Amplification in Ytterbium-doped fibers

Fiber lasers and amplifiers are quickly replacing conventional bulk optical devices in a variety of applications. Ytterbium-doped fibers are of particular interest in high power applications due to their numerous advantages arising from a simple electronic structure. The behavior of Ytterbium-doped fiber devices is however strongly influenced by the selection of absorption and emission wavelengths and other parameters. Careful theoretical analysis is required to optimize the performance of the fiber device and to estimate the influence of amplified spontaneous emission, photodarkening and other such phenomena. The objective of this thesis is to study the amplification process in Ytterbium-doped fibers experimentally and theoretically, as a preliminary step to designing a high power pump source. For this purpose, a fiber laser and an amplifier operating in the continuous wave regime have been experimentally realized based on Ytterbium-doped double-clad fibers in a free-space configuration. Theoretical models of these devices have been simulated using a commercial simulation software. The influence of various design and fiber parameters on the performance of the devices have been studied in simulations and good agreement between the results for both the fiber laser and amplifier is found

Protein Adsorption and Its Effects on Electroanalytical Performance of Nanocellulose/Carbon Nanotube Composite Electrodes

Protein fouling is a critical issue in the development of electrochemical sensors for medical applications, as it can significantly impact their sensitivity, stability, and reliability. Modifying planar electrodes with conductive nanomaterials that possess a high surface area, such as carbon nanotubes (CNTs), has been shown to significantly improve fouling resistance and sensitivity. However, the inherent hydrophobicity of CNTs and their poor dispersibility in solvents pose challenges in optimizing such electrode architectures for maximum sensitivity. Fortunately, nanocellulosic materials offer an efficient and sustainable approach to achieving effective functional and hybrid nanoscale architectures by enabling stable aqueous dispersions of carbon nanomaterials. Additionally, the inherent hygroscopicity and fouling-resistant nature of nanocellulosic materials can provide superior functionalities in such composites. In this study, we evaluate the fouling behavior of two nanocellulose (NC)/multiwalled carbon nanotube (MWCNT) composite electrode systems: one using sulfated cellulose nanofibers and another using sulfated cellulose nanocrystals. We compare these composites to commercial MWCNT electrodes without nanocellulose and analyze their behavior in physiologically relevant fouling environments of varying complexity using common outer- and inner-sphere redox probes. Additionally, we use quartz crystal microgravimetry with dissipation monitoring (QCM-D) to investigate the behavior of amorphous carbon surfaces and nanocellulosic materials in fouling environments. Our results demonstrate that the NC/MWCNT composite electrodes provide significant advantages for measurement reliability, sensitivity, and selectivity over only MWCNT-based electrodes, even in complex physiological monitoring environments such as human plasma.</p

Nanoselluloosa/nanohiilikomposiitit pienten molekyylien suoraan sähkökemialliseen havaitsemiseen

Nanocellulosic materials are rapidly developing into highly versatile and sustainable alternativesfor synthetic polymers in several high value applications. They are of particular interest in varioussensor architectures due to their unique properties such as high strength, large surface area withpotential for functionalization, hygroscopicity and film forming tendency. Further, their ability todisperse carbon nanomaterials in stable aqueous suspensions has resulted in an increased interesttowards the development of nanocellulose / nanocarbon electrochemical platforms for detectionof various drugs and biomolecules in the recent years. However, this field is still in its infancy, and there is an evident need to understand the role ofdifferent nanocellulosic materials in tailoring the electroanalytical performance of the resultantnanocellulose / nanocarbon composites. In this thesis, we have used nanocellulosic materials withdifferent geometries and functionalizations, to develop composite electrode architectures withcommercial multiwalled carbon nanotubes (MWCNT). The physical and chemical nature of thenanocellulosic materials, MWCNT, and their composites, are studied using several surface and bulkcharacterization methods and are correlated to the electrochemical performances of the compositesevaluated using both outer and inner sphere redox molecules. We have shown that both cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF) havingdifferent surface functionalizations, can be used to develop highly stable, robust electrochemicalplatforms with MWCNT, without compromising the electrochemical activity of the MWCNT. Thenanocellulose geometry is clearly demonstrated to have a significant effect upon the compositemorphology, where the highly functionalized CNFs result in open architectures with more exposedMWCNT surface, and CNCs result in denser architectures with the CNC packed closely around theMWCNT. Correspondingly, the CNF-based composites exhibit higher electrochemically active surface area,increased electrostatic effects and stronger redox currents for all measured analytes. The natureand degree of nanocellulose functionalization is shown to have a significant effect on the extent ofelectrostatic effects in the composite, offering a promising route towards tailoring the ionicselectivity. Finally, we demonstrate that all the nanocellulose / MWCNT composites proposed inthis work are capable of achieving significantly higher sensitivity and selectivity towards a cationicinner sphere redox molecule such as dopamine, compared to current commercial standardMWCNT electrodes.Nanoselluloosamateriaalit ovat nopeasti kehittymässä monipuoliseksi ja kestäväksi synteettisten polymeerien korvaajaksi useissa korkean lisäarvon sovelluksissa. Erityisen kiinnostava sovellusalue on erilaiset anturit, joissa nanoselluloosan käyttöä puoltavat sen ainutlaatuiset materiaaliominaisuudet: suuri lujuus ja ominaispinta-ala, laajalti kartoitetut kemialliset muokkausmekanismit, hygroskooppisuus sekä taipumus muodostaa kalvoja. Lisäksi nanoselluloosan kyky dispergoida hiilinanomateriaaleja stabiileihin vesisuspensioihin on mahdollistanut viime vuosina nanoselluloosa/nanohiili-pohjaisten sähkökemiallisten alustojen kehittämisen erilaisten lääkkeiden ja biomolekyylien havaitsemiseksi.Tämä ala on kuitenkin vielä lapsenkengissään, ja lisää ymmärrystä tarvitaan eri nanoselluloosamateriaalien vaikutuksesta syntyvien nanoselluloosa/nanohiilikomposiittien elektroanalyyttiseen suorituskykyyn. Tässä opinnäytetyössä olemme valmistaneet komposiittielektrodirakenteita yhdistämällä muodoltaan ja funktionaalisuudeltaan erilaisiananoselluloosamateriaaleja kaupallisten moniseinäisten hiilinanoputkien (MWCNT) kanssa. Nanoselluloosamateriaalien, MWCNT:n ja näitä yhdistävien komposiittien fysikaalista ja kemiallista luonnetta on tutkittu useilla pinta- ja bulkkikarakterisointimenetelmillä. Komposiittien ominaisuuksien on havaittu korreloivan niiden sähkökemiallisen suorituskyvyn kanssa, jota on arvioitu sekä ulko- että sisäkehän redox-molekyylejä käyttämällä. Olemme osoittaneet, että niin eri tavoin pintafunktionalisoituja selluloosan nanokiteitä (CNC) kuin selluloosan nanofibrillejäkin (CNF) voidaan käyttää MWCNT:n kanssa erittäin stabiilien ja kestävien sähkökemiallisten alustojen valmistamiseen vaarantamatta MWCNT:n sähkökemiallista aktiivisuutta. Nanoselluloosan muodolla on osoitettu olevan merkittävä vaikutus komposiittimorfologiaan; tiheästi funktionalisoidun CNF:n käyttö johtaa avoimiin rakenteisiin, joissa on enemmän esillä olevaa MWCNT-pintaa, kun taas CNC:n käyttö johtaa tiheämpiin rakenteisiin, joissa CNC on pakkautuneena tiiviisti MWCNT:n ympärille. Vastaavasti CNF-pohjaisilla komposiiteilla on suurempi sähkökemiallisesti aktiivinen pinta-ala, lisääntyneet sähköstaattiset vuorovaikutukset ja voimakkaammat redox-virrat kaikille mitatuille analyyteille. Nanoselluloosan funktionalisoinnin luonteen ja määrän on osoitettu vaikuttavan merkittävästi komposiitin sähköstaattisten vuorovaikutusten voimakkuuteen, mikä tarjoaa mahdollisuuksia ionisen selektiivisyyden räätälöintiin. Lopuksi olemme osoittaneet, että kaikki tässä työssä ehdotetut nanoselluloosa / MWCNT-komposiitit pystyvät saavuttamaan huomattavasti korkeamman herkkyyden ja selektiivisyyden kationiselle sisäkehän redox-molekyylille, kuten dopamiinille, verrattuna nykyisiin kaupallisiin MWCNT-pohjaisiin standardielektrodeihin

Picosecond supercontinuum light source for stroboscopic white-light interferometry with freely adjustable pulse repetition rate

Peer reviewe

Multiwalled Carbon Nanotubes/Nanofibrillar Cellulose/Nafion Composite-Modified Tetrahedral Amorphous Carbon Electrodes for Selective Dopamine Detection

We introduce a composite membrane comprised of multiwalled carbon nanotubes (MWCNTs) dispersed in a matrix of sulfated nanofibrillar cellulose (SNFC) and Nafion. The high negative charge densities of the SNFC and Nafion ionomers enhance the cationic selectivity of the composite. The composite is characterized by scanning electron (SEM) and transmission electron (TEM) microscopies as well as Fourier transform infrared (FTIR) and Raman spectroscopies. Tetrahedral amorphous carbon (ta-C) electrodes modified with the composite are investigated as potential dopamine (DA) electrochemical sensors. The composite-modified electrodes show significant selectivity and sensitivity toward DA in the presence of ascorbic acid (AA) and uric acid (UA) in physiologically relevant concentrations. A linear dopamine detection range of 0.05-100 μM with detection limits of 65 nM in PBS and 107 nM in interferent solution was determined using 100 mV/s cyclic voltammetry (CV) measurements. These results highlight the potential of the composite membrane for in vivo detection of neurotransmitters.Peer reviewe

Functionalized Nanocellulose/Multiwalled Carbon Nanotube Composites for Electrochemical Applications

Funding Information: This work was a part of the Academy of Finland?s Flagship Programme under projects nos. 318890 and 318891 (Competence Center for Materials Bioeconomy, FinnCERES). The authors acknowledge the provision of facilities by Aalto University Bioeconomy and OtaNano?Nanomicroscopy Center (Aalto-NMC) and RawMatters research infrastructure (RAMI). Publisher Copyright: ©Four different types of crystalline and fibrillar nanocellulosic materials with different functional groups (sulfate, carboxylate, amino-silane) are produced and used to disperse commercial multiwalled carbon nanotubes (MWCNT). Aqueous nanocellulose/MWCNT dispersions are drop-cast on tetrahedral amorphous carbon (ta-C) substrates to obtain highly stable composite electrodes. Their electrochemical properties are studied using cyclic voltammetry (CV) measurements with Ru(NH3)62+/3+, IrCl62-/3- redox probes, in electrolytes of different ionic strengths. All studied nanocellulose/MWCNT composites show excellent stability over a wide potential range (-0.6 to +1 V) in different electrolytes. Highly anionic and more porous fibrillar nanocellulosic composites indicate strong electrostatic and physical enrichment of cationic Ru(NH3)62+/3+ in lower-ionic-strength electrolytes, while lesser anionic and denser crystalline nanocellulosic composites show no such effects. This study provides essential insights into developing tailorable nanocellulose/carbon nanomaterial hybrid platforms for different electrochemical applications, by altering the constituent nanocellulosic material properties.Peer reviewe

Role of nanocellulose in tailoring electroanalytical performance of hybrid nanocellulose/multiwalled carbon nanotube electrodes

Publisher Copyright: © 2022, The Author(s).Nanocellulose has emerged as a promising green dispersant for carbon nanotubes (CNTs), and there is an increasing trend in developing nanocellulose/CNT hybrid materials for electrochemical detection of various small molecules. However, there have been very few comprehensive studies investigating the role of nanocellulosic material properties upon the electroanalytical performance of the resultant hybrid electrodes. In this work, we demonstrate the influence of both nanocellulose functionalization and geometry, utilizing sulfated cellulose nanocrystals, sulfated cellulose nanofibers, and TEMPO-oxidized cellulose nanofibers. Transmission electron microscopy tomography enables direct visualization of the effect of nanocellulosic materials on the hybrid architectures. High resolution X-ray absorption spectroscopy verifies that the chemical nature of CNTs in the different hybrids is unmodified. Electroanalytical performances of the different nanocellulose/CNT hybrid electrodes are critically evaluated using physiologically relevant biomolecules with different charge such as, dopamine (cationic), paracetamol (neutral), and uric acid (anionic). The hybrid electrode containing fibrillar nanocellulose geometry with a high degree of sulfate group functionalization provides the highest electroanalytical sensitivity and strongest enrichment towards all studied analytes. These results clearly demonstrate for the first time, the extent of tailorability upon the electroanalytical response of nanocellulose/CNT hybrid electrodes towards different biomolecules, offered simply by the choice of nanocellulosic materials.Peer reviewe