12
M. I. Stockman
γ (tot) / γ
γ (tot) / γ
R (nm)
R (nm)
20 40 60 80 100
2
4
6
8
10
10 20 30 40 50
2
4
6
8
10
(a)
(b)
Fig. 1.4 Ratio of the rates of the total to internal loss, γ (tot)
γ, for a nanosphere as a function of its
radius R for a silver and b gold. The blue, green, and red lines correspond to the embedding dielectric
with ε d = 1, 2, and 5, respectively. The computations are made at the SP frequency ω sp , which
for these value of ε d is for silver ω sp = 3.5, 3.2, 2.5 eV, and for gold ω sp = 2.6, 2.4, 2.0 eV,
correspondingly
resonance and a dark resonance coexist in a certain spectral range—which is not
unlikely, because the bright resonances are spanning relatively wide wavelength
ranges—then their optical fields interfere. This interference significantly enhances
the manifestation of the dark resonance: it acquires strength from the bright resonance
and shows itself as an asymmetric peak-and-dip profile characteristic of a Fano
resonance. An important, albeit counterintuitive, property of the Fano resonances
is that, exactly at the frequency of the Fano dip, the hot spots of the nanolocalized
optical fields in the nanosystem are strongest. This is because at this frequency the
nanosystem emits minimal light intensity and, consequently, it does not wastefully
deplete the energy of the plasmon oscillations. This leads to a decreased radiative
loss and a high resonance quality factor.
Thus at the frequency of a Fano resonance, the radiative loss is significantly
suppressed. The width of the Fano resonances is ultimately determined by the internal
(Ohmic) losses described by Im ε m . Summarizing, the Fano resonances enable one
using relatively large nanoplasmonic particles or plasmonic metamaterials to achieve
narrow spectral features with high local fields. These can be applied to plasmonic
sensing and to produce spasers and nanolasers—see Sect. 1.5.
1.2.4 Other Important Issues of Plasmonics in Brief
There are other very important issues and directions of investigation in plasmonics
that we will not be able to review in any details in this chapter due to the limitations
of time and space. Below we will briefly list some of them.
M. I. Stockman
γ (tot) / γ
γ (tot) / γ
R (nm)
R (nm)
20 40 60 80 100
2
4
6
8
10
10 20 30 40 50
2
4
6
8
10
(a)
(b)
Fig. 1.4 Ratio of the rates of the total to internal loss, γ (tot)
γ, for a nanosphere as a function of its
radius R for a silver and b gold. The blue, green, and red lines correspond to the embedding dielectric
with ε d = 1, 2, and 5, respectively. The computations are made at the SP frequency ω sp , which
for these value of ε d is for silver ω sp = 3.5, 3.2, 2.5 eV, and for gold ω sp = 2.6, 2.4, 2.0 eV,
correspondingly
resonance and a dark resonance coexist in a certain spectral range—which is not
unlikely, because the bright resonances are spanning relatively wide wavelength
ranges—then their optical fields interfere. This interference significantly enhances
the manifestation of the dark resonance: it acquires strength from the bright resonance
and shows itself as an asymmetric peak-and-dip profile characteristic of a Fano
resonance. An important, albeit counterintuitive, property of the Fano resonances
is that, exactly at the frequency of the Fano dip, the hot spots of the nanolocalized
optical fields in the nanosystem are strongest. This is because at this frequency the
nanosystem emits minimal light intensity and, consequently, it does not wastefully
deplete the energy of the plasmon oscillations. This leads to a decreased radiative
loss and a high resonance quality factor.
Thus at the frequency of a Fano resonance, the radiative loss is significantly
suppressed. The width of the Fano resonances is ultimately determined by the internal
(Ohmic) losses described by Im ε m . Summarizing, the Fano resonances enable one
using relatively large nanoplasmonic particles or plasmonic metamaterials to achieve
narrow spectral features with high local fields. These can be applied to plasmonic
sensing and to produce spasers and nanolasers—see Sect. 1.5.
1.2.4 Other Important Issues of Plasmonics in Brief
There are other very important issues and directions of investigation in plasmonics
that we will not be able to review in any details in this chapter due to the limitations
of time and space. Below we will briefly list some of them.