Anti-reflective (AR) coatings are widely utilized to minimize reflections from optical components. Laser direct writing (LDW) is employed to fabricate complex and multi-level micro-optical elements, such as micro-triplets. Conventional physical vapor deposition methods are insufficient to produce conformal coatings on complex shape and stacked substrates. The atomic layer deposition (ALD) technique offers a promising solution for achieving conformal coatings on free-form components. In this work, we demonstrate the deposition of an AR coating by ALD on LDW-fabricated microstructures and micro-lenses. The ALD-deposited AR coating successfully reduced reflection from 3.3% to 0.1% at 633 nm for one surface of SZ2080.

We have scaled up and improved an established Plasma Assisted Reactive Magnetron Sputtering (PARMS) system for high-precision volume manufacturing of complex optical filters. The system can process batches of substrates having a diameter of up to 300 mm. By means of 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. A comparison of coating results from this machine and its predecessor for substrates with a diameter of up to 200 mm is shown. Due to the improvements, the layer non-uniformity of oxides could be reduced from ±0.5 % down to about ±0.15 % compared to the predecessor, even though the substrate diameter was increased. Using the optical monitoring system an optical band pass filter was deposited on Ø300 mm glass wafers demonstrating the capability of the machine for production with high throughput and yield.

Light-absorbing black coatings are indispensable for many different optical applications. Thin-film interference coatings can be flexibly adapted to different wavelengths. To generate an effective (> 99 %) light absorption of an interference coating, the interference effect needs to be combined with a well-defined absorption of the layer’s material. On this basis, different black absorber coatings were developed and deposited on optical components for actual applications. A wideband black absorber for 400 -1000 nm wavelength on a space spectrometer slit, a bi-directional black coating for a single wavelength in the VIS, which can be wet-chemically etched for micro-patterning, and a black aperture for NIR and SWIR light on the exit face of a dispersion prism are presented.

Thin films of gold (Au) have found use in various optoelectronic applications due to their unique optical properties. Depending on the film morphology, the optical response can display localized surface plasmon resonance related to isolated metal clusters and a Drude-like response emerging from a connected metal network. Therefore, Au films, especially those with nearly percolated morphology display a very broad optical response that can be drastically varied by control of the fabrication conditions or post-deposition treatments. In this study, we investigate the optical and morphological changes observed in thin Au films subjected to thermal annealing as potential building units for optical-based thermal sensors. Three different film morphologies (island film, nearly percolated film, and compact film) are obtained by controlling the amount of deposited metal. The evolution of morphological properties of these three types of films upon thermal annealing follows different mechanisms, resulting in enhanced optical changes in different spectral regions. In addition, we show that the incorporation of nearly percolated films in multilayer interference coatings can significantly boost their potential as irreversible temperature sensors. Overall, we show that the unique morphological changes induced by annealing combined with interference effects hold great promise for thermal sensing.

Narrow bandpass filters featuring broadband blocking ranges find extensive applications in spectroscopy, imaging, illumination, distance measurements, remote sensing, space and earth observations. The interest in bandpass filters with low angular shift is permanently growing; but as narrow filter width and large angular fields are inherently conflicting requirements, researchers explore various approaches to reduce this shift. We develop immersed bandpass filters exhibiting (i) a narrow high transmittance range at 825-875 nm, (ii) blocking ranges at 200-780 nm and 900-1100 nm, and (iii) low blue shift for angles of incidence up to 25°. However, the design solution should also allow for the possibility of shifting the transmission range further into the visible or near-infrared regions. Due to the immersed nature of the filter, it is difficult to effectively address such a complex task using two materials only; at least three materials should compose the coating. To provide an ultra-broadband blocking range, absorbing thin film materials should be involved. At the same time, these materials should be transparent outside of this range to maintain the high transmittance. Therefore, in the design process, a balanced compromise should be found. Not all theoretical solutions or/and materials combinations can be realized due to limitations of the production tools. The monitoring concept as well as design robustness should be considered; the number of layers cannot be very high. 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 deposition technique, not equipped with load lock solution.

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 interfaces and gives more detailed information on the layers at the beginning of the stack. On the other hand, transmittance measurements can be used for designs with higher layer count with standard materials. In this contribution we show the integration of a broadband ellipsometer for the determination of thickness and material properties during the growing layers in a magnetron sputtering system with a turntable configuration. The ellipsometric angles Psi and Delta were measured at an angle of incidence of 70° and the deposition process was investigated for Ta₂O₅ and SiO₂. The control substrate passes the measurement position every 240 ms. The triggering was optimized to match the exact position on the moving control substrate. In addition, results for nanolaminates are presented from the combination of amorphous silicon and silicon dioxide. The non-reactive magnetron sputtering process with separate oxidation by plasma source gives smooth surfaces even for sub-nm layers as revealed by TEM measurements. The thicknesses are reproducible and in good agreement with ellipsometry.

All naturally occurring materials show a fixed combination of refractive index and bandgap energy, which correlates with their absorption. Both properties are material constants. Metamaterials are an alternative approach to vary these constants independently and increase the transparency range of existing optics in the UV. These metamaterials can be produced using quantum nanolaminates (QNLs). 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 anti-reflex coating as a substitute for the high-refractive coating material. All layers were produced by ion beam sputtering.

In this contribution we show encouraging results of photo-induced thermal emission measurements, in nanosecond regime, for metallic layers and multilayers. The experimental setup of the instrument is presented. A comparison with the results given by numerical simulation is also highlighted, which allows to estimate the thermal parameters of thin films.

The rapid progress in high-power laser technology requires an in-depth investigation of absorption within optical components, as well as a comprehensive understanding of photo induced effects in thin film stacks. For this purpose, Lock-In Thermography (LIT) setup has been developed to measure the total absorption of the coatings with sensitivity under 1 ppm. A modulated high power laser is used to induce heating into the coating stack, and the resulting internal temperature rise is measured with a thermal camera. The LIT experimental setup offers a non-destructive and non-contact measurement technique which enables mapping of absorbing defects and implementing other types of measurement (such as wavefront distortion) in the same set up. To theoretically study the photo induced effects in a thin film stack subjected to high-power laser heating, a finite element model has also been developed. This model provides an insight on the refractive index and thickness variations of each layer and allows to predict the spectral shift in optical function. From stress-induced deformation computation, the model can also assess wavefront deformations resulting from photo induced effects. Using these tools, we show a comparison of measured and modelled spectral shift of thin-film components under high power laser exposure. These results offer valuable insights into the impact of laser-induced heating on the optical properties of the coatings and provide guidelines for designing robust and reliable thin-film optical filters used with high power lasers.

The interest of the astrophysics community to make space observations in the vacuum ultraviolet (VUV, 100-200 nm) triggers the research to overcome the challenges to develop efficient VUV optics due to material absorption and the limited knowledge of optical constants. Future space observatories like the “Habitable Worlds Observatory, HWO/NASA” require efficient coatings capable of providing high-throughput image bandpasses in the VUV which is currently included as a NASA technology gap. Among the scarce transparent materials in this range, some metal fluoride materials exhibit the shortest cutoffs. Typically, high-reflective narrowband coatings consist of periodic combinations of fluoride multilayers (MLs), with relatively high contrasting refractive index, such as MgF₂/LaF₃ or AlF₃/LaF₃ MLs. In this context, GOLD-IO-CSIC group has been developing high-performance all-dielectric VUV coatings, with special emphasis on short wavelengths down to 120 nm. This short VUV range is relatively unexplored and shows a comparatively lower performance due to the increased absorption of fluorides towards shorter wavelengths. Here, we present 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 MLs; this improves the state-of-the-art at such short wavelengths. 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.

Multielement composition with both structural order and chemical disorder are known as high entropy alloys (HEAs). Such materials exhibit unexpected mechanical and catalytic properties. However, the effect of composition and the structure of HEAs on their functional properties including the optical ones is still not well studied. Therefore, this work focuses on the development of HEA thin films using a Cantor alloy (FeCrMnNiCo) base, modified by varying a sixth element (Pt, Al, and Ti) concentrations to evaluate the changes in the film's structure and microstructure. The films were deposited via DC magnetron co-sputtering, which provided control over stoichiometry and film morphology. Then, the structural, electrical, and optical properties were characterized using X-ray diffraction, high-resolution transmission electron microscopy, resistivity measurement, and optical reflection measurements. Moreover, the interaction of the films with coherent light was also examined, revealing their nonlinear optical response to photons of visible and near-infrared range. In details, the structural analysis shows abundant nanotwins in the initial Cantor (CrMnFeCoNi) and CrMnFeCoNiPt films, both of which possessed a single fcc crystalline structure. However, CrMnFeCoNiAl films transitioned from a single fcc phase to a duplex fcc + bcc phase structure, eventually stabilizing as a single bcc structure. Such duplex fcc+bcc phase exhibited a low degree of nanotwins with larger grains of each phase. In contrast, CrMnFeCoNiTi films displayed an amorphous structure at various Ti contents. The study also advances the understanding of structure-related functional properties of HEAs and sets the stage for their future utilization in non-linear optics and photonics.

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. When integrated into our Fabry-Pérot cavity, the electro-optic activity of the poled material can be observed in the short wavelength near infrared spectral range (approximately 900 nm - 1070 nm). 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. The resulting half-wave voltage-length product of the EOM setup is 0.25 Vcm. As an exemplary functional test, we demonstrated an intensity modulation of a 974 nm diode laser by applying ± 11.5 V alternating voltage to the EOM. Due to the all thin-film realization of the EOM setup, it is compatible to the substrate free, miniaturized interference filter fabrication method. With this method, thin-film elements with edge lengths between 25 μm and 2 mm can be fabricated. 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.

The laser-induced damage threshold (LIDT) is a commonly used method for testing optical thin films, where the sample is exposed to laser radiation of a defined intensity and observed for laser-induced damage. Sensitive evaluation of the damage is essential for the experiment and different approaches are used for this purpose. This work introduces a new approach to LIDT evaluation based on the second harmonic generation (SHG) principle for the detection of defects in thin films. The process of SHG is very sensitive to changes in the symmetry of the crystal lattice of the material, which can be very well exploited for the observation of defects and various changes in thin films. We developed a setup able to track the polarization-dependent SHG from the samples with micrometer resolution for a broad range of incident angles in both reflection and transmission regimes. We use this setup to study the polarization and angular dependence of SHG in pristine and irradiation-affected areas on various thin films (Si3N4, TiO2,...). Our measurements show that SHG makes it possible to reliably detect spots with subtle laser-induced changes in the material that are hardly detectable or even undetectable by scanning electron microscopy or other commonly used methods.

ISO standards are periodically reviewed to ensure their relevance to the best industry practices. Significant advancements have been observed in laser source development and related technologies over the last two decades. These advancements encompass new irradiation regimes, ranging from ultrashort pulses to kW-class continuous wave irradiation, with substantially increased peak- and average laser power levels. This new reality also necessitates the adaptation of pertinent laser damage testing standards. As high-power laser applications introduce optical elements with unique failure mechanisms and size constraints, there is a growing need for the introduction of alternative testing methods. In this paper, we provide a brief overview of recent standardization efforts undertaken by ISO TC 172 SC 9 WG 1 for the revision of the ISO 21254 series standards - ”Lasers and laser-related equipment — Test methods for laser-induced damage threshold”. Specifically, we discuss the need for the extension of ’classical’ damage criteria, the introduction of alternative test procedures, and possible improvements in interrogation methods and analysis. The overarching goal of this paper is to promote transparency in the standardization process and inspire discussion, ultimately leading to the enhancement of accuracy and reliability in laser damage testing.

In this work we introduce several developments of unique optics with specified reflected wave front error (RWE) of λ/10 (63nm P.V) before exposure to at least 40 seconds 200kilowatt laser power at 1064nm as well as during exposure. A 10μm thick broadband dielectric high reflection (HR) coating was deposited on a 400mm diameter fused-silica substrate. A 0.4% coating uniformity was achieved which is equivalent to 40nm P.V RWE. To compensate the RWE introduced by the stressed HR coating, a unique anti-reflection (AR) coating was deposited on the backside resulting in total RWE of less than λ/10 (63nm P.V). A post deposition thermal process resulted in a 1.2% spectrum red shift, absorption reduction from 20ppm to 3ppm and no change in the RWE. In a second case, a 130mm dichroic mirror with rigid tolerance limiting the acceptable spectral red shift post thermal treatment, was exposed to low temperature process, reducing absorption from ~25ppm to 6ppm. In a third case, a scanning mirror (R>99.995%) with high specific stiffness substrate material (absorbing) and λ/10 RWE measured during exposure to 72kW/cm² laser for 40 seconds is discussed. Keywords: Ion beam sputtering, laser damage threshold, high refection coating, anti-reflection coating, stress

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.

In this work, a new optical coating design concept is proposed for gravitational wave detector (GWD) utilising, microwave plasma assisted sputtering of a high reflector (HR) multi-material stack coating consisting of hydrogenated amorphous silicon (a-Si:H), Ta₂O5 and SiO₂ for GWD’s mirror coatings. This work includes the study of the optical, mechanical, structural and morphological properties of the coating to evaluate the potential of the materials for GWDs. Benefits of the microwave plasma assisted sputter deposition technique are described. a-Si is a promising alternative material for GWD mirror coatings, as it has been demonstrated to have reduced thermal noise, however, has optical absorption above the required level for GWDs. The HR multi-material coating design concept is a way potentially mediate the high absorption a-Si whilst taking advantage of its reduced thermal noise, incorporating the a-Si material into a Ta₂O₅ and SiO₂ based HR multilayer coating. Hydrogenating a-Si (a-Si:H) is another method to reduce the absorption with the hydrogen concentration being an important parameter, this work combines these techniques to further lower the absorption. The multi-material coating consists of an ‘upper stack’ of Ta₂O₅/SiO₂ low absorbing material on the incident side of the coating used to reflect the majority of the incident laser power and a ‘lower stack’ of a a-Si:H/SiO₂ higher absorbing materials at the bottom of the coating where there is less laser power to be absorbed. In addition to investigating the effectiveness of the two-stack approach for optimum compromise between optical and mechanical loss reduction, this work also studies the effect of annealing on the properties of the multi-material coating. Moreover, effects of the deposition parameters such as deposition rate on each material are investigated and utilised to optimise properties the two-stack coating approach.

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 PREPARE 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.

Metal oxides such as titanium oxide (TiO₂) and zirconium oxide (ZrO₂) have attracted a great 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 such as photocatalysis, mechanics and chemistry. They are also used in optical applications; as sensors, anti-counterfeiting devices, or in medical applications for dental implants. In this paper, we 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-nano structuring of films by optical 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.

Qualifying light scattering on optical surfaces is challenging: for high-end instruments with demanding requirements like gravitational wave detectors and satellite instruments, the impact of localized defects can be critical for the instrument performances. These defects, typically micrometric, emerge during manufacturing or integration, with a sparse distribution (less than one defect per 100 micrometer diameter disk). However, these defects can significantly contribute to scattering, necessitating precise quantification. To address this challenge, the Light Scattering Group (CONCEPT) of the Institut Fresnel has developed the SPatially and Angulary Resolved Scatterometry Equipment (SPARSE). This innovative instrument integrates the principles of a scatterometer with an imaging system, allowing for spatially resolved Bidirectional Reflectance Distribution Function (BRDF). SPARSE can resolve up to around 400 000 microsurfaces of 26 μm x 26 μm on a one-inch diameter component. The instrument can measure scattering levels (BRDF cos(θ)) as low as 10⁻⁷ sr⁻¹, and its data processing is designed to discern and quantify the influence of localized defects, contamination, scratches, and roughness within the scattering budget. Here, we provide a brief description of the experimental setup and its metrological qualification. Additionally, we showcase some examples of measurements taken on representative samples, highlighting the versatility of SPARSE in advancing our understanding of light scattering for both gravitational wave detectors optical surfaces and satellite instruments.

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 220-1700 nm based on PHOTON RT measurements (EssentOptics).

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. Ion Beam Sputtering (IBS) is a known technique to provide such high optical quality thin films. Indeed, it allows to achieve high density layers with low absorption and scattering. 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. A correlation between the effect of the chosen deposition method and parameters and the measurement performances were made with the aim of a better understanding of the level and the origin of losses in the coatings. Finally, highly reflecting mirror coatings for 1064 nm wavelength were fabricated with different designs and deposition parameters. The results of the different measurements of absorption, scattering and total losses using different equipment are presented and discussed.

Monochromatic monitoring by intermittent measuring technique is established as a standard optical thickness control for thin films in box coaters since 2005. A newly developed set-up of the optical path was designed for the Syruspro 1100 DUV box-coater series. A deuterium lamp in combination with an achromatic lens system extends the monitoring capabilities to the UV range for wavelengths from 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 (IPhotonics). Reflectance and transmittance were 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 estimation of 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 the ones included in the multilayer sample. The obtained results, based on the photometric and ellipsometric data, are in correspondence with each other. The algorithm delivers practical results and avoids overfitting.

Silicon nitride has been extensively studied as high-refractive index material for distributed Bragg’s reflectors planned to be used in the 3rd generation of Gravitational Wave Detectors working at cryogenic conditions. The absence of mechanical loss of this material at cryogenic conditions and its high refractive index, make this material be considered one of the best options for the mirrors of the GWDs. The optimization of composition and structure of SiN_x thin films to refine optical (refractive index, and optical absorption), and morphology (surface roughness, defects) have been carried out mainly using ion beam sputtering (IBS), plasma enhanced chemical vapor deposition (PECVD) and low-pressure CVD (LPCVD). This work reports the characterization of both silicon nitride (SiN_x) and a new alternative silicon oxynitride (SiO_xN_y) thin film, deposited by ammonia free based PECVD. We measured and analyzed the composition of the films, as well as their stress, surface roughness, and optical constants, including refractive index and extinction coefficient at λ = 1550 nm. Under our deposition conditions, superior properties in terms of high thickness uniformity – free of cracks – at wafer scale, low compressive stress (range of kPa), low surface roughness (<1 nm), and high refractive index 2.2 were achieved in both materials, with pure composition lacking contaminants.

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 antireflection 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 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 single-shot nanosecond pulses. 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.

Based on our simulations, 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 this approach in identifying high-performance multilayer mirrors for x-ray applications.

Optical interference filters allow achieving a wide range of spectral functions. To match with the theoretical performances, fabrication processes require accurate control of each of the layers’ thicknesses and precise refractive index knowledge. However, despite highly stable deposition process, thickness errors tend to accumulate as the number of deposited layers increases, which in turn can lead to severe degradation of the spectral response. Optical monitoring is one the common techniques used to reduce layer thickness errors during deposition. It consists of measuring the filter transmittance, at one or several monitoring wavelengths, and studying its variation during the whole deposition process. Those signals give real-time information on the spectral performances, and in turns, on the deposited optical thickness of the layers. Indeed, for a given filter, the monitoring system can compute the theoretical optical signal during the process and compare it with real-time measurement. Algorithms implemented in this system are then able to at least partially compensate thickness errors from the previous layers, by correcting the expected cut-off points for the current and next layers. In this study, we investigated a specific optical monitoring technique: polychromatic monitoring. This technique uses multiple wavelengths to monitor the layers’ deposition, instead of a unique wavelength for all layers such as conventional monochromatic monitoring. To evaluate the performance of this technique, we designed a numerical model to simulate the online monitoring signals during deposition, based on filter design and refractive index dispersion of the materials. Then, we developed an algorithm that applies several criteria on those simulated signals to automatically determine the most relevant wavelengths to monitor the filter layers - that is to say the ones that are expected to reduce layer thickness error during the deposition process. We also discuss the difficulties and limits when implementing such an approach, such as measured transmission errors or the critical instant for changing optical testglass. Afterwards, we experimentally tested these algorithms of determination of monitoring strategy on an error-sensitive multi-cavity bandpass filter.

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 yielding strong reflection at interfaces where the distance between two points of the Fresnel coefficients on the complex plane is far apart, as well as small absorption in the multilayer structure. Then film thicknesses of the multilayer structure were optimized by numerical calculation using IMD software, which results in practical high reflectivity between 43 to 50% on the Sc/Si, Sc/Mg, and Sc/Cr multilayer mirrors at the photon energy of 397.5 eV. In this presentation, we also report grazing incidence x-ray reflectivity results for multilayer mirrors deposited by a magnetron sputtering method.

As part of the investigations, quantum nanolaminates (QNLs) were produced from TiO₂, Nb₂O₅, and Z_rO₂ 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 antireflection infrared coatings for common infrared substrate materials.

Single HfO₂ layers were deposited on fused silica substrates using Hf as a starting material by PIAD technology. Inductively coupled RF plasma source was used, generating pure oxygen, as well as argon-oxygen mixture plasma. Mean plasma ion energies were varied from ~120 to ~270 eV. Optical properties, stress values, direct absorption for 1064 nm, surface roughness, film structure were determined for the samples and were also compared to pure e-beam and IBS formed HfO₂ single layers. It is shown, that by selecting proper plasma parameters it’s possible to obtain HfO₂ layer with 185 MPa compressive stress, suitable for making dense multilayer coatings with moderate compressive stresses. However, simultaneously obtained high optical absorption and extinction implies necessity for further investigations.

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 Scanning Electron Microscope (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), X-ray Diffraction (XRD), Atomic Force Microscope (AFM) and optical reflectance in the UV-IR range. The achieved SFMO film composition was close to the optimal one and samples were provided for further multilayered structure deposition to prototype and develop a spintronic sensor.

Metalenses exhibit significant potential in various fields due to their ability to access comprehensive, complex information. The ability to integrate multiple features into a single device, along with its compact and efficient design, allows for the creation of miniature microscopy systems that showcase remarkable performance. By applying unique design techniques, we have developed and implemented polarization-dependent metalens. This metalens makes smooth transitions between edge enhancement imaging and bright field imaging possible. Employing the principles of geometric phase, we design a dual mode metalens by using hydrogenated amorphous silicon to physically manifest the necessary phase profiles for operation in the visible spectrum. These profiles contain a conventional hyperbolic configuration intended for bright-field imaging, along with spiral metalens with a topological charge of +1, tailored for edge-enhanced imaging functions. When utilizing Left Circular Polarization (LCP), our designed lens enables bright field imaging. Conversely, Right Circular Polarization (RCP) facilitates image edge enhancement. We showcase through numerical demonstration the metalens capability to focus and generate vortices under various states of circular polarization and validate its potential for diverse applications.

The American Society of Cancer reports an annual average of 240,000 breast cancer diagnoses in the USA, resulting in approximately 42,000 women and 500 men succumbing to the disease each year. The conventional diagnosis of critical diseases like breast cancer, lung cancer, and skin cancer frequently necessitates invasive biopsy procedures, which involve the removal of a tissue sample for diagnostic analysis, potentially posing infection risks. However, conventional Optical Coherence Tomography (OCT) has emerged as a non-invasive imaging technique that mitigates these risks by generating cross-sectional biological sample images through the principles of light scattering and reflection. Although conventional OCT excels in its depth of focus, it faces challenges related to limited lateral resolution and diffraction constraints. Consequently, we propose a metalens-based OCT for high-resolution biomedical tissue imaging. Metalens-based OCT achieves optical system miniaturization by replacing traditional bulky lenses. The metalens is designed on a crystalline silicon dioxide (SiO₂) substrate with a 490 nm unit cell periodicity. Its dimensions are 380 nm in length, 185 nm in width, and 1100 nm in height. The suggested metalens operates in the 1300–1570 nm wavelength range and has over 65% transmission to provide improved depth of focus and lateral resolution. Simulated results indicate that metalens depth of focus and full-width half maximum approach 260 and 125 μm, respectively. Hence, our metalens proposal, offering high resolution and an increased depth of field, presents a viable choice for surgical and in vivo endoscopy imaging applications.