Wesley A. King

Laboratory preparation of highly pure As2Se3 glass

Abstract Arsenic selenide glass samples have been prepared using a combination of heat treatment and distillation techniques to remove impurities. Transmission spectra of the samples in the infrared region (2.5–20 μm) were measured. The spectra indicate that the majority of absorbing oxide species can be removed by a simple heat treatment. Chemical analysis shows that distilled samples contain less silicon impurity, indicating that Si is most likely incorporated during tube sealing procedures. Increased transmission for the purified samples in the 10–11 μm range shows the necessity of purification to obtain glasses with good transparency for CO 2 laser applications. The highest transmission values at 10.6 μm are greater than those suggested by simple theoretical relations. The high refractive index at this wavelength results in additional contributions to the transmitted intensity, most probably due to sample lensing effects arising from non-parallel sample faces or misalignment of the sample in the spectrophotometer beam.

Structural properties of As2Se3 fibers

Abstract Nuclear quadrupole resonance (NQR) studies of rapidly-drawn fibers of glassy As 2 Se 3 reveal that significant structural changes occur as a function of draw rate. Pulsed 75 As NQR echo measurements have been performed on freshly prepared and aged samples of glassy As 2 Se 3 fibers at three different draw rates (5, 41 and 75 m/min). The 75 As NQR lineshapes exhibit systematic trends in both the linewidths and line asymmetrics. Fibers drawn at the most rapid rate exhibit a second resolved peak in the NQR lineshape that is attributed to the presence of AsAs bonds even though the glass is nominally stoichiometric. Presumably the AsAs ‘wrong bonds’ are compensated by the presence of SeSe bonds. Annealing the fibers for several hours near 200°C produces changes in the NQR lineshapes but does not result in NQR lineshapes that are indicative of the bulk glass. These results are consistent with measurements of structural relaxation as obtained from differential scanning calorimetry in glassy As 2 Se 3 fibers.

Nuclear quadrupole resonance spectra of drawing-induced crystallization in As2Se3 fibers

Pulsed 75 As nuclear quadrupole resonance (NQR) experiments performed on fibers of As 2 Se 3 drawn at various rates (>100 m/min) reveal structural changes from the bulk, well-annealed glass. In addition to the presence of As-As bonds in the nominally stoichiometric fibers, a distorted crystalline phase (<10% by volume) occurs at the largest draw rates. Because they are highly distorted, these crystallites are not observable by X-ray diffraction spectroscopy in almost all cases. On the other hand, the NQR experiments show these crystalline regions very clearly as small width components in the NQR spectra between 56 and 60 MHz. In addition to being strained, the imbedded crystallites are dominated by surface effects because they partially revert to the amorphous phase over time when stored at 300 K. The nature of the distortions in these crystallites and the kinetics of this counter-intuitive annealing behavior are not well determined. Because large draw rates are important in commercial production of fibers, the drawing-induced crystallization in this prototypical chalcogenide glass may have implications for the use of these materials in infrared transmission applications.