Local-field enhancement effect on the nonlinear optical response of gold-silver nanoplanets

Ultrafast nonlinear absorption with multiple transformations and transient dynamics of gold nanobipyramids

The process and condition of saturable absorption (SA) and reverse saturable absorption (RSA) of ultrafast nonlinear optics in metal nanoparticles are essential for applications including light generation, amplification, modulation, and switching. Here, we first discover and explore the multiple transformations (SA-RSA-SA) of ultrafast nonlinear absorption behavior of metal nanoparticles in femtosecond pulses. Correspondingly, the energy level model and fitting formula of multiple transformations are established to illustrate the process of optical response. The femtosecond transient absorption spectra provide information about their ultrafast dynamics process and vibrational mode, which further reveals the multiple transformation mechanisms of nonlinear absorption in gold nanobipyramids (Au-NBPs). Furthermore, Au-NBPs exhibit a significantly higher SA modulation depth up to 42% in the femtosecond, which is much higher than the reported values of other nanomaterials. Our results indicate that Au-NBPs can be used as broadband ultrafast Q-switching and mode-locking, and the conversion offers new opportunities for metal nanostructures in applications of optical switching.

Thin Films of Nonlinear Metallic Amorphous Composites

We studied the nonlinear optical response of metallic amorphous composite layers in terms of a self-phase-modulated, third-order Kerr nonlinearity. A nonlinear effective medium theory was used to describe low densities of gold and iridium nanoparticles embedded in an equally nonlinear host material. The fill fraction strongly influences the effective nonlinear susceptibility of the materials, increasing it by orders of magnitude in the case of gold due to localized surface plasmonic resonances. The enhancement of the nonlinear strength in amorphous composites with respect to the bulk material has an upper limit in metallic composites as dominating absorption effects take over at higher fill factors. Both saturated and induced absorption in the thin films of amorphous composites were observed depending on the selected frequency and relative position to the resonant frequency of electron excitation in the metallic inclusions. We demonstrated the depths to which thin films are affected by nonlinear enhancement effects.

Rare-earth fluorescence thermometry of laser-induced plasmon heating in silver nanoparticles arrays

The laser-induced plasmon heating of an ordered array of silver nanoparticles, under continuous illumination with an Ar laser, was probed by rare-earth fluorescence thermometry. The rise in temperature in the samples was monitored by measuring the temperature-sensitive photoluminescent emission of a europium complex (EuTTA) embedded in PMMA thin-films, deposited onto the nanoparticles array. A maximum temperature increase of 19 °C was determined upon resonant illumination with the surface plasmon resonance of the nanoarray at the highest pump Ar laser power (173 mW). The experimental results were supported by finite elements method electrodynamic simulations, which provided also information on the temporal dynamics of the heating process. This method proved to be a facile and accurate approach to probe the actual temperature increase due to photo-induced plasmon heating in plasmonic nanosystems.

Ultra-fast dynamics in the nonlinear optical response of silver nanoprism ordered arrays

In this work we present the study of the ultra-fast dynamics of the nonlinear optical response of a honeycomb array of silver triangular nanoprisms, performed using a femtosecond pulsed laser tuned with the dipolar surface plasmon resonance of the nanoarray. Nonlinear absorption and refraction, and their time-dependence, were explored using the z-scan and time-resolved excite-probe techniques. Nonlinear absorption is shown to change sign with the input irradiance and the behavior was explained on the basis of a three-level model. The response time was determined to be in the picosecond regime. A technique based on a variable frequency chopper was also used in order to discriminate the thermal and electronic contributions to the nonlinearity, which were found to have opposite signs. All these findings propel the investigated nanoprism arrays as good candidates for applications in advanced ultra-fast nonlinear nanophotonic devices.

Spectral dependence of nonlinear absorption in ordered silver metallic nanoprism arrays

Ordered metallic nanoprism arrays have been proposed as novel and versatile systems for the observation of nonlinear effects such as nonlinear absorption. The study of the effect of the local field reinforcement on the fast optical third order nonlinear response around the Surface Plasmon Resonance is of great interest for many plasmonic applications. In this work, silver nanoprism arrays have been synthesized by the nanosphere lithography method. A low repetition rate tunable picosecond laser source was used to study the irradiance and wavelength dependence of the nonlinear absorption properties around the dipolar and quadrupolar resonances of the nanoarray with the use of the z-scan technique. The irradiance dependence of the on-resonance nonlinearity was studied, and a spectral region where nonlinear absorption is negligible was identified. This is important for the possible application of these materials in optical information processing devices.

Dichroic nonlinear absorption response of silver nanoprism arrays

The dichroic nonlinear absorption of Ag nanoprism arrays is interpreted using FEM simulations of the polarization-dependent local electric field distribution.

Amplified sensitization of Er3+ luminescence in silica by AuN quantum clusters upon annealing in a reducing atmosphere

Au_N quantum cluster sensitization of Er³⁺ photoemission in silica is boosted by H passivation of Si dangling bonds around the clusters.

Nonlinear optical response of platinum nanostructures and application for water detection in transformer oil

We report the fabrication of platinum nanostructures on an ITO substrate (Pt-NSs).

Z-scan studies of the nonlinear optical properties of gold nanoparticles prepared by electron beam deposition

This paper details the fabrication process for placing single-layer gold (Au) nanoparticles on a planar substrate, and investigation of the resulting optical properties that can be exploited for nonlinear optics applications. Preparation of Au nanoparticles on the substrate involved electron beam deposition and subsequent thermal dewetting. The obtained thin films of Au had a variation in thicknesses related to the controllable deposition time during the electron beam deposition process. These samples were then subjected to thermal annealing at 600°C to produce a randomly distributed layer of Au nanoparticles. Observation from field-effect scanning electron microscope (FESEM) images indicated the size of Au nanoparticles ranges from ∼13 to ∼48  nm. Details of the optical properties related to peak absorption of localized surface plasmon resonance (LSPR) of the nanoparticle were revealed by use of UV-Vis spectroscopy. The Z-scan technique was used to measure the nonlinear effects on the fabricated Au nanoparticle layers where it strongly relates LSPR and nonlinear optical properties.

Nonlinear absorption tuning by composition control in bimetallic plasmonic nanoprism arrays

The nonlinear absorption properties of bidimensional arrays of Au-Ag bilayered nanoprisms have been investigated by z-scan measurements as a function of the bimetallic nanoprism composition. A tunable ps laser system was used to excite the ultrafast, electronic nonlinear response matching the laser wavelength with the quadrupolar surface plasmon resonances, in the visible range, of each nanoprism array. Due to the strong electromagnetic field confinement effects at the nanoprism tips, demonstrated by finite element method simulations, these nanosystems proved to have enhanced nonlinear optical properties. Moreover, a tunable changeover from reverse saturable absorption (RSA) to saturable absorption (SA) can be obtained by properly controlling the bimetallic composition of the nanoprisms, without modifying the overall morphology of the nanosystems. This capability makes these nanosystems extremely interesting for the realization of solid-state nanophotonic devices with enhanced ultrafast nonlinear optical properties.

Au–Ag nanoalloy molecule-like clusters for enhanced quantum efficiency emission of Er3+ions in silica

(Au–Ag)_Nnanoalloy clusters made up ofN= 10–15 atoms increase by an order of magnitude the room temperature photoemission intensity of Er³⁺in silica, better than monometallic Au_Nclusters of the same size.

Plasmon assisted enhanced nonlinear refraction of monodispersed silver nanoparticles and their tunability

Nonlinear optical characterizations were performed on monodispersed silver (Ag) nanoparticles (NPs) of various sizes using a picosecond Z-scan technique with excitation wavelengths of 532 nm and 1064 nm. The Ag NPs were fabricated using a heterogeneous condensation technique in a gas medium. The nonlinear refraction values were higher for the monodispersed Ag NPs whose surface plasmon resonance (SPR) peak is closer to the excitation wavelength. The higher nonlinear optical response is explained in terms of an electric field enhancement near the SPR. Moreover, the fabrication method allows the tailoring of the nonlinear refraction index of the Ag NPs by tuning the SPR peak of the sample. A comparison of the nonlinear refraction index of the monodispersed and polydispersed Ag NPs showed that the nonlinear refractive index of the monodispersed Ag NPs is higher.

Near-infrared room temperature luminescence of few-atom Au aggregates in silica: a path for the energy-transfer to Er³⁺ ions

Ultra-small molecule-like AuN nanoclusters made by a number of atoms N less than 30 were produced by ion implantation in silica substrates. Their room temperature photoluminescence properties in the visible and near-infrared range have been investigated and correlated with the Er sensitization effects observed in Er-Au co-implanted samples. The intense photoluminescence emission under 488 nm laser excitation occurs in three different spectral regions around 750 nm (band A), 980 nm (band B) and 1150 nm (band C) as a consequence of the formation of discrete energy levels in the electronic structure of the molecule-like AuN nanoclusters. Indeed, energy maxima of bands A and C scale with N(-1/3) as expected for quantum confined systems. Conversely, the energy maximum of band B appears to be almost independent of size, suggesting a contribution of electronic surface states. A clear correlation between the formation of band B in the samples and Er-related photoemission is demonstrated: the band at 980 nm related to AuN nanoclusters resonant with the corresponding Er(3+) absorption level, is suggested as an effective de-excitation channel through which the Au-related photon energy may be transferred from Au nanoclusters to Er ions (either directly or mediated by photon absorption), eventually producing the Er-related infrared emission at 1540 nm.

Zn ion post-implantation-driven synthesis of CuZn alloy nanoparticles in Cu-preimplanted silica and their thermal evolution

Cu nanoparticles (NPs) were fabricated in silica by 45 keV Cu ion implantation at a fluence of 1.0 × 10(17) cm(-2) and were then subjected to implantation of 50 keV Zn ions at fluences of 1.0 × 10(16), 5.0 × 10(16), and 10.0 × 10(16) cm(-2), respectively. Our results clearly show that post Zn ion implantation could significantly modify structures and components of the preformed Cu NPs and thus the corresponding surface plasmon resonance (SPR) absorption can be modulated in a wide range. In particular, CuZn alloy NPs with unique SPR absorption were synthesized in Cu-implanted silica followed by Zn ion implantation at a fluence of 5.0 × 10(16) cm(-2). During subsequent annealing, two distinguished processes concerning CuZn alloy NPs (i.e., realloying and dealloying) were found that directly result from thermally driven diffusion of Zn atoms. Moreover, owing to Zn diffusion, lots of core-shell nanostructures consisting of Zn-related compound shells around Cu cores were observed after annealing at 500 °C and higher. The underlying mechanism concerning the formation and decomposition of CuZn alloy NPs is discussed and presented.

Optical Kerr phase shift in a nanostructured nickel-doped zinc oxide thin solid film

The optical Kerr effect exhibited by a nickel doped zinc oxide thin solid film was explored with femto- and pico-second pulses using the z-scan method. The samples were prepared by the ultrasonic spray pyrolysis technique. Opposite signs for the value of the nonlinear refractive index were observed in the two experiments. Self-defocusing together with a two-photon absorption process was observed with 120 ps pulses at 1064 nm, while a dominantly self-focusing effect accompanied by saturated absorption was found for 80 fs pulses at 825 nm. Regarding the nanostructured morphology of the resulting film, we attribute the difference in the two ultrafast optical responses to the different physical mechanism responsible of energy transfer generated by multiphoton processes under electronic and thermal effects.