be expeditiously computed by assessing the maximum deflection of minimum-energy modes generated by various errors. The analytical findings revealed that compliance with the stipulated gravity release error criterion of less than 6 nm (root-mean-square) necessitated the gravity unloading force error to fall within the range of ±0.1N. Additionally, the gravity unloading support position error was required to be within Φ0.5m m, and the measurement error pertaining to the rib thickness of the actual mirror blank had to be within ±0.02m m.

Adaptive decentralized fuzzy compensation control for large optical mirror processing systems

PurposeLarge optical mirror processing systems (LOMPSs) consist of multiple subrobots, and correlated disturbance terms between these robots often lead to reduced processing accuracy. This abstract introduces a novel approach, the nonlinear subsystem adaptive dispersed fuzzy compensation control (ADFCC) method, aimed at enhancing the precision of LOMPSs.Design/methodology/approachThe ADFCC model for LOMPS is developed through a nonlinear fuzzy adaptive algorithm. This model incorporates control parameters and disturbance terms (such as those arising from the external environment, friction and correlation) between subsystems to facilitate ADFCC. Error analysis is performed using the subsystem output parameters, and the resulting errors are used as feedback for compensation control.FindingsExperimental analysis is conducted, specifically under the commonly used concentric circle processing trajectory in LOMPS. This analysis validates the effectiveness of the control model in enhancing processing accuracy.Originality/valueThe ADFCC strategy is demonstrated to significantly improve the accuracy of LOMPS output, offering a promising solution to the problem of correlated disturbances. This work holds the potential to benefit a wide range of practical applications.

Ground-state mass of 22Al and test of state-of-the-art ab initio calculations* *Supported in part by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34000000), the CAS Project for Young Scientists in Basic Research (YSBR-002), the National Nature Science Foundation of China (12135017, 12121005, 11975280, 12105333, 12205340, 12322507, 12305126, 12305151), the Gansu Natural Science Foundation (22JR5RA123, 23JRRA614) and the

The ground-state mass excess of the drip-line nucleus Al is measured for the first time as keV using the newly-developed B ρ-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou. The new mass excess value allowed us to determine the excitation energies of the two low-lying states in Al with significantly reduced uncertainties of 51 keV. When compared to the analogue states in its mirror nucleus F, the mirror energy differences of the two states in the Al- F mirror pair are determined to be keV and keV. The excitation energies and mirror energy differences are used to test the state-of-the-art ab initio valence-space in-medium similarity renormalization group calculations with four sets of interactions derived from the chiral effective field theory. The mechanism leading to the large mirror energy differences is investigated and attributed to the occupation of the orbital.

Surface Analysis and Optimization of Large Aperture Mirror Supported by Elastic Expansion Sleeves

In order to meet the stability of the support structure of arrayed large aperture mirror and improve the surface accuracy of the mirror, the elastic expansion sleeve is proposed as the back-support structure of the large aperture mirror. The feasibility of the support method is verified by theoretical analysis and experiment. The PV value of additional wavefront distortion is about 75.3nm<λ/5(λ=632.8nm) when the torque of single mandrel screw is 40N·cm, which meets the technical specifications. The change trend of the support-induced surface is compared between the finite element simulation and the measured results under different mandrel screw torque conditions. When the support torque is increased in equal increments, there is a linear positive correlation between the PV value of support-induced surface and the support torque. Based on the change trend of the support-induced surface, the optimization design scheme of the initial surface is proposed. And the simulation results show that the optimized induced distortion is smaller than that of the ideal surface (the compensation ratio is 7.68%), which reduces the additional wavefront distortion under the actual mounting support.

Evaluation for Thermal Deformation of Large Segmented Mirror Structure Based on STOP Analysis

Evaluation for Thermal Deformation of Large Segmented Mirror Structure Based on STOP Analysis

Adjustment and testing method of large aperture mirror Bipod support structure

Adjustment and testing method of large aperture mirror Bipod support structure

Experiment study on large solar telescope mirror seeing

Experiment study on large solar telescope mirror seeing

Photovoltaic module augmented by commercial reflectors in Southern Algeria: Comparison between different reflective materials

Even though the southeast region of Algeria, especially Ouargla city, enjoys a lot of sunshine all over the year, fixed photovoltaic (PV) solar panels are not sufficient due to two main reasons. Firstly, these panels are unable to capture sunlight during the early morning and late afternoon, and secondly, their efficiency is low, requiring the use of economical methods to enhance their performance. To overcome these limitations, this research suggests incorporating commercial reflectors to enhance sunlight capture. Furthermore, this paper compares the effects of three types of reflective materials: mirrors, aluminium, and transparent glass, on the performance of the PV module. To achieve this objective, reflectors are installed at the top and bottom of the PV module at their optimal tilt angles. Moreover, the effect of the adjacent module's mirrors was studied by installing two big mirrors (3X). The obtained results show an average improvement of 14.24 %, 11.41 %, and 4.7 % in the electrical energy generated by the PV panel with mirrors, aluminium, and transparent glass, respectively, compared to the module without reflectors. Subsequently, in the large mirror case, the results were positive, with an average 20.84 % increase in the maximal electrical power produced compared to the conventional one.