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A composite optical bench made up of Carbon Fiber Reinforced Polymer (CFRP) skin and aluminum honeycomb has been developed for the Tunable Magnetograph instrument (TuMag) for the SUNRISE III mission within the NASA Long Duration Balloon Program. This optical bench has been designed to meet lightweight and low sensitivity to thermal gradient requirements, resulting in a low Coefficient of Thermal Expansion (CTE). In addition to the flight model, a breadboard model identical to the flight one has been manufactured, including embedded fiber Bragg temperature and strain sensors. The aim of this is to explore if the use of distributed fiber Bragg gratings (FBGs) can provide valuable information for strain and temperature mapping of an optical instrument on board a space mission during its operation as well as its on-ground testing. Furthermore, surface-mounted strain FBG sensors and thermocouples have been installed in the optical bench for intercomparison purposes. This paper presents the results obtained from a thermal vacuum test consisting of three thermal cycles with stabilization steps at 100 °C, 60 °C, 20 °C and −20 °C. Experimental results provide information about how FBG embedded temperature sensors can provide a proper and quick response to the temperature changes of the optical bench and that embedded FBG strain sensors are able to measure micro-deformation induced in a close-to-zero CTE optical bench., AEI/MCIN/10.13039/501100011033, Depto. de Óptica, Fac. de Óptica y Optometría, TRUE, pub

Received: 19 January; 2023 Accepted: 15 March 2023, In order to make accurate inferences about the solar interior using helioseismology, it is essential to understand all the relevant physical effects on the observations. One effect to understand is the (complex-valued) ratio of the horizontal to vertical displacement of the p- and f-modes at the height at which they are observed. Unfortunately, it is impossible to measure this ratio directly from a single vantage point, and it has been difficult to disentangle observationally from other effects. In this paper we attempt to measure the ratio directly using 7.5 h of simultaneous observations from the Polarimetric and Helioseismic Imager on board Solar Orbiter and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. While image geometry problems make it difficult to determine the exact ratio, it appears to agree well with that expected from adiabatic oscillations in a standard solar model. On the other hand it does not agree with a commonly used approximation, indicating that this approximation should not be used in helioseismic analyses. In addition, the ratio appears to be real-valued. © The Authors 2023., Agencia Española de Investigación, Federal Ministry for Economic Affairs and Energy (BMWi) (Alemania), Max Planck Gesellschaft (MPG) (Alemania), German Aerospace Center (DLR), Ministerio de Ciencia e Innovación de España, Centro Nacional de Estudios Espaciales (Francia), Depto. de Óptica, Fac. de Óptica y Optometría, TRUE, pub

Context. The High Resolution Telescope (HRT) of the Polarimetric and Helioseismic Imager on board the Solar Orbiter spacecraft (SO/PHI) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) both infer the photospheric magnetic field from polarised light images. SO/PHI is the first magnetograph to move out of the Sun–Earth line and will provide unprecedented access to the Sun’s poles. This provides excellent opportunities for new research wherein the magnetic field maps from both instruments are used simultaneously. Aims. We aim to compare the magnetic field maps from these two instruments and discuss any possible differences between them. Methods. We used data from both instruments obtained during Solar Orbiter’s inferior conjunction on 7 March 2022. The HRT data were additionally treated for geometric distortion and degraded to the same resolution as HMI. The HMI data were re-projected to correct for the 3° separation between the two observatories. Results. SO/PHI-HRT and HMI produce remarkably similar line-of-sight magnetograms, with a slope coefficient of 0.97, an offset below 1 G, and a Pearson correlation coefficient of 0.97. However, SO/PHI-HRT infers weaker line-of-sight fields for the strongest fields. As for the vector magnetic field, SO/PHI-HRT was compared to both the 720-second and 90-second HMI vector magnetic field: SO/PHI-HRT has a closer alignment with the 90-second HMI vector. In the weak signal regime (< 600 G), SO/PHI-HRT measures stronger and more horizontal fields than HMI, very likely due to the greater noise in the SO/PHI-HRT data. In the strong field regime (≳600 G), HRT infers lower field strengths but with similar inclinations (a slope of 0.92) and azimuths (a slope of 1.02). The slope values are from the comparison with the HMI 90-second vector. Possible reasons for the differences found between SO/PHI-HRT and HMI magnetic field parameters are discussed., BMWi - Bundesministerium für Wirtschaft und Energie (Alemania), AEI/MCIN/10.13039/501100011033, Ministerio de ciencia e innovación de España, Instituto Astrofísico de Andalucía (España), Agencia Estatal de Investigación (España), Fondo Europeo de Desarrollo Regional (Fondos FEDER), Centre national d'études spatiales (CNES) (Francia), CSIC (Centro Superior de Investigaciones Científicas) (España), Sección Deptal. de Óptica (Óptica), Fac. de Óptica y Optometría, TRUE, pub

©2011 Optical Society of America, The presence of uncontrolled mechanical vibrations is typically the main precision-limiting factor of a phase-shifting interferometer. We present a method that instead of trying to insolate vibrations; it takes advantage of their presence to produce the different phase-steps. The method is based on spatial and time domain processing techniques to compute first the different unknown phase-steps and then reconstruct the phase from these tilt-shifted interferograms. In order to compensate the camera movement, it is needed to perform an affine registration process between the different interferograms. Simulated and experimental results demonstrate the effectiveness of the proposed technique without the use of any phase-shifter device, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

This paper was published in Applied Optics and is made available as an electronic reprint with the permission of OSA. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law. We thank the European Space Agency for economic support of this work given by the “Validation of liquid crystal variable retarders for solar orbiter polarization modulation package” project, reference number 22334/09/NL/SFe., Liquid crystal variable retarders (LCVRs) are starting to be widely used in optical systems because of their capacity to provide a controlled variable optical retardance between two orthogonal components of incident polarized light or to introduce a known phase shifting (PS) between coherent waves, both by means of an applied voltage. Typically, the retardance or PS introduced by an LCVR is not homogeneous across the aperture. On the one hand, the LCVR glass substrates present a global bend that causes an overall variation of the retardance or PS. On the other hand, in the manufacturing process of an LCVR, there sometimes appears a set of micro-air bubbles that causes local retardance or PS inhomogeneities. In this work, we present an interferometric technique based on a Mach-Zehnder interferometer that is insensitive to vibrations and capable of inspecting and characterizing the LCVR's retardance or PS inhomogeneities. The feasibility of the proposed method is demonstrated in the experimental results, where the LCVR retardance is measured with an error of about 0:2 rad. The thickness of possible micro-air bubbles is obtained with a resolution of about 50 nm., European Space Agency, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

© 2002 Optical Society of America. The authors thank A. J. Fort for his helpful work on the growth of the TiO_2 films., An optical method to determine the nanostructure and the morphology of porous thin films is presented. This procedure is based on the response of a side-polished optical fiber with the film under study, when an adsorption-desorption cycle is carried out. Spectroscopic ellipsometry provides additional information about the optical properties and adsorption behavior of the film. Pore size distribution, anisotropy, and inhomogeneity of films can be determined by use of these two complementary techniques. To check the performances and suitability of the optical method, we have characterized a typical porous material: a TiO_2 film deposited by evaporation. Water vapor has been used for the adsorption cycles. The well-known columnar structure of the evaporated TiO_2 has been evidenced, and the relation between the nanostructure and the optical properties of the film is showed., Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

The ESA/NASA Solar Orbiter space mission has been successfully launched in February 2020. Onboard is the Polarimetric and Helioseismic Imager (SO/PHI), which has two telescopes, a High Resolution Telescope (HRT) and the Full Disc Telescope (FDT). The instrument is designed to infer the photospheric magnetic field and line-of-sight velocity through differential imaging of the polarised light emitted by the Sun. It calculates the full Stokes vector at 6 wavelength positions at the Fe I 617.3 nm absorption line. Due to telemetry constraints, the instrument nominally processes these Stokes profiles onboard, however when telemetry is available, the raw images are downlinked and reduced on ground. Here the architecture of the on-ground pipeline for HRT is presented, which also offers additional corrections not currently available on board the instrument. The pipeline can reduce raw images to the full Stokes vector with a polarimetric sensitivity of 10−3⋅Ic or better., BMWi - Bundesministerium für Wirtschaft und Energie (Alemania), MPG - Max-Planck-Gesellschaft (Alemania), Ministerio de Ciencia e Innovación de España - MCIU, Instituto de Astrofísica de Andalucía - CSIC (España), CNES - Centre National d'études spatiales (Francia), Fondos FEDER, Agencia Estatal de Investigación - AEI (ESpaña), Sección Deptal. de Óptica (Óptica), Fac. de Óptica y Optometría, TRUE, pub

The authors present the results of the ellipsometric characterization of thin layers of bismuth and aluminum oxide deposited over the waist of a tapered optical fiber by pulsed laser deposition. The characteristics of the deposits are studied by spectroscopic ellipsometry. From the effective thicknesses determined by the ellipsometric characterization, it is shown by simulations that surface plasmon resonances (SPRs) can occur in the fiber device, and it is demonstrated experimentally. These results show the feasibility of employing bismuth as a plasmonic material in SPR fiber sensors based on doubly-deposited uniform-waist tapered optical fibers, which show excellent performance and versatility.

The authors present the results of the ellipsometric characterization of thin layers of bismuth and aluminum oxide deposited over the waist of a tapered optical fiber by pulsed laser deposition. The characteristics of the deposits are studied by spectroscopic ellipsometry. From the effective thicknesses determined by the ellipsometric characterization, it is shown by simulations that surface plasmon resonances (SPRs) can occur in the fiber device, and it is demonstrated experimentally. These results show the feasibility of employing bismuth as a plasmonic material in SPR fiber sensors based on doubly-deposited uniform-waist tapered optical fibers, which show excellent performance and versatility., Ministerio de Ciencia e Innovación (MICINN)/FEDER, Universidad Complutense de Madrid/Banco de Santander, Sección Deptal. de Óptica (Óptica), Fac. de Óptica y Optometría, TRUE, pub

Different optical methods for phase recovering and therefore the wavefront are related with a set of direct techniques as interferometry, indirect ones like Shack-Hartmann sensing and iterative methods where an objective function is optimized. The aerospace industry has used techniques coming from optical metrology for the assembly and integration of instruments with optical properties. However, also other subjects use, involve and push the development of these kind of techniques, for example in microscopy. Currently, the wavefront retrieval techniques have been improved and strengthened by using algorithms coming from computer graphics. In addition, the design of filters and phase demodulation by using the theory of signals coming from electronic engineering and telecommunications. In addition to the improvements in algorithms, the experimental optical methods have triggered innovative developments considering the emergent technologies based on liquid crystal (spatial light modulators - SLMs) and its ability to modulate phase, amplitude or both easily. Furthermore, the performance in terms of response times, resolution and modulation capabilities, among others, of liquid crystal devices are improving constantly. This thesis proposes new methods and improvements in techniques for recovering the wavefront in order to be used in the corresponding processes of assembly and integration of optical instruments for space. A method able to recover the phase with abrupt differences of intensity in the incoming field is proposed from the conventional interferometry by using techniques coming from computer graphics and fringe normalization through filters described since the signal theory. A comparison between electronic speckle pattern interferometry (ESPI) and differential interferometry showing as a disadvantage that the last one does not recover the phase of an extended object. Moreover, the wavefront recovery in topographic applications is proposed in ESPI by using two wa, Los diferentes ḿetodos ́opticos para la recuperacíon de la fase y por tanto para el frente de onda pasan por una serie de t́ecnicas, como las interferoḿetricas y otras no directas entre las que destacan el sensado Shack-Hartmann y los ḿetodos iterativos en los que se minimiza una funcíon objetivo. La industria aeroespacial hace uso de estas t́ecnicas provenientes de la metroloǵıa ́optica para la integracíon de instrumentos esencialmente ́opticos. Sin embargo, no es la ́unica industria, ni ́area que hace uso de estas, un ejemplo es la microscopia, la cual tambíen ha aportado con nuevas t́ecnicas. Actualmente las t́ecnicas de recuperacíon del frente onda se han apropiado y robustecido desde la algoritmia de ́areas como la computacíon gŕafica, y desde el punto de vista del tratamiento de se˜nales provenientes de la ingenieŕıa electŕonica y de telecomunicaciones con el dise˜no de filtros y la demodulacíon de la fase en el espacio frecuencial. Por otro lado, no solo la algoritmia ha sido mejorada, los ḿetodos ́opticos experimentales han desencadenado en desarrollos novedosos con la aparicíon de tecnoloǵıas emergentes basadas en cristal-liquido (Moduladores espaciales de luz - SLMs). La gran ventaja de estos dispositivos es la capacidad de modular fase, amplitud o ambas con una relativa facilidad en su uso. Adicionalmente los nuevos dispositivos tienen cada vez mejor desempe˜nos en las capacidades de modulacíon, en los tiempos de respuesta, mayor resolucíon, entre otras. En resumen esta memoria de tesis propone ḿetodos novedosos e introduce mejoras en otros para las t́ecnicas de recuperacíon del frente de onda que son usados en los procesos de integracíon de instrumentos ́opticos para espacio. Desde la interferometŕıa convencional se propone un ḿetodo capaz de reconstruir la fase con diferencias de intensidad abruptas en el campo a reconstruir, usando t́ecnicas provenientes de la computacíon gŕafica y la normalizacíon de franjas a trav́es de fil

Different optical methods for phase recovering and therefore the wavefront are related with a set of direct techniques as interferometry, indirect ones like Shack-Hartmann sensing and iterative methods where an objective function is optimized. The aerospace industry has used techniques coming from optical metrology for the assembly and integration of instruments with optical properties. However, also other subjects use, involve and push the development of these kind of techniques, for example in microscopy. Currently, the wavefront retrieval techniques have been improved and strengthened by using algorithms coming from computer graphics. In addition, the design of filters and phase demodulation by using the theory of signals coming from electronic engineering and telecommunications. In addition to the improvements in algorithms, the experimental optical methods have triggered innovative developments considering the emergent technologies based on liquid crystal (spatial light modulators - SLMs) and its ability to modulate phase, amplitude or both easily. Furthermore, the performance in terms of response times, resolution and modulation capabilities, among others, of liquid crystal devices are improving constantly. This thesis proposes new methods and improvements in techniques for recovering the wavefront in order to be used in the corresponding processes of assembly and integration of optical instruments for space. A method able to recover the phase with abrupt differences of intensity in the incoming field is proposed from the conventional interferometry by using techniques coming from computer graphics and fringe normalization through filters described since the signal theory. A comparison between electronic speckle pattern interferometry (ESPI) and differential interferometry showing as a disadvantage that the last one does not recover the phase of an extended object. Moreover, the wavefront recovery in topographic applications is proposed in ESPI by using two wa