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Ultra-thin amorphous carbon (a-C) films are well established protective coatings of optical fibers. These coatings allow one to prevent degradation of the SiO2 fiber, which occurs due to diffusion of the water and hydrogen molecules into cladding and core. The a-C films typically contain impurities, such as oxygen and hydrogen, which are attached to organic moieties via chemical bonding. The formation of hydrogen- and oxygen-containing functional groups reduces the hermeticity of a-C coatings, and therefore, monitoring these impurities is of great importance. In this work, we develop a method for probing O- and H- containing moieties based on resonance anti-Stokes Raman spectroscopy. We measured Raman spectra of a-C films and observed that anti-Stokes to Stokes ratios of Raman peaks differ from those predicted by Boltzmann law. This effect caused by resonance enhancement of the anti-Stokes Raman scattering in defects of graphite-like crystals. To quantify this effect, we used a resonance factor, which is defined as a ratio of the anti-Stokes and Stokes scattering cross sections. We show that this indicator can be used to assess degree of enrichment/depletion of a-C with O- and H- containing functional groups. Understanding the physical mechanisms of the anomalous anti-Stokes Raman scattering will improve Raman thermometry.

This work is devoted to a study of temperature-dependent Raman scattering of amorphous carbon (a-C) thin films. An anomalous rise of the anti-Stokes intensity in respect to the Stokes intensity was observed. This result comes from the resonant enhancement of anti-Stokes scattering of defects of graphite-like crystals. The observed discrepancy is quantified through a coefficient, a, defined as a ratio of the anti-Stokes and Stokes scattering cross sections. Understanding the mechanism for anomalous enhancement of anti-Stokes scattering provides a way for correct probing the temperature of the a-C thin films exposed to cw laser illumination.

Azo-polymer materials found diverse applications in many interdisciplinary areas, including frequency conversion, surface relief grating and others. In such devices, stratified polymer systems are often used, in which each layer ranges from 5 nm to 100 nm in thickness. One of the key characteristics of the polymer is the glass transition temperature Tg, which indicates the thermal stability of polymer, depending on its thickness and environment. The method for determining Tg that used in this work is based on recording the dependence of the oscillation phase of an atomic-force microscope probe on the sample temperature. To study the possibility of determining the local Tg, a cross section of a multilayer polymer system, polyethylene/polyamide with the layer thicknesses of 50-100 nm, is used. Tg is measured by a change in the phase of oscillation of the cantilever, which is caused by the loss of energy of the cantilever due to the change in Gibbs energy of the polymer during the thermal expansion. It was possible to measure the local temperature within the glass transition points of the sample and for chemical identification methods used different areas of enhanced optical microscopy (nano - Raman and nano-IR).