Search

International audience; Variable filters are key components for compact spectral imagers. In this paper, we present a method for the fabrication of linearly variable filters based on Bühler HELIOS machine (plasma assisted reactive magnetron sputtering). These filters are obtained by producing a variation of the thickness of all the layers of the coating, using adapted masks placed in between the sputtering targets for the low and high refractive index materials and the substrates. Variable band pass filter from 550 nm up to 1000 nm is demonstrated.

International audience; In this paper we study the wavelength selection process for optical monitoring of thin film filters. We first discuss the technical limitations of monitoring systems as well as the criteria defining the sensitivity of different wavelengths to thickness errors. We then present an approach that considers the best monitoring wavelength for each individual layer with a monitoring strategy selection process that can be fully automated. We finally validate experimentally the proposed approach on several optical filters of increasing complexity. Optical interference filters with close to theoretical performances are demonstrated.

International audience; Antireflection coatings are critical elements for space applications as they will influence the overall performances of optical systems. They are among the most classical elements that are produced with optical coatings but remain a challenge when high performances are required. In this paper, we present some recent results based on thin film technology for the production of antireflection coatings dedicated to visible, near-IR and mid-IR spectral ranges. We first present a theoretical and experimental study of broadband antireflection coatings for [400-1100] nm spectral range. We then show antireflection coatings covering the [1.5-15] µm range. Experimental demonstrations and limitations are presented.

International audience; Permanent change of the refractive index of photo-thermo-refractive glass can be achieved by exposure to ultraviolet light followed by thermal development. The dependence of the change on the dosage is nonlinear because the photochemical process of photosensitivity involves saturation. With a holographic recording of Bragg gratings inside glass, a sinusoidally modulated dosage is imprinted into distorted modulation of the refractive index. We investigate this distorted modulation and derive analytical expressions for the amplitudes of its spatial harmonics.

International audience; Extending plasmonics into the ultraviolet range imposes the use of aluminum to achieve the best optical performance. However, water corrosion is a major limiting issue for UV aluminum plasmonics, as this phenomenon occurs significantly faster in presence of UV light, even at low laser powers of a few microwatts. Here we assess the performance of nanometer-thick layers of various metal oxides deposited by atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) on top of aluminum nanoapertures to protect the metal against UV photocorrosion. The combination of a 5 nm Al2O3 layer covered by a 5 nm TiO2 capping provides the best resistance performance, while a single 10 nm layer of SiO2 or HfO2 is a good alternative. We also report the influence of the laser wavelength, the laser operation mode and the pH of the solution. Properly choosing these conditions significantly extends the range of optical powers for which the aluminum nanostructures can be used. As application, we demonstrate the label-free detection of streptavidin proteins with improved signal to noise ratio. Our approach is also beneficial to promote the long-term stability of the aluminum nanostructures. Finding the appropriate nanoscale protection against aluminum corrosion is the key to enable the development of UV plasmonic applications in chemistry and biology.

International audience; Sb 2 Te 3 thin films are very promising candidates for nonlinear optics and several applications including super-resolution and nano-photoinscription. This work aims to offer a detailed study of the preparation of the thin films and their nonlinear optical properties under nanosecond laser excitation. Thin Sb 2 Te 3 films have been deposited by the electron beam deposition technique. The films have been protected by a thin silica layer, then annealed in order to enhance their nonlinearities by material crystallization. The annealing has been optimized by simultaneously recording the X-Ray diffraction diagrams. After this optimization, the annealing could be safely performed by heating in an oven. The nonlinear optical properties of the Sb 2 Te 3 thin films have been studied by means of the Z-scan technique employing 11 ns laser pulses at 1064 nm and 532 nm. High nonlinear absorption has been found showing the possibility to employ these materials for super-resolution, mode-locking and other applications.

International audience; Gold films do not adhere well on glass substrates, so plasmonics experiments typically use a thin adhesion layer of titanium or chromium to ensure a proper adhesion between the gold film and the glass substrate. While the absorption of light into gold structures is largely used to generate heat and control the temperature at the nanoscale, the influence of the adhesion layer on this process is largely overlooked. Here, we quantify the role of the adhesion layer in determining the local temperature increase around a single nanohole illuminated by a focused infrared laser. Despite their nanometer thickness, adhesion layers can absorb a greater fraction of the incoming infrared light than the 100 nm thick gold layer leading to a significant increase of the local temperature. Different experimental designs are explored, offering new ways to promote or avoid the temperature increase inside nanoapertures. This knowledge further expands the plasmonic toolbox for temperature-controlled experiments including single molecule sensing, nanopore translocation, polymerization, or nano-optical trapping.

International audience; The optimization of thin Sb 2 Te 3 films in order to obtain giant ultrafast optical nonlinearities is reported. The ultrafast nonlinearities of the thin film layers are studied by the Z-scan technique. Giant saturable absorption is obtained, which is the highest ever reported, by means of the Z-scan technique. There is a growing interest in materials exhibiting signicant ultrafast nonlinear optical (NLO) properties. 1 In particular, the saturable absorption is currently intensively being investigated because it can be directly applied to the mode-locking of laser systems. 2 Many different materials, for example, carbon nano-tubes, 3 graphene 4 and perovskites 5,6 have been reported in the past to exhibit a signicant saturable absorption. Moreover, nowadays, intense research is being carried out in the eld of nano-patterning materials in order to offer them unique optical/nonlinear optical properties. 7 This has a strong impact in many applications, for example, optical ltering, 8,9 diffractive element fabrication 10 and optical data storage, 11 to name a few. The direct laser writing technique, 12 using fs laser pulses, is one of the most promising and cost-efficient techniques used in order to pattern the matter with custom shapes. However, the resolutions are usually limited by diffraction. The latter can be surpassed by nonlinear phenomena, but the resolutions obtained are very highly dependent on the material used for patterning. 13,14 An improved way to surpass the diffraction limit is to use a super-resolution mask exhibiting a signicant saturable absorption. 15 A family of 2D materials, called topological insulators, exhibiting a "graphene-like" energy band gap structure, is currently very intensively being investigated, as these materials exhibit very high optical nonlinearities. 16,17 Among them, Sb 2 Te 3 is currently among the best candidates for the mode-locking of ultrafast laser systems. 18,19 Despite the high interest of this material for photonic applications, its NLO parameters at the ultrafast regime, are rather unknown. There is currently only one study reporting on the nonlinear absorption coefficient (b) of Sb 2 Te 3 using ultrafast pulses. 20 An optimization of its NLO response is very complex because it highly depends on its crystallization state. Research on this topic is of high interest because it will further enhance the applicability of Sb 2 Te 3 in the eld of photonics. Our group is aiming at using thin Sb 2 Te 3 layers as super-resolution masks in the ultrafast regime. Towards this objective , a thorough optimization of the crystallization state of Sb 2 Te 3 thin lms was initiated in order to obtain an optimal saturable absorption. In this work deposition, post treatment and NLO studies are presented. The crystallization was done by oven and laser annealing. In both cases, unprecedented nonlinear absorption parameters have been found, which are compared with state-of-the-art materials. The Sb 2 Te 3 thin lms were deposited using the electron beam deposition technique. The thickness of the lms has been determined to be 24 nm, by locally removing the thin layer and performing atomic force microscopy measurements (Fig. S1 †). A 10 nm thick silica layer was deposited over Sb 2 Te 3 , which allowed us to perform annealing in air without the oxidation of the layers. The substrate and the thin silica layer have been found to exhibit no optical nonlinearities under the experimental conditions used in this work. Aer the deposition, annealing was performed in two different ways. Firstly, the thin lms were annealed by using an oven at 300 C for 24 hours, following a procedure previously reported by our group. 21 A second alternative way to crystallize the thin lms has been employed in this work. In this case, laser annealing was performed by using a pump-probe setup (Fig. S2 and description in the ESI †). 22 During laser annealing the temperature on the sample was in situ measured by using a thermal camera throughout crystallization. Moreover, the relative reectance, which is well-known to be strongly dependent upon the crystallization state of the Sb 2 Te 3 material, 23 was

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.

We study, both theoretically and experimentally, tunable metasurfaces supporting sharp Fano-resonances inspired by optical bound states in the continuum. We explore the use of arsenic trisulfide (a photosensitive chalcogenide glass) having optical properties which can be finely tuned by light absorption at the post-fabrication stage. We select the resonant wavelength of the metasurface corresponding to the energy below the arsenic trisulfide bandgap, and experimentally control the resonance spectral position via exposure to the light of energies above the bandgap., 7 pages, 5 figures

International audience; Ultraviolet (UV) plasmonics aims at combining the strong absorption bands of molecules in the UV range with the intense electromagnetic fields of plasmonic nanostructures to promote surface-enhanced spectroscopy and catalysis. Currently, aluminum is the most widely used metal for UV plasmonics, and is generally assumed to be remarkably stable thanks to its natural alumina layer passivating the metal surface. However, we find here that under 266 nm UV illumination, aluminum can undergo a dramatic photocorrosion in water within a few tens of seconds and even at low average UV powers. This aluminum instability in water environments critically limits the UV plasmonics applications. We show that the aluminum photocorrosion is related to the nonlinear absorption by water in the UV range leading to the production of hydroxyl radicals. Different corrosion protection approaches are tested using scavengers for reactive oxygen species and polymer layers deposited on top of the aluminum structures. Using optimized protection, we achieve a ten-fold increase in the available UV power range leading to no visible photocorrosion effects. This technique is crucial to achieve stable use of aluminum nanostructures for UV plasmonics in aqueous solutions.

All-dielectric multilayer structures are emerging as optical components of great utility for experiments in which strong but localized fields are needed. These structures allow for an incoming field to resonantly interact with the layers in such a way as to create a giant field at the surface of the structure, where sensing, imaging, and other applications can take place. We present how we synthesize such structures to achieve optical responses with orders of magnitude field enhancements. Furthermore, we introduce and optimization method to achieve enhancements up to 104. We will then present the advantages and drawbacks, and discuss the impact of the illumination bandwidths (angular divergence and spectral range). Subsequently, we will estimate the fabrication errors (in thicknesses and refractive index) over the optical response of the all-dielectric component and especially the field enhancement at the free interface. We will finally give a brief comparison with the surface plasmon resonances to evidence the assets and drawbacks for each case in the context of sensing applications.

International audience; Single molecule Förster resonance energy transfer (smFRET) is widely used to monitor conformations and interactions dynamics at the molecular level. However, conventional smFRET measurements are ineffective at donor-acceptor distances exceeding 10 nm, impeding the studies on biomolecules of larger size. Here, we show that zero-mode waveguide (ZMW) apertures can be used to overcome the 10 nm barrier in smFRET. Using an optimized ZMW structure, we demonstrate smFRET between standard commercial fluorophores up to 13.6 nm distance with a significantly improved FRET efficiency. To further break into the classical FRET range limit, ZMWs are combined with molecular constructs featuring multiple acceptor dyes to achieve high FRET efficiencies together with high fluorescence count rates. As we discuss general guidelines for quantitative smFRET measurements inside ZMWs, the technique can be readily applied for monitoring conformations and interactions on large molecular complexes with enhanced brightness.

We show how to control the wavelength variations of the polarization degree of a beam reflected by specific thin film depolarizers. The design, manufacturing and characterization of the depolarizing device is detailed.

We present a thorough study of a bandpass filter for the near-infrared (IR) region, with bandwidth below 20 nm, high transmission, and a broad rejection band [350-1100] nm. This filter is angularly tunable between 0 and 50° and shows a shift of the central wavelength from 970 nm down to 880 nm, without major changes in its bandwidth and spectral shape for unpolarized light. We first provide a description of the design procedure and then carry out an experimental demonstration by using plasma-enhanced reactive magnetron sputtering. We finally present an accurate characterization of this class of filter by using a custom optical system.

International audience; Amorphous Ge33As12Se55 films have been deposited by electron beam physical vapor deposition and their optical properties have been studied using reverse engineering on spectrophotometric measurements. Definition of the different optical constants were made by Tauc-Lorentz model allowing simultaneous characterization in high and low absorption area. Moreover an investigation of the layer's photosensitivity with an exposure wavelength at ~808 nm has been carried out and reveals a photo-bleaching effect generating up to 0.04 refractive index variation at 1µm. Finally the stability of the fabricated layers is studied.

We present a thorough study of the use of As2S3 thin films for the fabrication of high-performance bandpass filters. We show that these layers can be included inside a multilayer Fabry–Perot structure in order to produce large-aperture narrow bandpass filters. These layers can also exhibit a large local refractive index change up to 0.1 when they are exposed to actinic radiation at 470 nm. Kinetics of photosensitivity are presented. We show that these effects can then be implemented to locally modify the spectral performance of a Fabry–Perot filter after deposition. Highly uniform 65×60 mm2 filters with a 4 nm bandpass at 800 nm and ±0.1% fluctuations of the central wavelength are demonstrated using this technique.

International audience; Frequency conversion is one of the main applications of nonlinear optical processes in which a signal is produced at a different wavelength from the excitation wavelength. In particular, four-wave mixing (FWM) is a third order nonlinear optical process that allows, for instance, the generation of visible frequencies by tuning near-infrared laser pumps. Here, in order to augment the very weak FWM conversion efficiency, we design silicon Mie resonators that exhibit two resonances of the internal electric field intensity around the frequency range of the laser pumps. The linear extinction spectrum of the individual Si resonator is first measured by bright field spectroscopy and compared with numerical simulations to confirm the existence of the two resonances corresponding to electric and magnetic dipole excitations. The FWM signal is then measured for a single Si nanoresonator when the first pump is set to the electric resonance while tuning the frequency of the second pump across the magnetic dipolar resonance. We show that the FWM signal generated in the visible spectrum is maximum when the frequency of the tunable pump corresponds to the maximum of the internal electric field intensity. At this position, the FWM signal is enhanced by more than 2 orders of magnitude compared with the FWM signal generated by the unpatterned silicon film.

The diffraction limit is one of the main difficulties in order to achieve nano-resolution. An evolution in this domain can allow a significant advance in the field of photonic circuit fabrication. Surpassing the diffraction limit can be achieved by employing significant optical nonlinearities (nonlinear refraction and/or nonlinear absorption). In this direction we investigate the nonlinear absorption efficiency of annealed Sb2Te3 chalcogenide thin films (20 nm thickness). The studies have been performed using the Z-scan technique, employing 11 ns duration pulses at 1064 nm. The Z-scan technique has been chosen as it allows the simultaneous determination of the nonlinear refraction and the nonlinear absorption of a material, under certain conditions. Our results indicate a significant nonlinear absorption, while the nonlinear refraction is at least one order of magnitude lower. The nonlinear absorption parameter has been found to be in the order of -10-3 m/W under infrared irradiation showing the importance of the prepared materials for laser photoinscription applications. Our values are compared with previous studies, which have been carried out in the visible part of the spectrum. The possibility to perform photonic component fabrication by local modification of the linear or the nonlinear properties of the materials is also discussed.

Metamaterials are artificial structures consisting of periodic sub-wavelength elements, they produce a particular electromagnetic response which often cannot be obtained from conventional media. One class of metamaterials called hyperbolic metamaterials (HMM) is widely studied nowadays due to their various applications such as subwavelength imaging and local density of states engineering. 1 In this work, HMM consisting of alternating gold, copper, and niobium pentoxide layers was designed and fabricated with plasma assisted electron beam deposition technique. For the accurate description of this material opto-geometrical parameters of thin layers composing it were determined separately using reflection and transmission measurements. Afterward, the produced material was structured using focused ion beam milling and its influence on the Alexa Fluor 647 biomolecules spontaneous emission was studied experimentally with fluorescence correlation spectroscopy and time-correlated single photon counting techniques. Combining these techniques enable the measurement of the fluorescence lifetime reduction together with the brightness enhancement per molecule. The same measurements were previously done for the structured gold films 3 which let us compare the results. HMM has shown significant emission enhancement compatible with the one produced by a single gold aperture which is known for its good plasmonic properties.

The characteristics of indoor light (intensity, spectral, spatial distribution) originating from outdoors have been studied using experimental and modeling tools. They are influenced by many parameters such as building location, meteorological conditions, and the type of window. They have a direct impact on indoor air quality through a change in chemical processes by varying the photolysis rates of indoor pollutants. Transmittances of different windows have been measured and exhibit different wavelength cutoffs, thus influencing the potential of different species to be photolysed. The spectral distribution of light entering indoors through the windows was measured under different conditions and was found to be weakly dependent on the time of day for indirect cloudy, direct sunshine, partly cloudy conditions contrary to the light intensity, in agreement with calculations of the transmittance as a function of the zenithal angle and the calculated outdoor spectral distribution. The same conclusion can be drawn concerning the position within the room. The impact of these light characteristics on the indoor chemistry has been studied using the INCA-Indoor model by considering the variation in the photolysis rates of key indoor species. Depending on the conditions, photolysis processes can lead to a significant production of radicals and secondary species.

International audience; Iridium-based coatings for mirrors of X-ray telescopes are studied. In particular, stress induced deformation is characterized and shown to be compressive and equal to -1786 MPa. Two methods for stress compensation are then studied. One relies on the deposition of silica on the back surface of the substrate and a second one relies on the deposition of a chromium sublayer. Advantages and drawbacks of each of these techniques are presented.

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.

International audience; We present experimental characterizations of 1D crossed Guided Mode Resonant Filters (GMRFs) in the near infrared fabricated by nanoimprint lithography. We will show that subwavelength gratings up to 4'' diameter can be fabricated using such techniques. We compare the performances of the GMRFs to the performances of Fabry-Perot filters and discuss the sensitivity to fabrication inhomogeneity of these components.

International audience; Dielectric multilayers, when properly optimized, have been shown to sustain giant optical field enhancement directly linked to the imaginary index of the materials. Such giant optical field is of great interests to increase tremendously the sensitivity of optoelectronic systems. Unfortunately, this ultra-sensitive system is also highly depending on the illumination conditions. We discuss here the effect of the angular divergence and the spectral bandwidth of the incident laser beam on the absorption and field enhancement. In this study, we clearly show that giant optical field enhancements, up to several decades, may be achievable when the incident conditions are down few μrad and pm in term of angular and spectral bandwidths respectively.

A non-polarizing beam splitter and a light color-mixing challenge were the topics of the design contest held in conjunction with the 2019 Optical Interference Coatings topical meeting of the Optical Society of America. A total of 10 designers from China, France, Germany, Japan, and the United States submitted over 70 designs for problems A and B. The design problems and the submitted solutions are described and evaluated.

International audience; We present a thorough description of high performance thin-film optical filters with high flatness. These components can combine several tens or hundreds of layers and are manufactured using plasma-assisted reactive magnetron sputtering. Stress compensation is achieved using dual side coatings with appropriate spectral function. Examples of highly reflecting mirrors at 515 nm with 15 nm flatness peak-to-valley over up to 75 mm diameter aperture, narrow bandpass filters and filters with broadband controlled transmission are described.

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.

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; We present a systematic study of a stress coefficient of dielectric materials (SiO2, Nb2O5, and HfO2). In particular, we show a thickness dependence of the stress coefficient on layer thickness, which shows that the determination of this coefficient is complex and requires careful analysis. We then apply the different models of the stress coefficient to multilayer structures and show that stress-induced deformation can be precisely predicted in final components with a few percent accuracy.

International audience; Photo-thermo-refractive (PTR) glass is an optically transparent photosensitive multicomponent silicate glass. UV-exposure produces silver nanoclusters, and NaF nanocrystals upon heating, giving rise to permanent refractive index changes. This is the basis for the production ofBragg gratings. In this article, we present a comprehensive overview of the photo-thermoinduced effects in PTR glass. We first give a general introduction of PTR glasses and their applications. Then, we perform a thorough analysis of the mechanisms of refractive index changes starting with the photo-induced process followed by the crystal nucleation mechanism and NaF crystallisation kinetics. Finally, we concentrate on the PTR glassnanostructure and its effect on the crystallisation mechanisms and properties, finishing with the kinetics and origin of the refractive index change. Despite the fact that much is known about this septuagenarian glass and that it is already being commercially produced, a number of open problems still exist that warrant further investigation.

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.

International audience; In this paper, we investigate the design and the fabrication of an advanced optical interference filter based on metal and dielectric layers. This filter respects the specifications of the 2016 OIC manufacturing problem contest. We study and present all the challenges and solutions that allowed achieving a low deviation between the fabricated prototype and the target.

International audience; Plasmonic antennas have a profound impact on nanophotonics as they provide efficient means to manipulate light and enhance light–matter interactions at the nanoscale. However, the large absorption losses found in metals can severely limit the plasmonic applications in the visible spectral range. Here, we demonstrate the effectiveness of an alternative approach using all-dielectric nanoantennas based on silicon dimers to enhance the fluorescence detection of single molecules. The silicon antenna design is optimized to confine the near-field intensity in the 20 nm nanogap and reach a 270-fold fluorescence enhancement in a nanoscale volume of λ3/1800 with dielectric materials only. Our conclusions are assessed by combining polarization resolved optical spectroscopy of individual antennas, scanning electron microscopy, numerical simulations, fluorescence lifetime measurements, fluorescence burst analysis, and fluorescence correlation spectroscopy. This work demonstrates that all-silicon nanoantennas are a valid alternative to plasmonic devices for enhanced single molecule fluorescence sensing, with the additional key advantages of reduced nonradiative quenching, negligible heat generation, cost-efficiency, and complementary metal–oxide–semiconductor (CMOS) compatibility.

Laser- induced damage thresholds and morphologies of laser ablated sites on dielectric thin films are studied based on experiments and simulations. The films are single layers of hafnia and niobia deposited on fused silica substrates with a magnetron sputtering technique. Laser experiments are conducted with 500 fs pulses at 1030 and 343 nm, and the irradiated sites are characterized with optical profilometry and scanning electron microscopy. The results, i.e., LIDT and damage morphologies, are compared to simulations of energy deposition in the films based on the single rate equation for electron excitation, taking into account transient optical properties of the films during the pulse. The results suggest that a critical absorbed energy as a damage criterion gives consistent results both with the measured LIDT and the observed damage morphologies at fluences close to the damage threshold. Based on the numerical and experimental results, the determined LIDT evolution with the wavelength is described as nearly constant in the near-infrared region, and as rapidly decreasing with laser wavelength in the visible and near-ultraviolet regions.

International audience; A large number of parameters is often required to describe optical dispersion laws, and it is only through the use of an appropriate global optimization procedure that an accurate thin-film index determination can be achieved. In this paper, we propose to investigate the respective performances of three different optimization algorithms, namely Simulated Annealing, Genetic Algorithm and Clustering Global Optimization and compare results with a commercial software dedicated to thin-film index determination. This study is restricted to the single-layer thin-film index determination of transparent and absorbing materials. It includes the theoretical study of simulated reflection and transmission spectra, and the experimental characterization of Ta2O5 and Si layers.

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.

International audience; A new alternative and versatile method for the production of Diffractive Optical Elements (DOEs) with up to 4 phase levels in AMTIR-1 (Ge33As12Se55) layers is demonstrated. The developed method proposes the use of the photosensitive properties of the layers and a specific in-situ optical monitoring coupled with a reverse engineering algorithm to control the trigger points of the writing of the different diffractive patterns. Examples of various volume DOEs are presented. Chalcogenide glasses (ChG) are composed from a chalcogen element such as Sulphur, Selenium, and Tellurium. To create a glass network, some other atoms are added such as As, Ge, Sb, Ga, Si or P. ChG are particularly interesting due to their specific optical properties. In fact they are transparent into the mid-infrared up to 20 µm depending on their chemical composition [1]. The refractive index is high n~2-3 and ChG possess also a high nonlinear refractive index n2 [2]. But one of the most striking property is their photosensitivity. Using light exposure with a wavelength below the optical bandgap, the chemical bonds can be rearranged. This effect directly modifies the optical properties of the ChG. This very specific property has led to different kinds of applications such as phase change memory [3]… As thin films, ChG were thoroughly studied and the impact of inserting a photosensitive layer into an optical filter to modify its spectral response was demonstrated [4]. As an example, it was shown, a few years ago, that it is possible to use the photo-bleaching or photo-darkening [5] effects to adjust the central wavelength of a Fabry-Perot filter and therefore generate ultra-uniform bandpass filters [6]. The ChG studied in this paper is AMTIR-1. It is composed in molar percent with 33% of germanium, 12% of arsenic and 55% of selenium and was provided by Amorphous Material Company. AMTIR-1 was already deposited as thin films by pulsed laser deposition [7], thermal or e-beam evaporation, and showed excellent optical properties [8]. Layers from AMTIR-1 were shown to be excellent candidates for the production of various optical elements such as ring resonators [9]… We recently showed that these layers are also a good candidate for the production of a new kind of optical elements [10]. Actually with the theoretical and experimental developments of diffractive optical elements, metamaterials or metasurfaces, there is a higher and higher demand for 3D micro-and nanostructuring of multilayer stacks. 1D-structures are easily obtained by the optical coating technology, while 3D-structures require micro-or nano-engineering the local thickness of the deposited structures using lithographic processes combined with etching techniques. We showed that for coarse structures, i.e. for structures having a pitch with size much larger than the wavelength (i.e. with size larger than 10 µm), it is possible to create volume phase structures by locally controlling the local refractive index of a photosensitive layer. Such an approach was applied to the fabrication of binary DOEs. However, it is well known that for many applications and in order to achieve higher diffraction efficiency, especially for the production of asymmetrical beams, the use of multi-level DOEs is mandatory. In this paper we demonstrate the possibility to photo-structure a photosensitive chalcogenide layer with 4 levels in order to produce a Volume Diffractive Optical Element (VDOE). Methods of production and monitoring are detailed. The chalcogenide layers and thin film stacks were produced using electron beam physical vapor deposition in a Balzers BAK600 chamber. The residual pressure inside the vacuum chamber was around ~10-6 mbar and the deposition rate was 10 ± 1 A/s. In a previous works [8] using those parameters, we first demonstrated that AMTIR-1 materials provide broad transparency range above 850 nm, high refractive index (n = 2.74 @ 1 µm) and photosensitive properties such as photo-bleaching effect. This effect occurs into the AMTIR-1 layers when exposed to a light with a wavelength whose energy is below the bandgap. This effect allows generating refractive index decrement down to-0.04 at 1 µm that was then applied to binary DOEs. Moreover, it was shown that this refractive index change is

Photo-thermo-refractive (PTR) glass is an optically transparent photosensitive sodium alumino silicate glass, containing NaF and KBr additives, along with cerium, silver, tin and antimony oxide dopants. UV-exposed regions of this glass produce NaF nanocrystals upon heating, giving rise to a permanent localized refractive index change. In this article we examine the initial stages of this crystallization process by continuous-wave and pulsed X-band electron paramagnetic resonance (EPR) spectroscopy. UV exposure of PTR glass produces unpaired electrons whose EPR spectrum is characterized by pronounced peak splitting arising from nuclear magnetic hyperfine interactions with spin-5/2 and spin-7/2 nuclei suggesting close proximity of the unpaired electrons with 121 Sb and 123 Sb nuclei. These results indicate that the Sb 2 O 3 dopant plays a key role in the initial stages of the crystallization mechanism. Upon thermal annealing, leading to the crystallization of NaF, these species disappear, indicating their transient nature. A number of other unpaired electron species identified in the dopant free matrix appear to be unrelated to the crystallization process. These results clearly challenge the classical mechanism proposed decades ago to explain the complex crystallization process of PTR glass. Together with more recent results from optical spectroscopy they support the Nikonorov model involving (1) photoionization of Ce 3 + , (2) transfer of this electron to Sb 5 + species to create a Sb 4 + species, (3) upon annealing electron transfer from Sb 4 + to Ag + ions, producing silver atoms, (4) coalescence of these species into Ag clusters, which (5) serve as nucleation catalysts for NaF nanocrystals.

We compare the effect of CO2 laser heating on silica samples of type II and III; these two materials having significant differences in composition and physical properties. For both types of silica, the crater shape and depths are similar through all the parameter ranges that were studied. This is particularly true when evaporation is the major mechanism of the crater formation process. Our numerical simulations of thermal heating are consistent with these results, and calculations with a physically based model of evaporation evaluate correctly the crater depths. Therefore, it can be conclude that the heating of silica surface by CO2 laser at temperatures sufficient to remove some material is independent of their metallic impurities and hydroxyl content, or the different values for the annealing and softening temperatures.

Due to market demand and technical progresses, a new generation of optical components requires much more sophisticated structures with a great number of layers. These complex structures enable to achieve severe optical performances but, at the same time, enhance light scattering processes. For these reasons, it is essential to develop a metrological tool which provides an accurate quantification of the spectral and angular scattering losses behavior with sufficient angular and spectral resolutions. In order to face this issue, new investigations were performed by our group at Institut Fresnel and led to the development of the new scatterometer SALSA (Spectral and Angular Light Scattering characterization Apparatus). The use of both a broad-band light source and a tunable filter allows to accurately select the illumination wavelength and the spectral bandwidth on the whole spectral range of CCD detectivity. In this paper we will present the performances of the setup and some experimental results.

International audience; Recording of volume Bragg gratings (VBGs) in photo-thermo-refractive glass is limited to a maximum refractive index change about 0.002. We discuss various saturation curves and their influence on the amplitudes of recorded gratings. Special attention is given to multiplexed VBGs aimed at recording several gratings in the same volume. The best shape of the saturation curve for production of the strongest gratings is the threshold-type curve. Twophotonabsorption as a mechanism of recording also allows increasing the strength of multiplexed VBGs.

International audience; Photo-thermo-refractive (PTR) glass is a photosensitive multicomponent silicate glass containing photosensitive agents such as cerium and silver. Photoinduced crystalline phase precipitation results in refractive index variations in exposed areas of PTR glass, which has been successfully used for phase hologram recording. Photosensitivity being the result of the partial absorption of the exposing radiation by cerium ions, it results in a gradient of refractive index (GRIN) along the exposure beam propagation. This GRIN is a parasitic effect that deteriorates the parameters of some types of volume Bragg gratings because of the beam deflection they produce. In this paper, the evolution of GRIN is investigated as a function of the dosage of UV exposure and the thermal treatment duration. We show that GRIN is a deterministic process that can be easily modeled and predicted using basic optics and glass science equations.

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 report on the sub-picosecond laser-induced damage of optical thin films of different thickness made by Magnetron sputtering, Ion assisted deposition and Ion plating, and submitted to single irradiation of the first and the third harmonics of an Ytterbium laser (1030 and 343nm). Using a single rate equation approach for free electron excitation coupled with calculation of the spatial and temporal distribution of the electric field, we investigate numerically the spatial density distribution of the absorbed energy and evaluate its capacity to describe damage phenomena especially damage threshold and morphologies (damage diameter, ablation deepness). Laser-induced damage thresholds are compared for different film thicknesses and different irradiation conditions.

International audience; Silver and gallium form an alloy Ag2Ga via a room temperature spontaneous self-assembly thatexhibits remarkable mechanical and electrical properties suitable for nanoscale measurements.However, whether photon excitation of plasmons in this emerging nanomaterial is retained or nothas not been established. Here, we present a thin film formation of Ag2Ga via a spreading-reactiveprocess of liquid Ga on an Ag film and a characterization of its dielectric function !(E)¼!1(E)þi!2(E) in the photon energy range 1.42 eV#E

International audience; Photo-thermo-refractive (PTR) glass is a photosensitive multi-component silicate glass that is commercially used for the recording of volume holographic elements and finds many applications in advanced laser systems. Refractive index decrement in this glass is observed after UV exposure followed by thermal development. This procedure also causes the appearance of Ag-containing particles that can then be optically bleached by using the second harmonic of a Nd:YAG laser. Despite the broad usage of this method, its mechanisms are still unclear. In this paper, a systematic study of the short pulse laser-induced destruction of Ag-containing particles’ kinetics versus incident energy per pulse and dosage is presented. We show that no bleaching of Ag-containing particles occurs for an energy density in laser pulses below 0.1 J/cm2 while above 1 J/cm2, the efficiency of bleaching saturates. Efficiency of bleaching depends on the type of particles to be bleached (Ag, AgBr…). Using a simple model of short pulse laser interaction with nanoparticles embedded in glass, the temperature of the Ag-containing particles reached during the laser interaction is shown to be large enough to produce complete dissipation of these particles which is expected to be the main mechanism of short pulse laser-induced destruction of Ag-containing particles.

Multispectral or hyperspectral images allow acquiring new information that could not be acquired using colored images and, for example, identifying chemical species on an observed scene using specific highly selective filters.

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.