The transmission of light through a fiber air core has revolutionized the world of optical fiber technology [1]. Recent advancements in antiresonant hollow core fibers have significantly pushed the field forward over the past decade, achieving lower attenuation than all-solid fused silica fibers [2-3]. With light propagating primarily in air, these fibers offer higher transmission speeds, reduced latency, lower nonlinear effects, and enhanced radiation resistance. They are particularly well suited for high-power laser delivery, including ultrashort pulsed lasers or high power cw lasers. Despite of these advantages, challenges remain for the specialty fiber applications, especially regarding system integration and operation under demanding environmental conditions. One critical issue is the formation of ammonium chloride (NH4Cl) crystals on the end faces fabricated from chlorine-rich fused silica (e.g., F300). These crystals cause absorption, scattering, beam degradation, and ultimately fiber failure. This work presents a systematic investigation of NH4Cl crystal growth, addressing three key aspects: the fiber manufacturing process, the handling and storage history of the drawn fiber, and the influence of environmental factors such as humidity, fiber length, fiber purging with N-2 and glass composition. A simplified capillary fiber model without an inner antiresonant structure was employed to accelerate testing while maintaining relevance to complex HCF designs. Based on these studies, several mitigation strategies were tested, including optimized handling procedures and the use of alternative fused silica materials. These approaches aim to enable reliable deployment of hollow core fibers in specialty applications by reducing or eliminating NH4Cl contamination.

Forest change detection and monitoring is a key part of the Copernicus Land Monitoring Service (CLMS) (https://land.copernicus.eu/). Various methodologies already implement near real-time (NRT) forest monitoring in tropical regions (e.g. Reiche et al., 2021) with the focus on timely detection of deforestation activities. However, there is not yet an operational pan-European product tracking forest dynamics at such temporal frequency, which has moreover the capability to separate also subtle disturbances of the tree canopy from signal noise. This kind of product is under demand by the user community, hence a new CLMS prototype on “Continuous Forest Monitoring”, with the goal to capture natural and human-induced forest disturbances by detecting tree cover vitality loss on a monthly basis is tested and implemented within the Horizon Europe project Evolution of the Copernicus Land Service portfolio (EvoLand). In a second instance, the feasibility to detect disturbance agents, i.e., (i) windthrow/storm damage, (ii) wildfire, (iii) insect infestations, as well as (iv) human-induced disturbances (e.g., forest clearing, clear-cutting, and thinning activities) is tested.Dense time series from Sentinel-2 serve as main input for both prototypes, supported by forest masks from the CLMS High Resolution Vegetated Land Cover Characteristics (HRL VLCC) and ancillary data on forest disturbance locations and agents. From a benchmarking of various tools, the Exponentially Weighted Moving Average (EWMA) – proposed by Brooks et al. (2014) for Landsat time series data and implemented as part of the JRC-NRT tool (https://github.com/ec-jrc/nrt) – yielded the most promising results, especially considering the balance between accuracy, NRT capability, and computational effort. It is an unsupervised data-driven approach using univariate input indices to detect location and timing of disturbances. A supervised classification to derive the disturbance agents is added on top.This study describes the implementation and results of this prototype and compares the detected forest disturbance locations and dates to the radar-based Tree Cover Disturbance Monitoring (TCDM) product and the 3-yearly VLCC forest change product. Two large EvoLand European sites were chosen for a first phase implementation: one in Germany (analysis years 2019-2021) and another in Spain (analysis years 2020-2022). The evaluation is carried by disturbance agent, concluding to different effects on either the physical structure of the trees and/or the spectral signal of the canopy, and hence also on the suitability of a method of detection. Products are delivered at pixel level (10m spatial resolution), improving the 20m resolution of the currently available CLMS forest change products, while increasing the change frequency from 3-yearly or yearly to monthly.The resulting information can be utilized to enhance forest management and planning, aid forest-related decision-making or contribute to reporting on forest-related EU policies. These two prototypes are proposed within EvoLand to enhance the CLMS forest portfolio and to meet or go beyond users' requirements and demands.

Multi-cladding (MC) fibers with undoped silica core and alternating highly fluorine doped and undoped silica cladding layers are a new standard for high power laser beam transmission. Such MC-fibers allow tailoring the output beam profile of a single laser source to the desired application. An important factor for these applications is to avoid additional scattering of the guided light in the different regions leading to an increased output divergence, so-called focal ratio degradation (FRD). In this work, we compare two possible measurement concepts to determine the beam divergence angle under controlled launch conditions to quantify FRD of MC fibers. One approach is the pinhole setup historically used in astronomy; another approach is the inverse far field method with selective excitation. The objective is to define a reliable setup for quality inspection. We show measurement results for FRD of MC fibers with both methods and evaluate the differences between the light-guiding sections. To our knowledge, this is the first time such data are presented. The objective described above is best fulfilled by a modified far field method with defined broad angular excitation.

Ionizable lipids are a class of pharmaceutical excipients with a main application in lipid nanoparticles for nucleic acid delivery. New ionizable lipids are needed to tune characteristics of lipid-based nucleic acid delivery systems, e.g. stability, nucleic acid loading capacity and binding strength, as well as bio-distribution. Herein, we present the synthesis of three novel ionizable lipids as putative excipients for lipid-based nucleic acid delivery systems. Langmuir monolayer experiments with classical surface pressure/area isotherm evaluation were used to understand the self-assembly behavior of the lipids. Additional experiments with surface sensitive techniques, namely grazing incidence x-ray scattering and infrared reflection-absorption spectroscopy (IRRAS), were performed to understand structural characteristics of lipid associates. The latter technique was also used to investigate the nucleic acid binding process between DNA and the ionizable lipids. Finally, first transfection experiments with the novel lipids formulated as cationic liposomes were performed providing first efficacy data. Although the alkyl chain pattern was comparable for all three ionizable lipids, the results demonstrated that with increasing head-group size the DNA binding capacity changed and the alkyl chain fluidity was increased. The lipid with the lowest phase transition temperature and the smallest packing parameter showed the highest DNA transfer efficiency.

Optical fibers made of fused silica have many applications like telecom, industrial, medical, or spectroscopy. These applications are as varied as are the requirements for the fibers. Large core step index multimode fibers made of high purity fused silica core and fluorine doped silica cladding are common standard in industrial high-power laser, minimal invasive medical and spectroscopic applications. One of the biggest factors influencing fiber performance is the utilized fused silica core material and its composition. Hydroxyl groups and trace impurities, for example, can influence the transmission properties of the fiber. But also, defect centers created by strong UV radiation or drawing induced absorption bands define the performance over time. Therefore, the choice of the right material is key for high performing fibers. In addition, the height of the refractive index step between the core and the cladding, which defines the numerical aperture, as well as the cladding thickness and cross section design of the fiber are important factors which should be balanced against performance and costs. Depending on the application wavelengths and performance requirements, different fused silica materials and fiber designs are recommended tailored to the application. We will present deeper insights in the optical properties of different fused silica materials and new silica material developments dedicated for the increasing utilization of blue and green lasers to give a guideline to choose the best fiber type depending on the application wavelengths.

The DIN standard 58145 “Measuring method for determination of solarization effect of fused silica optical fibers” was introduced over 5 years ago to standardize the quality control for UV fibers. A deuterium lamp with a lens-based imaging system, coupling a light power density of approx. 200 µW/(cm2 nm) at 214 nm into the fiber under test, was specified as light-source. With time, the availability of new powerful broadband light-sources stimulated new applications. Further, improvements in deuterium lamps and imaging coupling systems resulted in higher light power densities. It was quickly determined that these new conditions induced different spectral and temporal UV losses, which needed to be studied. As a result, the cw-power coupled into the fibers under test, referenced at 214 nm in the original set-up, increased. We observed that two measurement systems, both assembled by the DIN standards recommendations, showed significant deviations in solarization effects at 215 nm (E’ center) and 265 nm (NBOH center). Therefore, we investigated ideal lens coupling conditions, influence of lens aging (solarization) and the influence of N2 purging of light-source and detector on permanent and transient solarization effects in fibers. A closer analysis and selective change of the spectral power between 190 nm and 260 nm wavelength coupled into silica-based fibers with undoped high-OH silica core is presented and an improved system for solarization measurements on UV fibers is recommended.

In microelectromechanical system devices, thin films experience thermal processing at temperatures some cases exceeding the growth or deposition temperature of the film. In the case of the thin film grown by atomic layer deposition (ALD) at relatively low temperatures, post-ALD thermal processing or high device operation temperature might cause performance issues at device level or even device failure. In this work, residual stress and the role of intrinsic stress in ALD Al2O3 films grown from Me3Al and H2O, O3, or O2 (plasma ALD) were studied via post-ALD thermal processing. Thermal expansion coefficient was determined using thermal cycling and the double substrate method. For some samples, post-ALD thermal annealing was done in nitrogen at 300, 450, 700, or 900 °C. Selected samples were also studied for crystallinity, composition, and optical properties. Samples that were thermally annealed at 900 °C had increased residual stress value (1400–1600 MPa) upon formation of denser Al2O3 phase. The thermal expansion coefficient varied somewhat between Al2O3 made using different oxygen precursors. For thermal-Al2O3, intrinsic stress decreased with increasing growth temperature. ALD Al2O3 grown with plasma process had the lowest intrinsic stress. The results show that ALD Al2O3 grown at 200 and 300 °C is suitable for applications, where films are exposed to post-ALD thermal processing even at temperature of 700 °C without a major change in optical properties or residual stress.

EDITORIAL article Front. For. Glob. Change, 18 May 2022Sec. Forest Disturbance https://doi.org/10.3389/ffgc.2022.907537

Formulations based on ionizable amino-lipids have been put into focus as nucleic acid delivery systems. Recently, the in vitro efficacy of the lipid formulation OH4:DOPE has been explored. However, in vitro performance of nanomedicines cannot correctly predict in vivo efficacy, thereby considerably limiting pre-clinical translation. This is further exacerbated by limited access to mammalian models. The present work proposes to close this gap by investigating in vivo nucleic acid delivery within simpler models, but which still offers physiologically complex environments and also adheres to the 3R guidelines (replace/reduce/refine) to improve animal experiments. The efficacy of OH4:DOPE as a delivery system for nucleic acids is demonstrated using in vivo approaches. It is shown that the formulation is able to transfect complex tissues using the chicken chorioallantoic membrane model. The efficacy of DNA and mRNA lipoplexes is tested extensively in the zebra fish (Danio rerio) embryo which allows the screening of biodistribution and transfection efficiency. Effective transfection of blood vessel endothelial cells is seen, especially in the endocardium. Both model systems allow an efficacy screening according to the 3R guidelines bypassing the in vitro-in vivo gap. Pilot studies in mice are performed to correlate the efficacy of in vivo transfection.

A gene-activated surface coating is presented as a strategy to design smart biomaterials for bone tissue engineering. The thin-film coating is based on polyelectrolyte multilayers composed of collagen I and chondroitin sulfate, two main biopolymers of the bone extracellular matrix, which are fabricated by layer-by-layer assembly. For further functionalization, DNA/lipid-nanoparticles (lipoplexes) are incorporated into the multilayers. The polyelectrolyte multilayer fabrication and lipoplex deposition are analyzed by surface sensitive analytical methods that demonstrate successful thin-film formation, fibrillar structuring of collagen, and homogenous embedding of lipoplexes. Culture of mesenchymal stem cells on the lipoplex functionalized multilayer results in excellent attachment and growth of them, and also, their ability to take up cargo like fluorescence-labelled DNA from lipoplexes. The functionalization of the multilayer with lipoplexes encapsulating DNA encoding for transient expression of bone morphogenetic protein 2 induces osteogenic differentiation of mesenchymal stem cells, which is shown by mRNA quantification for osteogenic genes and histochemical staining. In summary, the novel gene-functionalized and extracellular matrix mimicking multilayer composed of collagen I, chondroitin sulfate, and lipoplexes, represents a smart surface functionalization that holds great promise for tissue engineering constructs and implant coatings to promote regeneration of bone and other tissues.

Sentinel-2 MSI is one of the core missions of the Copernicus Earth Observation programme of the European Union. This mission shows great potential to map the regional high-resolution spatio-temporal dynamics of land use and land cover. In tropical regions, despite the high revisiting time of 5 days including both Sentinel-2A and 2B satellites, the frequent presence of clouds, cloud-shadows, haze and other atmospheric contaminants are precluding the visibility of the Earth surface up to several months. In this paper we present four annual pan-tropical cloud-free composites computed and exported from Google Earth Engine (GEE) by making use of available Sentinel-2 L1C collection for the period spanning from 2015 to 2020. We furthermore propose empirical approaches to reduce the BRDF effect over tropical forest areas by showing pros and cons of image-based versus swath-based methodologies. Additionally, we provide a dedicated web-platform offering a fast and intuitive way to browse and explore the proposed annual composites as well as layers of potential annual changes as a ready-to-use means to visually identify and verify degradation and deforestation activities as well as other land cover changes.

Forest degradation often surpasses the area affected by deforestation and is therefore important under REDD+ monitoring, reporting and verification (MRV). Many studies dealing with forest degradation monitoring require the collection of sample data for algorithm training. The newly developed synthetic aperture radar (SAR)-based Forest Canopy Disturbance Monitoring (FCDM-radar) approach, implemented in Google Earth Engine and processing Copernicus Sentinel-1 data, allows the operational monitoring of evergreen and deciduous forest types without the need of collecting training data for calibration purposes. With a spatial resolution of 10 m it is able to detect small-scale forest canopy disturbance events such as single tree removals of 0.03 ha. Within a study area in central Cambodia (Prey Lang Wildlife Sanctuary), covering evergreen to semi-deciduous forests which are strongly affected by illegal selective logging activities, small-scale forest disturbances were successfully detected with an overall accuracy of 96.3% (user accuracy of 94.0%; producer accuracy of 79.1%).

The use of thin-films made by atomic layer deposition (ALD) is increasing in the field of optical sensing. ALD TiO2 has been widely characterized for its physical and optical properties, but systematic information about the influence of thermal history to optical and mechanical properties of the film is lacking. Optical applications require planar surface and tunability of the refractive index and residual stress. In addition, mechanical properties such as elastic modulus and film hardness influence the performance of the layer, especially, when optics is integrated with microelectromechanical systems. In this work, optical properties, density, elemental analysis, residual stress, elastic modulus and hardness of as-grown ALD TiO2 thin films on silicon were studied at temperature range from 80 to 350 degrees C and influence of post-ALD thermal annealing was studied on films annealed up to 900 degrees C. ALD TiO2 films were under tensile stress in the scale of hundreds of MPa. The stress depended both on the ALD temperature and film thickness in a complex way, and onset of crystallization increased the residual stress. Films grown at 110 and 300 degrees C were able to withstand post-ALD annealing at 420 degrees C without major change in residual stress, refractive index or extinction coefficient. Elastic modulus and hardness increased upon crystallization with increasing ALD temperature. The results presented here help to improve the design of the optical devices by choosing films with desired optical properties, and further help to design the post-ALD thermal budget so that films maintain their desired features.

Plasma outside deposition (POD) allows the incorporation of high fluorine contents in silica glass to manufacture multi-mode fibers. Due to all silica design and excellent material attributes, these so-called Fluosil fibers cover a wide spectrum of applications over a broad wavelength rage from UV to NIR including medical laser surgery, industrial materials processing, automotive, sensing, spectroscopy, and fiber bundles. These characteristics have allowed fiber designs to become more and more sophisticated in recent years. An overview of the current capabilities, characterization techniques, and fiber trends will be presented. Heraeus supports these new developments by offering a growing number of materials, preforms and services.

The need for accurate information to characterize the evolution of forest cover at the tropical scale is widely recognized, particularly to assess carbon losses from processes of disturbances such as deforestation and forest degradation1. In fact, the contribution of degradation is a key element for REDD+ activities and is presently mostly ignored in national reporting due to the lack of reliable information at such scale. Recently Vancutsem et al.2 produced a dataset at 30m resolution which delineates the tropical moist forest (TMF) cover changes from 1990 to 2019. The use of the Landsat historical time-series at high temporal and spatial resolution allows accurate monitoring of deforestation and degradation, from which the carbon losses from disturbances in TMFs can be estimated. A degradation event is defined here as temporary absence of tree cover (visible within a Landsat pixel during a maximum of three years duration) and includes impacts of fires and logging activities. We quantify the annual losses in above-ground carbon stock associated to degradation and deforestation in TMF over the period 2011-2019 by combining the annual disturbances in forest cover derived from the Landsat archive the pan-tropical map of aboveground live woody biomass density (AGB) from Santoro et al.3 at 100 m. To reduce the local variability within the estimation of AGB values, we apply a moving average filter under the TMF cover for the year 2010. The carbon loss due to degradation is accounted as full carbon loss within a pixel (like a deforestation). The reason is that logging activities usually remove large trees with higher biomass densities than the average value of the disturbed pixel indicated by the pan-tropical maps. To avoid double counting of carbon removal, deforestation happening after degradation is not accounted as carbon loss. Our results are compared with estimates of previous studies that cover different periods and forest domains: (i) Tyukavina et al.4 provide estimates of carbon loss from deforestation for the period 2000-2012 for all forests (evergreen and deciduous) discriminating natural forests from managed forests, and (ii) Baccini et al.5 provide estimates of carbon loss from deforestation and degradation for the period 2003-2014 for both evergreen and deciduous forests. In a further step, we will analyze the sensitivity of the results to the input AGB values by applying the same approach to other AGB maps (e.g. Baccini et al. 20126). Finally we intend to use Sentinel-2 data (10 m) for monitoring the location and extent of logging activities and burnt areas and further improve the estimates of carbon losses from forest degradation. 1. Achard F, House JI 2015 doi 10.1088/1748-9326/10/10/101002 2. Vancutsem C. et al. 2019 Submitted to Nat. Geoscience 3. Santoro M et al. 2018 doi 10.1594/PANGAEA.894711 4. Tuykavina A et al 2018 http://iopscience.iop.org/1748-9326/10/7/074002 5. Baccini A et al. 2017 doi 10.1126/science.aam5962 6. Baccini A et al. 2012 doi 10.1038/nclimate1354

We report on the first, to the best of our knowledge, implementation of a fluorine co-doped large-mode-area REPUSIL fiber for high peak power amplification in an ultrashort-pulse master oscillator power amplifier. The core material of the investigated step-index fiber with high Yb-doping level, 52 µm core and high core-to-clad ratio of 1:4.2 was fabricated by means of the REPUSIL powder-sinter technology. The core numerical aperture was adjusted by fluorine codoping to 0.088. For achieving high beam quality and for ensuring a monolithic seed path, the LMA fiber is locally tapered. We demonstrate an Yb fiber amplifier with near-diffraction-limited beam quality of M2=1.3, which remains constant up to a peak power of 2 MW. This is a record for a tapered single core fiber.

Biomaterials, which release active compounds after implantation, are an essential tool for targeted regenerative medicine. In this study, thin multilayer films loaded with lipid/DNA complexes (lipoplexes) were designed as surface coatings for in situ transfection applicable in tissue engineering and regenerative medicine. The film production and embedding of lipoplexes were based on the layer-by-layer (LbL) deposition technique. Hyaluronic acid (HA) and chitosan (CHI) were used as the polyelectrolyte components. The embedded plasmid DNA was complexed using a new designed cationic lipid formulation, namely, OH4/DOPE 1/1, the advantageous characteristics of which have been proven already. Three different methods were tested regarding its efficiency of lipid and DNA deposition. Therefore, several surface specific analytics were used to characterize the LbL formation, the lipid DNA embedding, and the surface characteristics of the multilayer films, such as fluorescence microscopy, surface plasmon resonance spectroscopy, ellipsometry, zeta potential measurements, atomic force microscopy, and scanning electron microscopy. Interaction studies were conducted for optimized lipoplex-loaded polyelectrolyte multilayers (PEMs) that showed an efficient attachment of C2C12 cells on the surface. Furthermore, no acute toxic effects were found in cell culture studies, demonstrating biocompatibility. Cell culture experiments with C2C12 cells, a cell line which is hard to transfect, demonstrated efficient transfection of the reporter gene encoding for green fluorescent protein. In vivo experiments using the chicken embryo chorion allantois membrane animal replacement model showed efficient gene-transferring rates in living complex tissues, although the DNA-loaded films were stored over 6 days under wet and dried conditions. Based on these findings, it can be concluded that OH4/DOPE 1/1 lipoplex-loaded PEMs composed of HA and CHI can be an efficient tool for in situ transfection in regenerative medicine.

One major disadvantage of nucleic acid delivery systems is the low transfection or transduction efficiency of large-sized plasmids into cells. In this communication, we demonstrate the efficient transfection of a 15.5 kb green fluorescent protein (GFP)-fused HIV-1 molecular clone with a nucleic acid delivery system prepared from the highly potent peptide-mimicking cationic lipid OH4 in a mixture with the phospholipid DOPE (co-lipid). For the transfection, liposomes were loaded using a large-sized plasmid (15.5 kb), which encodes a replication-competent HIV type 1 molecular clone that carries a Gag-internal green fluorescent protein (HIV-1 JR-FL Gag-iGFP). The particle size and charge of the generated nanocarriers with 15.5 kb were compared to those of a standardized 4.7 kb plasmid formulation. Stable, small-sized lipoplexes could be generated independently of the length of the used DNA. The transfer of fluorescently labeled pDNA-HIV1-Gag-iGFP in HEK293T cells was monitored using confocal laser scanning microscopy (cLSM). After efficient plasmid delivery, virus particles were detectable as budding structures on the plasma membrane. Moreover, we observed a randomized distribution of fluorescently labeled lipids over the plasma membrane. Obviously, a significant exchange of lipids between the drug delivery system and the cellular membranes occurs, which hints toward a fusion process. The mechanism of membrane fusion for the internalization of lipid-based drug delivery systems into cells is still a frequently discussed topic.

In this paper, we present our current work towards a highly efficient XLMA (extra-large mode area) fiber-based laser, which is being performed in the EKOLAS consortium within the BMBF-funded EffiLAS (efficient high-performance laser beam sources) research alliance. To this end, the complete manufacturing process chain of the XLMA fiber was reviewed and optimized. The work started with the material composition of the active XLMA preform with the goal of improving the purity and thus the background loss. A successfully implemented fluorine co-doping process allows refractive index adjustment of the active core material which improves the beam quality of the laser fibers without changing the concentration of active ions in the glass composition. The preform is subjected to a screening in which possible scatter centers, e.g. bubbles, inclusions or contaminants, are mapped and categorized, in order to identify defects, which could lead to a failure in the drawn fiber, already at an early production stage. The subsequent fiber drawing is monitored for scattering using the emissions from the heated preform as well as for inhomogeneities of the dopants using a phase measurement technique. Finally, the fiber is tested for residual impurities and background losses using a multi-mode OTDR to ensure that the fibers are free of any defects.

Imagery from medium resolution satellites, such as Landsat, have long been used to map forest disturbances in the tropics. However, the Landsat spatial resolution (30 m) has often been considered too coarse for reliably mapping small-scale selective logging. Imagery from the recently launched Sentinel-2 sensor, with a resampled 10 m spatial resolution, may improve the detection of forest disturbances. This study compared the performance of Landsat 8 and Sentinel-2 data for the detection of selective logging in an area located in the Brazilian Amazon. Logging impacts in seven areas, which had governmental authorization for harvesting timber, were mapped by calculating the difference of a self-referenced normalized burn ratio (ΔrNBR) index over corresponding time periods (2016–2017) for imagery of both satellite sensors. A robust reference dataset was built using both high- and very-high-resolution imagery. It was used to define optimum ΔrNBR thresholds for forest disturbance maps, via a bootstrapping procedure, and for estimating accuracies and areas. A further assessment of our approach was also performed in three unlogged areas. Additionally, field data regarding logging infrastructure were collected in the seven study sites where logging occurred. Both satellites showed the same performance in terms of accuracy, with area-adjusted overall accuracies of 96.7% and 95.7% for Sentinel-2 and Landsat 8, respectively. However, Landsat 8 mapped 36.9% more area of selective logging compared to Sentinel-2 data. Logging infrastructure was better detected from Sentinel-2 (43.2%) than Landsat 8 (35.5%) data, confirming its potential for mapping small-scale logging. We assessed the impacted area by selective logging with a regular 300 m × 300 m grid over the pixel-based results, leading to 1143 ha and 1197 ha of disturbed forest on Sentinel-2 and Landsat 8 data, respectively. No substantial differences in terms of accuracy were found by adding three unlogged areas to the original seven study sites.