Nano-Holographic Interferometry for In-Vivo Observations - Biomedical Optical Phase Microscopy and Nanoscopy - page 365

Figure 17.14
(A) Reconstruction of the NaCl nanocrystal of length 86 nm; (B) theoretical structure; (C) level
lines; (D) rotated cross-section of the upper face of the nanocrystal: the spacing between dotted
lines corresponds to size of three elementary cells [10] .
whispering-gallery modes (WGM). WGM result from light confinement due to TIR inside a
high-index spherical surface within a lower index medium and from resonance as the light
travels a round trip within the cavity with phase matching [24] . The WG modes are within
the Mie's family of solutions for resonant modes in light scattering by dielectric spheres.
The WG modes can be also derived from Maxwell's equations by imposing adequate
boundary conditions [25] . They can also be obtained as solutions of the Schrodinger-like
equation in quantum mechanics describing the evolution of a complex angular momentum
of a particle in a potential well. The WG modes form standing waves that can be recorded.
In the present case, since the FT of the spheres are available but the direct image is not, one
has to remember that, because of spherical symmetry, the FT will also be circular and the
WG modes will appear as bright spots since they are standing waves.
Figure 17.15A shows the diffraction pattern of a spherical nanoparticle of diameter 150 nm.
This image presents the typical whispering-gallery intensity distribution. Waves are