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Extrinsic 2D chirality: giant circular conversion dichroism from a metal-dielectric-metal square array.

Cao T, Wei C, Mao L, Li Y - Sci Rep (2014)

Bottom Line: Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region.Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures.This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Dalian University of Technology, China (P.R.C.).

ABSTRACT
Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region. Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures. Our structure consists of an array of thin Au squares separated from a continuous Au film by a GaAs dielectric layer, where the Au squares occupy the sites of a rectangular lattice. This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies.

No MeSH data available.


Related in: MedlinePlus

3D-FDTD simulation of (a) total electric field intensity distribution, (b) total magnetic field intensity distribution, and (c) displacement current (JD) distribution for the RCP incident light at θ = φ =  45° where λ = 2370 nm. Simulation of (d) total electric field intensity distribution, (e) total magnetic field intensity distribution, and (f) displacement current (JD) distribution for the LCP incident light at θ = φ =  45° where λ = 2370 nm.
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f4: 3D-FDTD simulation of (a) total electric field intensity distribution, (b) total magnetic field intensity distribution, and (c) displacement current (JD) distribution for the RCP incident light at θ = φ = 45° where λ = 2370 nm. Simulation of (d) total electric field intensity distribution, (e) total magnetic field intensity distribution, and (f) displacement current (JD) distribution for the LCP incident light at θ = φ = 45° where λ = 2370 nm.

Mentions: The giant CCD results from the coupling between the MDM multilayers, which gives rise to a strong magnetic response. Such a strong magnetic dipolar moment is connected to an antisymmetric charge-oscillation eigenmode, providing the combined plasmon mode a twist in the propagation direction of the wave to imitate 2D chirality45. To shed more light on the origin of the large 2D-chiroptical response, we then look at the electromagnetic field distribution in the MDM-MPAs induced by the off-normal incident light. The distributions of total electric field intensity , total magnetic field intensity and displacement current (JD) along β plane associated with A+ = 0.86 at λ = 2370 nm for the RCP incident light at θ = φ = 45° are shown in Fig. 4(a)–4(c). In the field maps of Fig. 4, the arrows show JD whereas the color shows the magnitude of the electric field and magnetic field. Figure 4(a) shows that the E field can be localized in both the aperture between the Au squares and the GaAs dielectric interlayer. Meanwhile, as can be seen in Fig. 4(b) the H field is efficiently confined in the GaAs layer between the Au layers. This is due to the formation of the JD loops shown in Fig. 4(c) and a concomitant coupling between surface plasmons counterpropagating on the two closely spaced interfaces46. Therefore, this structure provides a simultaneous excitation of an electric and magnetic resonance moment to enhance the localized electromagnetic fields. Correspondingly, the structure exhibits a near perfect absorbance for the RCP incident light. Figure 4(d)–4(f) show E, H and JD respectively, associated with A− = 0.47 at λ = 2370 nm for the LCP incident light at θ = φ = 45°. It shows that the patterns of E and H field distribution are similar with the ones for the RCP incident wave, which indicates that the electric and magnetic dipolar resonances are also simultaneously excited to lead to a main peak in the absorbance spectra. However, both E and H field intensities are weaker, which is consistent with the much lower absorbance shown in Fig. 2(a).


Extrinsic 2D chirality: giant circular conversion dichroism from a metal-dielectric-metal square array.

Cao T, Wei C, Mao L, Li Y - Sci Rep (2014)

3D-FDTD simulation of (a) total electric field intensity distribution, (b) total magnetic field intensity distribution, and (c) displacement current (JD) distribution for the RCP incident light at θ = φ =  45° where λ = 2370 nm. Simulation of (d) total electric field intensity distribution, (e) total magnetic field intensity distribution, and (f) displacement current (JD) distribution for the LCP incident light at θ = φ =  45° where λ = 2370 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4262820&req=5

f4: 3D-FDTD simulation of (a) total electric field intensity distribution, (b) total magnetic field intensity distribution, and (c) displacement current (JD) distribution for the RCP incident light at θ = φ = 45° where λ = 2370 nm. Simulation of (d) total electric field intensity distribution, (e) total magnetic field intensity distribution, and (f) displacement current (JD) distribution for the LCP incident light at θ = φ = 45° where λ = 2370 nm.
Mentions: The giant CCD results from the coupling between the MDM multilayers, which gives rise to a strong magnetic response. Such a strong magnetic dipolar moment is connected to an antisymmetric charge-oscillation eigenmode, providing the combined plasmon mode a twist in the propagation direction of the wave to imitate 2D chirality45. To shed more light on the origin of the large 2D-chiroptical response, we then look at the electromagnetic field distribution in the MDM-MPAs induced by the off-normal incident light. The distributions of total electric field intensity , total magnetic field intensity and displacement current (JD) along β plane associated with A+ = 0.86 at λ = 2370 nm for the RCP incident light at θ = φ = 45° are shown in Fig. 4(a)–4(c). In the field maps of Fig. 4, the arrows show JD whereas the color shows the magnitude of the electric field and magnetic field. Figure 4(a) shows that the E field can be localized in both the aperture between the Au squares and the GaAs dielectric interlayer. Meanwhile, as can be seen in Fig. 4(b) the H field is efficiently confined in the GaAs layer between the Au layers. This is due to the formation of the JD loops shown in Fig. 4(c) and a concomitant coupling between surface plasmons counterpropagating on the two closely spaced interfaces46. Therefore, this structure provides a simultaneous excitation of an electric and magnetic resonance moment to enhance the localized electromagnetic fields. Correspondingly, the structure exhibits a near perfect absorbance for the RCP incident light. Figure 4(d)–4(f) show E, H and JD respectively, associated with A− = 0.47 at λ = 2370 nm for the LCP incident light at θ = φ = 45°. It shows that the patterns of E and H field distribution are similar with the ones for the RCP incident wave, which indicates that the electric and magnetic dipolar resonances are also simultaneously excited to lead to a main peak in the absorbance spectra. However, both E and H field intensities are weaker, which is consistent with the much lower absorbance shown in Fig. 2(a).

Bottom Line: Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region.Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures.This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Dalian University of Technology, China (P.R.C.).

ABSTRACT
Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region. Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures. Our structure consists of an array of thin Au squares separated from a continuous Au film by a GaAs dielectric layer, where the Au squares occupy the sites of a rectangular lattice. This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies.

No MeSH data available.


Related in: MedlinePlus