6 Advanced Function Control of Photochemical Reactions …
99
a rectangular nanovoid (Fig. 6.4a, right), induces electromagnetic modes similar to
those of the nanowire. Babinet’s principle in electromagnetism states that the spectral
feature of the transmittance of a metal nanowire exhibits inverse with respect to the
transmittance of the metal nanovoid [40, 46]. This principle also states that the
electric field distributions induced in the metal nanowire coincide with the magnetic
field distributions inside the metal nanovoid when the structures are illuminated
by complementary polarized light. Figure 6.4c shows the simulated magnetic field
distribution inside the metal nanovoid. The spatial pattern in Fig. 6.4c is in good
agreement with that observed in Fig. 6.4b. This agreement theoretically demonstrates
that Babinet’s principle is applicable to a plasmonic system. This result also supports
that strong magnetic fields inside the nanovoid can boost magnetic dipole responses
in a molecular system.
To utilize the strong electromagnetic fields in metal nanowires and nanovoids in
practical applications, the optical complementarity in the near-field region needs to be
elucidated. For this purpose, we examined the genuine near-field transmission spectra
of a metal nanowire and nanovoid with same dimensions [47]. An ordinary near-field
transmission spectrum measured by the aperture-type SNOM contains both near- and
far-field components because the near-field optical fiber probe generates near- and
far-field components of light. Therefore, the far-field component has to be removed
from the ordinary near-field transmission spectrum to evaluate the genuine nearfield extinction spectrum. Figure 6.5 shows the genuine near-field extinction spectra
of the gold nanowire (red) and nanovoid (blue). The spectral features of the gold
nanowire in the figure are reasonably consistent with the inverted spectral features
of the nanovoid for wavelengths range longer than 620 nm. This result implies that
the Babinet’s principle is applicable even in the near-field optical region. It can also
Fig. 6.5 Near-field
extinction spectra of a gold
nanowire and nanovoid
obtained by subtracting the
far-field transmission spectra
from the near-field ones [47]
99
a rectangular nanovoid (Fig. 6.4a, right), induces electromagnetic modes similar to
those of the nanowire. Babinet’s principle in electromagnetism states that the spectral
feature of the transmittance of a metal nanowire exhibits inverse with respect to the
transmittance of the metal nanovoid [40, 46]. This principle also states that the
electric field distributions induced in the metal nanowire coincide with the magnetic
field distributions inside the metal nanovoid when the structures are illuminated
by complementary polarized light. Figure 6.4c shows the simulated magnetic field
distribution inside the metal nanovoid. The spatial pattern in Fig. 6.4c is in good
agreement with that observed in Fig. 6.4b. This agreement theoretically demonstrates
that Babinet’s principle is applicable to a plasmonic system. This result also supports
that strong magnetic fields inside the nanovoid can boost magnetic dipole responses
in a molecular system.
To utilize the strong electromagnetic fields in metal nanowires and nanovoids in
practical applications, the optical complementarity in the near-field region needs to be
elucidated. For this purpose, we examined the genuine near-field transmission spectra
of a metal nanowire and nanovoid with same dimensions [47]. An ordinary near-field
transmission spectrum measured by the aperture-type SNOM contains both near- and
far-field components because the near-field optical fiber probe generates near- and
far-field components of light. Therefore, the far-field component has to be removed
from the ordinary near-field transmission spectrum to evaluate the genuine nearfield extinction spectrum. Figure 6.5 shows the genuine near-field extinction spectra
of the gold nanowire (red) and nanovoid (blue). The spectral features of the gold
nanowire in the figure are reasonably consistent with the inverted spectral features
of the nanovoid for wavelengths range longer than 620 nm. This result implies that
the Babinet’s principle is applicable even in the near-field optical region. It can also
Fig. 6.5 Near-field
extinction spectra of a gold
nanowire and nanovoid
obtained by subtracting the
far-field transmission spectra
from the near-field ones [47]