Nano-Holographic Interferometry for In-Vivo Observations - Biomedical Optical Phase Microscopy and Nanoscopy - page 366

Figure 17.15
Spherical nanoparticle of estimated diameter 150 nm. (A) FT and zero-order filtered pattern; (B)
systems of fringes modulated by the particle; (C) color image of the particle [13] .
propagating around the diameter in opposite directions thus producing a standing wave with
seven nodes and six maxima. The light is trapped inside the particle and there is basically a
surface wave that only penetrates a small amount into the radial direction. The signal
recorded for this particle is noisier compared with the signal recorded for the prismatic
crystals. The noise increase is probably due to the Brownian motion of the spherical
particles. While the NaCl nanocrystals seem to grow attached to the supporting surface, the
nanospheres are not in the same condition. Of all resonant geometries, a sphere has the
capability of storing and confining energy in a small volume.
The method of depth determination utilized for the nanocrystals can also be applied to the
nanospheres. While in prismatic bodies made out of plane surfaces the pattern interpretation
is straightforward, in the case of curved surfaces, the analysis of the patterns is more
complex since light beams experience changes in trajectories determined by the laws of
refraction. In the case of a sphere, the analysis of the patterns can be performed in a way
similar to what is done in the analysis of the Ronchi test for lens aberrations. Figure 17.15
shows the distortion of a grating of pitch p 5 83.4 nm as it goes through the nanosphere.
The appearance of the observed fringes is similar to that observed in a Ronchi test. The
detailed application of this process is not included in this chapter for the sake of brevity.
Figure 17.16 shows a spherical particle of estimated diameter 187 nm, while Figure 17.16B
shows the average intensity. Figure 17.16C is taken from Pack [26] and shows the