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K. Huang
4.2 Chirality of Light
Chirality refers to an object or system cannot be superposed or brought to coincide
with itself by its mirror image. It exists in our daily life (left and right hands), physics
(spin of a particle), optics (circularly polarized light, optical vortices with opposite
topological charge) and chemistry (molecules). The interaction between chiral light
and matter dominates the dichromic responses of microscopic particles, molecules
and nano-structures, which becomes an efficient tool to detect or characterize the
properties of interested objects in both physics and chemistry. Here, the chirality
of light and optical metasurfaces and their interactions will be highlighted in this
chapter.
4.2.1 Spin of a Photon and Spin Angular Momentum
A circularly polarized (CP) monochromatic light contains two orthogonal components in its vector potential that can be expressed as [70]
A = u(x, y, z)e
i(kz−ωt)
· (e x + σ ie y ),
(4.1)
where the item σ = ±1 denotes the spin or chirality of light, the wave number is
k = ω/c, ω is the angular frequency and c is the speed of light in vacuum, e x and
e y are the unit vectors along x and y directions, respectively. Its vector rotates in
an anti-clockwise or clockwise way, which is determined by σ. Generally, σ = 1
indicates the left-handed circular polarized light while σ = −1 for the right-handed
CP light, as sketched in Fig. 4.2. The vectors show the mirror symmetry, implying
the feature of chirality. Under the Lorentz gauge, we have the electric and magnetic
fields [71]
Fig. 4.2 Sketched vectors of electric fields in left- (a) /right- (b) handed CP light
K. Huang
4.2 Chirality of Light
Chirality refers to an object or system cannot be superposed or brought to coincide
with itself by its mirror image. It exists in our daily life (left and right hands), physics
(spin of a particle), optics (circularly polarized light, optical vortices with opposite
topological charge) and chemistry (molecules). The interaction between chiral light
and matter dominates the dichromic responses of microscopic particles, molecules
and nano-structures, which becomes an efficient tool to detect or characterize the
properties of interested objects in both physics and chemistry. Here, the chirality
of light and optical metasurfaces and their interactions will be highlighted in this
chapter.
4.2.1 Spin of a Photon and Spin Angular Momentum
A circularly polarized (CP) monochromatic light contains two orthogonal components in its vector potential that can be expressed as [70]
A = u(x, y, z)e
i(kz−ωt)
· (e x + σ ie y ),
(4.1)
where the item σ = ±1 denotes the spin or chirality of light, the wave number is
k = ω/c, ω is the angular frequency and c is the speed of light in vacuum, e x and
e y are the unit vectors along x and y directions, respectively. Its vector rotates in
an anti-clockwise or clockwise way, which is determined by σ. Generally, σ = 1
indicates the left-handed circular polarized light while σ = −1 for the right-handed
CP light, as sketched in Fig. 4.2. The vectors show the mirror symmetry, implying
the feature of chirality. Under the Lorentz gauge, we have the electric and magnetic
fields [71]
Fig. 4.2 Sketched vectors of electric fields in left- (a) /right- (b) handed CP light