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6ALT'22
LASER-MATTER INTERACTION
LM-P-7
Enhanced Raman scattering in amorphous carbon films under cw laser irradiation
S. Saparina1, A. Gazizov 12, S. Kharintsevu
1-Kazan Federal University, Department Optics and Nanophotonics, Kremlevskaya 18, 420008, Kazan, Russia 2- Institute of Applied Research, Tatarstan Academy of Sciences, Bauman 20, 420111, Kazan, Russia
email address: sveta.saparina@yandex.ru
Ultra-thin amorphous carbon (a-C) films (10-100 nm) are well established protective coatings of optical fibers that operate in harsh environment. The formation of hydrogen- and oxygen-containing functional groups reduces the her-meticity of a-C coatings, and therefore, monitoring these impurities is of great importance [1]. In this work, we propose an approach for detecting of the hydrogen- and oxygen- containing functional groups in carbon composites.
In this work we observed anomalous features of Raman spectra of amorphous carbon films as the temperature varied. In particular, the magnitude of IaS/IS for the G band at room temperature was 1/10, whereas the value predicted by the Boltzmann law is 1/600 [2]. Moreover, the profile of the anti-Stokes spectrum is not mirror-symmetric with respect to the Stokes spectrum. We considered that this behavior can be attributed to the resonance Raman scattering and photo-induced heating of the a-C films under continuous wave laser excitation.
We first estimated the contributions of photo-heating in of IaS/IS ratio by investigating the Raman spectra at different laser power. The resonance Raman scattering was estimated by introducing a resonance factor as a ratio of anti-Stokes to Stokes scattering cross-sections [3]. We attribute the observed resonance Raman scattering with defect-induced modification of joint electronic density of states of a-C [4]. Thus, factor can be used to assess the degree of enrichment/ depletion of a-C with functional groups (hydroxyl, epoxy, carbonyl and carboxyl).
Understanding the physical mechanisms of the anomalous anti-Stokes Raman scattering will improve Raman ther-mometry.
This paper has been supported by the Kazan Federal University Strategic Academic Leadership Program (PRIOR-ITY-2030).
[1] S.V. Saparina, S.S. Kharintsev, A.I. Fishman, et.al., Water enrichment/depletion of amorphous carbon coatings probed by temperature-dependent dc electrical conductivity and Raman scattering, Appl. Surf. Sci., vol. 570, pp. 151052-151058, (2021).
[2] B.J. Kip and R.J. Meier, Determination of the Local Temperature at a Sample During Raman Experiments using Stokes and anti-Stokes Raman Bands, Appl. Spectrosc., vol. 44, pp. 707-711, (1990).
[3] G. Gordeev and S. Reich, Resonant anti-Stokes Raman Scattering in Single-Walled Carbon Nanotubes, Phys. Rev. B., vol. 96, p. 245415, (2007).
[4] P. Johari and VB. Shenoy, Modulating Optical Properties of Graphene Oxide: Role of Prominent Functional Groups, ACS Nano, vol. 5, pp. 7640-7647, (2011).
