RESUMEN
The glass transition temperature is a key parameter of polymer coating layers that protect optical fibers, and it affects the proper function of the fibers in their service environment. Established protocols for glass transition temperature measurements are destructive, require samples of specific geometries, and may only be carried out offline. In this work, we report the nondestructive measurement of the glass transition temperature of an acrylate polymer coating layer over a working standard fiber. The method is based on forward stimulated Brillouin scattering. A large decrease in the modulus of the coating layer above the glass transition temperature manifests in the narrowing of the modal linewidths in the forward Brillouin scattering spectrum. The transition temperature agrees with the standard dynamic mechanical analysis of samples made of the same polymer. The protocol can be useful for coating materials research and development, production line quality assurance, and preventive maintenance.
RESUMEN
Micro attenuated total reflection (micro-ATR) spectra of bulk silica glass were investigated for a variety of samples, including fused quartz slides, an optical fiber preform, and a series of optical fiber claddings. The experiments were performed at varied distances between the internal reflection element (IRE) and the sample. At certain conditions, a surface polariton peak is observed in the region 1100-1160 cm(-1). The position of this peak is affected by the type of IRE (Ge, Si, ZnSe, or diamond), IRE-sample distance, and the material used as an interlayer between the IRE and the sample (air or Nujol). From the experimental data, the dielectric constant of silica is determined in the region between 1100 and 1160 cm(-1). The polariton peak is also observed when glass is coated with a thin (40 nm) layer of carbon. It has also been found that the polariton peak position is affected by the thermal history of the glass, and an attempt is made to correlate the observed changes with the glass fictive temperature.
RESUMEN
Micro-attenuated total reflectance (ATR) infrared spectroscopy is one of the few methods applicable for an in situ analysis of polymer coatings. In this method, the information is collected using an internal reflection element (IRE), which is brought into contact with the coated substrate. Perfect optical contact is hardly achievable for non-flat substrates and/or for those samples that cannot be well aligned with respect to the IRE. Consequently, the infrared peak intensities, their ratios, and all quantities calculated from the spectra become dependent upon the optical contact quality. In this work, we suggest a model that describes the peak intensities in terms of the optical contact. As an illustration, we apply this model to polymer-coated optical fibers. Relatively small diameters of tested fibers and their cylindrical shape result in imperfect optical contact between the sample and the IRE. Spectroscopic approaches of determining the degree of cure of polymer coatings are analyzed in view of the obtained results. Ways of minimizing the error induced by imperfect optical contact are suggested.