Persona: Álvarez-Herrrero, Alberto
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Instituto Nacional de Técnica Aeroespacial
El Instituto Nacional de Técnica Aeroespacial es el Organismo Público de Investigación (OPI) dependiente del Ministerio de Defensa. Además de realizar actividades de investigación científica y de desarrollo de sistemas y prototipos en su ámbito de conocimiento, presta servicios tecnológicos a empresas, universidades e instituciones.
El INTA está especializado en la investigación y el desarrollo tecnológico, de carácter dual, en los ámbitos de la Aeronáutica, Espacio, Hidrodinámica, Seguridad y Defensa.
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Álvarez-Herrrero
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Publicación Restringido Imaging polarimeters based on liquid crystal variable retarders: an emergent technology for space instrumentation(SPIE Optical Engineering Applications, 2011-09-09) Álvarez-Herrrero, Alberto; Uribe Patarroyo, Néstor; García Parejo, Pilar; Vargas, J.; López Heredero, Raquel; Restrepo, R.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; López, A.; Fineschi, S.; Capobianco, G.; Georges, M.; López, M.; Boer, G.; Manolis, I.; López Heredero, R. [0000-0002-2197-8388]; Vargas, J. [0000-0001-7519-6106]; García Parejo, P. [0000-0003-1556-9411]; López Jiménez, A. [0000-0002-6297-0681]; Del Toro Iniesta, J. A. [0000-0002-3387-026X]; Álvarez Herrero, A. [0000-0001-9228-3412]; Capobianco, G. [0000-0003-0520-2528]; Restrepo Gómez, R. [0000-0002-3874-3032]; Georges, M. [0000-0002-0460-3912]; Martínez Pillet, V. [0000-0001-7764-6895]The use of Liquid Crystal Variable Retarders (LCVRs) as polarization modulators are envisaged as a promising novel technique for space instrumentation due to the inherent advantage of eliminating the need for conventional rotary polarizing optics hence the need of mechanisms. LCVRs is a mature technology for ground applications; they are wellknow, already used in polarimeters, and during the last ten years have undergone an important development, driven by the fast expansion of commercial Liquid Crystal Displays. In this work a brief review of the state of the art of imaging polarimeters based on LCVRs is presented. All of them are ground instruments, except the solar magnetograph IMaX which flew in 2009 onboard of a stratospheric balloon as part of the SUNRISE mission payload, since we have no knowledge about other spaceborne polarimeters using liquid crystal up to now. Also the main results of the activity, which was recently completed, with the objective to validate the LCVRs technology for the Solar Orbiter space mission are described. In the aforementioned mission, LCVRs will be utilized in the polarisation modulation package of the instruments SO/PHI (Polarimetric and Helioseismic Imager for Solar Orbiter) and METIS/COR (Multi Element Telescope for Imaging and Spectroscopy, Coronagraph).Publicación Acceso Abierto The Polarimetric and Helioseismic Imager on Solar Orbiter(EDP Sciences, 2020-10) Solanki, S. K.; Álvarez-Herrrero, Alberto; Barandiarán, J.; Bastide, L. ; Campuzano, C.; Cebollero Vidriales, Maria; Dávila, B.; Fernández Medina, A.; García Parejo, Pilar; Garranzo, Daniel; Laguna, H.; Martín, J. A.; Navarro, R.; Nuñez Peral, A.; Royo, M.; Sánchez, A.; Silva López, M.; Vera Trallero, Isabel; Villanueva, J.; Zouganelis, I.; Deutsches Zentrum für Luft- und Raumfahrt (DLR); Centre National D'Etudes Spatiales (CNES); Centros de Excelencia Severo Ochoa, INSTITUTO DE ASTROFISICA DE ANDALUCIA (IAA), SEV-2017-0709This paper describes the Polarimetric and Helioseismic Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and helioseismology instrument to observe the Sun from outside the Sun-Earth line. It is the key instrument meant to address the top-level science question: How does the solar dynamo work and drive connections between the Sun and the heliosphere? SO/PHI will also play an important role in answering the other top-level science questions of Solar Orbiter, while hosting the potential of a rich return in further science. Methods. SO/PHI measures the Zeeman effect and the Doppler shift in the Fe※ I 617.3 nm spectral line. To this end, the instrument carries out narrow-band imaging spectro-polarimetry using a tunable LiNbO3 Fabry-Perot etalon, while the polarisation modulation is done with liquid crystal variable retarders. The line and the nearby continuum are sampled at six wavelength points and the data are recorded by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data are reduced on board, including being inverted under the assumption of a Milne-Eddington atmosphere, although simpler reduction methods are also available on board. SO/PHI is composed of two telescopes; one, the Full Disc Telescope, covers the full solar disc at all phases of the orbit, while the other, the High Resolution Telescope, can resolve structures as small as 200 km on the Sun at closest perihelion. The high heat load generated through proximity to the Sun is greatly reduced by the multilayer-coated entrance windows to the two telescopes that allow less than 4% of the total sunlight to enter the instrument, most of it in a narrow wavelength band around the chosen spectral line. Results. SO/PHI was designed and built by a consortium having partners in Germany, Spain, and France. The flight model was delivered to Airbus Defence and Space, Stevenage, and successfully integrated into the Solar Orbiter spacecraft. A number of innovations were introduced compared with earlier space-based spectropolarimeters, thus allowing SO/PHI to fit into the tight mass, volume, power and telemetry budgets provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal) challenges posed by the mission's highly elliptical orbit.Publicación Restringido Ellipsometric characterization of Bi and Al2O3 coatings for plasmon excitation in an optical fiber sensor(AIP Publishing, 2019-10-17) Rodríguez Schwendtner, E.; Álvarez-Herrrero, Alberto; Mariscal, A.; Serna, R.; González Cano, A.; Navarrete, M. C.; Díaz Herrera, N.; Ministerio de Economía y Competitividad (MINECO); Agencia Estatal de Investigación (AEI); 0000-0001-9228-3412; 0000-0002-7178-1452; 0000-0002-7101-3947; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737The 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. Published by the AVS.Publicación Restringido Space-qualified liquid-crystal variable retarders for wide-field-of-view coronagraphs(SPIE Optical Engineering Applications, 2011-10-06) Uribe Patarroyo, Néstor; Álvarez-Herrrero, Alberto; García Parejo, Pilar; Vargas, J.; López Heredero, Raquel; Restrepo, R.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; López, A.; Fineschi, S.; Capobianco, G.; Georges, M.; López, M.; Boer, G.; Manolis, I.; Álvarez Herrero, A. [0000-0001-9228-3412]; Del Toro Iniesta, J. C. [0000-0002-3387-026X]; López Heredero, R. [0000-0002-2197-8388]; Vargas, J. [0000-0001-7519-6106]; López Jiménez, A. [0000-0002-6297-0681]; García Parejo, P. [0000-0003-1556-9411]; Capobianco, G. [0000-0003-0520-2528]; Georges, M. [0000-0002-0460-3912]; Restrepo Gómez, R. [0000-0002-3874-3032]; Martínez Pillet, V. [0000-0001-7764-6895]Liquid-crystal variable retarders (LCVRs) are an emergent technology for space-based polarimeters, following its success as polarization modulators in ground-based polarimeters and ellipsometers. Wide-field double nematic LCVRs address the high angular sensitivity of nematic LCVRs at some voltage regimes. We present a work in which wide-field LCVRs were designed and built, which are suitable for wide-field-of-view instruments such as polarimetric coronagraphs. A detailed model of their angular acceptance was made, and we validated this technology for space environmental conditions, including a campaign studying the effects of gamma, proton irradiation, vibration and shock, thermo-vacuum and ultraviolet radiation.Publicación Restringido Detailed design of the imaging magnetograph experiment (IMaX): a visible imager magnetograph for the Sunrise mission(SPIE Astronomical Telescopes Instrumentation, 2006-07-07) Álvarez-Herrrero, Alberto; Belenguer Dávila, T.; Pastor, C.; González, L.; López Heredero, Raquel; Ramos, G.; Reina Aranda, Manuel; Sánchez, A.; Villanueva, J.; Sabau, L.; Martínez Pillet, V.; Bonet Navarro, J. A.; Collados Vera, Manuel; Jochum, L.; Ballesteros, E.; Medina Trujillo, J. L.; Ruiz, C. B.; González, J. C.; Del Toro Iniesta, J. C.; López Jiménez, A. C.; Castillo Lorenzo, J.; Herranz, M.; Jerónimo, J. M.; Mellado, P.; Morales, R.; Rodríguez, J.; Domingo, V.; Gasent, J. L.; Rodríguez, P.; 0000-0003-0248-2771; 0000-0003-4343-6632; 0000-0002-6297-0681; 0000-0002-3387-026X; 0000-0002-6210-9648; 0000-0002-4944-5823; 0000-0001-7764-6895; 0000-0003-1661-0594; 0000-0001-9631-9558; 0000-0002-1225-4177In this work, it is described the Imaging Magnetograph eXperiment, IMaX, one of the three postfocal instruments of the Sunrise mission. The Sunrise project consists on a stratospheric balloon with a 1 m aperture telescope, which will fly from the Antarctica within the NASA Long Duration Balloon Program. IMaX will provide vector magnetograms of the solar surface with a spatial resolution of 70 m. This data is relevant for understanding how the magnetic fields emerge in the solar surface, how they couple the photospheric base with the million degrees of temperature of the solar corona and which are the processes that are responsible of the generation of such an immense temperatures. To meet this goal IMaX should work as a high sensitivity polarimeter, high resolution spectrometer and a near diffraction limited imager. Liquid Crystal Variable Retarders will be used as polarization modulators taking advantage of the optical retardation induced by application of low electric fields and avoiding mechanical mechanisms. Therefore, the interest of these devices for aerospace applications is envisaged. The spectral resolution required will be achieved by using a LiNbO3 Fabry-Perot etalon in double pass configuration as spectral filter before the two CCDs detectors. As well phase-diversity techniques will be implemented in order to improve the image quality. Nowadays, IMaX project is in the detailed design phase before fabrication, integration, assembly and verification. This paper briefly describes the current status of the instrument and the technical solutions developed to fulfil the scientific requirements.Publicación Acceso Abierto Evaluation of a liquid crystal based polarization modulator for a space mission thermal environment(Elsevier, 2017-09-21) Silva-López, Manuel; Bastide, L. ; Restrepo, R.; García Parejo, Pilar; Álvarez-Herrrero, AlbertoThe Multi Element Telescope for Imaging and Spectroscopy (METIS) is one of the remote sensing instruments to be onboard the future NASA/ESA Solar Orbiter mission. The science nominal mission orbit will take the spacecraft from 0.28 to 0.95 astronomical units from the Sun, setting challenging and variable thermal conditions to its payload. METIS is an inverted-occultation coronagraph that will image the solar corona in the visible and UV wavelength range. In the visible light path a Polarization Modulation Package (PMP) performs a polarimetric analysis of the incoming solar light. This PMP is based on liquid crystal variable retarders (LCVR) and works under a temporal modulation scheme. The LCVRs behavior has a dependence on temperature and, as a consequence, it is critical to guarantee the PMP performance in the mission thermal environment. Key system specifications are the optical quality and the optical retardance homogeneity. Moreover, the thermally induced elastic deformations of the mechanical mounts and the LCVRs shall not produce any performance degradation. A suitable thermal control is hence required to maintain the system within its allowed limits at any time. The PMP shall also be able to reach specific set-points with the power budget allocated. Consequently, and in order to verify the PMP thermal design, we have experimentally reproduced the expected thermal flight environment. Specifically, a thermal-vacuum cycle test campaign is run at the different mission operational conditions. The purpose is both to check the stability of the thermal conditions and to study the optical quality evolution/degradation. Within this test transmitted wavefront measurements and functional verification tests have been carried out. To do that we adapted an optical interrogation scheme, based on a phase shifting interferometric technique, that allows for inspection of the PMP optical aperture. Finally, measurements obtained at non-operational temperature conditions are also shown. These results demonstrate that the device meets the specifications required to perform its operational role in the space mission environment.Publicación Restringido Liquid-crystal variable retarders for aerospace polarimetry applications(OSA (The Optical Society) Publishing, 2007-01-25) López Heredero, Raquel; Uribe Patarroyo, Néstor; Belenguer Dávila, T.; Ramos, G.; Sánchez, A.; Reina Aranda, Manuel; Martínez Pillet, V.; Álvarez-Herrrero, Alberto; Álvarez Herrero, A. [0000-0001-9228-3412]; López Heredero, R. [0000-0002-2197-8388]; Martínez Pillet, V. [0000-0001-7764-6895]We present the optical effects of different tests that simulate the aerospace environment on the liquid-crystal variable retarders (LCVRs) used in the Imaging Magnetograph eXperiment postfocal instrument of the SUNRISE payload within the NASA Long Duration Balloon program. Analysis of the influence of vacuum, temperature, vibration, and gamma and ultraviolet radiation is performed by measuring the effects of these tests on the optical retardance, the response time, the wavefront distortion, and the transmittance, including some in situ measurements. Outgassing measurements of the different parts of the LCVRs are also shown. From the results obtained it can be concluded that these optical devices are suitable and seem to be excellent candidates for aerospace platforms.Publicación Acceso Abierto The Imaging Magnetograph eXperiment (IMaX) for the Sunrise Balloon-Borne Solar Observatory(Springer Link, 2011-01-17) Martínez Pillet, V.; Del Toro Iniesta, J. C.; Álvarez-Herrrero, Alberto; Domingo, V.; Bonet Navarro, J. A.; González Fernández, C.; López Jiménez, A. C.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.; Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer Dávila, T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados Vera, Manuel; Deutsch, W.; Feller, A.; Girela, F.; Grauf, B.; López Heredero, Raquel; Herranz, M.; Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.; Orozco Suárez, D.; Ramos, G.; Reina Aranda, Manuel; Ramos, J. L.; Rodríguez, P.; Sánchez, A.; Uribe Patarroyo, Néstor; Barthol, P.; Gandorfer, A.; Knoelker, M.; Schmidt, Walter; Solanki, S. K.; Vargas Domínguez, S.; Ministerio de Ciencia e Innovación (MICINN); Deutsches Zentrum für Luft- und Raumfahrt (DLR); National Aeronautics and Space Administration (NASA); López Jiménez, A. [0000-0002-6297-0681]; Balaguer, M. [0000-0003-4738-7727]; Del Toro Iniesta, J. C. [0000-0002-3387-026X]; Reina Aranda, M. [0000-0003-0248-2771]; Álvarez Herrero, A. [0000-0001-9228-3412]; Herranz de la Revilla, M. L. [0000-0003-4343-6632]; Morales Muñoz, R. [0000-0003-1661-0594]; Pastor, C. [0000-0001-9631-9558]; Gasent Blesa, J. L. [0000-0002-1225-4177]; Collados, M. [0000-0002-6210-9648]; Jerónimo, J. M. [0000-0002-4944-5823]; Bellot Rubio, L. R. [0000-0001-8669-8857]; Martínez Pillet, V. [0000-0001-7764-6895]The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter built by four institutions in Spain that flew on board the Sunrise balloon-borne solar observatory in June 2009 for almost six days over the Arctic Circle. As a polarimeter, IMaX uses fast polarization modulation (based on the use of two liquid crystal retarders), real-time image accumulation, and dual-beam polarimetry to reach polarization sensitivities of 0.1%. As a spectrograph, the instrument uses a LiNbO3 etalon in double pass and a narrow band pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four Stokes parameters at various points inside the spectral line. This allows vector magnetograms, Dopplergrams, and intensity frames to be produced that, after reconstruction, reach spatial resolutions in the 0.15 – 0.18 arcsec range over a 50×50 arcsec field of view. Time cadences vary between 10 and 33 s, although the shortest one only includes longitudinal polarimetry. The spectral line is sampled in various ways depending on the applied observing mode, from just two points inside the line to 11 of them. All observing modes include one extra wavelength point in the nearby continuum. Gauss equivalent sensitivities are 4 G for longitudinal fields and 80 G for transverse fields per wavelength sample. The line-of-sight velocities are estimated with statistical errors of the order of 5 – 40 m s−1. The design, calibration, and integration phases of the instrument, together with the implemented data reduction scheme, are described in some detail.Publicación Restringido IMaX: a polarimeter based on Liquid Crystal Variable Retarders for an aerospace mission(Wiley Online Library, 2008-05-08) Uribe Patarroyo, Néstor; Álvarez-Herrrero, Alberto; López Heredero, Raquel; Del Toro Iniesta, J. C.; López Jiménez, A. C.; Domingo, V.; Gasent, J. L.; Jochum, L.; Martínez Pillet, V.; Del Toro Iniesta, J. C. [0000-0002-3387-026X]; López Jiménez, A. [0000-0002-6297-0681]; López Heredero, R. [0000-0002-2197-8388]; Álvarez Herrero, A. [0000-0001-9228-3412]; Gasenta Blesa, J. L. [0000-0002-1225-4177]; Martínez Pillet, V. [0000-0001-7764-6895]IMaX is the Imaging Magnetograph eXperiment, an instrument part of the payload of SUNRISE, a stratospheric balloon mission in Antarctica. It is also the precursor of the Visible Imaging Magnetograph of the future ESA Solar Orbiter mission. It is essentially a diffraction-limited imager that carries out spectropolarimetric measurements of high resolution (bandwidth of < 100 mÅ at 525.02 nm), and relates the polarimetric properties of the incoming light through a telescope with magnetic fields in the Sun, via the Zeeman effect. At the core of the instrument there are the polarization modulation components, two Liquid Crystal Variable Retarders (LCVRs). A demodulation efficiency is defined and used as the figure of merit, and it serves to find the theoretical optimum states for the LCVRs as well as to judge the quality of the pre-flight calibration of the system. This calibration and the method used to optimize the actual efficiency is explained. Also, the space qualification of the LCVRs is presented, where ellipsometry played a major role in studying the effects of radiation, vacuum and temperature in the operation of the LCVRs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Publicación Acceso Abierto Fine tuning method for optimization of liquid crystal based polarimeters(Optica Publishing Group, 2018-04-18) Álvarez-Herrrero, Alberto; García Parejo, Pilar; Silva-López, Manuel; Ministerio de Economía y Competitividad (MINECO)Liquid crystal variable retarders (LCVR) based polarimeters perform temporal polarization modulation by applying a sequence of driving voltages to introduce different optical retardances. However, even after a careful design and fabrication, manufacturing tolerances (i.e., slight optical axis misalignments, instrument residual polarization, optical activity in the LCVRs...) or the final system configuration (i.e., LCVRs in a convergent optical beam, thermal gradient across the clear aperture...) produce deviations from the ideal setup. As a consequence, all of these effects can reduce the polarimetric modulation efficiency of the device and, therefore, its signal-to-noise ratio. Hence, the voltage sequence applied according to the LCVR calibration curves may not be suitable to reach the optimal theoretical polarimetric efficiencies. In this work, a systematic fine tuning method for the LCVRs driving voltages is described an experimentally demonstrated.
