Controlling Growth of Poly (Triethylene Glycol Acrylate-Co-Spiropyran Acrylate) Copolymer Liquid Films on a Hydrophilic Surface by Light and Temperature

A quartz crystal microbalance with dissipation monitoring (QCM-D) was employed for in situ investigations of the effect of temperature and light on the conformational changes of a poly (triethylene glycol acrylate-co-spiropyran acrylate) (P (TEGA-co-SPA)) copolymer containing 12–14% of spiropyran at the silica–water interface. By monitoring shifts in resonance frequency and in acoustic dissipation as a function of temperature and illumination conditions, we investigated the evolution of viscoelastic properties of the P (TEGA-co-SPA)-rich wetting layer growing on the sensor, from which we deduced the characteristic coil-to-globule transition temperature, corresponding to the lower critical solution temperature (LCST) of the PTEGA part. We show that the coil-to-globule transition of the adsorbed copolymer being exposed to visible or UV light shifts to lower LCST as compared to the bulk solution: the transition temperature determined acoustically on the surface is 4 to 8 K lower than the cloud point temperature reported by UV/VIS spectroscopy in aqueous solution. We attribute our findings to non-equilibrium effects caused by confinement of the copolymer chains on the surface. Thermal stimuli and light can be used to manipulate the film formation process and the film’s conformational state, which affects its subsequent response behavior

Boson peak, heterogeneity and intermediate-range order in binary SiO2-Al2O3 glasses

In binary aluminosilicate liquids and glasses, heterogeneity on intermediate length scale is a crucial factor for optical fiber performance, determining the lower limit of optical attenuation and Rayleigh scattering, but also clustering and precipitation of optically active dopants, for example, in the fabrication of high-power laser gain media. Here, we consider the low-frequency vibrational modes of such materials for assessing structural heterogeneity on molecular scale. We determine the vibrational density of states VDoS g(ω) using low-temperature heat capacity data. From correlation with low-frequency Raman spectroscopy, we obtain the Raman coupling coefficient. Both experiments allow for the extraction of the average dynamic correlation length as a function of alumina content. We find that this value decreases from about 3.9 nm to 3.3 nm when mildly increasing the alumina content from zero (vitreous silica) to 7 mol%. At the same time, the average inter-particle distance increases slightly due to the presence of oxygen tricluster species. In accordance with Loewensteinian dynamics, this proves that mild alumina doping increases structural homogeneity on molecular scale

Negative curvature hollow core fiber sensor for the measurement of strain and temperature

Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements

Negative curvature hollow core fiber sensor for the measurement of strain and temperature

Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements.publishe

Simultaneous measurement of refractive index and temperature using a double antiresonant hollow core fiber

In this work, an inline sensor based on a double antiresonant hollow core fiber is proposed for the simultaneous measurement of refractive index and temperature. The fiber, consisting of four silica capillaries with wall thickness of ~1.5 um and a cladding with a thickness of ~36.5 um, is spliced between two sections of single mode fiber. The spectral behavior, measured in transmission, results from the combination of different frequencies which enable the discrimination between the two parameters. The sensing head is subjected to refractive index measurements using aqueous solutions with different concentrations of ethanol. For a sensor with a length of ~10 mm, and considering the lower frequency signal, the sensitivity to refractive index is 389.6 nm/RIU, whereas for the higher frequency, the sensitivity attained is 2.8 nm/RIU. On the other hand, the sensing head presented a sensitivity to temperature of 25.5 pm/K and -27.6 pm/K for the higher and lower frequencies, respectively.publishe

Extruded suspended core fibers from lanthanum-aluminum-silicate glass

We report the use of the extrusion technique at highest temperatures to date (975 °C-1000 °C) for the fabrication of suspended core fibers (SCFs) from glass with molar composition 65 SiO2-20 Al2O3-15 La2O3 (SAL65). Through adjusting die design and fabrication conditions, extruded preforms for fibers with two different core sizes (1.2 µm and 3.1 µm) were successfully produced. Cross-sectional microstructure and material loss of these fibers highlight the potential of the extrusion technique for fabrication of microstructured optical fibers from glasses with high softening temperature and thus high thermal and mechanical stability. © 2020. All rights reserved

Plasma-based VAD process for multiply doped glass powders and high-performance fiber preforms with outstanding homogeneity

An innovative approach using the vapor axial deposition (VAD), for the preparation of silica-based high-power fiber laser preforms, is described in this study. The VAD uses a plasma deposition system operating at atmospheric pressure, fed by a single, chemically adapted solution containing precursors of laser-active dopants (e.g., Yb2O3), glass-modifier species (e.g., Al2O3), and the silica matrix. The approach enables simultaneous doping with multiple optically active species and overcomes some of the current technological limitations encountered with well-established fiber preform technologies in terms of dopant distribution, doping levels, and achievable active core diameter. The deposition of co-doped silica with outstanding homogeneity is proven by Raman spectroscopy and electron probe microanalysis. Yb2O3 concentrations are realized up to 0.3 mol% in SiO2, with simultaneous doping of 3 mol% of Al2O3

Sodium Ion Conductivity in Superionic IL-Impregnated Metal-Organic Frameworks: Enhancing Stability Through Structural Disorder

Abstract: Metal-organic frameworks (MOFs) are intriguing host materials in composite electrolytes due to their ability for tailoring host-guest interactions by chemical tuning of the MOF backbone. Here, we introduce particularly high sodium ion conductivity into the zeolitic imidazolate framework ZIF-8 by impregnation with the sodium-salt-containing ionic liquid (IL) (Na0.1EMIM0.9)TFSI. We demonstrate an ionic conductivity exceeding 2 × 10−4 S · cm−1 at room temperature, with an activation energy as low as 0.26 eV, i.e., the highest reported performance for room temperature Na+-related ion conduction in MOF-based composite electrolytes to date. Partial amorphization of the ZIF-backbone by ball-milling results in significant enhancement of the composite stability towards exposure to ambient conditions, up to 20 days. While the introduction of network disorder decelerates IL exudation and interactions with ambient contaminants, the ion conductivity is only marginally affected, decreasing with decreasing crystallinity but still maintaining superionic behavior. This highlights the general importance of 3D networks of interconnected pores for efficient ion conduction in MOF/IL blends, whereas pore symmetry is a less stringent condition

2 MW peak power generation in fluorine co-doped Yb fiber prepared by powder-sinter technology

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. © 2020 Optical Society of Americ

Two-Step-Model of Photosensitivity in Cerium-doped Fibers

The photosensitivity of various cerium-doped fibers has been experimentally investigated for both excimer- and femtosecond-laser illumination. The results of single-pulse, few-pulse and multi-pulse inscription of fiber-Bragg-gratings with both laser systems and the thermal aging of those gratings demonstrated the restrictions of the conventional color center model for cerium-doped fibers. To explain the short-term stability of single-pulse gratings against long-term stability of multi-pulse gratings, an extension into a two-step-model was deduced