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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. 7.

Fig. 7

Number of detected photons on a detector pixel as a function of the objective NA. Red curves are in a side-on/top illumination geometry with and without the use of a metallic substrate as indicated. With the dielectric substrate, we assume a Raman enhancement of ≈105. The dashed line indicates the maximum NA achievable in side-on illumination without the use of a parabolic mirror. The blue curve is under axial illumination (nsubstrate = noil = 1.5). The collection efficiency (inset) of the oil-immersion lens under axial illumination is based on results from ref. 106. The increased emission of light into the denser medium at angles greater than the critical angle is highly beneficial to TERS measurements. Thick green line represents the detection limit for 1 s acquisition time. It can be seen that side illumination benefits significantly from the increased field enhancement that arises due to plasmonic coupling to the metallic substrate. In contrast, the emission pattern of an emitter placed on a dielectric substrate significantly increases collection efficiency in an axial geometry when using oil-immersion objectives (Reprinted with permission from ref. 20. Copyright 2010 Elsevier.).