Biodetection Based on Fluorescence Quenching and Surface-Enhanced Fluorescence Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 224

metal-clad waveguide sample versus a non-corrugated one. 41 With
this corrugated metal-clad waveguide sample, the directionally
scattered bound-mode features are clearly visible. The emission
features can be attributed to the out-coupling of the three waveguide
modes (two transverse magnetically polarized modes and one
transverse electrically polarized mode). The prominent sharp peak
at θ ≈ 15° is associated with the SPP mode (i.e., the lowest transverse
magnetic-polarized-polarized mode). The direction of the light beam
is highly directional, following the moment conservation relation
that can be quite interesting to increase signal to noise ratios.

(A) (B)

Figure 10.6 Measured effective enhancement factor versus emission
angle θ for a corrugated metal-clad sample. The excitation
angle is θ exc = 45°. The metal-clad waveguide is composed
of glass/Ag/LiF/dye/air. The LiF thickness is d = 300 nm.
(A) On a uncorrugated sample. (B) On a corrugated sample,
the grating period is 640 nm and the grating depth is about
100 nm. Reprinted with permission from Ref. 41.

The eficiency with which a light beam can be recovered by
scattering from a corrugated surface can be as high as 80% for the
SPP propagating normal to the grooves. 42 This eficiency reaches
an average value of 60% independent of the SPP direction using a
bi-grating. 43 Recovering the energy transferred to the SPP modes by
using grating couplers effectively increases the yield of light emitting
diodes (LED), which necessarily incorporate metal contacts for
eficient electron injection. 44,45 The presence of the grating directly
affects the spontaneous emission of the emitters themselves since the
photonic mode density they experience will necessarily be different
from the planar case due to the different boundary conditions. Both
the distance dependence of the lifetime and the spatial distribution
of the emitted light signiicantly change upon the introduction of
a corrugation quite apart from the Bragg-scattered bound-mode
features. 46