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ARIEL, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was selected as the fourth medium-class mission in ESA’s Cosmic Vision program. ARIEL is based on a 1 m class telescope optimized for spectroscopy in the waveband between 1.95 and 7.8 micron and operating in cryogenic conditions. Fabrication of the 1.1 m aluminum primary mirror for the ARIEL telescope requires technological advances in the three areas of substrate thermal stabilization, optical surface polishing and coating. This article describes the qualification of the three procedures that have been set up and tested to demonstrate the readiness level of the technological processes employed. Substrate thermal stabilization is required to avoid deformations of the optical surface during cool down of the telescope to the operating temperature below 50 K. Purpose of the process is to release internal stress in the substrate that can cause such shape deformations. Polishing of large aluminum surfaces to optical quality is notoriously difficult due to softness of the material, and required setup and test of a specific polishing recipe capable of reducing residual surface shape errors while maintaining surface roughness below 10 nm RMS. Finally, optical coating with protected silver must be qualified for environmental stability, particularly at cryogenic temperatures, and uniformity. All processes described in this article have been applied to aluminum samples of up to 150 mm of diameter, leading the way to the planned final test on a full size demonstrator of the ARIEL primary mirror.

International audience

The development of high-power lasers requires optics with very low absorption to avoid detrimental thermal effects. In this work, we discuss our recent developments on the use of lock-in thermography to measure absorption. We apply this technique in a multipass configuration to increase the effective power on the tested samples. We present a system based on a kW-class ytterbium fiber laser operating at 1.07 µm wavelength, which enables exposing samples to 5 kW effective power and measuring absorption in the ppm range. The implementation, calibration procedure, and obtained performance are discussed with some applications to single-layer coatings of H f O 2 , T a 2 O 5 , T i O 2 , N b 2 O 5 , and S i O 2 deposited by plasma-assisted electron beam deposition.

We present hereafter the results on the manufacturing of complex optical coatings done with PIAD (Plasma-Ion Assisted Deposition) for various applications. Spectral and WFE measurements indicated that components are well within specifications.

The development of high power lasers implies specific needs of optics with very low absorption to avoid detrimental thermal effects up to damage of optical components, and associated metrology of these optics. In this work, we discuss on our recent developments of a thermographic-based technique to measure absorption: specifically, the Lock-In Thermography (LIT) technique applied in a multipass configuration to increase the effective power on the tested samples. We will present the system developed at the Institut Fresnel that is based on 1.5 kW Ytterbium fiber, that allows to submit samples to 5 kW effective power and measure absorption levels down to the ppm on optical coatings.

Optical coatings have been extensively characterized these last decades, due to more and more severe requirements. These characterizations include optical properties, uniformity, hardness, adhesion and stress, damage threshold, absorption, scattering and others… Despite this state of the art, photo-induced thermal radiation [1]–[3] in optical coatings was rarely investigated in detail until now, while emissivity plays a key role in numerous sectors related to energy and defence, space optics and MIR imaging... This is the scope of this paper to provide an exact theory of thermal radiation in optical multilayers submitted to an arbitrary illumination (continuous, pulsed, modulated). The spectral range of thermal radiation (TR) is temperature (Tp) dependent. Hence it varies with incident power, and with the imaginary indices of the thin film materials. Index dispersion also plays a key role for short duration beams. As always with thin films, the TR waves follow Maxwell equations and their angular and spectral patterns are shaped by the coating design, which may open an opportunity to control these patterns [4], [5]. Relying on the fluctuation dissipation theorem [1], we introduce in Maxwell equations the adequate currents responsible for thermal radiation. These currents are temperature related, for which reason the depth and time distribution of temperature is also calculated for arbitrary illumination regimes. The Tp calculation relies on the analogy [6], [7] between thermal (diffusion equation) and optics (propagation equation) in metallic media. The resulting currents are bulk currents which vary within the depth of the stack, which creates a similarity with luminescent micro-cavities [8]. Eventually we calculate the waves emitted from these currents and this gives the angular, wavelength and temporal patterns of thermal radiation which merges in free space. The TR patterns are analysed for a series of coatings and a few ideas are presented to reduce, confine, or enhance the thermal waves.

The increase of continuous wave laser power is an important topic in various new industrial and defence applications. One of the important limitation is due to the thin film component absorption (intrinsic and defects-related) that induces beam distortions and eventually laser-induced damages. In order to study this absorption, it is of prime importance to accurately measure low absorption levels and to determine the origin of this absorption. In this work, we present the use of Lock-In Thermography (LIT) to absorption measurement. This technique relies on the use of a pump laser beam at 1 μm that is modulated at low frequency and an infrared camera that images the thin-film sample that is being heated. By applying a lock-in treatment on thermal images, we show that we can obtain an image of the temperature increase over the optical component with low noise level. A LIT setup with a sensitivity of a few ppm and a ten times better accuracy is demonstrated. We also show that this setup can be used to make mappings of local absorption and can easily reveal local defects with absorption that can be one order of magnitude higher that intrinsic one. This setup is finally implemented to make measurements on different single layer thin-films. Layers made with different materials (Nb2O5, SiO2, TiO2, HfO2) and deposited by plasma ion assisted deposition or plasma-assisted reactive magnetron sputtering are studied. We explore also the effect of annealing on these dense coatings. Finally, we investigate how these intrinsic absorption levels can be used to investigate the absorption of multilayers structures.

Protection of silver mirror stacks from environmental degradation before launching is crucial for space applications. Hereby, we report a comparative study of the advanced protection of silver mirror stacks for space telescopes provided by SiO2 and Al2O3 coatings in conditions of accelerated aging by sulfidation. The model silver stack samples were deposited by cathodic magnetron sputtering on a reference silica substrate for optical applications and a surface-pretreated SiC substrate. Accelerated aging was performed in dry and more severe wet conditions. Optical micrographic observations, surface and interface analysis by Time-of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and reflectivity measurements were combined to comparatively study the effects of degradation. The results show a lower kinetics of degradation by accelerated aging of the stacks protected by the alumina coating in comparable test conditions., Comment: JOURNAL OF MATERIALS SCIENCE \& TECHNOLOGY, 2020, Advanced Corrosion-Resistant Materials and Emerging Applications

International audience; The role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H2S entry and Ag2S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H2S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO2 layer.

Atmospheric Remote-Sensing Infrared Exoplanet Large Survey (Ariel) has been adopted as ESA “Cosmic Vision” M4 mission, with launch scheduled for 2029. Ariel is based on a 1 m class telescope optimized for spectroscopy in the waveband between 1.95 and 7.8 μm, operating in cryogenic conditions in the range 40–50 K. Aluminum has been chosen as baseline material for the telescope mirrors substrate, with a metallic coating to enhance reflectivity and protect from oxidation and corrosion. As part of Phase B1, leading to SRR and eventually mission adoption, a protected silver coating with space heritage has been selected and will undergo a qualification process. A fundamental part of this process is assuring the integrity of the coating layer and performance compliance in terms of reflectivity at the telescope operating temperature. To this purpose, a set of flat sample disks have been cut and polished from the same baseline aluminum alloy as the telescope mirror substrates, and the selected protected silver coating has been applied to them by magnetron sputtering. The disks have then been subjected to a series of cryogenic temperature cycles to assess coating performance stability. This study presents the results of visual inspection, reflectivity measurements and atomic force microscopy (AFM) on the sample disks before and after the cryogenic cycles.

We present a new method for the in situ measurement of the amplitude and phase of the reflection coefficient of a plane substrate installed in a mechanical holder rotating at high speed (120 turns per minute) during the deposition of optical thin films. Our method is based on digital holography and uses a self-referenced scheme to cancel the effects of the severe constraints generated by the vibrational and thermal environment of the deposition machine.

The performances that are required today for optical components are increasingly demanding, both in terms of the spectral response and the conditions to which the components are subjected. So-called dense deposition techniques for thin film coating currently make it possible to respond in many cases to this ever-increasing requirement. Indeed, conventional evaporation techniques that can address a large number of applications such as metallic coatings, antireflection coatings, mirrors, are no longer sufficient and we currently rely on the dense deposition techniques such as, for instance, magnetron sputtering which allow implementing layers stable and low-ageing behavior. In this paper, we will review the recent achievements at CILAS by magnetron sputtering technique on high-performance silver coatings for space applications. In our premises in Aubagne, CILAS has implemented a large dimension in-line magnetron sputtering coating machine with which such silver coatings are realized. This equipment with oversized dimensions involving a 6 meters by 3 meters vacuum chamber, 12 turbomolecular pumps and 7 planar magnetrons over 2.50m long will be presented in detail. In particular, the wide range of configurations will also be illustrated with complex coatings achievements with respect to the capability of the machine which is equipped with magnetrons, that may be powered in Radio Frequency, Mid Frequency, Direct Current or pulsed Direct Current modes. For several years, CILAS has improved its coating processes to produce high quality silver coatings, taking into account spectral performances, environmental conditions and also coating uniformity over 2meter by 2 meter dimensions. Further developments have been led by CILAS with the support of the French Space Agency as part of Research and Development activities to improve environmental performance; we present here characterization results on samples before and after environmental qualification (temperature, humidity, vacuum heat ...) and on components with dimensions up to 600mm. A multi-year test campaign including stress measurements and adhesion tests on samples and mirror demonstrator will also be presented.

Stack Array Mirrors (SAM) technology offers high order correction, with up to several thousands of actuators, controllable at high frequency, up to several kHz. A new generation of piezo-electric actuators with high reliability has been developed during the last years. This technology is well-adapted for large deformable mirrors (DMs) with thousands of actuators for future needs for Extremely Large Telescopes. We present the design and the modelling of the two large DMs for NFIRAOS, the multi-conjugate adaptive optics system of the Thirty Meter Telescope (TMT): DM0 which shows 3125 actuators and DM11 which shows 4548 actuators. A DM prototype with 616 actuators has been manufactured to validate the manufacturing steps and the specifications of the future large DMs, including their behavior at both ambient and low temperature (-30°C). The prototype includes the new generation of piezo actuators with improved reliability thanks to an optimization of the fabrication processes. Experimental results of accelerated ageing tests and mechanical fatigue are presented. After complete assembly, the prototype is qualified in a specific cool chamber with interferometric measurements. The results are the following: operational stroke higher than 10 μm PV at both ambient and -30°C with uniformity better than 5%, overall non-linearity lower than 5%, resonance frequency of the actuators higher than 10 kHz. Based on the measurements done on the overall temperature range (+20°C to -30°C), the best flat is lower than the goal specification of 10 nm RMS mechanical. An enhanced protected silver coating done by magnetron sputtering allows a high level of reflectivity especially in the near infrared range and long-life durability.

Parasitic light is an important issue in optical systems and may be responsible for huge limitation of final performances. Use of absorbing coated surfaces is known to be an efficient means to reduce such parasitic light sources and various solutions exist that can be applied to mechanical surfaces such as black paints, carbon nanotubes or surface passivation. In this paper, we show how thin film multilayer coatings can be a solution to answer this problematic as it is possible to design accurate spectral response that presents a very low level of reflectance with a zero value of transmittance. After a description of the design steps, we will focus on the realization of such sophisticated metal-dielectric multilayer stacks using dense coating techniques; in particular, we will show that master of refractive index of very thin metallic layers is an asset to achieve accurate performances and how in situ optical broadband monitoring allows excellent reproducibility of production processes even for few nanometers-thick layers required in metal-dielectric absorbers. Spectral and angular measurements of different coatings solutions will be given on various types of substrates (glass or metallic). Environmental qualification tests and spectral characterizations are also presented showing the stability of the performances in severe conditions compatible with severe environment. In particular, coatings developed for various projects will illustrate this study.

Today high angular resolution telescopes for space observation satellites require primary mirrors with larger and larger dimensions. For such mirrors, high-performance silver coating is required and is a key part of the component. For more than 20 years, CILAS has developed an expertise in the field of thin film optical coatings in order to answer a wide range of spectral performances and produce high quality thin film coatings. Among the various coating technologies that may answer such demand, magnetron sputtering is particularly well-suited to produce dense layers with improved mechanical performances and a high level of uniformity.

During the last few years, the evolution of deposition technologies of optical thin films coatings and associated in-situ monitoring methods enables us today to successfully answer the increasingly request of space systems for Earth observation. Geostationary satellite COMS-1 (Communication, Ocean, Meteorological Satellite-1) of Astrium has the role of ensuring meteorological observation as well as monitoring of the oceans. It is equipped with a colour imager to observe the marine ecosystem through 8 bands in the visible spectrum with a ground resolution of 500m. For that, this very high technology instrument is constituted with a filters wheel in front of the oceanic colour imager with 8 narrow band filters carried out and qualified by Cilas.

CILAS is involved in a scientific project for SRON Netherlands Institute for Space Research, on the development of multilayer coatings for the silicon immersed grating prism, which is a key component of the short-wave-infrared (SWIR) channel of the TROPOMI imaging spectrometer. For the project, two specific coatings have been implemented and qualified by CILAS: first, an antireflection coating deposited on the entrance and exit facets of the immersed grating prism, which reaches a very low value of reflectivity in the infrared [2305nm; 2385nm] spectral range and for a wide angular range [0° to 47°] of incidence of the transmitted light, and second, a metal-dielectric absorbing coating for the third facet of the prism to eliminate parasitic light inside the silicon prism.

We present the status of our immersed diffraction grating technology, as developed at SRON and of their multilayer optical coatings as developed at CILAS. Immersion means that diffraction takes place inside the medium, in our case silicon. The high refractive index of the silicon medium boosts the resolution and the dispersion. Ultimate control over the groove geometry yields high efficiency and polarization control. Together, these aspects lead to a huge reduction in spectrometer volume. This has opened new avenues for the design of spectrometers operating in the short-wave-infrared wavelength band. Immersed grating technology for space application was initially developed by SRON and TNO for the short-wave-infrared channel of TROPOMI, built under the responsibility of SSTL. This space spectrometer will be launched on ESA's Sentinel 5 Precursor mission in 2015 to monitor pollution and climate gases in the Earth atmosphere. The TROPOMI immersed grating flight model has technology readiness level 8. In this program CILAS has qualified and implemented two optical coatings: first, an anti-reflection coating on the entrance and exit facet of the immersed grating prism, which reaches a very low value of reflectivity for a wide angular range of incidence of the transmitted light; second, a metal-dielectric absorbing coating for the passive facet of the prism to eliminate stray light inside the silicon prism. Dual Ion Beam Sputtering technology with in-situ visible and infrared optical monitoring guarantees the production of coatings which are nearly insensitive to temperature and atmospheric conditions. Spectral measurements taken at extreme temperature and humidity conditions show the reliability of these multi-dielectric and metal-dielectric functions for space environment. As part of our continuous improvement program we are presently developing new grating technology for future missions, hereby expanding the spectral range, the blaze angles and grating size, while optimizing performance parameters like stray light and wavefront error. The program aims to reach a technology readiness level of 5 for the newly developed technologies by the end of 2012. An outlook will be presented.

Stray light is an important issue in optical systems and may be responsible for huge limitation of final performances. Use of black coated surfaces is known to be an efficient means to reduce such parasitic light sources and various solutions exist that can be applied to mechanical surfaces such as black paints or black anodization; these coatings are relatively thick and to produce thin, black baffle edges, a thin layer technology is thus needed. In this paper, we show how thin film multilayer coatings can be a solution to answer this problematic as it is possible to design accurate spectral response that present a very low level of reflectance with a zero value of transmittance.

International audience; In this work, we addressed the local degradation mechanisms limiting the pre-launch environmental durability of thin-layered silver stacks for demanding space mirror applications. Local initiation and propagation of tarnishing were studied by combined surface and interface analysis on model stack samples consisting of thin silver layers supported on light-weight SiC substrates and protected by thin SiO2 overcoats, deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. The results show that tarnishing is locally initiated by the formation of Ag2S columns erupting above the stack surface. Ag2S growth is promoted at high aspect ratio defects (surface pores) of the SiC substrate as a result of an imperfect protection by the SiO2 overcoat. Channels most likely connect the silver layer to its environment through the protection layer, which enables local H2S entry and Ag2S growth. The silver sulfide columns grow in number and size eventually leading to coalescence with increasing H2S exposure. In more advanced stages, tarnishing slows down owing to saturation of all pre-existing imperfectly protected sites of preferential sulfidation. However, it progresses radially at the basis of the Ag2S columns underneath the protection layer, consuming the metallic silver layer and deteriorating the protecting overcoat.

International audience; Single cavity Fabry-Perot filters are one of the most popular designs for the production of narrow bandpass filters. The usual deposition strategy to create such filters based on optical monitoring at the filter central wavelength is well-known and has proven its strength over decades. We review in this paper the possible optical methods to monitor such a filter during production and analyze their strengths and weaknesses. Then, we discuss a new monitoring procedure, mixing different methods, to minimize the production errors of this filter while maintaining a precise filter centering. This strategy is applied on different bandpass filter designs.

This paper describes a new method, based on the use of a broadband monitoring system, that allows to determine the spectral dependence of the optical constants of a tantala layer without the use of a dispersion model.

International audience; One of the critical steps in the fabrication of complex optical interference filters is the precise control of the thickness of the layers during the fabrication process. However, the definition of the optimal optical monitoring strategy remains a challenge as it relies on user experience and there is no reliable automatic determination of this strategy. Here, we propose a semi-automated method that allows the determination of the optimal strategy. It is based on the combination of trinary mappings to select spectral regions that are compatible with optical monitoring and the use of the reflected phase error at a single wavelength versus optical monitoring wavelength. We show how this procedure can be used for the determination of either a single optical monitoring wavelength or a multi-wavelength procedure of a complex filter and confirm these theoretical results with an experimental demonstration.

We present hereafter a study of complex bandpass optical interference filters with central wavelengths ranging in blue region or in the near infrared. For these applications, the required functions are particularly complex as they must present a very narrow bandwidth as well as a high level of rejection over a broad spectral range. Moreover, these components must have a good flatness meaning that the stress induced by the different layers has to be taken in account in the filter design. We present a thorough study of these filters including their design, fabrication using Plasma Assisted Reactive Magnetron Sputtering (PARMS) and characterization. Excellent agreement between experimental and theoretical spectral performances associated with a final sag of 326 and 13 nm, and uniformity from −0.05 to 0.10 and −0.10 to 0.20% are demonstrated for the two manufactured filters.

We present recent developments on deformable mirrors (DM) for astronomy with ground-based telescopes. A new generation of actuators with high reliability and high performances has been developed for Stack Array Mirrors. These actuators are suitable for a large range of DMs, including future needs for Extremely Large Telescopes. Design and modelling of large DMs for Thirty Meter Telescope and European Extremely Large Telescope are presented. The Monomorph mirrors combines simplicity and efficiency to correct the wavefront deformation. Astronomical telescopes can benefit of the developments performed on this Monomorph technology for high power laser chains and for spaceborn instrumentation.

The capability to transfer a multilayer coating from the initial substrate on which it was deposited to another one is an interesting technique for the manufacturing of patterned components with a high number of different filters such as stripe filters. The two major technological steps of the transfer, namely the removal from the initial substrate, and the bonding onto the new one, are described in this paper. The principle of this approach is validated by the transfer of a band-pass filter with the typical sizes of a stripe.

International audience; An alternative new technique for the determination of efficient optical monitoring strategy of optical interference filters is presented. This technique relies on the analysis of optical monitoring signals for different optical monitoring wavelengths and the comparison of these signals with some pre-defined criteria in order to generate potential spectral path compatible with a dedicated trigger point monitoring technique. Trinary mappings are then generated in order to determine possible optical monitoring strategies. This technique is finally implemented on various filter designs and experimentally validated.

We present hereafter the results on the manufacturing of complex optical coatings done with dual ion beam sputtering technique (DIBS). Such technology uses a first ion beam gun for sputtering a target and a second one for compacting the sputtered material. The density of the deposited layer is very close to the bulk material and enables the coatings to be nearly insensitive to environmental parameters. This technology is well adapted to severe environments as it allows the production of very dense layers and high quality coatings. The use of an in-situ optical monitoring system in visible and near infrared range (up to 2500nm) permits to reach severe spectral specifications and to have a good agreement with the theoretical designs. In this paper, we will focus on some complex optical functions that have been manufactured with DIBS technique: narrow band-pass filters and wide band filters including large blocking range with more than 100 layers and 25 μm total thickness, antireflection coatings which reach very low values of reflectivity in the near infrared spectral domain for wide angular ranges, and also metal-dielectric absorbing coatings. We will also give an analysis of the cosmetics performances of the deposited layers, which shows the high quality of the coatings even with functions with large total thickness. Many experimental results of qualification tests in temperature, humidity, thermal vacuum, radiations,… are presented and show the reliability of these multidielectric components in space or cryo-vacuum environment.

In this paper, we will present recent achievements done with our large dimension magnetron sputtering coating machine that has been implemented by CILAS company in its premises in Aubagne. Such equipment called PACA2M (PulverisAtion CAthodique de 2M) is an inline coating system that has been designed to ensure uniform coating on large optical components, up to 2 meters by 2 meters, 40 centimeters thick and to 1.5 ton weight. We will see how its wide variety of configurations based on seven 2.5 meters-long planar magnetrons, that may be powered in various modes (RF, MF, DC, ..) allows us producing complex optical functions such as multilayer dielectric mirrors, antireflective coatings and protected or enhanced metallic mirrors from ultraviolet to infrared applications. Moreover, an all-fibered broadband optical monitoring system developed in collaboration by Institut Fresnel is installed on this industrial machine and allows extremely accurate monitoring carried out on samples and fine characterization directly on components. Many spectral measurements and cosmetic results will be given that show that this equipment is well adapted for producing large optical components with high quality for various applications in the fields of industry, space or astronomy. In particular, for space application, PACA2M coating machine can be used to produce in a same batch all the required models as it is possible to simultaneously coat flight models, qualification witnesses and spare models. The stability of the performances in severe environmental conditions compatible with space environment will be illustrated with qualifications tests and characterizations.

In this paper, we show how thin film absorbing coatings can be designed with multilayers using both metallic and dielectric materials involving some thicknesses that are very low down to some nanometers. Such multilayers enable to reach a very low level of reflectance and a zero value of transmittance, which can be a solution for stray light reduction in optical systems. After a description of the design steps, we will present the manufacturing of such multilayer stacks using magnetron sputtering technique and we will see how such coating technique is very well suited for production due to its high process reproducibility even for very thin layers required in metal-dielectric absorbers. Monitoring of such coatings is also presented with the help of a powerful in situ optical system developed in collaboration with Institut Fresnel that allows characterization of in-situ refractive indices of deposited materials and broadband monitoring of the multilayer stack. Many results will be given on qualification samples, such as environmental tests and spectral characterizations that show the stability of the performances in severe environmental conditions. At last, we will focus on the spectral and angular scattering behavior of such absorbing coatings and we will present several measurements performed on glass or metallic substrates with different roughnesses.

We present hereafter the results on the fabrication of complex optical filters within the Institut Fresnel in close collaboration with CILAS. Bandpass optical interference filters, with central wavelengths ranging in near ultraviolet or in the near infrared, were deposited on both sides of glass substrates with a very good congruence with theoretical designs. For these applications, the required functions are particularly complex as they must present a very narrow bandwidth as well as a high level of rejection over a broad spectral range. Moreover, in order to satisfy more and more critical specifications on flatness of the component treated on both faces, the stress induced by the different layers has to be taken in account in the filter design. All these components were manufactured using Plasma Assisted Reactive Magnetron Sputtering (PARMS) technics offered by the HELIOS machine and monitored in real time with an OMS5000 in-situ optical monitoring, both developed by BUHLER Optics. Compressive mechanical stress of 364 MPa and 55 MPa respectively for SiO 2 and Nb 2 O 5 are measured, final sag of 326 nm and 13 nm, and uniformity from -0.05% to 0.10% and from -0.10% to 0.20% are obtained respectively for the two manufactured filters.

A statistical model of nanoprecursors threshold distribution for the interpretation of laser-damage probability curves is investigated. Each kind of precursor is characterized by a Gaussian distribution of threshold. Accurate probability curves of laser-induced damage (1-on-1, 5-ns single shot at 1.064-μm) are plotted in the bulk and at the surfaces of optical components. Results are then fitted with the model presented. A good agreement is obtained between theory and experiment, which permits to identify different kinds of defects and extract their densities and threshold distribution. The interpretation of these data is then discussed according to their nature and origin (cleaning and polishing).

This paper extends a method previously applied to the determination of the optical constants of a high-index thin film to a dielectric bilayer. This method is based on the time recording of the spectral transmittance of the stack during its deposition with the help of an in situ broadband monitoring system.

We present hereafter the results on the fabrication of complex optical filters within the Institut Fresnel in close collaboration with CILAS. Bandpass optical filters dedicated to astronomy and space applications, with central wavelengths ranging from ultraviolet to near infrared, were deposited on both sides of glass substrates with performances in very good congruence with theoretical designs. For these applications, the required functions are particularly complex as they must present a very narrow bandwidth as well as a high level of rejection over a broad spectral range. In addition to those severe optical performances, insensitivity to environmental conditions is necessary. For this purpose, robust solutions with particularly stable performances have to be proposed.

With the aim to expand its capability to offer state-of-the-art space qualified multispectral optical filters assemblies, Sodern continues its effort to evaluate and incorporate new technologies in its designs. For many years, Sodern has been developing complex optical devices incorporating spectral filters.

We present recent experimental results obtained with CILAS deformable mirrors (DMs) or demonstration prototypes in solar and night-time astronomy (with ground-based telescopes) as well as observation of the Earth (with space telescopes). These important results have been reached thanks to CILAS technology range composed of monomorph and piezostack deformable mirrors, drivers and optical coatings. For instance, the monomorph technology, due to a simple architecture can offer a very good reliability for space applications. It can be used for closed or open loop correction of the primary mirror deformation (thermal and polishing aberrations, absence of gravity). It can also allow a real-time correction of wavefront aberrations introduced by the atmosphere up to relatively high spatial and temporal frequencies for ground-based telescopes. The piezostack technology is useful for very high order correction at high frequency and under relatively low operational temperature (down to -30°C), which is required for future Extremely Large Telescopes (ELTs). This wide range of applications is exposed through recent examples of DMs performances in operation and results obtained with breadboards, allowing promising DMs for future needs., Adaptive Optics Systems IV, June 22-27, 2014, Series: Proceedings of SPIE; no. 9148

The possibility of enhanced mirrors for laser megajoule reflectors has been studied, and preliminary samples have been realized with magnetron sputtering technology. Spectral measurements of improved reflectivity and cosmetics analysis are presented.

IRDIS filters were designed, manufactured with DIBS technology and tested after integration in the instrument. Spectral and WFE measurements indicated that filters are well within specifications, allowing differential aberrations below 10nm rms.

Due to the improvement of deposition technologies and polishing techniques, light scattering has been considerably reduced in optical coatings these last decades, with the result of high quality dense optical filters with minimal losses. However such improvements coupled with modern monitoring techniques have also allowed designing and producing more complex coatings with layer numbers exceeding several hundred in some situations. Within this framework light scattering must again be revisited and analysed in detail, including global loss levels together with angular and spectral analysis. This paper is devoted to the optical balance of sophisticated components for Earth Observation, where the same scene is observed simultaneously in several adjacent wavebands. Self-blocking multilayer stacks are involved to eliminate out-of band harmonics in the instrument but the filter performances are degraded due to an increase of cross talk originating from light scattering. To address this problem we use the theories of light scattering from surface roughness and bulk heterogeneity, which allows to quantity cross-talk levels and choose more adequate filters. A special emphasis is given to the case of hyperspectral filters assemblies located in the focal plane for image filtering.

In this paper, we present in detail the new deposition magnetron sputtering machine so-called PACA2M, that CILAS has implemented for coating large optics up to 2 meters, within a dedicated consortium, with the financial support of the French Department of Industry and of the local administrations, and with the help and the expertise of the French OPTITEC optical cluster. Our innovative large size deposition machine is equipped with 2.5 meters-long planar magnetrons (seven cathodes), to ensure uniform coating on large optical components, up to 2 meters by 2 meters, 40 centimetres thick and to 1.5 ton weight. Some magnetrons are adapted to a DC, Mid Frequency (MF) or Radio Frequency (RF) operation, which allows the deposition of metals and also dielectric oxides under reactive atmosphere. Moreover, PACA2M is equipped with a powerful broadband optical monitoring system that permits to reach sophisticated spectral specifications and a good agreement with theory, which will be presented in detail in another paper of the conference. As the magnetron sputtering technique leads to very dense layers close to bulk material, it is particularly well suited for applications that require environmental resistance, as for example the LMJ (Laser MegaJoule) French laser fusion program in which CILAS is in charge of the metallic mirrors on large complex-shaped reflectors for laser chains amplifiers. Numerous experimental results are presented here such as protected and enhanced metallic mirrors, metal-dielectric absorbing coatings or multi-dielectric coatings, deposited on different kinds of substrates, for which qualification tests have been done.

In the field of optical coatings production, in situ determination of thin films properties during deposition process is a key point for the achievement of high performance filters. Using a spectral measurement over a wide range is a way to improve the robustness of the reverse engineering methods implemented for the monitoring of thin film thickness and the in-situ determination of material refractive index. In the framework of the development of a magnetron sputtering deposition machine for 2-meter optics driven by CILAS, the Optical Thin-Film Research group of Institut Fresnel has designed and qualified a dedicated Broadband Optical Monitoring covering the visible and near infrared spectral range from 280 nm to 2 200 nm. An all-fibered system, well adapted to the extremely large size of the machine, is used to select the location of the measurement point inside the vacuum chamber (among 9 possible). Moreover, this system allows to achieve uniformity studies at the surface of large size substrates along a straight line perpendicular to the cathode main axis with the help of the motorized displacement system of the substrate in front of the magnetron cathodes. A real-time monitoring of the physical thickness is thus done offering possibilities for automatic deposition process and in-line design re-optimization.

Many optical filtering problems require the use of assemblies of layers with thicknesses that bear no obvious relationship to each other. Here we present the results obtained for a number of examples in which optical monitoring is performed with a change of control wavelengths for each layer of the stack. For this, it is necessary to determine for each layer the different wavelengths that provide an extremum of transmittance when the required thickness is achieved. We show that this leads, in some cases, to making the benefit of error compensation analogous to the well-known method used in the production of quarter-wave stacks. Because ion-assisted deposition and ion-plating techniques are suitable from the point of view of refractive-index reproducibility, optical monitoring can be used at a good level of performance. However, the production of high-quality optical thin films needs more than just the choice of a monitoring process. In particular, problems of uniformity are critical for high-performance coatings. Here we show how uniformity can be determined for each material involved.

A detailed presentation of this new magnetron sputtering machine, the largest in Europe for optical coatings, will be given. The main features of this equipment will be illustrated through a few representative achievements.

We report on the development and characteristics of infrared solid state laser as compact and robust light sources for Directed Infrared Countermeasures (DIRCM). DIRCM against infrared missile seekers requires wavelength tunable laser sources. When adding an optical parametric oscillator to a pump laser source, it is possible to cover the 2-5 μm wavelength transmission windows. For more than five years, CILAS has developed critical technologies for the development of a laser source adapted for DIRCM application. This includes: The choice of the crystals, the optical coatings in band II, the thermal management and an optimized oscillator configuration insensitive to repetition rate variation in a wide range. The scope of this presentation is to recall performances of the technologies developed and to present the technical base line of our laser concept. This work is supported by the French MOD (DGA).

Numerical calculation is performed to validate the principles of a single optical technique devoted to real time probing or imaging of submultilayers within interferential coatings.