The European Solar Telescope (EST) will be built at the Observatorio del Roque de los Muchachos, a site known for its excellent atmospheric seeing conditions. The fundamental design of EST lies on two premises to improve the local seeing: placing the primary mirror as far as possible from the ground layer and using an open-air configuration. In this setting, the telescope will benefit from undisturbed wind allowing natural ventilation. These considerations aim to optimize the site conditions; however, the design itself may introduce local seeing. As the design evolves from conceptual to preliminary phase, the shape of the EST has profoundly changed, and the fundamental aspects shall be re-evaluated. In this article, strategic aspects of the current design are studied, including elements from the telescope structure, the pier, and the enclosure. These trade-offs considered the local seeing as a driving force seeking to optimize the optical performance and provide feedback to the current design of EST. This study uses transient Computational Fluid Dynamics (CFD) to estimate the air temperature and refractive index as it flows over the observatory and the telescope. The air refractive index inside the optical path is then analyzed using postprocessing scripts to obtain appropriate seeing metrics. Predominant wind directions and median wind speed at the site together with environmental conditions and different telescope orientations were used to thoroughly analyze the local seeing conditions. Optical results enabled the characterization of the spatial distribution of turbulence, assimilating it to a Kolmogorov law. These results are valuable input for the telescope’s error budget in terms of local seeing.
The European Solar Telescope (EST) is a 4-m class-solar telescope that will become part of the next generation of groundbased facilities. Located at the “Observatorio del Roque de los Muchachos” in La Palma (Spain), it will be aimed to study the magnetic connectivity of the solar atmosphere with high spatial and temporal resolution. The EST optical design has been optimized during the preliminary design phase to maximize throughput, balance the instrumental polarization and to reduce the image rotation due to the change in orientation during operation. The optical system consists of a 4.2m active primary mirror located above the elevation axis to ensure natural air flushing and minimize local seeing degradation and a secondary mirror assembled as an Adaptive Secondary Mirror (ASM). Both arranged in an on-axis Gregorian configuration to deliver an aplanatic secondary focal plane. These are followed by four fold mirrors, which will be upgraded to deformable mirrors and are conjugated to different layers of the atmosphere. These, together with the ASM, M7 and two wavefront sensors, will make up the Multi-Conjugate Adaptive Optics system. Finally, a dioptric system, housed in a vacuum vessel, transfers the light to the science focus, which will be delivered to the Scientific Instrumentation by a dedicated distribution system. EST ultimately provides a diffraction-limited telecentric F/50 science focal plane covering a FOV of 90×90 arcsec2 over a wavelength range from 380nm to 2300nm. Along the contribution, details about the preliminary optical design of EST and its subassemblies will be presented. The expected performance is also discussed.
The effects of atmospheric dispersion on the performance of astronomical Adaptive Optics (AO) were already described in the 70’s, and they are generally regarded irrelevant to nighttime AO, except for the very specific case of Extreme AO for the next generation of 30 and 40-m class large ground-based telescopes. However, the situation changes when evaluating the impact of chromatic aspects for solar AO observations, due mostly to three factors. First, the usually more turbulent ground-layer conditions experienced during daytime observations. Second, solar telescopes operating at mountain sites need to be designed to be efficient at low elevation angles, when the atmospheric turbulence is usually the best. Last but not least, as in the case of the European Solar Telescope (EST), the solar AO simultaneously feeds several instruments probing the light spectrum from the Near-Ultraviolet (NUV) to the Near-Infrared (NIR). In this contribution, we review the literature to assess the impact of atmospheric dispersion in the context of a 4.2-m solar telescope as planned for the EST and how the chromatic AO errors can impact the wavefront sensing and correction architectures.
The European Solar Telescope (EST) is a 4.2-m telescope which has been redesigned with a fully integrated Multi-Conjugate Adaptive Optics (MCAO) into the optical path right after the EST primary mirror. The current baseline configuration considers four altitude Deformable Mirrors (DM) conjugated to 5, 9, 12 and 20 km above the telescope entrance pupil and an Adaptive Secondary Mirror (ASM) conjugated to the entrance pupil. The wavefront sensing will be performed by a set of correlation-based Shack Hartmann wavefront sensors (WFS) combining an on-axis High-Order WFS (HOWFS) to be used either in Single Conjugate AO (SCAO) to drive the ASM as well as operating simultaneously with a Multi-Directional WFS (MDWFS) to drive the MCAO. Beyond the current baseline configuration, different alternatives are currently being investigated both in the wavefront sensing strategy by evolving from a HOWFS+MDWFS into possibly a single High Order Multi Directional WFS (HOMDWFS) and/or wavefront sensors operating at different observing bands.
One of the main goals of the European Solar Telescope (EST), a 4.2-m telescope, is to clarify the roots of the magnetic processes taking place in the solar atmosphere. This goal has a top-level requirement: perform simultaneous spectropolarimetric measurements in multiple spectral lines. For this purpose, EST will be equipped with a set of instruments working simultaneously in diverse spectral ranges. In this regard, we are designing a Coudé Light Distribution (CLD) responsible for delivering the incoming solar radiation to each instrument. The CLD is formed by a series of optical elements like dichroic and intensity beam splitters, flat mirrors, and optical compensators that will be interchangeable to offer the solar community maximum flexibility for performing observations. In developing the CLD, we are paying great attention to controlling aberration effects generated by the different elements that constitute the light distribution system. Also, we are defining the CLD to reach a balance between throughput, image quality, and a compact distribution of the instruments in the Coudé room. Our aim is to describe in this contribution the current design of the CLD. The present design constitutes the basis of the CLD, with enough flexibility to improve it in the future, if indeed, and adapt it to the evolution of other sub-systems like the instruments, the adaptive optics, or the telescope structure to guarantee that it fulfils the science requirements.
The European Solar Telescope (EST) aims to become the most ambitious ground-based solar telescope in Europe. Its roots lie in the knowledge and expertise gained from building and running previous infrastructures like, among others, the Vacuum Tower Telescope, Swedish Solar Telescope, or the GREGOR telescope. They are installed in the Canary Islands observatories, the selected EST site. Furthermore, the telescope has a novel optical design, including an adaptive secondary mirror (ASM) that allows reducing the number of optical surfaces to 6 mirrors (plus two lenses) before the instruments’ focal plane. The latter, combined with a configuration of mirrors that are located orthogonally oriented to compensate for the instrumental polarisation induced by each surface, makes EST a reference telescope in terms of throughput and polarimetric accuracy. In its main core design, EST also includes a Multi-Conjugated Adaptive Optics (MCAO) system where the ASM compensates for the ground layer turbulence. The rest of the mirrors on the optical train correct for the atmospheric turbulence at different layers of the atmosphere. The MCAO guarantees that the large theoretical spatial resolution of the 4-metre EST primary mirror is achieved over a circular FOV of 60 arcsec. Those main elements, combined with a set of instruments with capabilities for spectropolarimetry, make EST the next frontier in solar ground-based astronomy. In this contribution, we will cover the main properties and status of all the mentioned sub-systems and the following steps that will lead to the construction phase.
We present a new wave front sensing technique based on detecting the propagating light waves. This allows the user to acquire millions of data points within the pupil of the human eye; a resolution several orders of magnitude higher than current industry standard ophthalmic devices. The first instrument was built and tested using standard calibration surfaces in addition to using an artificial eye. The paper then presents the first characterization of the optics of a real human eye measured using the newly developed high-resolution wave front phase sensing technique showing the complexity of the human eye’s ocular optics.
We present our latest advances in the design and implementation of a tunable automultiscopic display based on the tensor display model. A design comprising a three-layer display was introduced. In such design, front and rear layers were enabled to be controlled in a six-degree of freedom manner related to the central layer of the system. A calibration method consisting on displaying a checkerboard pattern in each layer was proposed. By computing the homography of these patterns with respect to the reference plane, it was possible to estimate the needed adjustments. An implementation based on such design was carried over and calibrated following the aforementioned technique. The obtained results demonstrated the feasibility of such implementation.
In this work we present a novel wave front phase sensing technique developed by Wooptix. This new wave front phase sensor uses only standard imaging sensor, and does not need any specialized optical hardware to sample the optical field. In addition, the wave front phase recovery is zonal, thus, the obtained wave front phase map provides as much height data points, as pixels in the imaging sensor. We will develop the mathematical foundations of this instrument as well as theoretical and practical limits. Finally, we will expose the application of this sensor to silicon wafer metrology and comparisons against industry standard metrology instruments.
KEYWORDS: 3D displays, LCDs, Lanthanum, Optical engineering, Reconstruction algorithms, Signal to noise ratio, Multiplexing, 3D image processing, Translucency, Display technology
Tensor display is an option in glasses-free three-dimensional (3-D) display technology. An initial solution has to be set to decompose the light-field information to be represented by the system. We have analyzed the impact of the initial guess on the multiplicative update rules in terms of peak signal-to-noise ratio, and proposed a method based on depth map estimation from an input light field. Results from simulations were obtained and compared with previous literature. In our sample, the initial values used have a large influence on results and convergence to a local minimum. The quality of the output stabilizes after a certain number of iterations, suggesting that a limit on such numbers should be imposed. We show that the proposed methods outperform the pre-existing ones.
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