Tip-Enhanced Raman Spectroscopy
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Fig. 4 a Z-polarization generated through a z-polarizer. b Polarization perpendicular to the tip
axis, generated by focusing ordinary linearly polarized light
an angle larger than the critical angle, as illustrated in Fig. 5. Therefore, the total
internal reflection occurs, which enables the so-called evanescent illumination to the
tip apex, where no propagating light reaches the tip apex and it is illuminated only by
the evanescent light. This reduces the possible far-field Raman scattering from the
sample. Compared with the case without the mask, this evanescent illumination can
therefore eliminate the unwanted far-field background scattering from the sample as
Fig. 5 Evanescent
illumination at the tip apex
enabled by a spatial mask