Arsenic Selenide Glass Research Articles

Mid-infrared supercontinuum generation in liquid-filled chalcogenide suspended core fiber

A design of liquid-filled suspended core microstructured optical fiber based on arsenic-selenide glass has been proposed to generate supercontinuum in the mid-infrared region. Two different non-linear liquids with high non-linear refractive index, such as chloroform and carbon disulfide have been employed in the air holes of the proposed design. From simulation results it is demonstrated that, ultra-wideband supercontinuum spectra ranging from 0.9 µm to 13 µm is made possible using only 2 mm long chloroform-filled suspended core fiber. • Numerically analyzed the ultra-wideband supercontinuum generation using liquid filled suspended core fiber • Two different non-linear liquids such as chloroform and carbon disulfide have been used to obtain wideband SC spectra • By using only 2 mm long chloroform-filled suspended core fiber, supercontinuum spectra from 0.9 µm to 13 µm is made possible • Higher order dispersion coefficients and confinement losses are analyzed for three different cases • The effect of different pulse duration and peak power are also analyzed

Se-H-free As2Se3 fiber and its spectral applications in the mid-infrared.

The complete removal of the impurities like Se-H in Se-based chalcogenide glasses has been challenging in the development of highly transparent chalcogenide glass fiber. In this paper, several purification methods, including dynamic distillation, static distillation, and combined distillation method, were adopted with an aim of purifying arsenic selenide glass with ultra-low content of the impurities. The experimental results demonstrated that the Se-H can be completely eliminated in the arsenic selenide glass host and fiber without the introduction of any chloride. We further explored the applications of such low loss and Se-H-free chalcogenide glass fiber in the mid-infrared. It was found that, using such a Se-H free fiber, a flattened supercontinuum spectrum above the -30 dB level from 1.2 to 13 µm was generated from the Se-H free fiber with a 5.5 µm laser pumping. The sensitivity was found to be improved 5.1 times for CO2 gas in the 3 to 6 µm wavelength range.

Thermal tuning of arsenic selenide glass thin films and devices.

We present a method of post-deposition tuning of the optical properties of thin film dielectric filters and mirrors containing chalcogenide glass (ChG) layers by thermally adjusting their refractive index. A common challenge associated with the use of ChG films in practical applications is that they suffer from slight run-to-run variations in optical properties resulting from hard-to-control changes in source material and deposition conditions. These variations lead to inconsistencies in optical constants, making the fabrication of devices with prescribed optical properties challenging. In this paper, we present new work that takes advantage of the large variation of a ChG films' refractive index as a function of annealing. We have carried out extensive characterization of the thermal index tuning and thickness change of arsenic selenide (As2Se3) ChG thin films and observed refractive index changes larger than 0.1 in some cases. We show results for refractive index as a function of annealing time and temperature and propose a model to describe this behavior based on bond rearrangement. We apply thermal refractive index tuning to permanently shift the resonance of a Fabry-Perot filter and the cutoff wavelength of a Bragg reflector. The Bragg reflector, consisting of alternating As2Se3 and CaF2 layers, exhibits high reflectance across a ∼550 nm band with only five layers. Modeling results are compared with spectroscopic measurements, demonstrating good agreement.

Effect of aluminum and tellurium tetrachloride addition on the loss of arsenic selenide optical fiber

Abstract Arsenic selenide glass optical fibers typically possess extrinsic absorption bands in the infrared wavelength regions associated with residual hydrogen and oxygen related impurities, despite using 6N purified elemental precursors. Consequently, special additives and refined processing steps are utilized in an attempt to reduce these and other impurities. We investigate the formation of particulate impurities during a purification process based on the addition of 0.1 wt% elemental aluminum (Al) and 0.2 wt% tellurium tetrachloride (TeCl 4 ) during glass synthesis. It was found that during purification and melting steps, Al reacts with TeCl 4 to form AlCl 3 , which in turn reacts with oxygen and hydrogen impurities and the fused quartz (SiO 2 ) ampoule to produce HCl and stable submicron Al 2 SiO 5 compounds in the As-Se glass and fibers. The intensity of the H-Se absorption band centered at 4.57 μm has been significantly reduced from 18 dB/m to 0.8 dB/m. Using thermodynamic data, we have identified stable Al 2 SiO 5 submicron inclusions in the glass and fibers. A two-step gettering process is proposed as a solution to eliminating these inclusions.

Structure of arsenic selenide glasses by Raman and 77Se NMR with a multivariate curve resolution approach

Solid-state Nuclear Magnetic Resonance and Raman data are usually reconstructed using devoted software. Most of the time, the experimental results must be compared to structural models obtained, for example, by Molecular Dynamics or Reverse Monte Carlo. This procedure is sophisticated, time consuming and requires specialized skills. In this paper, it is shown that chemometric unsupervised methods provide quickly interesting information from poorly resolved experimental data. In particular, it is shown that correlation maps and multivariate curve resolution enable to distinguish structural contributions and provide spectral reconstructions when applied to sets of 77Se solid-state NMR and Raman spectra of glasses with varying compositions in the AsxSe1 − x glassy system, corroborating previous works. Interestingly, such an approach may provide a new way to assign unknown Raman vibration modes.

Crossover between cooperative and fractal relaxation in complex glass-formers

Kinetics of physical aging at different temperatures is studied in situ in arsenic selenide glasses using high-precision differential scanning calorimetry technique. A well-expressed step-like behaviour in the enthalpy recovery kinetics is recorded for low aging temperatures. These fine features disappear when the aging temperature (Ta) approaches the glass transition temperature (Tg). The overall kinetics is described by stretched exponential function with stretching exponent close to 3/5 at Ta > ~0.95 Tg almost independent on glass composition, and 3/7 when the aging temperature drops to ~0.9 Tg. These values are consistent with the prediction of Phillips’ diffusion-to-traps model. Further decrease in aging temperature to ~0.85 Tg leads to the appearance of step-like behaviour and stretching exponent of 1/3 for the overall kinetics, which is the limiting value predicted by random walk on the fractal model. Such behavior is explained as crossover from homogeneous cooperative relaxation of non-percolating structural units to high-dimensional fractal relaxation within hierarchically-arranged two-stage physical aging model.

Preparation of low-loss core–clad As–Se glass fibers

Abstract Arsenic selenide glass with the low content of residual impurities (hydrogen ⩽0.02 ppm wt, oxygen 30 Se 70 –As 40 Se 60 glass compositions are drawn. The minimum optical loss in unclad As 35 Se 65 glass fiber of diameter 200 μm is 70 dB/km at wavelengths of 2.7 and 3.8 μm. The minimum optical loss in core–clad As 40 Se 60 /As 38 Se 62 glass fiber is 67 dB/km in the 6–6.5 μm spectral range, which is the best result for the core–clad As–Se glass fibers.

Structure of Arsenic Selenide Glasses Studied by NMR: Selenium Chain Length Distributions and the Flory Model

Five homogeneous arsenic selenide glasses with target compositions As2Se3, AsSe2, AsSe3, AsSe4.5, and AsSe6 were studied quantitatively by 77Se Carr–Purcell–Meiboom–Gill magic-angle spinning NMR and transmission electron microscopy–energy-dispersive X-ray spectroscopy. The entire set of NMR spectra is simultaneously fitted with six distinct environments taking into account the effect of first and second neighbors on the position of the 77Se resonance. The selenium chains are bound at each end to trivalent arsenic atoms, and the chain length distribution can be modeled with the Flory theory, which is well-known in polymer science and is used here for the first time to model the probability of finding each selenium environment in a selenide glass. No arsenic homopolar bond is detected in our experiments.

Structural and Topological Control on Physical Properties of Arsenic Selenide Glasses

The structures of Ge-doped arsenic selenide glasses with Se contents varying between 25 and 90 at. % are studied using a combination of high-resolution, two-dimensional (77)Se nuclear magnetic resonance (NMR) and Raman spectroscopy. The results indicate that, in contrast to the conventional wisdom, the compositional evolution of the structural connectivity in Se-excess glasses does not follow the chain-crossing model, and chemical order is likely violated with the formation of a small but significant fraction of As-As bonds. The addition of As to Se results in a nearly random cross-linking of Se chains by AsSe3 pyramids, and a highly chemically ordered network consisting primarily of corner-shared AsSe3 pyramids is formed at the stoichiometric composition. Further increase in As content, up to 40 at. % Se, results in the formation of a significant fraction of As4Se3 molecules with As-As homopolar bonds, and consequently the connectivity and packing efficiency of the network decrease and anharmonic interactions increase. Finally, in the highly As-rich region with <40 at. % Se, the relative concentration of the As4Se3 molecules decreases rapidly and large clusters of As atoms connected via Se-Se-As and As-Se-As linkages dominate. These three composition regions with distinct structural characteristics and the corresponding mixing entropy of the Se environments are reflected in the appearance of multiple extrema in the compositional variation of a wide range of physical properties of these glasses, including density, glass transition temperature, thermal expansivity, and fragility.

Step-wise kinetics of natural physical ageing in arsenic selenide glasses

The long-term kinetics of physical ageing at ambient temperature is studied in Se-rich As–Se glasses using the conventional differential scanning calorimetry technique. It is analysed through the changes in the structural relaxation parameters occurring during the glass-to-supercooled liquid transition in the heating mode. Along with the time dependences of the glass transition temperature (Tg) and partial area (A) under the endothermic relaxation peak, the enthalpy losses (ΔH) and calculated fictive temperature (TF) are analysed as key parameters, characterizing the kinetics of physical ageing. The latter is shown to have step-wise character, revealing some kinds of subsequent plateaus and steep regions. A phenomenological description of physical ageing in the investigated glasses is proposed on the basis of an alignment–shrinkage mechanism and first-order kinetic equations.

Purification of glass melts in the As-Se system with vacuum distillation

The behavior of macrocomponents and impurities during vacuum distillation of glass melts in the As-Se system with arsenic concentrations of 30 and 40 at % in closed and open systems has been investigated. The possibility of using vacuum distillation in an open system for purifying arsenic selenide glass melts from oxygen and hydrogen impurities has been demonstrated.

Composition dependence of the viscosity and other physical properties in the arsenic selenide glass system

The viscosity of the AsxSe100−x family of glasses has been measured for 10 ≤ x ≤ 40 using beam bending and parallel plate viscometry, and fit with the Vogel-Fulcher-Tamann (VFT) viscosity model. Measurement of other physical properties of the glasses, including the density, glass transition temperature, and coefficient of thermal expansion has been conducted in order to accurately calculate the viscosity as a function of temperature and glass composition. The variation in fragility of the glasses is explained in the context of frozen-in configurational entropy in the glasses. This configurational entropy has minima at the endpoints of the one-dimensional network of amorphous selenium and the fully three-dimensional network of As40Se60, and an apparent maximum at the composition As30Se70. The frozen-in configurational entropy can be well described by a modified entropy of mixing of two solid solutions model, implying that the topological contribution to configurational entropy is nearly constant across the composition space studied.

Study of microindentation cracks in bismuth-doped arsenic selenide glasses

Abstract The formation of radial cracks from Vickers indentations on the surfaces of both unirradiated and irradiated samples of (As1 − xBix)2Se3 glasses with x ≤ 0.1 is investigated as a function of indentation load P. It was found that radial cracks around indentations are produced on the surfaces of all samples at loads exceeding a particular applied load Pcapp but this threshold load is higher by a factor of 15 to 30 from the value of Pc calculated from the theoretical dependence of ratio c/d of crack length c measured from the center of indentation impression to indentation impression diagonal d on applied load P. By fitting the experimental P(c3/2) data in an expression relating c and P according to expanding cavity for elastic/plastic solid and from a theoretical expression relating load-independent hardness H and threshold load Pc for crack formation estimated from the experimental data of the dependence of c/d on P, the value of indentation fracture toughness KC of As2Se3 glasses, irrespective of Bi content in the samples and their irradiation, was found to be about 0.52 MPa⋅m1/2.

First time microwave synthesis of As 40Se 60 chalcogenide glass

Abstract Arsenic sulfide and arsenic selenide glasses, batched from elemental precursors in stoichiometric proportions, are synthesised in ≤ 35 min via microwave heating in a domestic microwave oven (DMO). The DMO products are compared with the stoichiometric glasses made by conventional resistive furnace melting using: X-ray diffraction (XRD); transmission electron microscopy with selected area electron diffraction (TEM-SAED); analytical scanning electron microscopy; optical microscopy; differential thermal analysis (DTA); and Fourier transform infrared spectroscopy. From XRD and TEM-SAED, only part of the DMO As–S product is amorphous and exhibits up to three DTA glass transitions (Tgs) showing that homogenisation has not taken place. In contrast, As40Se60 glass is readily prepared in the DMO and has similar properties to conventionally melted As40Se60 glass. Furthermore, the DMO As40Se60 glass can be patterned using hot embossing and drawn to fibre.

Coordination defects in bismuth-modified arsenic selenide glasses: High-resolution x-ray photoelectron spectroscopy measurements

The possibility of coordination defects formation in Bi-modified chalcogenide glasses is examined by high-resolution x-ray photoelectron spectroscopy. The results provide evidence for the formation of positively charged fourfold coordinated defects on As and Bi sites in glasses with low Bi concentration. At high Bi concentration, mixed ${\mathrm{As}}_{2}{\mathrm{Se}}_{3}\text{\ensuremath{-}}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ nanocrystallites are formed in the investigated Se-rich As-Se glasses.

Radiation-induced physical ageing of the structure of an arsenic–selenide glass

Abstract The effect of γ -irradiation (Co 60 sources) on 20 years stored As 10 Se 90 glass is studied using high-resolution X-ray photoelectron spectroscopy (XPS) technique. It is shown that high-energy irradiation treatment stimulates studied chalcogenide glasses (ChG) towards a more thermodynamically equilibrium state which cannot be attained when making glass by the conventional melt-quenching method.

Extrusion of hollow waveguide preforms with a one-dimensional photonic bandgap structure

An extrusion technique is used to make an all-dielectric, hollow waveguide preform. The structure consists of radially alternating dielectric layers of high/low refractive index pairs. By requiring that the two dielectric materials have a high index contrast, it is possible to make a preform that will have a photonic bandgap structure when drawn into a fiber optic. The preform is made by an extrusion process in which a stack-of-plates, composed of alternating disks of chalcogenide glass and a polymer, is extruded through a die into both solid and hollow-core structures. Laminar flow during extrusion forces the periodicity from an axial to a radial orientation in the final extruded preform. For these experiments the high index material was arsenic selenide glass (As2Se3,n=2.6) and the low index material was polysulfone (PSU,n=1.55), which gives an index contrast of 1.68.

Effect of heating on the optical loss in the As-Se glass fiber

The increase in the optical loss of the IR-transmitting arsenic-selenide glass fiber in the temperature range of 150/spl deg/C /spl ges/T/spl ges/ 20/spl deg/C was investigated. Between the wavelength region of 1.3 and 8 /spl mu/m, there is a small increase in the loss in which the contribution of free-carrier absorption is small. At high temperature T=150/spl deg/C and /spl lambda//spl ges/8 /spl mu/m, both the free-carrier and multiphonon absorption contributed to the total loss. From a practical perspective, the As-Se fiber loss increases only slightly under normal operating temperatures and so can still be used for many applications.

Fabrication of Arsenic Selenide Optical Fiber with Low Hydrogen Impurities

Arsenic selenide glass optical fibers typically possess extrinsic absorption bands in the infrared wavelength region associated with residual hydrogen and oxygen related impurities, despite using purified precursors. We report a purification process based on the addition of 0.1 wt% tellurium tetrachloride (TeCl4) to the glass. During melting, the chlorine from TeCl4 reacts with the hydrogen impurities to produce volatile products (e.g., HCl) that can be removed by subsequent dynamic distillation. The processing conditions have been modified accordingly to give very low H–Se impurity content. Consequently, the H–Se absorption band centered at 4.57 μm has been reduced from tens of dB/m to 0.2 dB/m.

Fabrication of Arsenic Sulfide Optical Fiber with Low Hydrogen Impurities

Arsenic sulfide glass optical fibers typically possess extrinsic absorption bands in the infrared wavelength region associated with residual hydrogen and oxygen related impurities, despite using purified precursors. We report a purification process based on the addition of tellurium tetrachloride (TeCl4) to the glass. During melting, the chlorine from TeCl4 reacts with the hydrogen impurities to produce volatile products (e.g., HCl) that can be removed by subsequent dynamic distillation. The processing conditions have been modified accordingly to produce optical fibers with significantly reduced loss due to hydrogen sulfide impurity content (1.5 dB/m).