On the physical contributions to the third-order nonlinear optical response in plasmonic nanocomposites

Abstract

Au and Ag isotropic and anisotropic nanocomposites were prepared using the ion implantation technique. Their optical properties were studied at several wavelengths in the optical range 300–800 nm, across their plasmon resonances. The linear regime was characterized by measuring the absorption spectrum and the third-order nonlinear regime by means of the Z-scan technique using a tunable picosecond pulsed laser system (26 ps). Open-aperture Z-scan traces show a superposition of different optical nonlinear absorption (NLA) processes in the whole range studied. We associate these phenomena with the excitation of inter- and intra-band electronic transitions, which contribute with a positive sign to NLA, and to the formation of hot-electrons, which contribute with opposite sign to NLA. Closed-aperture traces for measuring nonlinear refraction (NLR) show different signs for Au and Ag samples, and a change of sign in Au is found when purely inter-band transitions are excited. In this work, for the appropriate wavelength, it is worth remarking on the free-electron response to the exciting light and its strong contribution to the nonlinear optical properties for low (intra-band) and high (hot-electrons) irradiances.

The Water-Based Synthesis of Platinum Nanoparticles Using KrF Excimer Laser Ablation

“…The presence of such a band is not observed in simulations calculated for monodisperse, well separated, spherical nanoparticles, as in [ 56 ]. This gives us reason to assume that the appearance of the band is rooted in the following possible factors: (a) presence in the colloid of individual, well separated nanoparticles with a diameter greater than 20 nm [ 58 ]; (b) presence in the colloid of elongated nanoparticles, i.e., with a shape deviating from the spherical one, in which longitudinal resonance can be observed [ 56 , 59 ]; (c) an effect of aggregation and the subsequent partial adhesion of nanoparticles and formation of different nanostructures. The explanation for this band requires further investigation.…”

Effect of the Composition on the Nonlinear Optical Response of AuxAg1–x Nano-Alloys

“…The NLO behavior of Au NPs observed in the present study has been also reported previously. 63,64 However, some studies have reported switching from SA to RSA 71,81 and some others only RSA. 67,82 Similarly for Ag NPs, both switching from SA to RSA 69,74 and only RSA have been reported.…”

“…The NLO response of Au and Ag NPs is usually described in terms of contributions being related with the interband transitions (between the d -band and the conduction s–p band), the intraband transitions (within the s–p band), the hot electrons’ contributions and the contribution of free carriers. ,− Briefly, the interband transitions are taking place when the photon energy exceeds the energy gap, which is 1.7 and 4 eV for Au and Ag, respectively. , The interband transitions are responsible for saturable absorption, corresponding to a negative sign contribution to Im χ (3) , in the same way as it occurs in a two-level system when it is strongly pumped. Since interband transitions are one-photon processes, they are expected to be more intense in the case of Au excitation under 532 nm radiation.…”

Simulation of the Linear and Nonlinear Optical Properties of Colloids Containing Metallic Core–Dielectric Shell Nanoellipsoids

“…However, some works reveal important insights about the nonlinearities of oriented metal NEs [11][12][13][14].…”

“…However, due to the anisotropy, the NL response of the NEs is different in each axis, and detailed information is necessary to model the NL third-order susceptibility. In recent papers, the NL response of aligned nanorods was measured at selected wavelengths and geometries, and important information about the NPs NL response was reported [11][12][13][14]. For randomly oriented ellipsoids, the NL optical properties were measured for colloids containing gold nanorods, and a comparative table of the two-photon absorption coefficient under different conditions was given [15].…”