Optical Stacks Research Articles

Tracking element-mineral associations with unsupervised learning and dimensionality reduction in chemical and optical image stacks of thin sections

In-situ chemical analysis on thin sections is a cornerstone of geochemical research. Despite massive advances in digital image analysis, the interpretation of such data within the optical petrological context of the thin section has largely remained an analogue task in geochemistry. In this contribution, we registered optical and micro-chemical images from large thin section areas. Chemical datasets from scanning electron microscopy energy dispersive spectrometry (SEM-EDX) and Synchrotron X-ray fluorescence microscopy (S-XFM) were exported from proprietary software. We then evaluated two dimensionality reduction techniques against false-colour images and phase maps to test whether previously unnoticed features became discoverable. Principal component analysis (PCA) and deep sparse autoencoder (DSA) neural networks were used to summarise the multi-channel SEM-EDX and S-XFM into one single red-green-blue (RGB) representation each.Applied to an oceanic gabbro, a cratonic peridotite, and a pelagic limestone, the PCA-based dimensionality reduction was found to produce crisp RGB maps of phases with less noise than false-colour three-element RGB maps. They were registered with optical images to form a simple multi-channel input for pixel-based classification into classes (i.e., semantic segmentation). This was fast and worked well for typical igneous and metamorphic rocks (1–3 h routine). In the chemically quite homogenous limestone, the combined optical and S-XFM PCA input was successfully classified into many phases that were unclassifiable on the conventional SEM-EDX phase map. From the segmented optical and S-XFM PCA map, we exported pixel locations of classified accessory phases back into the original proprietary S-XFM software. This allowed quantification of trace elements whose X-ray peaks were invisible in the original S-XFM quantification.The DSA-based approach yielded phase maps with greater noise, but the technique was very strong at detecting subtle features. In the gabbro sample, the DSA image identified cryptic relict cores in clinopyroxene more clearly than in the previously used Cr concentration map. A DSA training set can be obtained on a small ROI to generate a consistent large area DSA image from which more fragmental cores were observed. For a ROI on the gabbro thin section, the DSA representation map and the blended optical image were segmented and inspected with a loupe tool. This allowed us to generate interactive histograms and bin-scatter concentration plots of selected phases and to search for co-variations of element concentrations. This approach can be expanded to include data from any in situ geochemical acquisition tools and may help discover previously unseen features in complex elemental imagery.

Evaluation of Microlenses, Color Filters, and Polarizing Filters in CIS for Space Applications.

For the last two decades, the CNES optoelectronics detection department and partners have evaluated space environment effects on a large panel of CMOS image sensors (CIS) from a wide range of commercial foundries and device providers. Many environmental tests have been realized in order to provide insights into detection chain degradation in modern CIS for space applications. CIS technology has drastically improved in the last decade, reaching very high performances in terms of quantum efficiency (QE) and spectral selectivity. These improvements are obtained thanks to the introduction of various components in the pixel optical stack, such as microlenses, color filters, and polarizing filters. However, since these parts have been developed only for commercial applications suitable for on-ground environment, it is crucial to evaluate if these technologies can handle space environments for future space imaging missions. There are few results on that robustness in the literature. The objective of this article is to give an overview of CNES and partner experiments from numerous works, showing that the performance gain from the optical stack is greater than the degradation induced by the space environment. Consequently, optical stacks can be used for space missions because they are not the main contributor to the degradation in the detection chain.

A Numerical Method of Aligning the Optical Stacks for All Pixels

Reducing performance verification time is significant in product launch and production costs. This is especially true because aligning the optical stacks of off-axis pixels is a time-consuming task, but it is important to maintain sensitivity. In this paper, a numerical method to align the optical stacks of off-axis pixels is suggested in order to reduce performance test time. The components of the numerical method are the optical stack height, refractive index, and chief ray angle in order to calculate the optical stacks' optimal shift distance. The proposed method was investigated to confirm effectiveness by using optical simulation. The sub-micron backside illumination (BSI) pixels were simulated, having 2 × 2 microlens, quad-color filter array, and in-pixel deep trench isolation (DTI). Moreover, the proposed method was evaluated for various pixel pitches, microlens shapes, and CRAs. As a result, the optical stacks were optimized by using the numerical method and validated via optical simulation. Therefore, the proposed numerical method is expected to help reduce the time and cost.

Designing chromatic optical retarder stacks for segmented next-generation easySTED phase plates.

Fluorescence nanoscopy methods based on the RESOLFT principle, such as beam-scanning STED nanoscopy, require the co-alignment of optical beams for molecular state (on/off) switching and fluorescence excitation. The complexity and stability of the beam alignment can be drastically simplified and improved by using a single-mode fibre as the sole light source for all required laser beams. This in turn then requires a chromatic optical element for shaping the off-switching beam into a focal-plane donut while simultaneously leaving the focal intensity distributions at other wavelengths shaped as regular focal spots. Here we describe novel designs of such so-called 'easySTED phase plates' and provide a rationale how to find the desired spectral signature for combinations of multiple wavelengths.

61‐4: Display Visual Security: From Laptop Privacy to No Driver Distraction for Automotive Passenger Infotainment

An electrically switchable privacy display technology using proprietary optical stacks developed by the authors has now shipped in more than 1 million laptop PCs, delivering best‐in‐class protection from off‐axis visual hackers and high image visibility to display users. In parallel the authors have been developing a new generation of switchable automotive front‐seat Passenger Infotainment Displays (PID). Differences between the user needs for PID and laptop are discussed. Presented is a method to quantify ‘No Driver Distraction’ (NDD) in PID and image security to visual hackers in laptops, including a means of determining the limits of NDD/security. Proprietary optical stack structures for PID and laptop are compared. A PID technology demonstrator achieves less than 1% of head‐on luminance for a driver offset by just 25° from a passenger, and a shipping laptop provides no image visibility at >45° at 1lux/nit using a switchable reflectivity optical stack with total screen thickness of less than 2.3mm.

Hubble Space Telescope Observations of GW170817: Complete Light Curves and the Properties of the Galaxy Merger of NGC 4993

Abstract We present the complete set of Hubble Space Telescope imaging of the binary neutron star merger GW170817 and its optical counterpart AT 2017gfo. Including deep template imaging in F814W, F110W, F140W, and F160W at 3.4 yr post-merger, we reanalyze the full light curve of AT 2017gfo across 12 bands from 5 to 1273 rest-frame days after merger. We obtain four new detections of the short γ-ray burst 170817A afterglow from 109 to 170 rest-frame days post-merger. These detections are consistent with the previously observed β = −0.6 spectral index in the afterglow light curve with no evidence for spectral evolution. We also analyze our limits in the context of kilonova afterglow or IR dust echo emission but find that our limits are not constraining for these models. We use the new data to construct deep optical and IR stacks, reaching limits of M = −6.3 to −4.6 mag, to analyze the local environment around AT 2017gfo and low surface brightness features in its host galaxy NGC 4993. We rule out the presence of any globular cluster at the position of AT 2017gfo to 2.3 × 104 L ⊙, including those with the reddest V − H colors. Finally, we analyze the substructure of NGC 4993 in deep residual imaging and find shell features that extend up to 71.″8 (14.2 kpc) from NGC 4993. The shells have a cumulative stellar mass of 6.3 × 108 M ⊙, roughly 2% of NGC 4993, and mass-weighted ages of >3 Gyr. We conclude that it was unlikely that the GW170817 progenitor system formed in the galaxy merger.

Colored optic filters on c‐Si IBC solar cells for building integrated photovoltaic applications

AbstractBuilding Integrated Photovoltaic systems can produce a significant portion of the energy demand of urban areas. Despite their potential, they remain a niche technology that architects and project engineers still find esthetically limited. The dark blue or black color of standard photovoltaic panels is considered inappropriate for restoration projects of historic buildings and represents a major constraint on the development of new projects. This work will provide insight into how the use of optic filters can offer new pathways for architectural acceptance of photovoltaic panels. Optic filters selectively reflect or transmit light by interference and can be designed and fabricated using cost‐effective and industrially compatible processes. By using in‐house developed ray tracing software coupled with TCAD Sentaurus, more than 400 colors were obtained, and their impact on the opto‐electrical performance of interdigitated back‐contacted solar cells was studied. Results show a maximum efficiency loss of 1.6% absolute at the perpendicular incidence of light on the range of obtained colors when compared with a standard dark blue solar cell. Simulations for different angles of incidence showed that the current reduction on the standard device could be modeled using a cosine relationship. The colored cells, however, deviated significantly from this relationship. We propose that the angular behavior of any cell (colored or standard) could be simulated by modifying the effective irradiance with scaling factors equal to the ratios of the photogenerated current at any angle with respect to the value at normal incidence. We demonstrate that this approach accurately models the effect of the color filter and allows for an easy transition from a bare cell to an encapsulated one. Due to the spectral effect of the filter, we developed both a spectrally resolved optical model and a two‐dimensional finite volume transient thermal model. In case of the optical model, we demonstrate an accuracy in the prediction of the reflectance produced by the color with values of mean bias error (MBE) between 2.0% and 3.9%. As for the thermal model, it was validated by first analyzing a standard model under conditions of nominal operating cell temperature and then comparing its results with published scientific literature. Later, we compare its prediction against 2 weeks of measurements. In both cases the thermal model proves an adequate accuracy, yielding differences below 1.5°C with respect to other scientific works and an MBE value of 0.89°C as well as a root‐mean‐square error value of 2.10°C for the entire measurement period. With the validated models, we studied the effect of the encapsulation on the color perception. We present two options of color filters. The first one produces relatively low reflectance losses and presents relative annual direct current (DC) energy losses of up to 6.4% for Delft, in the Netherlands, and up to 5.9% for Alice Springs in Australia. However, this first option has very poor color brightness. The second studied filter produces highly saturated bright colors. Improving brightness can increase the annual DC relative losses up to 13.7% and 13.5% for Delft and Alice Springs, respectively. Overall, we demonstrate that colored filters based on multilayer optical stacks are a versatile option for coloring cells that allow a good compromise between esthetics and performance.

Back-side illuminated optical stack optimized with a high refractive index micro-lens array for CMOS image sensors

We simulate a simplified optical stack model with Lumerical FDTD over wide ranges of optical parameters: wavelength, 550 nm to 1.4 μm, and pixel array pitch, 1 to 10 μm. By increasing the lens and the planarization layer refractive indices from the usual 1.5 to 2, we study the improved lens focalization abilities, in terms of spot width, power, and depth below the micro-lens. We show an NIR wavelength range benefit from slightly increasing the optical stack index to 1.7 while visible wavelengths have less interest. Indeed, increasing the lens and planarization layer index enables thinner back-side illuminated optical stacks for higher quantum efficiencies and angular response improvement.

Correction of topological errors in automated traces of neurites.

Our understanding of synaptic connectivity in the brain relies on the ability to accurately trace sparsely labeled neurons from 3D optical microscopy stacks of images. A variety of automated algorithms and software tools have been developed for this task. These algorithms can capture the general layout of neurites with high fidelity, but the resulting traces often contain topological errors such as broken and incorrectly merged branches. Even a small number of isolated topological errors can drastically alter the connectivity, and therefore, their detection and correction are paramount for connectomics studies. Here, we describe an automated trace proofreading approach that utilizes machine learning to correct trace topology. Multiple stacks of neuron images were traced by two users to create a labeled dataset and assess the baseline of inter-user variability. All traces were then disconnected at branch points and a deep neural network was trained to detect the correct way of reconnecting the branches. Custom morphological features were generated for each cluster of branch points, in a way that is dependent on a merging scenario but invariant to translations, rotations, and reflections of the cluster in the imaging plane. The features and image volume centered at the branch point were used for training a neural network that concatenates these input streams and outputs the confidence measure for different branch merging scenarios. The designed method significantly reduces the number of topological errors in automated traces and comes close to the accuracy achieved by expert users which is the gold standard in the field.

Grayscale stencil lithography for patterning multispectral color filters

Flat optics for spatially resolved amplitude and phase modulation usually rely on 2D patterning of layered structures with spatial thickness variation. For example, Fabry–Perot-type multilayer structures have been applied widely as spectral filter arrays. However, it is challenging to efficiently fabricate large-scale multilayer structures with spatially variable thicknesses. Conventional photo/eBeam-lithography-based approaches suffer from either low-efficiency and high-cost iterative processes or limitations on materials for spectral tunability. In this work, an efficient and cost-effective grayscale stencil lithography method is demonstrated to achieve material deposition with spatial thickness variation. The design of stencil shadow masks and deposition strategy offers arbitrarily 2D thickness patterning with low surface roughness. The method is applied to fabricate multispectral reflective filter arrays based on lossy Fabry–Perot-type optical stacks with dielectric layers of variable thickness, which generate a wide color spectrum with high customizability. Grayscale stencil lithography offers a feasible and efficient solution to overcome the thickness-step and material limitations in fabricating spatially thickness-varying structures. The principles of this method can find applications in micro-fabrication for optical sensing, imaging, and computing.

Design of a 10 kW level diode laser optical stack with a line shape beam spot.

We designed and simulated a diode laser with output power of more than 10 kW and a line shape beam spot of approximately ${14 - 58}\;{\rm mm} \times {1.6}\;{\rm mm}$14-58mm×1.6mm (${{\rm 1/e}^2}$1/e2 width). The diode laser was assembled with high fill factor diode laser bars that can be cooled with filtered tap water. The diode laser bar was beam shaped with a tilted cylindrical lens array to twist the slow axis of individual emitters by 90 deg, and then the slow axis was collimated with a single cylindrical lens. From the simulation, 20 laser diode bars with the same wavelength formed a diode laser optical stack with an output power of more than 3.5 kW, a beam spot of ${31}\;{\rm mm} \times {12}\;{\rm mm}$31mm×12mm size, and full divergence angles of around 6 mrad in both the horizontal and vertical directions. Then, three laser diode optical stacks with different wavelengths were wavelength-multiplexed to obtain an output power of more than 10 kW. Finally, the diode laser optical stack was transformed by simple cylindrical lenses to form a line shape spot with a working distance longer than 250 mm. Our diode laser design is much simpler than previous devices with similar output power and can find various applications such as high-speed laser cladding.

The effect of increasing Si content in the absorber layers (CrAlSiNx/CrAlSiOyNx) of solar selective absorbers upon their selectivity and thermal stability

In this work, the effect of increasing Si content in the absorber layers (CrAlSiNx/CrAlSiOyNx) of solar selective absorbers upon their selectivity and thermal stability are studied. The two optical stacks presented consist of four magnetron sputtered layers on stainless steel substrates. In both cases, tungsten is used as back-reflector, CrAlSixN/CrAlSiOyNx as absorber layers with different Si/(Cr + Al + Si) atomic ratio (0.15 and 0.30, respectively) and finally the SiAlOx antireflection layer. The structures were theoretically designed by SCOUT software depended on experimental transmittance (T) and reflectance (R) of thin single layers deposited on glass substrates. It is observed that optical stack coatings with higher silicon content show better selectivity values, high solar absorptance, α = 95.9%, and low emissivity, ε = 9.7% (calculated for 400 °C), with higher thermal stability at 600 °C in vacuum, for 650 h. Additionally, with the annealing at 600 °C an increase of surface roughness was found, which was smaller for sample with higher Si content.

Large-Area Layer Counting of Two-Dimensional Materials Evaluating the Wavelength Shift in Visible-Reflectance Spectroscopy

An advanced and highly scalable approach for determining the number of layers of two-dimensional (2D) materials via optical spectroscopy is introduced. Based on appropriate subjacent layer stacks, the reflectance spectra of the 2D material assemblies exhibit wavelength shifts in distinct minima, which are linearly related to the number of layers. A linear correlation enables straightforward data interpretation, which is essential for implementing simple and comparatively fast measurement routines for process control on wafer scale. The structure of the optical layer stacks as well as the complex refractive indices of 2D materials were found to strongly influence the spectral position of the reflectance minima as well as the magnitude and the linearity of the wavelength shifts. We experimentally prove this method to be applicable for large-area layer counting of subsequently stacked chemical vapor deposition graphene films on a layer stack consisting of silicon nitride and silicon oxide. The measurement re...

CrAlSiN barrier layer to improve the thermal stability of W/CrAlSiNx/CrAlSiOyNx/SiAlOx solar thermal absorber

The influence of adding CrAlSiN barrier layer between the back-reflector tungsten (W) and stainless-steel substrate on thermal stability has been investigated. In previous work, after the annealing in vacuum at 600 °C, tungsten diffusion from the back-reflection layer towards the stainless-steel substrate was found. In this study, a barrier layer was added and its influence upon the W diffusion was studied. Several designs of multilayer solar selective absorber for high temperature applications were used to test the thermal and chemical stability and oxidation resistance after vacuum annealing. These samples were characterized by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS), X-ray diffraction (XRD), Fourier-transform Infrared Spectroscopy (FTIR) and UV–VIS–NIR spectroscopy. All absorber tandems show good thermal stability after vacuum annealing at 600 °C and the changes in optical constants solar absorptance (α) and thermal emittance (ε) are negligible. In some cases, small changes in the reflectance curves after the first step of annealing were seen. Some changes were found in the oxide layer, due to the incomplete oxidized Si atoms, as confirmed by FTIR analyses. This cannot justify the increase of NIR reflectance observed in the optical stacks after annealing, which can be due to the phase changes of the back-reflector tungsten layer. All layers of stacks are amorphous, except the tungsten layer, which is polycrystalline and shows a columnar growth. The addition of a CrAlSiNP = 0.11 Pa barrier layer between tungsten and stainless-steel substrate proved to be a good solution to control the diffusion of W atoms towards the substrate, whereas using higher nitrogen partial pressure in the high and the low absorption layers reduce the diffusion of Cr from those layers to surface.

A crucial factor affecting the power conversion efficiency of oxide/metal/oxide-based organic photovoltaics: Optical cavity versus transmittance

Considerable effort has been directed at improving the power conversion efficiency of organic photovoltaics, using oxide/metal/oxide multilayers as transparent electrodes, because of their numerous advantages including lower sheet resistance, higher transmittance, and higher flexibility in comparison to typical indium tin oxides. However, to date, most organic photovoltaics based on oxide/metal/oxide electrodes exhibit a lower conversion efficiency than indium tin oxide-based organic photovoltaics, without any clarification. In this investigation, we identify crucial factors that influence the power conversion efficiency of oxide/metal/oxide-based organic photovoltaics to fully exploit the potential of these devices, based on the correlation between the optical cavity and the transmittance. For this purpose, we fabricate five sets ofinverted organic photovoltaics using poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) and [6,6]-Phenyl C71 butyric acid methyl ester-based active layers and ZnO/Ag/ZnO electrodes with top ZnO layers of varying thicknesses, with reference organic photovoltaics using indium tin oxides, on both rigid and flexible substrates. The highest power conversion efficiency of 8.71% and 7.53% is obtained from single-junction organic photovoltaics with 40/9/8-nm-thick ZnO/Ag/ZnO electrodes on each substrate, due to strong micro-cavity effects between the top and bottom Ag layers, despite the relatively low transmittance of the electrode. This result is supported by the relation between the electric-field intensity and the transmittance curves of the ZnO/Ag/ZnO/solution-based ZnO/active bulk optical stacks based on simulation results. Furthermore, flexible organic photovoltaics with the ZnO/Ag/ZnO electrodes demonstrate much better performance in mechanical bending tests in comparison to the performance of standard indium tin oxide-based organic photovoltaics, and the previously reported oxide/metal/oxide-based organic photovoltaics.

Thermal noise of beam splitters in laser gravitational wave detectors

We present the calculation of thermal noise in interferometric gravitational-wave detectors due to the thermal fluctuations of the beam splitter (BS). This work makes use of a recently developed method of the analysis of thermal noise in mirrors from first principles, based on the fluctuation dissipation theorem. The evaluation of BS thermal noise is carried out for the two different grav- itational wave observatories, GEO600 and the Advanced Laser Interferometer Gravitational Wave Observatory (aLIGO). The analysis evaluates thermal noise from both the substrate and the optical reflective and antireflective stacks located on the BS surface. We demonstrate that the fluctuations of both reflecting and anti-reflecting surfaces significantly contribute to the total thermal noise of the BS. The oscillating intensity pattern couples small-scale distortions of the surface to the overall phase readout, and therefore increases the overall thermal noise. In the case of aLIGO, the BS contribution is with $0.3\%$ negligibly small. At a frequency of 500Hz, the BS causes about $10\%$ of GEO600's sensitivity limit. BS noise impairs the feasible sensitivity of the GEO-HF design proposal by about $50\%$.

Three-Dimensional Microscopy Demonstrates Series and Parallel Organization of Human Peripapillary Capillary Plexuses.

To define the three-dimensional topologic organization of the human peripapillary capillary plexuses in order to better understand the hemodynamic characteristics of this retinal circulation. The retinal microvasculature was perfusion labeled in five normal human donor eyes, and optical stacks were collected from regions immediately superior, temporal, inferior, and nasal to the optic disk by using confocal scanning laser microscopy. The spatial location and morphometric characteristics of capillary plexuses were compared. Three-dimensional visualization strategies were used to document the organization of vascular conduits that interconnect capillary beds and to study the communications between capillary beds and precapillary arterioles and postcapillary venules. The peripapillary microcirculation is composed of four capillary plexuses, including the radial peripapillary capillary plexus at the level of the nerve fiber layer, the superficial capillary plexus (SCP) at the level of the ganglion cell layer, the intermediate capillary plexus located at the inner boundary of the inner nuclear layer, and the deep capillary plexus located at the outer boundary of the inner nuclear layer. Capillary diameter and density were significantly different between the four plexuses (both P ≤ 0.011). The SCP is the only capillary bed that receives feeding and draining branches directly from precapillary arterioles and postcapillary venules, respectively. Four different inflow and outflow patterns characterized the communication between the SCP and surrounding capillary beds. The capillary plexuses of the human peripapillary microcirculation are arranged in series and parallel and manifest specializations that likely reflect the unique metabolic demands and biochemical environment of the retinal layers.

P‐102: Switchable Privacy Display Design and Optimisation

The visibility of electronically controlled switchable privacy display to both primary viewers and unwanted observers (snoopers) is reviewed and a method for comparison of privacy display performance is proposed. We report results from privacy display optical stacks that employ luminance and contrast control using directional backlights, switchable retardance stacks and liquid crystal pixel bias voltage control.

Quantitative Study of the Macular Microvasculature in Human Donor Eyes.

To precisely quantify the macular microvasculature density using microperfusion and labeling techniques in human donor eyes. Such information may be useful in understanding the role of the macular microvasculature in coping with the metabolic requirements of the neurons in this densely packed region, and provide a reference point for clinical studies using recently developed optical imaging techniques. The macular microvasculature was perfusion-labeled in 18 human donor eyes and optical stacks collected from regions superior, temporal, inferior, and nasal to the foveola using confocal microscopy. The optical slices were separated into the deep macula vascular layer (DL), and the superficial layer (SL) in which all the vessels superficial to the deep macular vessel layer were included. The DL and SL images were analyzed and vessel density measured according to their orientation from the foveola and in foveal and parafoveal regions. Vessel densities were compared across regions and age groups. Both the SL and DL showed an increase in vessel density with increasing eccentricity from the foveal to parafoveal regions. Vessel density was found to rank in the order of inferior > superior > temporal > nasal in both SL and DL layers. The SL vascular density was approximately 31%, whereas DL was approximately 17%. The DL was planar in nature and density not affected by age. Age-related increase in vessel density was observed in the SL. Microperfusion and labeling techniques in combination with confocal microscopy has enabled collection of reliable data on vascular density in the macula region. Regional differences may reflect well-matched vascular supply and neuronal demands. Age-related changes might indicate the importance of stable blood supply for the human macula.

Duty cycle control in reactive high-power impulse magnetron sputtering of hafnium and niobium

Instabilities in reactive sputtering have technological consequences and have been attributed to the formation of a compound layer on the target surface (‘poisoning’). Here we demonstrate how the duty cycle of high power impulse magnetron sputtering (HiPIMS) can be used to control the surface conditions of Hf and Nb targets. Variations in the time resolved target current characteristics as a function of duty cycle were attributed to gas rarefaction and to the degree of poisoning of the target surface. As the operation transitions from Ar driven sputtering to metal driven sputtering, the secondary electron emission changes and reduces the target current. The target surface transitions smoothly from a poisoned state at low duty cycles to a quasi-metallic state at high duty cycles. Appropriate selection of duty cycle increases the deposition rate, eliminates the need for active regulation of oxygen flow and enables stable reactive deposition of stoichiometric metal oxide films. A model is presented for the reactive HIPIMS process in which the target operates in a partially poisoned mode with different degrees of oxide layer distribution on its surface that depends on the duty cycle. Finally, we show that by tuning the pulse characteristics, the refractive indices of the metal oxides can be controlled without increasing the absorption coefficients, a result important for the fabrication of optical multilayer stacks.