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See detailOptical study of diffraction grating/Fresnel lens combinations applied to a spectral-splitting solar concentrator for space applications
Michel, Céline ULg; Loicq, Jerôme ULg; Thibert, Tanguy ULg et al

in Applied Optics (2015), 54(22), 6666-6673

This paper presents a new design of a planar solar concentrator with spectral splitting of light for space applications. This concentrator spectrally splits the incident light into mainly two parts. Each ... [more ▼]

This paper presents a new design of a planar solar concentrator with spectral splitting of light for space applications. This concentrator spectrally splits the incident light into mainly two parts. Each part is then focused onto specific spatially separated photovoltaic cells, allowing for independent control of respective cells output power. These advantages of both spectral splitting and light focusing are here combined thanks to a specific diffraction grating superimposed on a Fresnel lens. The theoretical principle of the optical design is presented, with optimization of each element and improvement steps, including optimization of grating period evolution along the lens, and testing of two kinds of gratings (a blazed and a lamellar one). First numerical results are presented, highlighting the possibility to design a concentrator at about 10× or more for each cell, with an output power larger than that of a classical concentrator focusing on a GaAs SJ cell, and less than 10% of losses for tracking errors up to ±0.8°. Some experimental results are also presented. [less ▲]

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See detailPolarization holography for vortex retarders recording: laboratory demonstration
Piron, Pierre ULg; Blain, Pascal ULg; Décultot, Marc ULg et al

in Applied Optics (2015), 54(15), 4765--4770

This paper will present a prototype of the first set of vortex retarders made of liquid crystal polymers recorded by polarization holography. Vortex retarders are birefringent plates characterized by a ... [more ▼]

This paper will present a prototype of the first set of vortex retarders made of liquid crystal polymers recorded by polarization holography. Vortex retarders are birefringent plates characterized by a rotation of their fast axis. Liquid crystals possess birefringent properties and they are locally orientable. Their orientation is defined by the perpendicular to the local orientation of the recording field. Polarization holography is a purely optical recording method. It is based on the superimposition of coherent and differently polarized beams. It is used to shape the electric field pattern to enable the recording of vortex retarders. The paper details the mathematical model of the superimposition process. The recording setup is exposed; it is characterized by a nearly common path interferometer. Two sets of measurements allowing the prediction of the retarder’s features are presented and compared. Finally, the experimentally recorded retarder is shown, its characteristics are investigated and compared to the predicted ones. [less ▲]

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See detailSingle Wavelength Coarse Phasing In Segmented Telescopes
Simar, Juan Felipe ULg

in Applied Optics (2015), 54

Space observations of fainter and more distant astronomical objects constantly require telescope primary mirrors with a larger size. The diameter of monolithic primary mirrors is limited to 10 m because ... [more ▼]

Space observations of fainter and more distant astronomical objects constantly require telescope primary mirrors with a larger size. The diameter of monolithic primary mirrors is limited to 10 m because of manufacturing limitations. For space telescopes, the primary mirrors are limited to less than 5 m due to fairing capacity. Segmented primary mirrors thus constitute an alternative solution to deal with the steadily increase of the primary mirror size. The optical path di erence between the individual segments must be close to zero (few nm) in order to be di raction limited. We propose in this paper a new inter-segment piston sensor based on coherence measurement of a star image. This sensor is intended to be used in the co-phasing system of future segmented mirrors. [less ▲]

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See detailFeature issue of digital holography and 3D imaging (DH): introduction
Hayasaki, Yoshio; Liu, Jung-Ping; Georges, Marc ULg

in Applied Optics (2015), 54(1), 1-2

The OSA Topical Meeting “Digital Holography and 3D Imaging (DH)” was held in Seattle, Washington, 13–17 July 2014. Feature issues based on the DH meeting series have been released by Applied Optics (AO ... [more ▼]

The OSA Topical Meeting “Digital Holography and 3D Imaging (DH)” was held in Seattle, Washington, 13–17 July 2014. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. In this year (2014), Optics Express (OE) and AO jointly decided to have one such feature issue in each journal. The feature issue includes 27 papers and covers a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The DH meeting will continue in the future, as expected, and the next meeting is scheduled to be held on24–28 May 2015, at Shanghai Institute of Optics and Fine Mechanics, Shanghai, China. [less ▲]

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See detailPerformances of Volume Phase Holographic grating for space applications: study of the radiation effect
Loicq, Jerôme ULg; Georges, Marc ULg; Stockman, Yvan ULg et al

in Applied Optics (2013), 52(34),

The special properties of volume phase holographic gratings make them promising candidates for spectrometry applications where high spectral resolution, low levels of straylight, and low polarization ... [more ▼]

The special properties of volume phase holographic gratings make them promising candidates for spectrometry applications where high spectral resolution, low levels of straylight, and low polarization sensitivity are required. Therefore it is of interest to assess the maturity and suitability of volume phase holographic gratings as enabling technologies for future space missions, with demanding requirements for spectrometry. One of the main areas of research is related to grating ageing under space radiation. In the present paper, two volume grating technologies are analyzed and compared under gamma irradiation. The performances of both technologies, the photo–thermo–refractive glass and the Dichromated Gelatin, are tested on samples and assessed in the and near-infrared bands. The diffraction efficiency degradation under gamma irradiation is assessed. [less ▲]

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See detailPolarization holography for vortex retarders recording
Piron, Pierre ULg; Blain, Pascal ULg; Mawet, Dimitri et al

in Applied Optics (2013), 52(28), 7040-7048

We present an original static recording method for vortex retarders (VRs) made from liquid crystal polymers (LCPs) using the superimposition of several polarized beams. VRs are birefringent plates ... [more ▼]

We present an original static recording method for vortex retarders (VRs) made from liquid crystal polymers (LCPs) using the superimposition of several polarized beams. VRs are birefringent plates characterized by a rotation of their fast axis about their center. The new method is based on polarization holography and photo-orientable LCP. Combining several polarized beams induces the polarization patterns required for the recording process of VRs without mechanical action. A mathematical description of the method, the outcomes of the numerical simulations, and the first experimental results are presented. [less ▲]

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See detailDigital holographic interferometry with CO2 lasers and diffuse illumination applied to large space reflectors metrology
Georges, Marc ULg; Vandenrijt, Jean-François ULg; Thizy, Cédric ULg et al

in Applied Optics (2013), 52(1), 102-116

Digital holographic interferometry in the long wave infrared domain has been developed by combining a CO2 laser and a microbolometer array. The long wavelength allows large deformation measurements which ... [more ▼]

Digital holographic interferometry in the long wave infrared domain has been developed by combining a CO2 laser and a microbolometer array. The long wavelength allows large deformation measurements which are of interest in the case of large space reflectors undergoing thermal changes when in orbit. We review holography at such wavelengths and present some specific aspects related to this spectral range on our measurements. For the design of our digital holographic interferometer we studied the possibility of illuminating specular objects by a reflective diffuser. We discuss the development of the interferometer and the results obtained on a representative space reflector, first in the laboratory and then during vacuum cryogenic test. [less ▲]

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See detailNondestructive testing by using long wave infrared interferometric techniques with CO2 lasers and microbolometer arrays
Alexeenko, Igor; Vandenrijt, Jean-François ULg; Pedrini, Giancarlo et al

in Applied Optics (2013), 52(1), 57-67

We describe three different interferometric techniques (electronic speckle pattern interferometry, digital holographic interferometry, digital shearography), using a long wave infrared radiation produced ... [more ▼]

We describe three different interferometric techniques (electronic speckle pattern interferometry, digital holographic interferometry, digital shearography), using a long wave infrared radiation produced by a CO2 laser and recording on a microbolometers array. Experimental results showing how these methods can be used for nondestructive testing are presented. Advantages and disadvantages of these approaches are discussed. [less ▲]

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See detailDesign, manufacturing, and performance analysis of mid-infrared achromatic half-wave plates with diamond subwavelength gratings
Delacroix, Christian ULg; Forsberg, Pontus; Karlsson, Mikael et al

in Applied Optics (2012), 51

In this paper, we present an elegant solution for creating robust monolithic achromatic half-wave plates (HWPs) for the infrared, based on the form birefringence of subwavelength gratings (SWGs) made out ... [more ▼]

In this paper, we present an elegant solution for creating robust monolithic achromatic half-wave plates (HWPs) for the infrared, based on the form birefringence of subwavelength gratings (SWGs) made out of diamond. We use the rigorous coupled wave analysis to design the gratings. Our analysis shows that diamond, besides its outstanding physical and mechanical properties, is a suitable substrate to manufacture mid-infrared HWPs, thanks to its high refractive index which allows etching SWGs with lower aspect ratio. Based on our optized design, we manufactured a diamond HWP for the 11-13.2 µm region, with an estimated mean retardance ~3.143 ± 0.061 rad (180.08 ± 3.51°). In addition, an antireflective grating was etched on the backside of the wave plate, allowing a total tansmittance between 89 and 95% over the band. [less ▲]

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See detailCalibration of force actuators on an adaptive secondary prototype
Ricci, Davide ULg; Riccardi, Armando; Zanotti, Daniela

in Applied Optics (2008), 47

In the context of the Large Binocular Telescope project, we present the results of force actuator calibrations performed on an adaptive secondary prototype called P45, a thin deformable glass with magnets ... [more ▼]

In the context of the Large Binocular Telescope project, we present the results of force actuator calibrations performed on an adaptive secondary prototype called P45, a thin deformable glass with magnets glued onto its back. Electromagnetic actuators, controlled in a closed loop with a system of internal metrology based on capacitive sensors, continuously deform its shape to correct the distortions of the wavefront. Calibrations of the force actuators are needed because of the differences between driven forces and measured forces. We describe the calibration procedures and the results, obtained with errors of less than 1.5%. [less ▲]

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See detailAssessment of space radiation effects on solid-state Brillouin phase conjugate mirrors
Brignon, Arnaud; Richard, Sébastien; Gusarov, Andreï et al

in Applied Optics (2007), 46(22), 5329-5335

Optical phase conjugation (OPC) provides a means of dynamical correction of thermally induced aberrations in high-power laser systems. This method is particularly interesting for space applications ... [more ▼]

Optical phase conjugation (OPC) provides a means of dynamical correction of thermally induced aberrations in high-power laser systems. This method is particularly interesting for space applications because it is passive, mechanically simple, and allows for improved beam quality with only a small loss in power. To exploit it one has to assess the effect of the space environment, and in particular of space radiation, on the properties of the materials that are suitable for phase-conjugating mirrors (PCMs). We have investigated both materials providing OPC via stimulated Brillouin scattering and actual PCMs with regard to their radiation hardness. Proton- and gamma-irradiated PCMs in the form of 30-cm long silica rods and 5-cm long TeO2 crystals were tested in a single frequency flash-lamp pumped Nd:YAG system delivering up to 220 mJ pulses with a 20 ns duration at a 50 Hz repetition rate. The difference in the reflectivity between irradiated and nonirradiated components was found to be within the measurement errors. Gamma irradiation of TeO2 resulted in a decrease of the laser-induced damage threshold, while for silica possible changes were below the detection limit. Our results show that synthetic fused silica, and Lithosil in particular, can be used for generating the OPC in laser systems operating in a space radiation environment. [less ▲]

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See detailInstrumental stability requirements for exoplanet detection with a nulling interferometer: variability noise as a central issue
Chazelas, Bruno; Brachet, Frank; Bordé, Pascal et al

in Applied Optics (2006), 45

We revisit the nulling interferometer performances that are needed for direct detection and the spectroscopic analysis of exoplanets, e.g., with the DARWIN [European Space Agency-SCI 12 (2000)] or TPF-I ... [more ▼]

We revisit the nulling interferometer performances that are needed for direct detection and the spectroscopic analysis of exoplanets, e.g., with the DARWIN [European Space Agency-SCI 12 (2000)] or TPF-I [JPL Publ. 05-5, (2005)] missions. Two types of requirement are found, one concerning the mean value of the instrumental nulling function <nl(lambda)> and another regarding its stability. The stress is usually put on the former. It is stringent at short wavelengths but somewhat relaxed at longer wavelengths. The latter, which we call the variability noise condition, does not usually receive enough attention. It is required regardless of telescope size and stellar distance. The results from three nulling experiments performed in laboratories around the world are reported and compared with the requirements. All three exhibit 1/f noise that is incompatible with the performances required by the mission. As pointed out by Lay [Appl. Opt. 43, 6100-6123 (2004)], this stability problem is not fully solved by modulation techniques. Adequate solutions must be found that are likely to include servo systems using the stellar signal itself as a reference and internal metrology with high stability. [less ▲]

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See detailSubwavelength surface-relief gratings for stellar coronagraphy
Mawet, Dimitri; Riaud, Pierre ULg; Surdej, Jean ULg et al

in Applied Optics (2005), 44 Issue 34

We present a new design of a phase mask coronagraph implemented with subwavelength diffractive optical elements consisting of optimized surface-relief gratings. Phase mask coronagraphy is a recent ... [more ▼]

We present a new design of a phase mask coronagraph implemented with subwavelength diffractive optical elements consisting of optimized surface-relief gratings. Phase mask coronagraphy is a recent technique that seeks to accommodate both high dynamic and high angular resolution imaging of faint sources around bright astrophysical objects such as exoplanets orbiting their host stars. The original design we propose is a new, integrated, and flexible solution to the pi phase-shift chromaticity of the phase mask coronagraphs. It will allow broadband observations, i.e., shorter integration times and object characterizations, by means of spectroscopic analysis. The feasibility of the component manufacturing is also considered through a tolerance study. [less ▲]

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See detailHigh transmission efficiency for surface plasmon resonance by use of a dielectric grating
Lenaerts, Cedric ULg; Michel, Fabrice ULg; Tilkens, Bernard et al

in Applied Optics (2005), 44(28), 6017-6022

The efficiency of the transmission of surface plasmon waves by use of a dielectric diffraction grating is discussed. The Kretschmann device allows us to obtain a surface plasmon resonance that consists of ... [more ▼]

The efficiency of the transmission of surface plasmon waves by use of a dielectric diffraction grating is discussed. The Kretschmann device allows us to obtain a surface plasmon resonance that consists of an absorption peak in the reflection spectrum. When surface plasmon resonance occurs, the TM-polarization mode of the incident electromagnetic wave is neither transmitted nor reflected. The procedure to transform an absorption peak into a transmission peak is described. Transmittivity of 68% is obtained for a simple structure that consists of a thin-film layer of Ag coated on a volume diffraction grating and embedded between two dielectric media. The results presented herein were obtained by numerical simulations that were carried out by use of an algorithm based on the rigorous coupled-wave theory. [less ▲]

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See detailAtmospheric Trace Molecule Spectroscopy (ATMOS) experiment version 3 data retrievals
Irion, Fredrick W.; Gunson, Michael R.; Toon, Geoff C. et al

in Applied Optics (2002), 41(33), 6968-6979

Version 3 of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment data set for some 30 trace and minor gas profiles is available. From the IR solar-absorption spectra measured during four Space ... [more ▼]

Version 3 of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment data set for some 30 trace and minor gas profiles is available. From the IR solar-absorption spectra measured during four Space Shuttle missions (in 1985, 1992, 1993, and 1994), profiles from more than 350 occultations were retrieved from the upper troposphere to the lower mesosphere. Previous results were unreliable for tropospheric retrievals, but with a new global-fitting algorithm profiles are reliably returned down to altitudes as low as 6.5 km (clouds permitting) and include notably improved retrievals of H2O, CO, and other species. Results for stratospheric water are more consistent across the ATMOS spectral filters and do not indicate a net consumption of H-2 in the upper stratosphere. A new sulfuric-acid aerosol product is described. An overview of ATMOS Version 3 processing is presented with a discussion of estimated uncertainties. Differences between these Version 3 and previously reported Version 2 ATMOS results are discussed. Retrievals are available at http://atmos.jpl.nasa.gov/atmos. (C) 2002 Optical Society of America. [less ▲]

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See detailPattern recognition with a digital holographic microscope working in partially coherent illumination
Dubois, Frank; Minetti, Christophe; Monnom, Olivier et al

in Applied Optics (2002), 41(20), 4108-4119

We describe the implementation of the automatic spatial-frequency-selection filter for recognition of patterns obtained with a digital holographic microscope working with a partially coherent source. The ... [more ▼]

We describe the implementation of the automatic spatial-frequency-selection filter for recognition of patterns obtained with a digital holographic microscope working with a partially coherent source. The microscope provides the complex-optical-amplitude field that allows a refocusing plane-by-plane of the sample under investigation by numerical computation of the optical propagation. By inserting a correlation filter in the propagation equation, the correlation between the filter and the propagated optical field is obtained. In this way, the pattern is located in the direction of the optical axis. Owing to the very weak noise level generated by the partially coherent source, the correlation process is shift invariant. Therefore the samples can be located in the three dimensions. To have a robust recognition process, a generalized version of the automatic spatial-frequency-selection filters has been implemented. The method is experimentally demonstrated in a two-class problem for the recognition of protein crystals. (C) 2002 Optical Society of America. [less ▲]

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See detailPhase-shifting real time interferometry that uses bismut silicon oxide crystals
Georges, Marc ULg; Lemaire, Philippe

in Applied Optics (1995), 34(32), 7497-7506

A bismuth silicon oxide crystal is used in the diffusion regime as a dynamic recording medium in a real-time holographic interferometer based on anisotropic self-diffraction. This device is connected with ... [more ▼]

A bismuth silicon oxide crystal is used in the diffusion regime as a dynamic recording medium in a real-time holographic interferometer based on anisotropic self-diffraction. This device is connected with an interferogram-analysis method that uses the phase-shifting technique for quantitative measurement of diffusive-reflecting object deformations. In addition to the usual error sources in phase shifting, the temporal interferogram erasure is studied and is found weakly perturbative for the measured phase. Itis shown that quantitative measurements are possible for low-intensity object beams (8 μW/cm2) and a large observed area. Apractical situation of defect monitoring in a composite structure is presented. [less ▲]

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See detailDesign for polarizing holographic optical elements
Habraken, Serge ULg; Renotte, Yvon; Roose, Stéphane ULg et al

in Applied Optics (1995), 34(19), 3595-3602

We present results of the application of a three-dimensional rigorous-vector coupled-wave theory to the design of polarizing holographic optical elements. Two different cases have been selected giving ... [more ▼]

We present results of the application of a three-dimensional rigorous-vector coupled-wave theory to the design of polarizing holographic optical elements. Two different cases have been selected giving rise to two types of element, one of which is completely original. Experimental realizations were performed. The recording material was dichromated gelatin because of its outstanding performance related to diffraction efficiency. A fair agreement between the theoretical previsions and the experimental results was achieved. [less ▲]

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