Ring-shaped image field

Figure 21. Six sequential images of the same sample area of individual carbocyanine dye molecules spread over a polymethylmethacrylate (PMMA) film as recorded by scanning near field optical microscopy. The image dimensions are 2.3 x 2.7-/nn cut out from 4 x 4-fim records of 256 x 256 data points. The excitation polarization was random in (A-D) and linear along y and x, respectively, in ( ) and (F). The emission polarization was measured along y and x in (B) and (C) and not otherwise. Some fluorescence spots are labeled for discussion in the text. The various shapes of the fluorescence peaks (circular spots, rings, arcs, and double arcs) are striking. These shapes can be explained by molecular dipoles being excited by the inhomogeneous electric field at the aperture. (Adopted from [83].)...

Fig. 4.63. A cut-away view of the Theimo Fisher Orbitrap mass analyzer. Ions are moving in spirals around a spindle-hke-shaped central electrode (a) that creates an axial field gradient. An outer electrode (b) is split in half by an insulating ceramic ring (c). An image current induced by moving ions is detected via a differential amplifier between the two halves of the outer orbitrap electrode. The m/z of different ions in the orbitrap can be determined from respective frequencies of oscillation after a Fourier transform. Reproduced from Ref. [206] with permission. Wiley-VCH, Weinheim, 2006.

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