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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