Anomalous behavior of the second and third harmonics generated by femtosecond Cr:forsterite laser pulses in SiC-polymer nanocomposite materials as functions of the SiC nanopowder content

• Published in: Journal of Raman spectroscopy 2003-12, Vol.34 (12), p.999-1006
• Main Authors: Konorov, S. O., Akimov, D. A., Ivanov, A. A., Alfimov, M. V., Zabotnov, S. V., Sidorov-Biryukov, D. A., Fedotov, A. B., Podshivalov, A. A., Fornarini, L., Carpanese, M., Avella, M., Errico, M. E., Fantoni, R., Zheltikov, A. M.
• Format: Article
• Language: English
• Subjects: Agglomeration; femtosecond pulses; harmonic generation; Harmonic generations; Nanocomposite materials; Nanocomposites; nanocrystals; Nanomaterials; Nanostructure; Polymethyl methacrylates; Silicon carbide
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.1082

Femtosecond pulses of 1.25 µm Cr:forsterite laser radiation were used to study second‐ and third‐harmonic generation in silicon carbide nanopowders embedded in a poly(methyl methacrylate) (PMMA) film. Harmonic generation processes extend the analytical and sensing abilities of light‐scattering techniques, including Raman spectroscopy, offering a convenient and efficient approach to the analysis of nanocomposite materials where nanoparticles tend to agglomerate, masking informative features in Raman spectra. The second‐ and third‐harmonic yields are shown to display an anomalous, counterintuitive behavior as functions of the SiC nanopowder content in a polymer film. Whereas harmonic generation in polymer films with a high content of SiC nanocrystals is quenched by the absorption of agglomerating nanoparticles, the influence of absorption is less detrimental in nanocomposite films with a lower SiC content, leading to the growth of the second‐ and third‐harmonic yields. Nanocomposite films with a lower SiC content are also characterized by a higher breakdown threshold, allowing pump pulses with higher fluences to be applied for more efficient harmonic generation. Copyright © 2003 John Wiley & Sons, Ltd.