The Optical Security and Performance (OSP) division of VIAVI Solutions just celebrated its 75th anniversary. With over $300M annual revenue OSP is one of the largest optical coating providers worldwide. OSP’s market focus is on anti-counterfeiting, automotive, consumer electronics, government & aerospace, and spectral sensing. In this presentation we will highlight some of OSPs industrial challenges and recent accomplishments to serve our customers. One focus will be on consumer electronics filters with rapid innovation demand especially towards miniaturization, while demanding high volumes with exceptional optical performance, accompanied by large price pressure. A second focus will be on components for free-space optical communications, where optics tend to be larger form factors. Tight wavefront aberration requirements drive tight specifications for substrate quality and coating requirements. We will discuss metrology investments that enable development and product assurance.

For several years, CILAS has developed an expertise in the field of optical thin films deposition and in-situ optical monitoring techniques that enables today to successfully answer growing requests of optical coatings for astronomy and space applications, with large dimensions. In particular DIBS, PIAD and Magnetron sputtering techniques allow us to guarantee the production of dense coatings well adapted to severe environments. In this paper, we will first focus on recent projects realized for astronomy: antireflection coating on large diameter and high curvature CaF2 lenses, enhanced aluminum coating on 1.8m diameter secondary mirrors. Then we will present space-qualified enhanced silver and unprotected gold coatings dedicated to reflective surfaces (telescope mirrors, gratings) of instruments for Earth observation and black absorber coatings for parasitic light reduction. Finally, some complex optical functions developed and qualified for various space applications will be presented: mapping sources and sinks of carbon dioxide (MicroCarb) ; determining the composition of the Venus surface (Envision and Veritas) ; communicating in free-space (TELEO).

Examples of optical filters and their applications in telecommunications and satellite communications will be presented. Specific examples will include low error function gain flattening filters, dual band transmission filters, and solar rejection filters.

Physical vapor deposition equipment based on evaporation, sputtering or ion beam sputtering will be compared based on results achieved for selected challenging Interference filter. Examples are oxides coatings in the DUV spectral region or step edge filters for the VIS and NIR.

In this work, we present a new-generation atomic layer deposition (ALD) technology that revolutionizes the production of conformal optical coatings: the spatial ALD. In spatial ALD, the substrate is rotated across successive process zones to achieve ultra-fast, high-precision and conformal thin film deposition. We present our latest results obtained with our novel C2R spatial ALD system, including the fabrication of SiO2, Ta2O5, Al2O3 and TiO2 with deposition rates reaching > 1 µm/h. We also show that these materials exhibit low surface roughness (<1 Å RMS), low optical loss (<10 ppm @ 1064 nm) and excellent uniformity (< 2% over 200 mm)

Dispersive coating is the enabling technology of state-of-the-art ultrafast laser systems. This paper presents the research progress range from the multi-objective design method, coating materials, advanced monitoring technique to improve the performance of the dispersive mirrors.

Transparent and conductive oxides offer metal-like conductivity and high transmission in the visible spectrum. However, they suffer from reflection losses at the film interface due to their high refractive index. A method for producing an ITO nanostructure through plasma etching in a conventional deposition plant equipped with an APS plasma source is presented, resulting in conductive nanostructures with an effective refractive index as low as 1.3. This nanostructure was combined with an AR coating achieving minimal reflectance while maintaining a conductive surface that enables the removal of surface charges as it is needed in AR coatings for quantum computing applications.

Quantizing nanolaminates (QNLs) are a promising alternative as high-index material in thin film coatings providing high flexibility with respect to their refractive index and bandgap energy. However, the fabrication of QNLs requires high precision in the deposition of the layers. Common monitoring strategies are not applicable due to the nanometer to subnanometer layer thicknesses needed to achieve a significantly increased bandgap energy. This contribution investigates the impact of thickness errors on the bandgap energy of QNLs. Calculations show a diminishing of the bandgap energy increase due to thickness errors in a single layer. This effect will be investigated experimentally. Moreover, the QNLs linear and nonlinear absorption will be tested as function of layer numbers determining the impact of the increased interfaces of QNL structures. Applying the new insights, the final goal is the fabrication of functional QNL-coatings with optimized electrical field intensity and increased LIDT for the ultra-short pulse regime.

At sufficiently high intensities the electronic nonlinear behavior of optical materials dominates the classical linear phenomena. Through laser calorimetric absorption (LCA) measurements this behavior has been characterized and an increase in absorption of over one order of magnitude has been observed. Quantum nanolaminates (QNLs) are uniquely suited to investigating these phenomena as it is possible to tune the refractive index and bandgap. The absorption and electronic behavior of QNLs deposited with Titania and Niobia in conjunction with Silica were investigated using LCA. The impact of defects on the measurements are also discussed.

Vapor deposited amorphous oxide mixtures of TiO2 and Ta2O5 are used as the high index layer in interference coatings for gravitational wave detectors (GWD). The addition of Ti to Ta2O5 with a cation concentration of ∼25% reduces internal friction when the thin films are annealed at temperatures below the crystallization temperature [1,2]. A similar behavior observed in mixtures of ZrO2 and Ta2O5 was explained as being due to modifications in the bonding of Ta-O polyhedra in which the population of edge- and corner-shared polyhedra decreases and that of corner-shared polyhedra increases [3]. These structural modifications at the medium range, i.e. within a few nanometers, correlate with the reduction of internal friction with annealing.

Photo-induced thermal phenomena are omnipresent in precision optical systems. Interferential filters are subjected to optical powers that are weakly absorbed but lead to temperature rises that can alter system performance: spectral drift, wave-front modification, damage, etc. In addition, absorption processes lead to heat transfers by conduction, radiation and convection that are important to predict or control. In this context, we have developed a comprehensive model dedicated to photo-induced thermal phenomena in interference filters, with the particularity that these models are developed and implemented with the same tools commonly used to address optical properties in thin films. These results lead us to address a number of inverse problems concerning the determination of thermal parameters or imaginary indices of thin-film materials, as well as the control of thermal radiation. Also, we investigate the detail of thermal energy transferred to the guided modes of a multilayer.

With the recent advances in photonic integrated circuits and their use as sensor platforms, the requirements for environmental temperature stability are increasing. Substrate free miniaturized thin film filters, used for spectral filtering, multiplexing, and demultiplexing, are affected by this requirement. Therefore, we investigate the thermal behavior of optical thin films fabricated by IBS and compare coatings on glass substrates to our substrate free miniaturized integrable alternative. We determined the relative change in optical thickness for various materials during spectral transmission measurements under sample temperature variation. Additionally, we adapted a thin film simulation software to estimate the linear coefficient of thermal expansion and thermo-optic coefficient of the materials. Since the thermal behavior of coatings is influenced by thermal expansion of the underlying substrate, we also measured the thermal behavior of simultaneously fabricated substrate free miniaturized filter elements. Comparing these results allows to pre estimate the thermal stability of the filter elements.

The precise characterization of thin layers in microelectronics or related fields is more and more challenging as the targeted thicknesses are decreasing into the nanometer range. Combined XRR-GIXRF analysis is a powerful technique that combines the advantages of the elemental sensitivity of X-ray fluorescence with the thickness and density sensitivity of X-ray reflectivity. This method is performed in a reference-free mode which relies on the precise knowledge of some physical quantities.

Development of multilayer mirrors for the water window (a region between absorption edges of carbon and oxygen, from 282 to 533 eV) remains quite a challenge. Proposed 25 years ago, the Cr/Sc multilayer provides theoretical reflectivity about 60% at near-normal incidence near the Sc L2,3 edge. However, the maximum measured peak reflectance achieved so far just slightly exceeds 20%. We report on our approach to design highly reflective Cr/Sc-based multilayer coatings using a process of nitridation of chromium during deposition and adding boron carbide as a third material in the multilayer structure. We will report on our strategy of optimisation of the CrN/B4C/Sc multilayer system and discuss the main findings and results. The peak reflectance as high as 32% at 397 eV was measured with this type of coating which proves to be potentially interesting for various water window applications such as x-ray microscopy.

La1-xAlxF3 nanocomposites with different AlF3 doping ratios were synthesized using a dual-source electron beam co-evaporation technique to achieve amorphous La1-xAlxF3 coatings with low loss and tensile stress. We analyzed the evolution laws of optical constants, microstructures, film stress, and film loss of La1-xAlxF3 nanocomposites with the change of element content. When x ≥ 0.30, high-refractive-index nanocomposites La1-xAlxF3 demonstrated reduced absorption, integrated amorphous structure, and lower tensile stress. The nanocomposite exhibited superior performance with an excellent overall structure, as well as reduced tensile stress. Additionally, this material was employed to create a high-performance reflective film with a high reflectivity.

The talk presents concepts for integrating essential active optical functions into thin film coatings, which allows a high degree of miniaturization compared to classical alternatives. Due to the amorphous structure of thin film coating materials, only uneven orders of nonlinear effects will be considered. The chosen applications comprise a concept for frequency tripling mirrors, where the third harmonic generation is performed in the thin film stack, and an all-optical switch, the so-called Kerr-band-switch based on the optical Kerr-effect. The chosen materials, design considerations, and measurements validating the function of the concepts will be presented.

Information technology advancements are revolutionizing optical components, necessitating a solid theoretical foundation for optically active components. Optical thin films are traditionally designed using the transfer matrix method to calculate linear spectral responses. However, recent developments also address nonlinear optical responses by integrating nonlinearities into the matrix formalism or by applying a maxwell solver, which offers spatially and temporally resolved pulse propagation simulations in thin films. The transfer matrix method has been extended to include third harmonic generation and ultrafast switching via the Kerr effect. We compare the results from the nonlinear transfer matrix method to results obtained by a maxwell solver. Furthermore optimization routines for nonlinear response design like Monte Carlo algorithms and machine learning with neural networks are shown.

To enhance the PETawatt Aquitaine Laser (PETAL) operation, efforts are directed towards increasing the Laser-Induced Damage Threshold (LIDT) of transport mirrors. Three approaches are being considered : i) changing the design of thin film stacks, ii) the materials, and iii) the deposition process. Monolayers of pure SiO2, HfO2, Sc2O3 and mixtures of HfO2/SiO2 and Sc2O3/SiO2 were elaborated by magnetron sputtering using oxide targets. Laser damage tests, combined with optical and physicochemical characterizations, revealed that the Sc2O3/SiO2 mixture exhibits the highest LIDT. The introduction of a small amount of oxygen into the plasma reduced the refractive index and improved the LIDT. A Bragg mirror, designed for PETAL's specifications (R > 99% at 1053 nm for s polarization at 45° incidence) is being manufactured using HfO2 (high refractive index) and Sc2O3/SiO2 (low refractive index). The films thicknesses are finely controlled with the quartz crystal microbalance technique.

To build quarter-wave plate components for a high-power laser application, the Laboratory for Laser Energetics has developed a 21-layer silica coating fabricated by GLancing Angle Deposition. This stack alternates columnar birefringent layers with isotropic layers. We present a study on the SiO2 matrix state, the sub-stoichiometry and presence of oxygen vacancies that affect robustness and a reduced laser damage resistance. The composition throughout the film thickness is investigated thanks to GD-OES and Tof-SIMS combined with photoelectron spectroscopies for the composition. Anisotropic and isotropic layers exhibit differences in composition, between them and throughout the depth. Photoluminescence measurements show a peak that could represent oxygen vacancies that may reduce the damage threshold. Vibrational characterization further supports our findings. This comprehensive overview is discussed in relation to deposition process and resistance to laser-induced damage and will enable us to improve our current coatings.

The era of attosecond physics requires complex EUV and soft X-ray optical components with challenging specifications. Interference coatings with high efficiency, good stability, enhanced selectivity and/or broad bandwidth and phase control are key components to manipulate the ultra-short pulses generated by coherent sources like High Harmonic Generation or X-ray Free Electron Lasers. In this talk, we will discuss details of novel, tailored multilayer optics that we have been developing for the last 20 years for ultrafast sources. We will show that phase-controlled interference coatings provide a powerful tool towards transporting or even compressing attosecond pulses. Measuring the spectral phase of such mirrors requires specific methods that have been developed for the EUV range and extended up to the soft X-ray domain. Finally, we will present the recent development of a delay line with advanced multilayer optics for the femto/attosecond beamlines in Paris-Saclay (ATTOLAB).

Ever since invention of aperiodic optical multilayer structures have been driving the advancement of ultrafast laser technology towards ever broader bandwidth and ever shorter pulses. Deposition of dozens of dielectric layers with sub-nanometer accuracy permits manipulation of the spectral phase and amplitude of optical radiation over a full octave and beyond. We make overview on the progress on dispersive optics since their invention in 1994. Many years of development bring to the benefit that the attosecond physicists could study the electron dynamics in atoms and molecules. The non-linear effects in multilayer ultrafast coating shortly before damage threshold are overviewed as well. We describe ways how to use or post-pone these effects to higher fluences.

The paper discusses requirements and solutions for antireflection coatings applicable for a fused silica cell which is attended to manipulate Rydberg atoms as qubits. Multiple laser beams at various wavelengths and light incidence angles pass the different window areas of the cell. AR-coatings were designed and deposited on the window areas to receive an optimal solution for each of the lasers. Some of the coatings optimized for the internal surfaces of the cell contain nanostructured layers as an option to improve the polarization properties at higher light incidence angles. Cleaning, handling and outgassing of these layers was investigated in particular.

The VEM (Venus Emissivity Mapper) instrument is a DLR contribution to the EnVision (ESA – Cosmic Vision M5) and VERITAS (NASA-JPL – Discovery 15) missions. The role of this instrument will be to determine the composition of the surface by studying thermal emissions with observation in narrow spectral bands in the near-infrared. To map the surface of Venus, the VEM instrument uses an infrared detector on which the selection of 14 narrow spectral bands is projected along a track on the ground. The multispectral filter, which contains these 14 bands, is integrated into an optical telescope called VEM-O. LESIA is responsible for supplying VEM-O to DLR. CNES assists LESIA in supplying the filter for VEM-O and entrusts BERTIN WINLIGHT and CILAS to design, develop, qualify and finally assemble the multispectral filters flight models. In this paper, we will focus on the design of the 14 narrow bandpass filters constituting the multispectral assembly. For each filter, a specific design as been done involving Fabry-Perot and blocking functions, taking into account central wavelengths, spectral bandwidth, rejection spectral range and flatness requirements.

Thermochromic materials are of high interest for their potential applications in spacecraft thermal control, with systems exhibiting variable emissivity able to manage the heat rejection and absorption. VO2 presents one of the most prominent technological options for thermochromic behaviors, with a transition temperature around 68°C limiting its practical utility for spacecraft thermal control notably. Here, we report the synthesis of strongly thermochromic tungsten doped vanadium dioxide coatings on silicon wafers obtained in an industrial-size vacuum deposition chamber. Samples with various W doping rates were deposited by magnetron sputtering, exhibiting thermochromic transition temperatures from 38°C to as low as 5°C, with optical transmission contrasts at a wavelength of 12 µm maintained between 40% and 58%, enabling enhanced control of heat exchange at low temperature and broader usability. The variable emissivity radiators were measured to have emissivity contrasts up to 40%, with transition temperatures as low as 10°C, demonstrating the potential use of the VO2-based thermochromic coating.

Antireflection coatings with sapphire-like hardness are highly desired in advanced engineering applications. Currently, classic (LH)^n structures based on Si3N4/SiO2 stacks are widely used to obtain high optical transparency and surface hardness in industry. However, it still suffers from low durability and multiple failures after wear and scratch tests. Herein, we selected Ta2O5/Si3N4 nanolaminates to fabricate toughened AR coatings with similar refractive indices, overcoming the brittleness of thick nitride films. Furthermore, we proposed another graded AR coating, using a“Step up-step down" method to combine the hardness gradient structure with optical design. The toughened AR coating exhibited a low reflectance of 0.8% (420-780 nm) and a remarkable hardness of 22.8 GPa, meanwhile demonstrating the ability to withstand abrasion from steel wool up to 3,000 times. The graded AR coating achieves high transparency (Tave>98.8%, 420-720 nm), high surface hardness (H>23 GPa), and low residual stress (~680 MPa). Notably, no additional damage was observed during 6 months after the scratch test, such as cracking, peeling, and delamination.

Optical coatings are enabling technology for modern optical systems, they are almost applied on every surface of the optical components. However, due to the uniform structure of the optical coatings, optical coatings have limited capability manipulating electromagnetic characteristics. Optical metasurfaces can locally manipulate optical field and enhance light–matter interactions, thus offering fascinating possibilities to control various properties of light, such as amplitude, phase, and polarization. While many new physical effects and applications were demonstrated based on metasurfaces, their practical application still faces challenges of low optical efficiency. Here, we propose the quasi-three-dimensional subwavelength structures, consisting of optical coatings and metasurfaces, to promote the efficiency of metasurfaces. We will present our recent advances in high-efficiency quasi-three-dimensional subwavelength structure devices. Our results pave the way to realizing optical meta-devices facing strict efficiency requirements in realistic applications.

This work presents the investigation of 2D periodic structures made by conformal deposition of dielectric thin films on the modulated surface, where the deposited layers repeat the primary surface. Depending on the architecture, spatial filtering and polarization control may be performed in transmission or reflection with the incidence of radiation perpendicular to the surface. In the presentation, the overview of different technologies to form conformal coatings on periodically modulated surfaces will be presented. As the proposed 2D photonic structure can be considered a promising component for intracavity spatial filtering, the integration into a microchip laser will be presented. A significant reduction of M2 and brightness increase of two times was recorded for the microchip laser when the fabricated spatial filter was used as one of the resonator mirrors.

This paper will present an overview of the recent progress made by the Institut Fresnel for the metrology of ultra-low optical fluxes. A focus will be dedicated to the development of a breakthrough instrument designed for a global analysis of complex optical coatings : a Spectrally and Angularly resolved Light Scattering characterization Apparatus (SALSA). A panel of applications will illustrate the capabilities of the instrument, such as measuring the optical responses of linearly variable filters or characterizing the scattering losses of very high performance optical coatings.

Dielectric multilayers can be designed and fabricated to reach large optical field enhancement when working under total internal reflection. In an objective based total internal reflection fluorescence microscopy (TIRF-M), we propose to use the resulting large field enhancement supported in such resonant coverslip to improve TIRF-M sensitivity by amplifying the collected fluorescence signal. Scattering effects due to roughness of the substrate may parasite the optical response of our designed multilayer-based component. We present here the numerical model of the roughness impact over the multilayer optical response.

Development of modern mid-infrared laser applications requires high-quality optical elements operating in the broadband spectral ranges from visible to 15 um. ZnS/YbF3 coatings on ZnSe substrates are perspective candidates for such elements since these thin-film materials and the substrate are transparent in this region and provide sufficient refractive index contrast. Experiments demonstrate that spectra of ZnS/YbF3 multilayers on ZnSe and glass substrates are shifted with respect to each other significantly. This issue plays a key role in the monitoring concept of YbF3/ZnS-coatings since typically the monitoring is conducted on a glass, and the final optical elements are on the ZnSe substrates. The study reports sophisticated experiments on the deposition of ZnS layers, its in-depth analysis on different substrates, and innovative reverse engineering of double-sided ZnS/YbF3 optical elements in the spectral ranges from 400 nm to 12 um. The results can be interesting for optical coating and laser engineers.

Light scattering due to interface and coating imperfections is a significant concern for optical components, while on the other hand, scattered light contains valuable information about its source. This turns scattering based techniques into excellent tools for the characterization of surfaces and thin film coatings. At Fraunhofer IOF, angle resolved light scattering techniques are developed and used for the characterization of optical surfaces, coatings, and components for a broad range of applications. Examples will be shown, such as the analysis of ultra-low optical losses of an ultra-high reflecting mirror. Beyond that, the non-contact, fast, and robust measurement approach makes the technique even suitable for integration into fabrication processes or test environments. We show approaches for integration of a light scattering sensor into a roll-to-roll process for fabrication of colorshift foil by evaporation, as well as the sensor integration into even a magnetron sputtering coating system.

Contaminations can lead to a reduction of the laser-induced damage threshold (LIDT) leading to an unexpected damage of the components coating inducing damaged areas significantly larger than the beam size. In this study, we developed a process to contaminate the surface of anti-reflective and high-reflective coated optics with Polyether ether ketone particles of the size 10-100 µm. Contaminated samples were then irradiated with a ns-pulsed high repetition 1 µm laser system regarding the determination of the LIDT. We especially illustrate detection as well as the irradiation and monitoring of a single particles during laser irradiation. In conclusion, we have not observed any damages on clean samples up to an energy density of 1 J/cm². However, the particles got already damaged one to two magnitudes below this leading to a significant decrease in the surface damage threshold.

A new approach for direct third-harmonic generation is the generation inside a stack of dielectric layers. At present, our highest conversion efficiency achieved is 3.5%. This contribution provides an overview of the design process, production, measurement results, and their agreement with simulation results. To create the frequency tripling mirror designs, we use a combination of a Monte Carlo algorithm and a Meep-based algorithm to solve Maxwell's equations. Mandatory for the production of the mirrors is a very precise knowledge of the dispersion data of the materials used. For this purpose, the dispersion data of the coating materials are re-fitted using in-situ transmission data of a BBM after each coating run. In combination with various measures to maintain a stable refractive index of the used Hf_xAl_yO, high coating thickness accuracies are achieved in this way. Finally, experimental measurements and simulation results are compared using the post-fitted dispersion and layer thickness data.