122
H. Ishihara et al.
5.3.3 Optical Current
To gain a better understanding of the optical force that rotates the NP inside the
metallic nanocomplex, we considered the x-y component of the Poynting vector,
which is zero for plane wave light. This vector, which is also referred to as optical
current, contributes to the dissipative force exerted on the NP [62, 63]. The optical
current is classified into orbital and spin parts [63]. In Fig. 5.8 a, b, we depict the
orbital part of the time-averaged optical current inside the metallic nanocomplex
when the circularly polarized light with s = +1 is irradiated. Whether irradiating
only the manipulation light (resonant to the 0–1 transition) or only the pump light
(resonant to the 0–2 transition), the optical current flows clockwise inside the metallic
nanocomplex. These results are consistent with the rotational force discussed in
Fig. 5.7c, and also with the relation between population inversion and the rotational
direction of the NP. In addition, it is observed that the direction of the rotational flow
in the metallic nanocomplex depends on the direction of the optical current at the
four gap positions. If the manipulation scheme suggested here is realized, the basic
elements of manipulating the NP (pushing, pulling, and rotating) are also achieved.
This will introduce new technologies not only for nanofabrication but also for nanooptomechanics that involve chiral materials and highly sensitive and selective chiral
sensing.
5.4 Summary
Light–nanomatter chiral interaction has been a central subject of research in various domains for a long time. The development of nanofabrication technologies and
single-molecular detection techniques take the study of this domain to a new stage.
Particularly, the chiral interaction between light and metallic nanostructures has garnered attention because of its wide potential applications. Further, this phenomenon
is the basis of our understanding of the nonlocal optical response, which is beyond the
conventional model based on LWA or DA. For example, a strong CD of the localized
field appears due to the geometric effect of the entire structure of the samples. The
conversion of the spin angular momentum of light to orbital angular momentum via
multipole excitation of nanoscale metallic complexes is also a peculiar manifestation
of nonlocalty.
One of the interesting aspects of optical response is the fact that its manifestation
appears not only as optical signals but also as mechanical force induced on matter
systems. Accordingly, in this chapter, we discussed the chiral interaction between
light and metallic structures visualized and appearing in optical-force effects.
The first topic is the manner in which we can visualize the 3D NF-CD that appears
in the vicinity of chiral metallic structures. The aperture-type scanning near-field
optical microscope is a powerful tool to unveil the chiral near field. However, it
is difficult to elucidate the 3D structure of superchiral field, especially around the
H. Ishihara et al.
5.3.3 Optical Current
To gain a better understanding of the optical force that rotates the NP inside the
metallic nanocomplex, we considered the x-y component of the Poynting vector,
which is zero for plane wave light. This vector, which is also referred to as optical
current, contributes to the dissipative force exerted on the NP [62, 63]. The optical
current is classified into orbital and spin parts [63]. In Fig. 5.8 a, b, we depict the
orbital part of the time-averaged optical current inside the metallic nanocomplex
when the circularly polarized light with s = +1 is irradiated. Whether irradiating
only the manipulation light (resonant to the 0–1 transition) or only the pump light
(resonant to the 0–2 transition), the optical current flows clockwise inside the metallic
nanocomplex. These results are consistent with the rotational force discussed in
Fig. 5.7c, and also with the relation between population inversion and the rotational
direction of the NP. In addition, it is observed that the direction of the rotational flow
in the metallic nanocomplex depends on the direction of the optical current at the
four gap positions. If the manipulation scheme suggested here is realized, the basic
elements of manipulating the NP (pushing, pulling, and rotating) are also achieved.
This will introduce new technologies not only for nanofabrication but also for nanooptomechanics that involve chiral materials and highly sensitive and selective chiral
sensing.
5.4 Summary
Light–nanomatter chiral interaction has been a central subject of research in various domains for a long time. The development of nanofabrication technologies and
single-molecular detection techniques take the study of this domain to a new stage.
Particularly, the chiral interaction between light and metallic nanostructures has garnered attention because of its wide potential applications. Further, this phenomenon
is the basis of our understanding of the nonlocal optical response, which is beyond the
conventional model based on LWA or DA. For example, a strong CD of the localized
field appears due to the geometric effect of the entire structure of the samples. The
conversion of the spin angular momentum of light to orbital angular momentum via
multipole excitation of nanoscale metallic complexes is also a peculiar manifestation
of nonlocalty.
One of the interesting aspects of optical response is the fact that its manifestation
appears not only as optical signals but also as mechanical force induced on matter
systems. Accordingly, in this chapter, we discussed the chiral interaction between
light and metallic structures visualized and appearing in optical-force effects.
The first topic is the manner in which we can visualize the 3D NF-CD that appears
in the vicinity of chiral metallic structures. The aperture-type scanning near-field
optical microscope is a powerful tool to unveil the chiral near field. However, it
is difficult to elucidate the 3D structure of superchiral field, especially around the