Nano-Holographic Interferometry for In-Vivo Observations - Biomedical Optical Phase Microscopy and Nanoscopy - page 367

Figure 17.16
Spherical nanoparticle of estimated diameter 187 nm and numerical simulations. (A) Original
image; (B) average intensity image; (C) numerical simulation of whispering modes; (D) average
intensity of numerical simulation [13] .

numerical solution for the WGM of a polystyrene sphere of diameter 1.4 m, while

Figure 17.16D shows the average intensity. There is good agreement between the
experimental results and numerical simulation. The electromagnetic resonance occurs at the
wavelength λ 5 386 nm which corresponds to UV radiation. The color camera is sensitive
to this frequency and Figure 17.15C shows the color picture of the D 5 150 nm nanosphere;
the observed color corresponds approximately to the resonance wavelength mentioned
above.

μ

Four spherical particles with radius ranging between 150 and 228 nm were analyzed. For
example, Figure 17.17 shows the different stages involved by the determination of the
D 5 150 nm nanoparticle. The FT of the image is shown in Figure 17.17A while
Figure 17.17B shows the FT of the real part of the image (see Section 17.1 , Eq. (17.8) ).
Figure 17.17C shows the intensity distribution of the order 0. Different peaks corresponding
to fringe systems present in the image can be observed. Figure 17.17D and E shows the
cross-sections of the zero order with the corresponding peaks observed in Figure 17.17C .
These patterns are similar to those observed in the case of the prismatic nanocrystals [23] .
The gray-level intensity decays from 255 to 20 within 75 nm; this quantity corresponds
to the radius of the nanosphere.

An alternative way to determine diameter from experimental data is based on the WGM
properties that relate the diameter or radius of the nanosphere to the standing waves which
in turn are characterized by the number of zero nodes or the number of maxima. These
numbers depend on the index of refraction and on the radius of the nanosphere. The
numerical solution of the WG mode of polystyrene sphere developed by Pack [26] was
utilized in this study as the resonance modes occur approximately at the same wavelength,
λ 5 386 nm. Figure 17.18A shows the equatorial wavelength of the WG plotted versus the
particle radius. The experimentally measured wavelengths are plotted in a graph that
includes the numerically computed value (radius of 700 nm). Very good correlation was
obtained showing that the edge detection gradient utilized yields values that are consistent