Large Raman Gain in a Stable Nanocomposite Based on Niobiosilicate Glass

Abstract

Nanocomposities are random media containing domains or inclusions that are on the nanometric size scale. The optical properties of composite materials can be adjusted by controlling the constituents and morphology of the composite structure. The optical nanocomposite approach offers opportunities to produce high-performance and relatively low-cost optoelectronic media suitable for many applications. 1 "Stimulated Raman scattering (SRS)" is one of the first discovered nonlinear optical effects: a pump laser beam enters a nonlinear medium and spontaneous generation and amplification lead to a beam at a frequency different from the pump. SRS belongs to a class of nonlinear optical processes that can be called quasi-resonant. Although none of the fields is in resonance with the vibrations in the lattice of the medium (optical phonons), the difference between the pump and generated beam equals the transition frequency. 2 SRS is used in tunable laser development, high energy pulse compression, etc. One of the most important perspectives is the realization of micro/nanosources, with improved performances.In bulk semiconductors, lasing by SRS was first discovered in GaP. 3 Most recently, Raman lasers have been demonstrated in silicon microwaveguides. 4 SRS from spherical droplets and microspheres, with diameters 5À20 μm, has been also observed using both pulsed and continuous wave probe beams. 5 Except for a report of SRS from individual single walled carbon nanotubes, 6 the observation of SRS from semiconductor nanowires 7 and from silicon nanocrystals, 8,9 we find no other evidence for this important nonlinear optic effect in nanostructured materials.In this paper, the microstructural and the optical characterizations of glasses with composition 30K 2 O 3 30Nb 2 O 5 3 40 SiO 2 (KNS 30À30À40) with different thermal treatments were carried out by differential thermal analysis (DTA), highresolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ellipsometry, and Raman spectroscopy. Our findings prove that as a consequence of the thermal treatment, a nanostructuring process is obtained, which can be considered a powerful tool to make functional nanocomposite glassy materials especially for optical applications. 10,11 In addition, strong changes in the Raman spectra of nanocomposite material with respect to KNS glass are proved and discussed. Finally, a significant enhancement of Raman gain (up to 25 times higher) and of its bandwidth of both KNS glasses and nanocomposite material with respect to SiO 2 glass is reported. ABSTRACT:The optical properties of composite materials can be adjusted by controlling the constituents and morphology of the composite structure. The optical nanocomposite approach offers opportunities to produce high-performance and relatively low-cost optoelectronic media suitable for many applications. In this paper, a nanocomposite material obtained by a high niobium content glass belonging to the K 2 OÀNb 2 O 5 ÀSiO 2 (KNS) glass-forming system is prepared and characterized. We focu...

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