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(a) Confocal optical microscope for simultaneously measuring spectra and imaging both sample surface and back focal plane of the collecting objective. (b) SEM image of a nanohole chain with , . (c) A series of scattering spectra under white light illumination of nanohole chains for 11 different interhole distances within (-axis on the left). The color red (blue) denotes high (low) intensity on the pseudocolor map, with maximum counts. The dashed black curve represents the dependence of SPP wavelength on free-space wavelength (-axis on the right) and the vertical black solid line at marks the scattering peak position of a single hole. The solid red curve is the corresponding single hole spectrum displaying the spectral width of the resonance. White open circles are the scattering peak positions for nanohole chains for varied , extracted from the results presented in Ref. 12.
Measured far-field radiation patterns (-space images) of the nanohole chains in pseudocolor map, where the color red (blue) denotes maximum (minimum) intensity. The full angular range is measured to be 89°. Narrowing of the pattern depending on the number of nanoholes per chain , 3, 8, 24, and 96, , with (a) , and (b) . (c) Series of -space images taken with the same acquisition time at for a fixed number of holes , for varying interhole distances . The fine fringes in the images originate from the propagation of highly coherent beams through imperfect optical elements, and are not related to beaming properties of the nanostructures.
(a) Dependence of intensity of light scattered by the nanohole chains for different excitation wavelengths (, 675, 780, and ) on the edge-to-edge distance between holes ; the data points are extracted from -space images; solid lines represent the data extracted from spectral measurements, shown in Fig. 1(c), for corresponding excitation wavelengths; the intensity data for is scaled by a factor of 4. (b) Comparison between beaming properties of nanohole chains and a modeled uniform chain of dipoles. Dipole-dipole distance obtained by fit to the model vs the actual center-to-center distance between the holes . The unity line is shown for comparison. Gray region shows the upper bound for the cumulative uncertainty resulting from fabrication, -space measurements and data processing.
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