Large Aperture Telescope Research Articles

Electrohydraulic high‑accuracy position and orientation control system of the primary mirror for a large-aperture high resolution telescope

Electrohydraulic high‑accuracy position and orientation control system of the primary mirror for a large-aperture high resolution telescope

Design of truss adjusting mechanism for secondary mirror of large aperture telescope

Design of truss adjusting mechanism for secondary mirror of large aperture telescope

Parallel adjustment mechanism for large aperture telescope based on flexible hinges

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Review on the measurement methods of mirror seeing of large-aperture telescope

Review on the measurement methods of mirror seeing of large-aperture telescope

Millimeter/Submillimeter VLBI with a Next Generation Large Radio Telescope in the Atacama Desert

The proposed next generation Event Horizon Telescope (ngEHT) concept envisions the imaging of various astronomical sources on scales of microarcseconds in unprecedented detail with at least two orders of magnitude improvement in the image dynamic ranges by extending the Event Horizon Telescope (EHT). A key technical component of ngEHT is the utilization of large aperture telescopes to anchor the entire array, allowing the connection of less sensitive stations through highly sensitive fringe detections to form a dense network across the planet. Here, we introduce two projects for planned next generation large radio telescopes in the 2030s on the Chajnantor Plateau in the Atacama desert in northern Chile, the Large Submillimeter Telescope (LST) and the Atacama Large Aperture Submillimeter Telescope (AtLAST). Both are designed to have a 50-meter diameter and operate at the planned ngEHT frequency bands of 86, 230 and 345 GHz. A large aperture of 50 m that is co-located with two existing EHT stations, the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Pathfinder Experiment (APEX) Telescope in the excellent observing site of the Chajnantor Plateau, will offer excellent capabilities for highly sensitive, multi-frequency, and time-agile millimeter very long baseline interferometry (VLBI) observations with accurate data calibration relevant to key science cases of ngEHT. In addition to ngEHT, its unique location in Chile will substantially improve angular resolutions of the planned Next Generation Very Large Array in North America or any future global millimeter VLBI arrays if combined. LST and AtLAST will be a key element enabling transformative science cases with next-generation millimeter/submillimeter VLBI arrays.

Simons Observatory: characterizing the Large Aperture Telescope Receiver with radio holography.

We present near-field radio holography measurements of the Simons Observatory Large Aperture Telescope Receiver optics. These measurements demonstrate that radio holography of complex millimeter-wave optical systems comprising cryogenic lenses, filters, and feed horns can provide detailed characterization of wave propagation before deployment. We used the measured amplitude and phase, at 4K, of the receiver near-field beam pattern to predict two key performance parameters: 1)the amount of scattered light that will spill past the telescope to 300K and 2)the beam pattern expected from the receiver when fielded on the telescope. These cryogenic measurements informed the removal of a filter, which led to improved optical efficiency and reduced sidelobes at the exit of the receiver. Holography measurements of this system suggest that the spilled power past the telescope mirrors will be less than 1%, and the main beam with its near sidelobes are consistent with the nominal telescope design. This is the first time such parameters have been confirmed in the lab prior to deployment of a new receiver. This approach is broadly applicable to millimeter and submillimeter instruments.

Correction performance uniformity on ground-layer adaptive optics

ABSTRACTGround-layer adaptive optics (GLAO) is generally used to improve the seeing for large-aperture ground-based optical telescopes across a wide field of view with uniform imaging quality. In this paper, a new criterion, which is defined as the weighted sum of the mean and mean-square-error values of the full width at half-maximum of the field-dependent point spread function of the image over the whole field of view, is proposed to evaluate GLAO performance uniformity. An analytic model of the GLAO-corrected point spread function based on spatial filtering methods is used to investigate the uniformity and image quality over the whole field of view for different guide-star layouts, telescope apertures, numbers of actuators for the deformable mirror, and turbulence profiles. Simulations are performed on the GLAO configurations for the 1-m New Vacuum Solar Telescope at Fuxian Solar Observatory. The results show that, compared with that of the classical evaluation, the correction uniformity improves by 63 per cent, with the resolution sacrificing only 5 per cent for a measured turbulence profile at Fuxian Solar Observatory. Furthermore, this criterion is applied to various requirements, and some critical system parameters are suggested for the wide field-of-view GLAO.

Development of large-aperture radio telescopes and applications of coupled structural-electromagnetic theory

<p indent="0mm">The smooth operation of radio telescopes is essential in radio astronomy. This paper establishes the importance of radio telescopes via examples of the discovery of gravitational waves, the merger of neutron stars, and the first black hole photograph. As radio astronomy advances, radio telescopes require larger apertures and higher pointing accuracy, resulting in a closer structural-electromagnetic coupling. To solve the coupled structural-electromagnetic problem of radio telescopes, the development of a coupled structural-electromagnetic theory is key to the smooth and efficient operation of large-aperture radio telescopes. To this end, this paper describes the development of radio telescopes built and put into operation in the last decade, as well as those under construction and to be built, and emphasizes the importance of coupled structural-electromagnetic theory in the design, manufacture, and operation of radio telescopes. Then, the paper systematically summarizes the application of coupled structural-electromagnetic theory in radio telescopes. Finally, future research hotspots of electromechanical coupling are proposed based on the development of radio astronomy and the performance requirements of large-aperture radio telescope antennas.

Analytical correction of pupil-offset off-axis telescopes with complex figure errors and misalignments based on nodal aberration theory

Active optical correction is necessary for space large-aperture optical telescopes, especially for systems with high performance requirements. This paper proposes an analytic correction method for pupil-offset off-axis optical telescopes with misalignments and complex figure errors on the basis of nodal aberration theory (NAT). An analytical description of the wave aberration contribution from the complex surfaces in off-axis telescopes is derived, which gives a unified description for the impacts of the complex surfaces located at the stop and away from the stop. Using the analytical description, a correction model for off-axis telescopes with figure errors and misalignments is established. The off-axis optical telescope with trefoil and astigmatic figure errors and lateral misalignments is taken as a typical example, the presented method is discussed. After the corresponding correction, the perturbed off-axis telescope is almost restored to the system nominal states, which can meet the specification requirements well. Finally, the Monte Carlo simulations are implemented to demonstrate the effectiveness of the presented approach.

Wheel Setting Error Modeling and Compensation for Arc Envelope Grinding of Large-Aperture Aspherical Optics

Precision grinding is a key process for realizing the use of large-aperture aspherical optical elements in laser nuclear fusion devices, large-aperture astronomical telescopes, and high-resolution space cameras. In this study, the arc envelope grinding process of large-aperture aspherical optics is investigated using a CM1500 precision grinding machine with a maximum machinable diameter of Φ1500 mm. The form error of the aspherical workpiece induced by wheel setting errors is analytically modeled for both parallel and cross grinding. Results show that the form error is more sensitive to the wheel setting error along the feed direction than that along the lateral direction. It is a bilinear function of the feed-direction wheel setting error and the distance to the optical axis. Based on the error function above, a method to determine the wheel setting error is proposed. Subsequently, grinding tests are performed with the wheels aligned accurately. Using a newly proposed partial error compensation method with an appropriate compensation factor, a form error of 3.4 μm peak-to-valley (PV) for a Φ400 mm elliptical K9 glass surface is achieved.

First Implementation of Pulsed Sodium Guidestars Constellation for Large-aperture Multi-conjugate Adaptive Optics Telescopes

Multiple synthetic beacons are required for atmospheric-turbulence compensation in an extended-field-of-view multi-conjugate adaptive optics (MCAO) telescope. In this paper, we report on the first successful implementation of a microsecond-pulse sodium guidestars constellation laser system, based on a small angle precise polarized combining and splitting technology. At Lijiang Observatory of China, four-ways ∼20 W yellow laser beam with kHz repetition-rate and hundred-μs pulse width were projected into the sky through one small-aperture launching telescope, and generated a distinctive four-point grouping on a field of view of 40″ with variable configurations of linear, parallelogram, rhomboid and square. The sodium return signal could easily avoid Rayleigh light interference by the pulse synchro controlling technology delivering a higher spatial resolution. Moreover, the increase in return photons for alternated circularly and alternated linearly polarized light has been investigated. We believe that the above results could serve as a future reference for the MCAO system on large-aperture telescopes worldwide.

Reflective astronomical telescopes with a large field of view and a wide wave band.

Large-aperture ground-based astronomical telescopes are expected to have a large field of view (FoV) and a wide working wave band. We design two coaxial reflective telescopes based on a low-order even asphere and a high-order Q-con polynomial. Both telescopes have a primary mirror with a diameter of 6.5 m, a focal length of 24 m, and a working wavelength that stretches from ultraviolet to near-infrared (0.365-2.4 µm). The telescopes using an asphere and a Q-con polynomial have spectroscopic-survey fields of 3° and 3.4°, respectively. In these fields, the EE80D (diameter of 80%-enclosed light energy) values that can characterize the telescope image quality is less than 0.58'', and the spectral data can be obtained using fibers at the focal surface of the telescopes. Additionally, the two reflective telescopes can image celestial targets in a 0.4° FoV, and the root mean square diameters of the standard spot diagrams are less than 27 µm. By combining precise imaging measurements with the spectral data, the properties of celestial bodies can be better analyzed. The designed telescopes could enable the realization of astronomical spectroscopic surveys with both a large FoV and a wide waveband.

Adaptive Imaging and Stabilization System for a Large-Aperture Solar Telescope

Adaptive Imaging and Stabilization System for a Large-Aperture Solar Telescope

Co-phase state detection for segmented mirrors by dual-wavelength optical vortex phase-shifting interferometry.

The application of large-aperture telescopes requires the support of co-phase measurement techniques for segmented mirrors. This paper proposes a novel method to detect the co-phase state of segmented mirrors by applying a dual-wavelength phase-shifting interferometer based on optical vortex. Theory and experiments indicate that the wrapped phase map edges obtained by phase-shifting interference of the vortex beam are distributed in the form of a Fermat spiral. The piston error of the segmented mirrors corresponds to the rotation of the standard Fermat spiral center. In contrast, the tip/tilt error corresponds to the alteration of the center position of the deformed Fermat spiral. The rotation angle and the center position of the spiral are obtained by curve fitting, and the co-phase errors can be inversely solved. The experiments achieved an accuracy of approximately 4.04 nm in the piston and 0.16″ in the tip/tilt. The method avoids using complex lens arrays and devices, has an extended measurement range, high accuracy, and allows the co-phase errors between all sub-mirrors to be obtained in real-time. This study provides a novel and general method for detecting co-phase errors in a segmented primary mirror.

Mersenne Beam-Compressor with Field-Flattener Optics as Main Telescope Design for Extremely Large Telescopes and Telescope Arrays

The Mersenne beam-compressor is the fundamental arrangement for two mirror reflecting telescopes. The Mersenne beam-compressor consists of two confocal paraboloids. The design produces an aberration-free, collimated output beam, which makes it easy to relocate the beam to any distant location. This property of Mersenne beam compressors makes them near-ideal for telescopes with requirements for ultra-stable instruments and interferometric applications. The only problem against such application is the Petzval field curvature that is induced in the output beam. This becomes very pronounced at very high compression ratios, which are required for interferometry with large aperture telescopes. The high compression ratio is a problem because, such large aperture telescopes are also required to deliver good performance at Nasmyth and Coude locations, to be feasible. This is not possible at high compression ratios using conventional design of Mersenne beam-compressor, due to prohibitively strong field curvature. Here, we propose powered and un-powered field-flattener optics to address the problem of field curvature in Mersenne beam-compressor. After passing through this set of optics, the output beam is completely aberration free. This arrangement can produce very high compression ratios, which are useful for various special applications. We also illustrate the performance of such a system using example designs. The performance analysis shows that such a design can give considerably high performance at distant locations of foci as compared to existing relay systems.

Piston Error Extraction from Dual-Wavelength Interference Patterns Using Phase Retrieval Technique

As next-generation large-aperture telescopes, synthetic aperture is a promising method for realizing high resolution observations. Co-phasing the misaligned segmented aperture is an important procedure for high-resolution observations with segmented telescopes. In this paper, a piston error detection method is proposed based on two interference patterns. Two interference patterns are generated by using a lens placed across two adjacent pupils in the exit pupil plane at two wavelengths and a method based on phase retrieval technique is proposed to extract the piston error from the two interference patterns. The introduction of dual-wavelength in the scheme overcomes the 2π ambiguities problem and expands the piston error detection range. Meanwhile, the proposed piston error extraction method based on phase retrieval technique allows high precision measurement of the piston error and is robust to offset lens. Various simulations are demonstrated and the feasibility of the proposed piston error detection method is validated.

Single photonic integrated circuit imaging system with a 2D lens array arrangement.

The segmented planar imager is an advanced optical interferometric telescope with a photonic integrated circuit (PIC). It provides a significant reduction in size, weight, and power consumption as compared to traditional optical interferometry. In this article, we propose the combination of a single PIC with a two-dimensional (2D) lens array to achieve single-PIC imaging. Unlike previous designs which require a large number of PIC arrangements in different directions for imaging, a single-PIC imaging system requires only one PIC for 2D frequency domain sampling and imaging. In addition, the single-PIC imaging system can form a larger equivalent aperture through modularization. Since PIC can be mass-produced, the modularization ability of the single-PIC imaging system greatly shortens the production and development cycle of large-aperture telescopes.

Simons Observatory: Constraining inflationary gravitational waves with multitracer B -mode delensing

We introduce and validate a delensing framework for the Simons Observatory (SO), which will be used to improve constraints on inflationary gravitational waves (IGWs) by reducing the lensing noise in measurements of the $B$-modes in CMB polarization. SO will initially observe CMB by using three small aperture telescopes and one large-aperture telescope. While polarization maps from small-aperture telescopes will be used to constrain IGWs, the internal CMB lensing maps used to delens will be reconstructed from data from the large-aperture telescope. Since lensing maps obtained from the SO data will be noise-dominated on sub-degree scales, the SO lensing framework constructs a template for lensing-induced $B$-modes by combining internal CMB lensing maps with maps of the cosmic infrared background from Planck as well as galaxy density maps from the LSST survey. We construct a likelihood for constraining the tensor-to-scalar ratio $r$ that contains auto- and cross-spectra between observed $B$-modes and the lensing $B$-mode template. We test our delensing analysis pipeline on map-based simulations containing survey non-idealities, but that, for this initial exploration, does not include contamination from Galactic and extragalactic foregrounds. We find that the SO survey masking and inhomogeneous and atmospheric noise have very little impact on the delensing performance, and the $r$ constraint becomes $\sigma(r)\approx 0.0015$ which is close to that obtained from the idealized forecasts in the absence of the Galactic foreground and is nearly a factor of two tighter than without delensing. We also find that uncertainties in the external large-scale structure tracers used in our multi-tracer delensing pipeline lead to bias much smaller than the $1\,\sigma$ statistical uncertainties.

Evaluation of wavefront aberrations induced by overlay errors in stitching computer-generated holograms

The emergence of large-aperture telescopes has fueled the need for testing and assisted alignment of large-scale optical systems. Computer-generated holograms (CGHs) have proven to be a useful method for aspheric optical testing and assisted alignment, and large-sized CGHs are required for large-scale aspherical systems. However, the maximum size of CGH is generally in the range of 6 to 9 inches owing to its current lithography capability. Stitching technology is a promising method for realizing larger-sized CGHs. As a proof of concept, a CGH with an aperture of 80 mm is fabricated using multistep lithography to investigate the overlay errors in stitching. Theoretical derivations reveal that additional tip/tilt aberrations are introduced owing to the overlay errors, which commonly couple with aberrations from adjustment errors. Therefore, to budget the effects of overlay errors, an evaluation method is proposed in this study. The evaluation results guide the separation and compensation of coupling aberrations in measurement. It is verified that the accuracy of a stitching CGH is considerably improved from 0.156λ to 0.017λ in terms of RMS after compensation. The findings obtained in this study during the development of stitching method and error evaluation are expected to promote the technology development and improvement of testing accuracy in stitching CGHs.

Modular deployable structures

Large aperture antennas and telescopes, long baselines and long focal lengths in space have important applications for Telecommunications, Earth Observation and Science missions. Within this context, an ESA TRP activity is currently under development, carried out by COMET Ingenier&iacute;a, PROSIX Engineering and Airbus DS (CASA Espacio), with the aim of designing overall structural assemblies based on unit cells developing representative parts of deployable masts (linear structures) and rings (antenna or radiotelescope aperture). This paper presents the current status of this project and the results obtained until the date of presentation of this paper. The results of these paper will be confirmed during next PDR to be celebrated at ESA-ESTEC.