Length distributed measurement of temperature effects in Yb-doped fibers during pumping

We demonstrate a distributed measurement technique to observe temperature changes along pumped Yb-doped fibers. This technique is based on an array of fiber Bragg gratings acting as a temperature sensor line. The Bragg gratings are inscribed directly into the Yb-doped fiber core using high-intensity ultrashort laser pulses and an interferometric setup. We studied the temperature evolution in differently co-doped Yb fibers during optical pumping and identified different effects contributing to the observed temperature increase. We found that preloading of fibers with hydrogen supports the formation of Yb2+ during UV irradiation and has a large impact on fiber temperature during pumping. The proposed technique can be applied to investigate the homogeneity of pump absorption in active fibers and to support spatially resolved photodarkening measurements

"Killing them softly" … challenges in the Bacillus subtilis spore inactivation by plasma sterilization

The elimination of bacterial endospores is absolutely essential in numerous fields, ranging from hospital hygiene, the food processing industry, all the way to the space industry. A major goal of space exploration is the search for signatures of life forms and biomolecules on other planetary bodies and moons in our solar system. The transfer of microorganisms or biomolecules of terrestrial origin to critical areas of exploration is of particular risk to impact the development and integrity of life-detection missions.1 Plasma sterilization is a promising alternative to conventional sterilization methods for spaceflight purposes. Due to their extraordinary resistance properties, spores of the Gram-positive bacterium Bacillus subtilis are used as biological indicators for decontamination studies to identify the relevant mechanism that leads to the rapid bacterial inactivation.1,3 Here, we present novel insights into the key factors involved in spore inactivation by low pressure plasma sterilization using a double inductively-coupled plasma reactor. (2,4) In order to standardize the assessment of inactivation efficiencies by plasma discharges, an electrically driven spray deposition device was developed, allowing fast, reproducible, and homogeneous preparation of B. subtilis spore monolayers. We demonstrate that plasma discharges caused significant physical damage to spore surface structures as visualized by atomic force microscopy. A systematic analysis of B. subtilis spores lacking individual coat and crust layers - the first barrier to environmental influences – revealed the coat to be one of the contributing factors in the spore resistance to plasma sterilization. (2-4) Furthermore, we identified spore-specific and general protection mechanisms and DNA repair pathways during spore germination and outgrowth after plasma treatment, leading to a better understanding of the complex molecular mechanisms involved in the inactivation by plasma sterilization processes

Fiber Vector Bend Sensor Based on Multimode Interference and Image Tapping

A grating-less fiber vector bend sensor is demonstrated using a standard single mode fiber spliced to a multimode fiber as a multimode interference device. The ring-shaped light intensity distribution at the end of the multimode fiber is subject to a vector transition in response to the fiber bend. Instead of comprehensive imaging processing for the analysis, the image can be tapped out by a seven-core fiber spliced to the other end of the multimode fiber. The seven-core fiber is further guided to seven single mode fibers via a commercial fan-out device. By comparing the relative light intensities received at the seven outputs, both the bend radius and its direction can be determined. Experiment has shown that a slight bend displacement of 10 µm over a 1.2-cm-long multimode fiber in the X direction (bend angle of 0.382 ◦ ) causes a distinctive power imbalance of 4.6 dB between two chosen outputs (numbered C4 and C7). For the same displacement in the Y direction, the power ratio between the previous two outputs C4 and C7 remains constant, while the imbalance between another pair (C3 and C4) rises significantly to 7.0 dB. © 2019 by the authors. Licensee MDPI, Basel, Switzerland

Bending insensitivity of fiber Bragg gratings in suspended-core optical fibers

This Letter presents simulation and experimental results that explore bending insensitivity of fiber Bragg gratings in suspended-core optical fibers. The implementation of thin silica bridge in the fibers enhances index contrast of the fiber core and reduces bending-induced strain transfer to the fiber core. This fiber design lead to a reduction of over 7 times in strain-induced fiber Bragg grating resonant peak shifts in the suspended-core fiber compared with that in standard telecommunication fiber, and an 0:14dB bending loss at a bending radius of 6:35mm. © 2011 Optical Society of America

Suspended-core fiber Bragg grating sensor for directional- dependenttransverse stress monitoring

This Letter presents simulation and experimental results of orientation-dependent transverse stress fiber sensors using fiber Bragg gratings (FBGs) inscribed in four-hole suspended-core fibers. Resonant peak shifts and splitting of FBGs were studied as functions of the applied transverse load and fiber orientation. Both simulation and experimental results revealed that the response of FBGs in suspended-core fibers is sensitive to both the orientation and magnitude of an applied transverse stress. © 2011 Optical Society of America

Experimental and computational investigations of electron dynamics in micro atmospheric pressure radio-frequency plasma jets operated in He/N2 mixtures

The electron power absorption dynamics in radio frequency driven micro atmospheric pressure capacitive plasma jets are studied based on experimental phase resolved optical emission spectroscopy and the computational particle in cell simulations with Monte Carlo treatment of collisions. The jet is operated at 13.56 MHz in He with different admixture concentrations of N2 and at several driving voltage amplitudes. We find the spatio-temporal dynamics of the light emission of the plasma at various wavelengths to be markedly different. This is understood by revealing the population dynamics of the upper levels of selected emission lines/bands based on comparisons between experimental and simulation results. The populations of these excited states are sensitive to different parts of the electron energy distribution function and to contributions from other excited states. Mode transitions of the electron power absorption dynamics from the Ω- to the Penning-mode are found to be induced by changing the N2 admixture concentration and the driving voltage amplitude. Our numerical simulations reveal details of this mode transition and provide novel insights into the operation details of the Penning-mode. The characteristic excitation/emission maximum at the time of maximum sheath voltage at each electrode is found to be based on two mechanisms: (i) a direct channel, i.e. excitation/emission caused by electrons generated by Penning ionization inside the sheaths and (ii) an indirect channel, i.e. secondary electrons emitted from the electrode due to the impact of positive ions generated by Penning ionization at the electrodes

Techno-ökonomischer Benchmark von Flüssigluftenergiespeichern und Lithium-Ionen Batterien in Verbindung mit Photovoltaik in ausgewählten Industrieländern

Die zeitliche Verschiebung und Verstetigung von elektrischer Energie aus Photovoltaik-Systemen (PV) mittels Tagesspeicher stellt eine Flexibilitätsoption dar energetische Ausgleichsmaßnahmen im Verbundnetz zu verringern. Das Ziel dieser Arbeit ist die Analyse der technischen und ökonomischen Konkurrenzfähigkeit von PV-Systemen mit adiabaten Flüssigluftenergiespeichern (A-LAES) und Lithium-Ionen Batterien (BESS) gegenüber am Markt etablierten solarthermischen Kraftwerken (CSP) in Bezug auf die Stromgestehungskosten (LCOE) in Spanien, den USA und China. Entsprechend den länderspezifischen Untersuchungen sind die Kombinationen aus PV-System und A-LAES bzw. BESS gegenüber den jeweiligen CSP in Bezug auf die LCOE tendenziell konkurrenzfähig. Dabei ist der BESS bei einer Kapazität von 7,5 h dem A-LAES vorzuziehen. In China sind die LCOE der A-LAES Kombinationen jedoch infolge des größeren Kostenreduktionspotenzials und der niedrigeren Materialpreise geringer als die der BESS Kombinationen

Influence of photon energy and photon / particle fluxes on the inactivation efficiency of B. subtilis\textit {B. subtilis} spores in low-pressure plasmas

Das Ziel der vorliegenden Arbeit ist die Untersuchung des Einflusses von Photonen- und Teilchenflüssen auf die Inaktivierungseffizienz von $\textit {B. subtilis}$ Sporen in Niederdruckplasmen. Hierzu wurden Plasmen mit unterschiedlichen Gaszusammensetzungen hinsichtlich ihrer Elektronendichte, Elektronenenergieverteilungsfunktion und Gastemperatur charakterisiert sowie die metastabilen und resonanten Zustände von Argon im Plasma bestimmt. Anschließend wurden die gemessenen Plasmaparameter bzgl. ihrer Reproduzierbarkeit und Eignung zur Anwendung in Stoß-Strahlungsmodellen untersucht und in einem Stoß-Strahlungsmodell für atomaren Sauerstoff verwendet. Weiterhin wurden die Photonenflüsse auf die biologischen Proben in den verschiedenen Plasmen im Bereich von 116 nm bis 840 nm analysiert. Abschließend konnte mit dem Vergleich von Inaktivierungsexperimenten der wellenlängenabhängige Einfluss, sowie der Einfluss von Teilchenflüssen auf die Inaktivierungseffizienz von $\textit {B. subtilis}$ Sporen bestimmt werden.The aim of this thesis is the analysis of the influence of photon and particle fluxes on the inactivation efficiency of $\textit {B. subtilis}$ spores in low-pressure plasmas. Therefore, plasmas of different gas mixtures are characterized regarding their electron density, electron energy distribution function, gas temperature, as well as their metastable and resonant state densities of argon. Afterwards, the determined plasma parameters are checked for their reproducibility and applicability in collisional radiative models and used in a model for atomic oxygen. Furthermore, the photon flux on the biological samples in the different gas mixtures is measured in the range from 116 nm to 840 nm. By comparing the results with inactivation experiments, the wavelength dependent photon influence as well as the influence of the particle fluxes on the inactivation efficiency of $\textit {B. subtilis}$ spores is determined