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. Author manuscript; available in PMC: 2014 Feb 21.
Published in final edited form as: Chem Soc Rev. 2014 Feb 21;43(4):1248–1262. doi: 10.1039/c3cs60258c

Fig. 6.

Fig. 6

(a) Schematic of an experimental setup employing on-axis illumination of a transparent sample used to observe simultaneous Raman scattering and photoluminescence of carbon nanotubes.21 A sharp metal tip is positioned in a tightly focused radially polarized laser beam. The optical signal is detected either by two avalanche photodiodes (APDs) for the VIS and NIR spectral range or by a combination of a spectrograph and a CCD. (b) Side-illumination of the tip on top of a non-transparent substrate. (c) Focusing of light using a parabolic mirror with high numerical aperture. To generate a strong field component parallel to the tip axis required for efficient field enhancement, scheme (a) and (c) utilize a radially polarized laser mode.97-99