Baltog, I., Baibarac, M., Smaranda, I. & Lefrant, S. (2011) Abnormal anti-Stokes Raman emission as a coherent anti-Stokes Raman scattering-like process in disordered media. J. Phys. B-At. Mol. Opt. Phys. 44 095401.
Added by: Laurent Cournède (2016-03-10 21:32:20)
|Type de référence: Article
Numéro d'identification (ISBN etc.): 0953-4075
Clé BibTeX: Baltog2011
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Mots-clés: carbon nanotubes, graphite, microscopy, spectroscopy
Créateurs: Baibarac, Baltog, Lefrant, Smaranda
Collection: J. Phys. B-At. Mol. Opt. Phys.
Consultations : 14/562
Indice de consultation : 1%
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In this paper, we demonstrate that, by continuous single beam excitation, one can generate an abnormal anti-Stokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering (CARS). The effect has been observed in materials which possess intrinsically nonlinear properties (LiNbO(3) and CdS), which have the electric susceptibility of third order different from zero, chi((3)) not equal 0, as well as in materials that become nonlinear under resonant optical excitation. In the latter case, we used poly-3,4-ethylendioxythiophene (PEDOT) in its undoped state deposited electrochemically on Au support. Raman studies corroborated with images of optical microscopy demonstrate that the production of AASRE is conditioned by the existence of a particular morphology of the sample able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, it was found that LiNbO3 and CdS in powder form as well as the PEDOT films layered on a rough Au substrate are suitable morphological forms. We explain AASRE as resulting from a wave-mixing mechanism of the incident laser light omega(l) with a Stokes-shifted Raman light omega(S) produced by a spontaneous Raman light scattering process, both strongly scattered inside the sample. As a CARS process, AASRE is conditioned by the achievement of phase-matching requirements, which makes the difference between the wave vectors of mixing light close to zero, Delta k = /2k(l) - k(S) - k(CARS) /approximate to 0. In condensed media, the small dispersion of the refractive index makes Delta k approximate to 0 so that the formation of a favourable phase-matching geometry may be accomplished even at a crossing angle. of travelling scattered light omega(l) and omega(S). For tightly focused beams, the requirement of phase matching relaxes; it is no longer sensitive to the Raman shift, so that a wide intense anti-Stokes Raman spectrum is observed at an angle larger than the Stokes Raman spectrum.
Added by: Laurent Cournède