Spectral dependence of third-order susceptibility of Au triangular nanoplates

Abstract

We experimentally investigated the spectral dependence of the third-order susceptibility χ (3) of Au triangular nanoplates in a broad wavelength region (400-1,000 nm). Complex shaped plasmonic nanoparticles provide a promising route to achieve control of their optical properties at the nanoscale. However, little is known about the effects of geometrical parameters to the optical nonlinearities and underlying mechanisms of the plasmon modes. Here, we obtained the χ (3) of Au triangular nanoplates featuring a narrow plasmon resonance that is tunable in the visible and near-IR regions. This work demonstrates that the plasmonic triangular nanoplates simultaneously shows selffocusing and-defocusing, and saturable and reverse-saturable absorption properties at specific wavelength regions. Maximum amplitudes of real and imaginary components are − 6.8 × 10 −18 m 2 /V 2 at 668 nm and − 6.7 × 10 −18 m 2 /V 2 at 646 nm, respectively. Spectral dependence of the quantity χ (3) enables comparison between different shaped plasmonic NPs to boost active plasmonic applications performance. Metallic nanoparticles (NPs) have attracted extensive interests because of their unique plasmonic properties 1. The light-driven collective motion of electrons within the NP is known as localized surface plasmon resonance (LSPR) 2. This resonance can boost both linear and nonlinear optical (NLO) properties 2. Thus, a plasmonic NP can feature large optical nonlinearity while exhibiting ultrafast response 3. These unique properties have been applied to various nonlinear optical functionalities, such as surface-enhanced Raman scattering (SERS), photonic waveguides and ultrafast all-optical switching 1,3-5. Among various plasmonic NPs, Au has been one of the best and common studied materials in nonlinear photonics due to its large optical nonlinearity and chemical stability 6,7. Triangular Au nanoplates is promising for strong local field enhancement expected at their sharp tips. Also, the LSPR of triangular nanoplates can be easily tuned from visible to near-IR regions by controlling their thickness and edge length 8. Besides, Au nanoplates have been reported with a large wavelength dependence of nonlinear refraction and a tiny change of nonlinear absorption 9. These results imply that Au nanoplate is a good candidate for optical switches 9,10. However, previous studies on spherical and elongated Au NPs have shown that third-order susceptibility χ (3) exhibits a strong wavelength-dependent dispersion at LSPR region 11,12. Real and imaginary components of χ (3) consist of successively positive and negative peaks. This result indicate that Au simultaneously exhibit nonlinear absorption (saturable absorption SA and reversed saturable absorption RSA) and refraction (self-focusing and self-defocusing) at different wavelengths. To clarify and understand the reported abnormal optical nonlinearity on Au nanoplates, a spectral dependent dispersion of χ (3) is necessary. To the best of our knowledge, previously reported investigations on Au nanoplates were p...

Structural Correlations of the Nonlinear Optical Response in Polydiacetylene Nanotubes Hybridized with Gold Nanoparticles

“…The broadening effect in a transient excitation state would be responsible for the spectral behavior that {(Δ T (ω) + T (ω)}/ T (ω) became less than unity mainly in the long-wavelength region in Figure S3. The nonequilibrium transient electron state (fast mode) would not be perhaps detectable because the pulse width of the incident laser was 150 fs, and the broadening effect would reflect the transient electron state (slow mode) at the equilibrium state. , In fact, the transient transmittance peak was bleached by the broadening effect, and then Δ T (ω) increased, but Δ T (ω) reversely decreased in the wing region of the spectrum …”

“…51,69 In fact, the transient transmittance peak was bleached by the broadening effect, and then ΔT(ω) increased, but ΔT(ω) reversely decreased in the wing region of the spectrum. 70 However, it is still unclear in Figure 3 whether or not χ (3) (ω) was enhanced by the LSPR effect in hybridized PDA NTs, and it is so difficult to directly discuss the structural correlation of χ (3) (ω) because the obtained χ (3) (ω) is usually affected by some experimental factors: optical density and scattering loss at the time of measurement and so on. 44,66 So, FOM is an important and effective indicator and is often introduced to avoid the above-mentioned influences.…”