Biomedical Engineering Reference
In-Depth Information
Figure 11.12
SEM micrographs of (a)
μ
spiral and (b)
π
spiral gold
nanoparticle arrays on a fused silica substrate. Measured far-field diffrac-
tion patterns for (c)
μ
spiral and (d)
π
spiral, taken from respective arrays
shown in Fig. 11.12a and b.
In Fig. 11.13a, we show the optical set-up used to measure
the complex far-field of scattered radiation from the fabricated
structures. A HeNe laser was utilized in these experiments and
weakly focused to a spot size of 50
μ
m, from the rear of the sample
and the scattered light from the array was collected by a 50X (NA
=
0.75) objective. Two additional lenses were added to image the
far-field at the plane of the CCD [47].
In order to measure the phase of the far-field radiation, a
referencebeamwasreflectedfromthepiezostagemountedmirrors,
expanded and directed to the CCD. Multiple interference patterns
were collected by increasing the piezo bias voltage, scanning the
phaseofthereference beam.Aphaseretrievalalgorithmwasfinally
usedtorecover thephase ofthescattered lightrelativetotheoneof
thereferencebeam.Theanalyticallycalculatedphaseofthefar-field
