Advances in Optical Thin Films VIII

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)

Laser 3D nanolithography enables the fabrication of free-form and stacked micro-optical components. In such micro-optics the presence of numerous interfaces often leads to the undesirable accumulation of reflection losses. This work demonstrates the application of atomic layer deposition (ALD) to deposit an antireflective (AR) coating on hybrid-polymer SZ2080™ stacked microstructures and micro-lenses of spatial dimensions < 100 μm. The AR coating successfully reduced reflection from 3.3 % to 0.1 % at 633 nm for one surface of SZ2080™, while significantly increasing the transmittance of the three stacked microstructures from 80 % to 99 %.

Deposition systems based on plasma assisted reactive magnetron sputtering (PARMS) have been established as benchmark tools for mass production of complex optical coatings for high-end applications in optoelectronic industry. The coatings are used for devices like powerful lasers, fluorescence microscopes, 3D imagers, ambient light sensors, waveguides, or smart glasses. The market for these devices is growing rapidly requiring production tools with increasing throughput while exhibiting a flawless optical performance and high coating uniformity. To meet this trend, we have scaled up and improved an established PARMS deposition system for high-precision volume manufacturing of complex optical filters. The system can coat batches of substrates with a diameter of 300 mm. Enabled by rotatable targets for the sputter deposition, a planetary drive system for the substrate holders, and an optical monitoring system for in-situ process control, deposition of highly complex optical filters can be performed. At the conference a comparison of the coating results from the machine and its older variant will be presented.

The arrival of ChatGPT, Google Bard, and other highly advanced artificial intelligence model show us just how brilliantly tasks can be reproduced by those engines. So, it's legitimate to wonder how our field (or any fields) might be affected in the future. We've already seen the beginnings of the possibilities, notably with LensNet [1], which provides optical designers with starting points for common cases; we can also study a solution space of certain type of lenses using deep learning [2]; and more recently, papers on the use of deep learning to simulate the entire chain of an optical system from object to final image processing, including tasks such as recognition. These latest end-to-end simulations have shown that in some cases, it is even necessary to redefine the optical optimization criteria to maximize certain computer tasks. In short, the computer doesn't necessarily need a good image in terms of MTF to perform its task. In this context, how the future will be affected or enhanced by these new AI approaches. In this presentation, I will first give a brief history of how AI has impacted optical system design since 40 years. Then I will use examples to discuss the extraordinary acceleration in works over the past 5 years, the choices that have or haven't been made, and the importance of having access to source code from publications. Finally, I will conclude with some thoughts on what may or may not lie ahead, and how we can introduce these new technologies into the training of future optical system designers. [1] Geoffroi Côté, Jean-François Lalonde, and Simon Thibault, "Deep learning-enabled framework for automatic lens design starting point generation," Opt. Express 29, 3841-3854 (2021). [2] Geoffroi Côté, Yueqian Zhang, Christoph Menke, Jean-François Lalonde, and Simon Thibault, "Inferring the solution space of microscope objective lenses using deep learning," Opt. Express 30, 6531-6545 (2022).

Freeform optics for illumination, pioneered over 20 years ago, are now widely used to light up streets, automobiles, architecture and more. But many questions remain: Do we have good, accessible design methods, especially for extended sources? Do we have proven processes to estimate and specify tolerances, to ensure full production yield without overengineering? Do we fully understand diffractive structures on freeform surfaces? The talk discusses the progress of design and manufacturing methods over the last 30 years, shows the knowledge gaps we’re suffering from, and concludes with an outlook to a non-obvious but exciting new approach for coherent light: What happens when we combine freeform surfaces with scattering and spatial light modulation?

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.

Light-absorbing black coatings are indispensable for many different optical applications. Thin-film interference coatings are extremely flexible in adapting to different wavelengths and in the choice of coating materials. To generate an effective (> 99%) light absorption of such an interference coating, the interference effect needs to be combined with a well-defined absorption of the layer’s materials. In this contribution, we present our development of black thin-film absorber coatings, tailored for different applications. Some examples for already manufactured coatings on applicable components are presented. A wideband black absorber for 400 -1000nm wavelength on a space spectrometer slit, a black aperture for NIR and SWIR light on the exit face of a dispersion prism, and a bi-directional black coating for a single wavelength in the VIS which can be wet-chemically etched for micro-patterning.

Thin gold (Au) films exhibit distinct optical properties dependent on their morphology. We explore how thermal annealing influences the optical and morphological characteristics of Au films, offering the potential for optical-based thermal sensors. Varying film morphologies produce different optical changes, and integrating nearly percolated films in multilayer interference coatings enhances their performance as irreversible temperature sensors. These findings highlight the promise of annealing-induced morphological changes and interference effects for thermal sensing.

Narrow bandpass filters featuring broadband blocking ranges and low angular shift find extensive applications in industry. The filters are challenging since narrow transmittance width and large angular fields are inherently conflicting requirements. We develop immersed bandpass filters exhibiting a narrow transmission range around 850 nm, blocking ranges at 200-780 nm and 900-1100 nm, and low blue shift for incidence angles up to 30°. The solution should also allow for the possibility of shifting the transmission range further into the visible or near-infrared regions. Optimal choice of materials should provide an ultra-broadband blocking range and high transmission zone. Therefore, materials absorbing in the blocking range and transparent outside of this range should be used. The design robustness is considered. Double-sided optical elements composed as front side filter and back side blocker hold promise in this regard. The solutions are oriented at Ion Beam Sputtering technique without load lock solution.

Rudolf Kingslake is widely regarded as one of the founders of modern optical design. When educating his students at The Institute of Optics, Professor Kingslake championed the importance of lens design fundamentals as a complement to computer-aided design. At that time, ray tracing speed was a major bottleneck in the lens design process. Now that lens designers can trace rays in fractions of a second and have access to powerful computational tools like global optimization and AI are these same fundamentals needed? Should we keep teaching them? One of Kingslake’s biggest fears was that we would forget “our laboriously acquired knowledge of geometrical optics and substitute for it the mathematical problem of optimizing a merit function”. There is no question that computers have done wonders for lens design and have enabled far more advanced designs than thought possible. The issue at hand is if mastery of both lens design fundamentals and computer software is required for success. Unfortunately, the current educational landscape places much more emphasis on the latter than the former, and many of the fundamentals impressed by Kingslake have been lost. However, three boxes of index cards belonging to Rudolf Kingslake were recently uncovered. Included in the collection are 171 lens design exam problems which present a fascinating perspective on lens design as it was taught in the pre-computer age. In this talk we’ll take a closer look at several of these forgotten problems and discuss how their solutions are still relevant for modern lens design today.

In 2017, the European Southern Observatory (ESO) awarded a contract for the Polishing, integration and final figuring of the Segment Assemblies of the primary mirror (M1) for the Extremely Large Telescope (ELT) to Safran Reosc. Since then, the design and commissioning of a production unit dedicated to ELT M1 has been accomplished and the plant has been producing many mirrors since spring 2022. We will introduce the smart factory, its processes and their automation that enabled reaching the current throughput of one mirror per day. We will then present the status of the project, some lessons learned and highlight the successes that have been achieved so far.

The concept of quantum nanolaminates (QNL) postulates the decoupling of band gap and refractive index, which in regular dielectric materials is linked. We will show that the quantization effect can be observed in nanolaminate structures of the material combinations Ta2O5-SiO2 and amorphous silicon-SiO2, which were deposited by magnetron sputter deposition. These nanolaminates were characterized by a variety of different methods, which confirmed the layer structure in the nanometer range and the shift of the absorption edge to shorter wavelength. Furthermore, the use of the QNL as the high refractive index material in optical interference coatings was successfully demonstrated in anti-reflection and long pass filter coatings.

Optical thickness monitoring is implemented in almost all coating machines for high precision optical interference filters. Standard broadband transmittance monitoring comes to the limit of thickness resolution when e.g. nanolaminates are deposited. Ellipsometry is more sensitive for material dispersion and. Transmittance measurement can be used for higher layer count with standard materials. We use a turntable configuration at 250 rpm with magnetron sputtering from cylindrical targets. We show the integration of a broadband ellipsometer for the determination of thickness and material properties during the growing layers. The ellipsometric angles were measured and the deposition process was investigated. The triggering was optimized to match the exact position on the moving control substrate. Ex situ ellipsometry is in good agreement. Results for nanolaminates are presented from the combination of amorphous silicon and silicon dioxide. With TEM we found smooth surfaces for sub-nm layers. The thicknesses are reproducible and consistent with ellipsometry.

All naturally occurring materials show a fixed combination of refractive index and the band gap energy, which correlates with their absorption. Both properties are material constants. Metamaterials are an alternative approach to varying these constants independently and increase the transparency range of existing optics in the UV. These metamaterials can be produced using quantum nanolaminates (QNL). The special type of material sequence in the QNLs coatings opens up a wide range of possible material parameters without the process problems which occur with mixed materials that are commonly used in this context. This presentation is going to investigate the concept of nanolaminates made from the high-refractive index material hafnia (HfO2) and the low-refractive index material silica (SiO2). In order to reach a blue shift of the absorption edge, the QNLs were applied in an antireflex coating as a substitute for the high-reflectivity material. All layers were produced by ion beam sputtering.

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.

Photo-induced thermal radiation (PhTR) has not yet been deeply studied in optical thin films. Now that a complete PhTR theory has been published for arbitrary illumination regimes, we focus on a PhTR facility under development, which aims to perform a temporal, spectral and angular characterization of PhTR. The sample is illuminated with a nano-second pulsed laser operating at 20Hz. The resulting absorption is at the origin of the temperature elevation which creates a pulsed PhTR that we record in different MIR spectral ranges at all directions. Preliminary results on multilayer broad-band absorbers are highlighted, and successfully compared with theory. These first results allow to identify the difficulties that arise when dealing with all-dielectric stacks, whose absorption levels are lower by several decades. In particular the signal must be maximized while respecting the damage thresholds, which leads to compromises and favors spectral windows in connection with the choice of detectors.

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.

This study discusses absorption in thin film optical filters and its influence on spectral shift and wavefront deformation under high power laser exposure. Lock-In Thermography method has been developed to measure coating absorption with high sensitivity (1 ppm). Additionally, a finite element model created with COMSOL is presented. It predicts optical function spectral shifts and wavefront deformations in thin film optical filter under high power laser exposure. Comparison between theoretical predictions and measured data is used to validate the model and provide valuable insights for designing reliable thin-film optical filters used in high power laser systems.

The interest of the astrophysics community in making space observations in the vacuum ultraviolet (VUV, 100-200 nm) triggers the research to overcome the challenges of developing efficient VUV imaging bandpasses, particularly for future space observatories like the HWO/NASA. Typically, high-reflective narrowband coatings consist of periodic combinations of fluoride multilayers (MLs). In this context, GOLD-IO-CSIC group has been developing coatings based on combinations of MgF2/LaF3 and AlF3/LaF3 MLs, which can be tuned at any VUV wavelength >120 nm with a remarkable performance above 85% at H Ly-α (121.6 nm) for AlF3/LaF3. We also present a comparative study on the nanostructural morphologies of the two sets of MLs. Both the selection of the ML materials and the introduction of some aperiodicity on the ML designs allow choosing the bandwidth or the desired optical profile with remarkable freedom. Below ~120 nm there is no suitable combination of fluorides since all fluorides but LiF turn absorbing. We, then, present narrowband coatings based on Al, LiF, and SiC films, tuned at ~100 nm, with a strong rejection at the close H Ly-α line that could mask the observations.

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 Instrumentation Division of the Instituto de Astrofísica de Canarias (IAC) is involved since several years in upgrading its capacities to design and manufacture optical components. To this end, we have created a new laboratory (Centre for Advanced Optical Systems, CSOA) which will be capable to design, fabricate and qualify large optical elements. Within these efforts, an optical coating facility is being built aimed at coating and surface finishing of different components, such filters, mirrors and alike, with sizes ranging from few cm to about 1.5 m. The facilities are still in construction and we have already started to experience with medium size filters and mirrors, using a large variety of metallic coatings, both for anti-reflection properties and spectral band selection. Our present capacities included a sputtering coating machine, capable to treat pieces up to half a meter of diameter, and E-beam and thermal evaporation. In this contribution we describe the current laboratory setup and report on the results achieved so far in the field of surface coating with different materials.

In this work, an all-dielectric light polarizing element with 0 degree angle of incidence was fabricated and investigated. Linear polarizer for 1064 nm wavelength was formed by conformal deposition of dielectric thin films on the structured substrate. Its potential in laser applications was tested with laser-induced damage threshold evaluation for nanosecond pulses by 1-on-1 testing method. Despite only dielectric materials, the optical resistance of the periodically structured element is several times inferior to that of the planar element. Differences in optical resistance correlate with formed electric field peaks within the modulated structure, revealing the problem to be solved in the ongoing work.

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.

We have developed a systematic approach to identifying suitable materials for short-period multilayer mirrors operating at 30 keV. We tested many materials and evaluated the performance of each possible combination, focusing on two key figures of merit: integrated reflectivity and peak reflectivity. While it is typical to optimize a multilayer structure to maximize the peak reflectance, we found that this approach can lead to bias. Instead, we propose using integrated reflectivity as a more robust criterion for material selection. Our results demonstrate the effectiveness of our approach in identifying high-performance multilayer mirrors for X-ray applications.

High intensity laser facilities require large area optics for reliable operation. ELI-Beamlines, together with Vacuum Innovations, has developed and commissioned a large-scale electron-beam evaporation system (ELIAS) for precision optical coatings. Ultrafast components for extreme power laser applications with up to 1.2 m diameter can be coated with high uniformity by metal and dielectric thin films. Current status and initial results are presented together with the future plans.

The Laser Megajoule (LMJ) facility requires smoothing the intensity profile of its 176 beams. A quarter-wave plate coating fabricated by GLancing Angle Deposition and applicable in polarization smoothing processes is investigated. The Laboratory for Laser Energetics designed a 21-layer coating of silica alternating columnar birefringent layers with isotropic layers. We present a comprehensive comparison of retardance measurement techniques for our specific coating. Linear retardance is measured using either a birefringence mapper, a Stokes polarimeter or a spectroscopic ellipsometer with three different models. The analysis of the latter technique uses the structural information obtained by Scanning Electron Microscopy. As we find very consistent results between the three different methods, the choice of the method will depend on the cost, versatility, ease of implementation.

Optical interference filters allow achieving a wide range of spectral functions. To match with the theoretical performances, fabrication processes require very accurate control of each of the layers thicknesses. This study explores optical monitoring techniques used to control the process, specifically polychromatic and broad-band monitoring. A numerical model was first used to simulate online monitoring signals during deposition, based on filter design and refractive index of the materials. An original algorithm was then implemented to automatically identify the most relevant wavelengths or spectral ranges for monitoring filter layers, reducing thickness errors of each layer during deposition. When minimalist errors are not possible anymore, the algorithm suggests the critical instant for changing the testglass. Finally, this approach was experimentally validated on error-sensitive filters, such as narrow multi-bandpass and notch filters.

We report the results of an optical design study of a multilayer mirror that provides high reflectivity in the 400 eV region. First, the material pair selection rule proposed by Yamamoto was applied to examine the coating materials. Using the optical constants table by Palik, we calculate the Fresnel coefficients for various materials at angle of incidence of 60 deg. Following the selection rule, we looked for two materials where the distance between two points on the complex plane is far apart and also as close to the real axis as possible. And the film thickness was optimized by numerical calculation using IMD software, which results in practical high reflectivity of 50% on the Sc/Cr multilayer mirror at the photon energy of 397.5eV. In this presentation, we also report grazing incidence x-ray reflectivity results for multilayer mirrors deposited by a magnetron sputtering method.

Optical elements are improving each day and are widely used in numerous laser systems. To gain benefits in optical resistivity or spectral performance, a fairly new method is developed using nanostructured thin films coated by glancing angle deposition method. By combining porous layers of low refractive index material with standard dense layers of high refractive index materials, the spectral performance of mirror is enhanced. Induced porosity in silica layers allowed to form broader high reflectivity mirrors with low GDD properties for ultrafast optics.

In the frame of development of optical diagnostic for fusion reactor, CILAS is currently in charge of the design and qualification of several types of anti-reflective (AR) coatings on fused silica substrates. In this paper, we will first focus on the design of the 4 anti-reflective coatings covering different spectral ranges between 380nm and 1875nm, with expected low reflectivity (<0.5%). Then we will present the results of the manufacturing done with PIAD (Plasma-Ion Assisted Deposition). 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 (300-2500nm) permits to reach severe spectral specifications and to have a very good agreement with the theoretical designs. Finally, some qualification results will be shown such as thermal cycling with very high temperature, and high number of cycles, nuclear radiations, water steam, outgassing, and more classical tests (adhesion, abrasion, cleanability, spectral measurements, WFE measurements).

As part of the investigations, QNLs were produced from TiO2, Nb2O5, and ZrO2 using IBS which are presented here. Complex layer systems, such as edge filters or polarizers, are produced using a system control specially adapted for such a large number of layers and the complete automation of the coating process. With these coatings, the focus was also on exploiting the blue-shift caused by quantization. Subsequent investigations are intended to demonstrate their applicability to other areas of optics production. The applications range from high laser damage thresholds to low mechanical losses for the mirrors of gravitational wave detectors or optical clocks.

This study investigates the feasibility of using hydrogenated carbon thin films deposited by pulsed DC sputtering as an alternative durable optical thin film material for infrared applications. The study focuses on how the mechanical and optical characteristics of the deposited carbon thin films vary with hydrogen content. To precisely control the hydrogen incorporation in the carbon layers, pulsed DC deposition was used in conjunction with a controlled hydrogen generator. This allowed for a methodical investigation of the link between hydrogen content, stresses, transmittance, reflectance, and absorptance. Results of increasing hydrogen content within the carbon films demonstrate a reduction in stress, absorptance and hardness. The hydrogen acts to alleviate the compressive stress levels and mitigate the mechanical durability challenges within the film. Such films have applications in systems that require mechanically robust optical coatings such as anti-reflection infrared coatings for common infrared substrate materials.

HfO2 is widely used as a high refractive index material for making high LIDT optical coatings. Advances in laser and photonic technologies quite often require additional important properties like flatness, very high reflectance, low losses, environmental stability and others to be achieved besides high LIDT. Investigation of single HfO2 layers deposited by PIAD technology with different plasma parameters are presented, analyzing optical properties, stress, bandgap, direct absorption, surface roughness, morphology and film structure. It is shown, that by selecting proper plasma parameters it is possible to obtain dense HfO2 layers having small compressive stress, which is favorable for applications, requiring control of optical component flatness.

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.

Strontium ferromolybdate Sr2FeMoO6 (SFMO) is a promising material for spintronic, photonic and plasmonic devices operating at room temperatures due to its high spin polarisation and high Curie temperature. Variations in SFMO lattice and material composition greatly impact magnetic properties and application range of spintronic devices. A high-quality SFMO film is difficult to obtain due to unavoidable defects and nonstoichiometry. Using multitarget reactive magnetron sputtering technology it is possible to achieve high density and precise composition of deposited films. The aim of this work is to reach an optimum SFMO film composition for the further development of multilayered magnetic film structures for spintronic devices. Films were deposited using an industrial sputtering system on 150 mm diameter platinized silicon wafers using high-purity Sr, Fe and Mo targets. For precise control of partial oxygen pressure, a plasma emission monitor (PEM) was used. Deposition parameters were adjusted and fine-tuned according to the evaluation of deposited SFMO films. The latter ones were investigated using SEM, EDX, XRD, AFM and optical reflectance in the UV-IR range.

It is common to control the radius of curvature and the polish quality of the two interfaces of an optical component by interferometric means. The setup we have developed under the name BARRITON (for BAckscattering and Retro-Reflection by InterferomeTry with lOw coherence) allows to extend the use of this highly sensitive approach to a wide range of opto-mechanical properties for simple optical components. Moreover, in the case of a silica window, this instrument alone allows us to determine the wavelength dependence of the retroreflection coefficient of each of its two faces (spectral resolution 0. 2 nm, sensitivity better than one part per million, exact normal incidence), the angular dependence of the light power backscattered by each of these faces (angle-resolved scattering up to 10-4 sr-1, spatial frequency resolution about 10-4 µm-1), the optical thickness of this plate (resolution better than 0.1 µm), and the lack of parallelism of its faces (resolution better than one arcsecond). These characterization performances meet the requirements of very demanding applications, such as the giant interferometers developed for the detection of gravitational waves, in particular in space (LISA, Laser Interferometer Space Antenna). In this poster, we will describe the optical layout of our setup (low-coherence interferometer with balanced detection) and identify the main parameters that determine the signal-to-noise ratio of our measurements. In addition, we will give some examples of results obtained on single components and/or optical assemblies.

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.

This research delves into high-entropy alloy (HEA) thin films, modifying a Cantor alloy base with elements like Pt, Al, and Ti to study their structure-related optical properties. Employing DC magnetron co-sputtering and comprehensive characterization techniques, the study uncovers distinct structural transitions and their effects on nonlinear optical responses. Results show promising applications for HEA films in nonlinear optics, with the potential for innovative planar photonic devices.

We report on an integrable thin-film Fabry-Pérot type electro-optic modulator (EOM) centered around an electro-optically active so-called guest-host polymer. This polymer material contains novel synthesized chromophore molecules (C3), which are aligned by electro-poling inside an amorphous polycarbonate host-matrix. Electro-optic activity of the poled material can be observed in the near infrared spectral range. We derived a value of ~220 pm/V for its linear electro-optic coefficient at 988 nm from spectral transmission measurements with increasing direct voltages applied to the EOM. We demonstrated modulation of the intensity of a 974 nm diode laser by application of ± 11.5 V alternating voltage to the EOM. Due to the all thin-film realization of the EOM setup, it allows for substrate free, miniaturized interference filter fabrication. In combination with the demonstrated low drive voltage, these compact EOM filters are excellent candidates for hybrid integration into photonic platforms, as shown in this contribution.

This work introduces a new approach for the detection of defects and damage in thin layers (including damage from LIDT process) based on the second harmonic generation principle (SHG). SHG is very sensitive to even subtle changes in the layer, therefore, it is a promising way to detect damaged spots, which could be hardly detectable (or even undetectable) by other methods. We present our results from measurements and provide a comparison to other commonly used methods.

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.

In the last two decades, laser technology has undergone transformative advancements, expanding options for new laser irradiation regimes from ultrashort pulses to continuous waves featuring significantly higher power levels. The evolving landscape demands alignment of laser damage testing standards with recent technological developments. As high-power laser applications reveal unique failure mechanisms, there is also a need for novel testing approaches like "R(S)-on-1" or “raster scan” and reevaluation of classical routines such as "1-on-1" or “S-on-1”. Recent standardization activities for the revision of ISO 21254 family standards will be discussed with the main focus on damage criteria, test procedures, and result analysis to enhance accuracy and reliability while addressing new challenges in laser damage testing.

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.

This study investigated the damage mechanism and laser-induced damage threshold (LIDT) of MLDG. Clean and contaminated gratings with and without gold nanoparticles were prepared on HfO2/SiO2 high reflection coatings using atom layer deposition and ion beam sputtering. After nanosecond laser irradiation at 1064 nm, it was found that under the local strong field, both the softening and cracking of defects intensify, and damage is more likely to occur at contamination points, leading to a decrease in LIDT. Modeling of the electric and thermomechanical response for contaminated MLDG was also performed to understand the damage mechanism and cracking preferential position.

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.

In high energy laser (HEL) systems, large diameter optics and low wave front error are critical in order to achieve high resolution in far distances. In this work, we introduce recent developments of several unique optics with final specification of λ/10 (63nm P.V) reflected wave front error (RWE) measured before exposure to at least 30 seconds 200kilowatt laser power at 1064nm as well as during exposure. Different challenges were overcome and are reported in this work.

Distributed Bragg reflectors (DBRs) have been developed as an effective way for reflecting light in several applications. In this work, a cavity medium is introduced between the DBR and substrate to increase the reflection by stimulating the cavity modes. The DBR has been designed carefully based on the quarter-wavelength rule utilizing the transfer matrix method (TMM). The thickness, number of layers, and material composition have been optimized, and the surface reflectance of a DBR-coated substrate with and without a cavity layer is compared. Employing FDTD simulations, the optimal thickness of the cavity layer for the incident wavelength of the interest is obtained. The results show a significant enhancement in the reflection by introducing the cavity in the design.

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.

This work investigates the optical, mechanical, structural and morphological properties of a high reflector multi-material optical coating. The coating consists of hydrogenated amorphous silicon (a-Si), Ta2O5 and SiO2 deposited using microwave plasma assisted sputtering and evaluates the potential of the coating as a gravitational wave detector mirror coating. The advantages of microwave plasma assisted sputtering are described and influence of the deposition parameters such as deposition rate. This work also studies the properties of the coating for post deposition annealing temperatures.

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.

With an increasing degree of automation in mobility, the demands on the sensors and the number of sensors in the vehicle are steadily increasing. For sensor integration and combination an efficiently manufacturable compound system including LiDAR, radar and lighting system has been designed. In the pilot project “Smart Headlight” of the PREAPRE program of the Fraunhofer Society the Fraunhofer institutes FEP, IOF, ILT, IMS and FHR will prove the integration of such a sensor-lighting combination into automotive headlights under shared coaxial decoupling in driving direction, covering a wavelength range of some nanometers up to millimeters. Optical multilayer coating designs are developed and sputtered at FEP Dresden to demonstrate the feasibility of this coaxial combiner system integrated into the automotive headlight.

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.

Metal oxides such as titanium oxide (TiO2) and zirconium oxide (ZrO2) have attracted a great deal of interest in recent years due to their many remarkable physical and chemical properties. The high performance of these materials allows their use in a wide range of applications including coatings against corrosion, wear and oxidation. They are also used in optical applications, as sensors anti-counterfeiting devices, or in medical applications for dental implants. The authors will present a process for structuring thin films of metal oxides using a sol-gel deposition method. Unlike more conventional methods such as reactive sputtering, chemical vapor deposition and atomic layer deposition, this technique facilitates the micro-nanostructuring of films by lithography techniques, in particular colloidal lithography.

Zirconium nitride (ZrN) combines plasmonic properties in the visible and near infrared spectral region with good mechanical properties, high thermal and chemical stability making it a very promising alternative to noble metals for optical applications at high temperature or in extreme environments. The authors present a new process for the elaboration of micro-nanostructured ZrN from a photo-patternable ZrO2 sol-gel and a nitridation process, by rapid thermal annealing. This sol-gel is patternable by optical lithography, it allows to easily and quickly produce patterned ZrN layer by rapid thermal annealing.

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.

SPARSE (SPatially and Angulary Resolved Scatterometry Equipment), developed at Institut Fresnel by the CONCEPT Group, addresses the challenge of qualifying light scattering performances of optical surfaces from surface quality. This innovative instrument combines the principles of a classical scatterometer with an imaging system to precisely quantify the impact of localized defects, contamination, scratches, and roughness. It has the ability to measure scattering levels as low as $10^{-7}\ sr^{-1}$, and provides valuable insights through spatially resolved Bidirectional Reflectance Distribution Function (BRDF). A detailed description of the experimental setup and measurements on representative samples will be presented.

Accurate knowledge of the substrate optical properties is crucial for the theoretical designing and monitoring of optical coatings and characterization of produced optical coatings. Typically, substrate characterization is performed based on reflectance and transmittance data in the relevant spectral range. Measurement errors (offsets of spectral characteristics and noise) are inevitable. Neglecting scattering and assuming transparent spectral ranges, offset values of experimental data can be estimated as a difference between 100% and the sum of the measured transmittance and reflectance. It doesn't provide insights into which spectral characteristic(s), reflectance, transmittance, or both, contribute to the offset or to what extent. We suggest an approach that allows one to estimate the offset values in reflectance and transmittance separately, estimate the effect of these offsets on the determination of substrate optical constants and characterize the substrates reliably. We demonstrate the approach characterizing various substrates in the range 220-1700nm based on Photon RT measurements.

Ion Beam Sputtering systems are well established as state-of-the-art deposition tools for the coating of high quality optical thin films with high density and low losses. These coatings are used for many laser applications, with an ever-increasing demand for higher sustained fluence. In this work, various coatings were developed using Bühler IBS technology. Then, total losses were measured using Cavity Ring Down, absorption using Laser Induced Deflection or Laser thermography, and Total Integrated Scatter using dedicated scatterometers. the corelation between the performance of the coatings and the parameters used for the deposition will be presented in this study. The improvements in the visible wavelength range and in the near UV will be presented at the conference.

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.

Monochromatic monitoring by intermittent measuring technique is established as a standard monitoring system in box coaters of since 2005. A halogen lamp inside the chamber enables monitoring wavelengths in the range of app. 330nm up to 2500nm. A newly developed set-up of the optical path was designed for the Syruspro 1100 DUV box-coater series. The substrates are placed on a planetary drive, while the monitoring glass is located between two planets. A deuterium lamp in combination with an achromatic lens system result in a high light throughput in the DUV range. The light transmitted through the monitor glass is focused into a fibre optic. A standard optical monitor, type OMS5100 equipped with a PMT detector is connected to the fibre optic. This assembly enables monitoring wavelengths in the range 200nm up to 380nm. We present the hardware set-up and coating results for various DUV coatings.

Multilayer optical coatings operating across broad spectral ranges from visible to mid-infrared, play a crucial role in numerous industrial and scientific applications. MgF2, YF3, and Al2O3 are promising low-index materials within this range, Ge and Si can be harnessed as high-index materials. One of the key prerequisites to producing high-quality optical components is accurate knowledge of optical constants of thin-film materials as well as their environmental properties, which are dependent on deposition technology and process parameters. The present study reports characterization of monolayer samples of Ge, Si, YF3, Al2O3, and MgF2 on Silicon and Fused Silica substrates produced by e-beam evaporation with ion assistance technology. Deposition of the samples was performed at ORTUS-700 vacuum coater (I-Photonics). Reflectance and transmittance was measured using Photon RT spectrophotometer (Essent Optics) in the range 300-5000 nm. The samples were numerically characterized using advanced algorithms of OTF Studio software; layer optical constants were reliably determined.

The study focuses on reliable reverse engineering of electron-beam deposited TiO2/SiO2 coatings. It is known that optical constants of evaporated TiO2 films are dependent on deposition conditions and may vary from layer to layer. Also, the nominal optical constants, used during the theoretical designing, may differ from the actual optical constants of coating layers, determined based on characterization of thicker single layers. Typically, post-production characterization of e-beam evaporated coatings is based on spectral photometric or/and ellipsometric data measured ex-situ. The study reports a new reliable algorithm that allows reliable estimating layer thicknesses and optical constants based on ex-situ measurements. The reliability of the results is verified using a specially produced unique set of samples including single layers identical to those ones included in the multilayer sample. The results obtained based on the photometric and ellipsometric data are in correspondence with each other. The algorithm delivers practical results and avoids overfitting.

Highly reflective (HR) optical mirrors are key components within large interferometers used for the detection of gravitational waves (GW) created through cosmological events. Precise detection and deep analysis improve our understanding of the Universe providing unique opportunities challenging aspects of General Relativity and opening new fields into Astronomy. Unresolved factors affecting the sensitivity of GW detectors (GWDs) include quantum noise and Brownian coating thermal noise. This presentation delves into an extensive examination of the optical and structural characteristics of silicon nitride (SiNx) as a thin film material for GWDs, exploring their variations under different plasma-enhanced chemical vapor deposition (PECVD) conditions. The investigation encompasses the analysis of refractive index, absorption coefficient, composition, stress, surface morphology, roughness, and mechanical loss of the coating. Additionally, the study involves the optical design of a high reflectivity (HR) coating, employing a combination of a-Si/SiNx and pure SiNx with high and low indices (h-index and l-index, respectively), executed using Essential McLeod.

A novel Microwave Plasma-Assisted pulsed DC Sputter (MPAS) process has previously been shown to produce dense amorphous, defect free films. In this work the production of materials for infrared BPF’s using the MPAS process is described. This is shown to produce dense, low porosity films, key to minimizing thermal drift of filter performance. A range of coating materials provide a flexible design space. Combined with different coating designs this allows filters to be optimized for thermal and angular shift. The use of Ge and oxides SiO2 and Nb2O3 allows for high index contrast, lower thickness filters to be produced. The merits of these versus all oxide designs is discussed and a summary of the performance of a range of H/L material combinations is presented.