Soft Glass Research Articles

Relating laser powder bed fusion process parameters to (micro)structure and to soft magnetic behaviour in a Fe-based bulk metallic glass

This work aims to establish fundamental processing-(micro)structure-property links in a commercial Fe-based Kuamet6B2 bulk metallic glass (BMG) processed by laser powder bed fusion (LPBF). With that purpose, amorphous powders were processed using a pulsed-wave system and a simple meander strategy. The laser power, the scan speed, and the hatch distance were varied over wide intervals within the conduction regime. The processability window leading to samples with good dimensional accuracy and mechanical stability was determined. Within this window, the manufactured samples were crystalline/amorphous composites and the crystalline regions were formed by equiaxed ultrafine and nanograins with random orientations. Processing parameters yielding the densest prints caused severe crystallization while, conversely, parameter sets allowing the material to retain a high amorphous fraction led to significant lack-of-fusion defects and residual cracking along directions perpendicular to crystalline/amorphous interfaces. Comparatively, for a fixed hatch distance, the scanning speed had a stronger effect than the laser power in the resulting amorphous fraction due to its stronger influence on the melt pool size and, in turn, on the corresponding HAZ volume. The saturation magnetization and the coercive field were inversely related to the amorphous fraction. This work allows to derive fundamental guidelines for the successful additive manufacturing of soft magnetic Fe-based bulk metallic glasses (BMGs) by laser powder bed fusion (LPBF).

Isocompositional liquid-liquid transition in dilute aqueous LiCl solutions

We here demonstrate that small amounts of LiCl dissolved in water extend the existence window of deeply supercooled liquid water. This shift allows us to observe the isocompositional, sharp liquid-liquid transition (LLT), while this is not possible in pure water. Upon heating at ambient pressure, the hyperquenched and densified glass first turns into the high-density liquid (HDL) and then experiences the LLT to the low-density liquid (LDL) at 137–141 K and ambient pressure. At the LLT the viscosity suddenly jumps up by an order of magnitude, from ∼4.3×109Pas in HDL to ∼3.7×1010Pas in LDL for the 3.1 mol % solution based on our calorimetric analysis. That is, the LLT takes place clearly in the ultraviscous liquid domain at ambient pressure. By contrast, the viscosity of the emerging LDL at the LLT is still in the domain of the soft glass for pure water and for solutions exceeding 5 mol % LiCl that were studied in the past. This is owing to our observation that, first, the LDL's glass transition is lowered by about 8 K to 126 K in the presence of small amounts LiCl, whereas the HDL's glass transition remains at 118 K. Second, the stability of HDL at ambient pressure is increased by high-pressure annealing, shifting the LLT to higher temperatures. Published by the American Physical Society 2024

Design and fabrication of a tellurite hollow-core anti-resonant fiber for mid-infrared applications

The hollow core anti-resonant fibers (HC-ARFs) based on soft glass are in high demand for 3-6 µm laser delivery. A HC-ARF based on tellurite glass with 6 touching capillaries as cladding was designed and fabricated for the first time, to the best of our knowledge. A relatively low loss of 3.75 dB/m at 4.45 µm was realized in it. The effects of capillary number, core diameter, wall thickness of capillary, and material absorption loss on the loss of the HC-ARF were analyzed by the numerically simulation. The output beam quality was measured and the influence of bending on the fiber loss was discussed. The results of numerical simulation suggested that the theoretical loss of the prepared fiber can be reduced to 0.1 dB/m, indicating that tellurite HC-ARFs have great potential for mid-infrared laser applications.

Influence of airborne particle abrasion on dentin bonding effectiveness of a 2-step universal adhesive

ObjectiveTo determine the effect of airborne particle abrasion (APA) on micro-tensile bond strength (µTBS) to dentin using different air-abrasion/polishing powders. MethodsThe bonding effectiveness of G2 Bond Universal (G2B), used in etch-and-rinse (E&R) and self-etch mode (SE), was tested on bur-cut dentin and dentin air abraded/polished using six different powders (aluminum oxide 29 µm (AO29) and 53 µm (AO53), aluminum trihydroxide (AT), sodium bicarbonate (SB), sodium bicarbonate soft (SBsoft) and bioactive glass (BG); Velopex). Adhesive-composite resin specimens were immersed in distilled water at 37 °C for one week and cut into microspecimens. Half of the specimens were subjected to 50,000 thermocycles (aged). Immediate and aged μTBS to dentin were measured. Statistical analysis was performed using linear mixed-effects (LME) modeling (p < 0.05). ResultsComparing the aged bond strengths to air-abraded/polished dentin with bur-cut dentin, pretreatment with SB and SBsoft in combination with G2B used in E&R mode, and BG air polishing in combination with both application modes (E&R, SE), resulted in a significantly higher bond strength. Dentin bond strength was only significantly lower when air abraded with AO29 and using G2B in SE mode. Aging did not significantly influence bond strength for both application modes (E&R, SE), except for AO29 and AT-treated dentin, where bond strengths decrea sed significantly using G2B in SE mode. In general, G2B reached significantly higher bond strengths on air-abraded/polished dentin in E&R mode than in SE mode. ConclusionAir-abrasion/polishing did not impair dentin bond strength using G2B, except when dentin was air abraded with AO29 and using G2B in SE mode. Air polishing positively influenced the bond strength to dentin in specific groups. Clinical significanceAPA is safe concerning bonding to dentin. The E&R application mode is preferred using G2B as adhesive on air-abraded/polished dentin. Air polishing with BG positively influenced dentin bond strength for both application methods.

Observation of Visible Upconversion Luminescence of Soft Glass Multimode Fibers

This research investigates the visible upconversion luminescence which is induced by multiphoton absorption of soft glass fiber defects. The study of this phenomenon has thus far been restricted to standard silica fibers. We observed the emission of green and cyan light as a consequence of fiber material ionization. We investigate both the commercial ZBLAN step index and in-house-made tellurite nanostructured graded-index fibers. For the latter, the analysis of the luminescence signal permits us to determine the core and cladding refractive index difference. Upconversion luminescence is a powerful tool for characterizing soft glass fibers and a promising platform for innovative photonic technologies and mid-IR applications.

An intrinsic connection between the liquid-liquid transition and fragile-to-strong transition in soft magnetic Fe-based metallic glasses: Comparisons with other metallic glasses

There are two significant abnormal transitions observed in metallic glass forming liquids (MGFLs), i.e., liquid-liquid transition (LLT) above liquidus temperature and fragile-to-strong (F-S) transition in supercooled region. In this study, we focus on the correlation between LLT and F-S transition in Fe-based soft magnetic metallic glasses (MGs) for the first time. We find that the more distinct the LLT is, the weaker is the F-S transition, and the smaller is the glass forming ability (GFA). By employing molecular dynamics simulation, we identify that this relationship is due to the inherent correlated evolution trends of crystal-like clusters between the LLT and the F-S transition regions. Moreover, we analyze a general rule regarding the LLT and F-S transition in MGs, along with their composition-dependent peculiarities. This work sheds light on the process of liquid-solid inheritance of different MGs, and deepens the understanding of the liquid dynamics of MGs and their following GFA.

P T-symmetry breaking in dual-core phosphate-glass photonic crystal fibers.

We investigate the properties of a soft glass dual-core photonic crystal fiber for application in multicore waveguiding with balanced gain and loss. Its base material is a phosphate glass in a P2O5-Al2O3-Yb2O3-BaO-ZnO-MgO-Na2O oxide system. The separated gain and loss cores are realized with two cores with ytterbium and copper doping of the base phosphate glass. The ytterbium-doped core supports a laser (gain) activity under excitation with a pump at 1000 nm wavelength, while the CuO-doped is responsible for strong attenuation at the same wavelength. We establish conditions for an exact balance between gain and loss and investigate pulse propagation by solving a system of coupled generalized nonlinear Schrödinger equations. We predict two states of light under excitation with hyperbolic secant pulses centered at 1000 nm: 1) linear oscillation of the pulse energy between gain and loss core (P T-symmetry state), with strong power attenuation; 2) retention of the pulse in the excited gain core (broken P T-symmetry), with very modest attenuation. The optimal pulse energy levels were identified to be 100 pJ (first state) and 430 pJ (second state).

Acoustically transparent polybutadiene-based polyurethane encapsulants for deep-sea and transducers

Copolyether polyurethane (PUR), as a typical encapsulation material, is widely used for underwater acoustic transducers. Two novel types of polybutadiene-based PURs were prepared using a one-step method and compared with copolyether PURs. The polybutadiene-based PUR exhibited excellent mechanical properties. Epoxidized hydroxyl-terminated polybutadiene (EHTPB)–based PUR exhibited tensile strength and hardness of up to 17.3 MPa and Shore A95, respectively, which were 76.5% and 13.3% higher than those of copolyether PURs. The molecular chain of hydroxyl-terminated polybutadiene (HTPB)-based PUR exhibited good flexibility, a soft segment glass transition temperature (Tg) (approximately -52 °C), and complete microphase separation. Compared with HTPB-based PUR, EHTPB-based PUR exhibited a higher molecular chain rigidity and a lower degree of microphase separation. The insertion losses of HTPB-based PUR at 350 and 700 kHz were 69.8 dB/m and 204.6 dB/m, respectively, which were 57.4% and 47.1% lower than those of copolymer PUR. The water absorption and water vapor transmission coefficient of HTPB-based PUR were an order of magnitude lower than those of copolymer PUR. EHTPB-based and copolymer PURs exhibited similar insertion losses at 350 kHz. EHTPB-based PUR exhibited the lowest water vapor transmission coefficient of 7.2 × 10−14 g·cm/cm2·s·Pa, which was approximately 1/15th of that of copolyether PUR.

Research Progress of Mid-infrared Supercontinuum Generation Based on Soft Glass Fiber

Research Progress of Mid-infrared Supercontinuum Generation Based on Soft Glass Fiber

Generation of high-order optical vortices with nanostructured phase masks

We report theoretical and experimental studies on generation of high-order optical vortex beams using fiber-based nanostructured gradient index converters. The components were made of two types of in-house developed soft glasses with lead, bismuth, gallium compositions to ensure the high refractive contrast of the synthesized glasses. As a result, the vortex components, fabricated using the stack-and-draw method, allow converting Gaussian beam into vortex beams with high-order topological charges in the visible and near-infrared regions. We experimentally verified the formation of optical vortex beams with topological charge up to 5 by using the free-space binary-nanostructured vortex components. In addition, the vortex converter integrated into the standard fiber tip generated optical vortex beams with topological charge up to 4.

Mid-infrared second-harmonic generation and its red-shift signal induced by cross-phase modulation in an AsSe2 soft glass microstructured optical fiber

In this study, we investigate an AsSe2 soft glass microstructured optical fiber (MOF) featuring a hexagonal arrangement of six holes. The MOF is subjected to femtosecond laser pumping, employing a pump wavelength range spanning from 3950 nm to 4100 nm. Our experimental results reveal an intriguing outcome: a tunable mid-infrared second-harmonic generation (SHG) effect is observed, yielding a wavelength range of ∼ 1980 nm to ∼ 2203 nm. The maximum conversion efficiency is achieved at 4100 nm with a power of 130 mW, which can be up to 9.2E-5. The observed SHG is primarily due to the surface nonlinearity polarization at the core-cladding interface. Additionally, we increase the additional degrees of freedom of the SH signal by strong third-order nonlinearity, and demonstrate that strong self-phase modulation (SPM) of pump and cross-phase modulation (XPM) of SH signal help broaden the SH signal by means of generating new wavelength lobes. To the best of our knowledge, this is the first time that strong XPM-based SH signal is observed in an optical fiber in the mid-infrared wavelength region. The realized strong second-order and third-order nonlinearity might expand the fundamental physical mechanism of SHG in optical fiber especially in mid-infrared region, which would have important applications in telecommunications, laser technology, and quantum photonics.

Soft glass optical fiber characterization with X-ray computed microtomography

The high loss due to the presence of strong phonon resonances makes silica fibers unfit for applications in the mid-infrared spectral range. This has led to the development of specialty optical fibers, based on novel materials and manufacturing techniques. In some cases, the characterization of these new fibers by means of standard techniques may be challenging. Fiber manufacturers would strongly benefit from a tool, which is capable of checking the geometrical and optical properties of fibers (either after fiber drawing, or even in real-time, during the drawing process). Here, we propose and demonstrate that absorption contrast X-ray computed microtomography is a non-destructive technique, capable of characterizing both geometrical and optical properties of specialty optical fibers. We experimentally verified that the tomographic intensity profile in the fiber core has the same shape as the refractive index profile, which we determined via energy-dispersed X-ray spectroscopy. We tested step- and graded-index soft glass fibers, both purchased and made in-house. Owing to the presence of high atomic number elements, which provide higher X-ray cross-section, soft glasses were more suitable than silica for their characterization via X-ray computed microtomography.

A life off the beaten track in biomechanics: Imperfect elasticity, cytoskeletal glassiness, and epithelial unjamming.

Textbook descriptions of elasticity, viscosity, and viscoelasticity fail to account for certain mechanical behaviors that typify soft living matter. Here, we consider three examples. First, strong empirical evidence suggests that within lung parenchymal tissues, the frictional stresses expressed at the microscale are fundamentally not of viscous origin. Second, the cytoskeleton (CSK) of the airway smooth muscle cell, as well as that of all eukaryotic cells, is more solid-like than fluid-like, yet its elastic modulus is softer than the softest of soft rubbers by a factor of 104-105. Moreover, the eukaryotic CSK expresses power law rheology, innate malleability, and fluidization when sheared. For these reasons, taken together, the CSK of the living eukaryotic cell is reminiscent of the class of materials called soft glasses, thus likening it to inert materials such as clays, pastes slurries, emulsions, and foams. Third, the cellular collective comprising a confluent epithelial layer can become solid-like and jammed, fluid-like and unjammed, or something in between. Esoteric though each may seem, these discoveries are consequential insofar as they impact our understanding of bronchospasm and wound healing as well as cancer cell invasion and embryonic development. Moreover, there are reasons to suspect that certain of these phenomena first arose in the early protist as a result of evolutionary pressures exerted by the primordial microenvironment. We have hypothesized, further, that each then became passed down virtually unchanged to the present day as a conserved core process. These topics are addressed here not only because they are interesting but also because they track the journey of one laboratory along a path less traveled by.

3D soft glass printing of preforms for microstructured optical fibers

We report on the development of a 3D printing process dedicated to the production of soft glass optical fibers. Direct printing with a miniaturized crucible for melting glass blocks with a pneumatic extrusion head was established. For 3D printing, a developed in-house heavy metal oxide glass was used. Contrary to previous studies on 3D printing of optical fiber preforms, the proposed process is based on the deposition of straight horizontally-oriented lines with a diameter of 300–500 µm to replace standard stack-and-draw manual assembly technique typically used in the development of microstructured optical fiber preforms. A test fiber preform composed of 2500 microrods with dimensions of 60x25x25 mm was printed. As a proof of concept, a photonic crystal fiber preform composed of a solid core and 3 rings of air holes in photonic crystal cladding was printed, and further processed into the optical fiber using a standard fiber drawing tower. We measured a single mode performance of fabricated fibers at 1.55 µm, and flat dispersion in the range of 1.6 – 2.2 µm with zero dispersion wavelength at 1.70 µm.

Theoretical Study of Multicascade Raman Microlasers Based on TeO2–WO3–Bi2O3 Glass

The development and investigation of miniature narrow-line coherent light sources based on microresonators with low-power-consumption whispering gallery modes (WGMs) is an actual trend in modern photonics. Raman WGM microlasers can operate at wavelengths inaccessible to traditional laser media and provide a huge pump frequency tuning range. Here, we propose and theoretically study multicascade Raman microlasers based on soft tellurite TeO2–WO3–Bi2O3 glass WGM microresonators (microspheres) which can operate in the near-IR and mid-IR with the pump in the telecommunication range. Thanks to a large Raman gain (120 times exceeding the maximum Raman gain of silica glass) and a huge Raman frequency shift of 27.5 THz for this glass, the Raman waves at 1.83 µm, 2.21 µm, 2.77 µm, and 3.7 µm in the first, second, third, and fourth cascades, respectively, are theoretically demonstrated with a pump at 1.57 µm. We analyze in detail the influence of different factors on the characteristics of the generated Raman waves, such as microsphere diameters, Q-factors, pump powers, and detuning of the pump frequency from exact resonance. We also solve a thermo-optical problem to show that the temperature of a soft glass microresonator heated due to partial thermalization of pump power remains below the glass transition temperature. To the best of our knowledge, mid-IR tellurite glass Raman WGM microlasers have not been studied before.

Nonlinearity shaping in nanostructured glass-diamond hybrid materials for optical fiber preforms

Nanodiamond integration with optical fibers has proved a compelling methodology for magneto-optics. We reveal that the applicability of nanodiamonds in nonlinear optics goes beyond the previous demonstrations of frequency converters. Instead, we exploit the recently reported volumetric integration of nanodiamonds along the optical fiber core and show that the nonlinear response of glasses can be manipulated by nanodiamonds. By taking the mature z-scan approach we measure the nonlinear absorption and nonlinear refraction of three dielectric materials containing nanodiamonds in different concentrations and sizes. The work begins with nanodiamond-water suspensions, which offer the advantage of rapidly assessing the dependence of the nonlinear refractive index on the nano-particle concentration and size. Subsequently we investigate two fiber preforms based on silica and soft glass doped with nanodiamonds to evaluate the feasibility of nonlinearity shaping. We achieve a nearly 20% reduction of the nonlinear refractive index of fused silica containing trace amounts of nanodiamonds relative to a pristine reference. The demonstration of such a noticeable impact on the nonlinear response of the key optical material widely accepted by ultrafast optics practitioners provides a guideline for future work on the novel concept of negative nonlinearity fibers, which could disrupt the established chromatic dispersion-nonlinearity landscape.

Visible to Mid-IR Supercontinuum Generation in Cascaded PCF-Germanate Fiber Using Femtosecond Yb-Fiber Pump

Broadband supercontinuum (SC) fiber sources covering the mid-IR range have many significant applications, largely due to their compactness, reliability, and ease of use. However, most of the existing SC fiber sources cannot boast of either high reliability or a wide bandwidth. Thus, supercontinuum sources based on silica fibers are robust, but are not capable of generating SC in the mid-IR range. Sources based on soft glasses (tellurite, chalcogenide, etc.) generate broadband SC in the mid-IR range but are not used commercially, due to the poor mechanical and chemical characteristics of such fibers. In this work, we propose a new approach consisting of cascade generation of a supercontinuum sequentially in a silica photonic crystal fiber (PCF) and a germanate fiber. Using a standard ytterbium chirped-pulse amplification (CPA) laser system for pumping, we have demonstrated a supercontinuum in the range of 450–2950 nm in PCF and germanate fiber firmly connected by a standard fusion splicing technique. Further optimization of the cascade pump will make it possible to create a compact and reliable all-fiber SC source from the visible to mid-IR range.

Investigation by ESR Spectroscopy of Biology Active Electron-Rich 1,10-Phenanthrocyanines of d-Elements (Soft Colloidal Glasses)

Investigation by ESR Spectroscopy of Biology Active Electron-Rich 1,10-Phenanthrocyanines of d-Elements (Soft Colloidal Glasses)

Hollow Core Double-Clad Fiber Coupler for Nonlinear Micro-Endoscopy

We report the design, fabrication and characterization of the first hollow core double-clad fiber coupler for nonlinear micro-endoscopy. It is made of a pure silica negative curvature hollow core double-clad fiber and a highly multimode fiber fused along each other. The fabrication of such a coupler was made possible thanks to the use of a soft (borosilicate) glass multimode fiber which can be fused along the negative curvature fiber without altering its geometry, thanks to its much lower fusion temperature. A 60% power transfer from the double-clad fiber to the multimode one was measured at 500 nm. Demonstration of two-photon fluorescence and second harmonic generation imaging was performed on unlabeled biological tissues with an endoscopic head mounted on the hollow core double-clad fiber coupler to demonstrate its applicability. This device greatly simplifies the integration of nonlinear micro-endoscopes based on hollow core double clad fibers.

Dual network interpenetrating degradable waterborne polyurethanes with hydrogen bonded cross‐linked modified β‐cyclodextrin hydrophobic cavities

AbstractThe study gives an investigation on the properties of β‐cyclodextrin (β‐CD) waterborne polyurethane (WPU) composites with cross‐linked network structure and hydrogen bonding system. The polyurethane films modified with β‐CD/PEG exhibit superior thermal stability and biodegradability, it is capable to be applied to bio‐degradable plastic coatings. To improve the distribution of β‐CD in WPU, the β‐CD was modified by three different molecular weights of polyethylene glycol hydrophile (PEG). Since the chain segments and hydrophilic hydroxyl groups of PEG interact with the hydrophobic cavities and edges of β‐CD to form new complexes, thus enhancing the flexibility and structural integrity of WPU chains and conferring better biological properties. The analysis focuses on the changes of thermal stability and biodegradability after modification. The results indicated that the temperature of maximum thermal weight loss rate (Tmax) of β‐CD/PEG/WPU composites reached 394.1°C and the soft segment glass transition temperature (Tg) was −42.4°C after the introduction of β‐CD/PEG. Both are significantly improved compared to WPU, with degradation rates of 31.2% in lipase PBS solution and 14.8% in soil, and can therefore be better applied to current medical devices and biodegradable coatings, as well as other bio‐environmental areas.