This article describes the mounting system of lenses in a coronagraph ASPIICS (Association of Spacecraft for Polarimetric Imaging Investigation of the Corona of the Sun). ASPIICS is developed and produced in cooperation of twenty partners from seven countries. It is a part of the ESA's PROBA-3 mission, which includes a formation flight of a pair of satellites at orbit. Coronagraph itself consists of three objectives, where the last one is composed by one objective tube for each lens plus holder and Lyot stop. To achieve high accuracy of mounting of the individual lenses, it was necessary to achieve tight geometric and dimensional tolerances for manufacturing of the objectives barrels. In order to minimize the stress and to prevent the displacement of the lens from ideal position during a temperature change on orbit, an athermal solution was proposed. This is achieved by inserting a Teflon ring of a suitable thickness between the lens surface, objective barrel and the spring washer with a precisely defined contact force. It was necessary to find a suitable technological process of manufacturing, because of the specific behavior of PTFE during turning and complex design of other parts. All parameters of mounting system were repeatedly verified by a thermomechanical analysis in FEM software, based on tests of real parts.
High demands on the final surfaces micro-roughness as well as great shape accuracy have to be achieved under the manufacturing process of the precise mirrors for Metis orbital coronagraph. It is challenging engineering task with respect to lightweight design of the mirrors and resulting objectionable optical surface shape stability. Manufacturing of such optical elements is usually affected by number of various effects. Most of them are caused by instability of temperature field. It is necessary to explore, comprehend and consequently minimize all thermo - mechanical processes which take place during mirror cementing, grinding and polishing processes to minimize the optical surface deformation. Application of FEM simulation was proved as a useful tool to help to solve this task. FEM simulations were used to develop and virtually compare different mirror holders to minimize the residual stress generated by temperature changes and to suppress the shape deformation of the optical surface below the critical limit of about 100 nm.
KEYWORDS: Digital holography, Tomography, Holography, Holographic interferometry, Temperature metrology, 3D metrology, Digital cameras, Holograms, Cameras, Refractive index
A digital holographic interferometry (DHI) for 3D measurement of temperature distributions in moving fluid is presented in this paper. The measurement uses digital holographic setup for measurement of a flow of fluid propagated through an orifice and tomographic approach for 3D reconstruction of the flow. The periodic character of the flow and synchronization between the digital camera and external trigger driving the phenomenon allows us to measure phenomena with much higher frequency when compared to frame rate of the digital camera. Furthermore one can capture a large number of the flow projections from different viewing directions which are later used for 3D tomographic reconstruction of the whole temperature field of the flow. The measurement results are verified and compared with hot wire method (CTA) in the paper.
The entry of CNC machining processes into optics brought the possibility of nearly arbitrary shape generation. Obviously the measurement of the generated shape increasingly gains the importance, because the generation has to be performed in an iterative manner as the required precision increases. Often mid spatial frequency error is neglected because it is not an easy task to be measured. Unfortunately those unwanted residual deviation in a shape left after grinding could dramatically complicate a subsequent polishing procedure. Mid spatial frequency content if not controlled well could spoils significantly the performance of the optical system. Elimination of mid spatial residuals originated in grinding process is nearly impossible or very difficult by sub-aperture polishing. Hence it is important to measure the grinded surface with sufficient lateral resolution. Tactile probes (usually used for shape measurement of grinded surfaces) can measure with sufficient lateral resolution but only at the expense of time. Interferometer based techniques fail when applied to scattering surfaces due to speckles. The authors have proposed multi-wavelength multi-directional digital holography – the method perfectly suitable for grinded surfaces shape measurement. Naturally, reconstructed phase maps are affected by speckle noise implying significant errors in the calculation of the shape of the surface. In order to reduce the effect of speckle noise and hence to increase the sensitivity of the measurement of the grinded surface shape, we propose to apply windowed digital holography. This paper describes the principle of the windowed digital holography and the way of straightforward application of the method in shape measurement of grinded surfaces.
Etienne Renotte, Andres Alia, Alessandro Bemporad, Joseph Bernier, Cristina Bramanti, Steve Buckley, Gerardo Capobianco, Ileana Cernica, Vladimir Dániel, Radoslav Darakchiev, Marcin Darmetko, Arnaud Debaize, François Denis, Richard Desselle, Lieve de Vos, Adrian Dinescu, Silvano Fineschi, Karl Fleury-Frenette, Mauro Focardi, Aurélie Fumel, Damien Galano, Camille Galy, Jean-Marie Gillis, Tomasz Górski, Estelle Graas, Rafał Graczyk, Konrad Grochowski, Jean-Philippe Halain, Aline Hermans, Russ Howard, Carl Jackson, Emmanuel Janssen, Hubert Kasprzyk, Jacek Kosiec, Serge Koutchmy, Jana Kovačičinová, Nektarios Kranitis, Michał Kurowski, Michał Ładno, Philippe Lamy, Federico Landini, Radek Lapáček, Vít Lédl, Sylvie Liebecq, Davide Loreggia, Brian McGarvey, Giuseppe Massone, Radek Melich, Agnes Mestreau-Garreau, Dominique Mollet, Łukasz Mosdorf, Michał Mosdorf, Mateusz Mroczkowski, Raluca Muller, Gianalfredo Nicolini, Bogdan Nicula, Kevin O'Neill, Piotr Orleański, Marie-Catherine Palau, Maurizio Pancrazzi, Antonios Paschalis, Karel Patočka, Radek Peresty, Irina Popescu, Pavel Psota, Miroslaw Rataj, Jan Rautakoski, Marco Romoli, Roman Rybecký, Lucas Salvador, Jean-Sébastien Servaye, Cornel Solomon, Yvan Stockman, Arkadiusz Swat, Cédric Thizy, Michel Thomé, Kanaris Tsinganos, Jim Van der Meulen, Nico Van Vooren, Tomáš Vit, Tomasz Walczak, Alicja Zarzycka, Joe Zender, Andrei Zhukov
KEYWORDS: Coronagraphy, Sensors, Sun, Solar processes, Field programmable gate arrays, Light emitting diodes, Electronics, Staring arrays, Space operations, Information operations
The “sonic region” of the Sun corona remains extremely difficult to observe with spatial resolution and sensitivity sufficient to understand the fine scale phenomena that govern the quiescent solar corona, as well as phenomena that lead to coronal mass ejections (CMEs), which influence space weather. Improvement on this front requires eclipse-like conditions over long observation times. The space-borne coronagraphs flown so far provided a continuous coverage of the external parts of the corona but their over-occulting system did not permit to analyse the part of the white-light corona where the main coronal mass is concentrated. The proposed PROBA-3 Coronagraph System, also known as ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun), with its novel design, will be the first space coronagraph to cover the range of radial distances between ~1.08 and 3 solar radii where the magnetic field plays a crucial role in the coronal dynamics, thus providing continuous observational conditions very close to those during a total solar eclipse. PROBA-3 is first a mission devoted to the in-orbit demonstration of precise formation flying techniques and technologies for future European missions, which will fly ASPIICS as primary payload. The instrument is distributed over two satellites flying in formation (approx. 150m apart) to form a giant coronagraph capable of producing a nearly perfect eclipse allowing observing the sun corona closer to the rim than ever before. The coronagraph instrument is developed by a large European consortium including about 20 partners from 7 countries under the auspices of the European Space Agency. This paper is reviewing the recent improvements and design updates of the ASPIICS instrument as it is stepping into the detailed design phase.
KEYWORDS: Temperature metrology, Digital holography, Holograms, Holographic interferometry, Holography, Cameras, Tomography, Digital cameras, Interferometers, Digital recording
The presented paper shows possibility of using digital holographic interferometry (DHI) for temperature field measurement in moving fluids. This method uses a modified Twymann-Green setup having double sensitivity instead of commonly used Mach-Zehnder type of interferometer in order to obtain sufficient phases change of the field. On the other hand this setup is not light efficient as Mach-Zehnder interferometer. For measurement of the fast periodical phenomenon is not necessary to use always the high speed camera. One can consider this field to coherent phenomenon. With employing one digital camera synchronized to periodic field and external triggered one can capture whole period of the phenomenon. However the projections form one viewing direction of asymmetrical temperature field maybe misguided. Hence for sufficient examination of the asymmetrical field one should capture a large number of the phenomenon’s projections from different viewing directions. This projections are later used for 3D tomographic reconstruction of the whole temperature field and its time evolution. One of the commonly used method for temperature field measurement in moving fluids is hot wire method - constant temperature anemometry (CTA). In contrast to whole field measurement of DHI it is an invasive point temperature measurement method. One of the limiting factor of using CTA in moving fluids is frequency of temperature changes. This changes should not exceed 1 kHz. This limitation could be overcome by using of optical methods such as DHI. The results of temperature field measurement achieved by both method are compared in the paper.
The presented paper shows results and a comparison of FEM numerical simulations and optical tests of the assembly of a precise Zerodur mirror with a mounting structure for space applications. It also shows how the curing of adhesive film can impact the optical surface, especially as regards deformations. Finally, the paper shows the results of the figure quality analysis, which are based on data from FEM simulation of optical surface deformations.
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