Mariusz Zdanowicz

Dipole limit in second-harmonic generation from arrays of gold nanoparticles

We present a multipolar tensor analysis of second-harmonic generation from arrays of noncentrosymmetric gold nanoparticles. In contrast to earlier results, where higher multipoles and symmetry-forbidden signals arising from sample defects play a significant role, the present results are completely dominated by symmetry-allowed electric-dipole tensor components. The result arises from significant improvement in sample quality, which suppresses the higher-multipole effects and enhances the overall response by an order of magnitude. The results are a prerequisite for metamaterials with controllable nonlinear properties.

Second-harmonic response of multilayer nanocomposites of silver-decorated nanoparticles and silica

We perform a detailed characterisation of the second-order nonlinear optical response of nanocomposites consisting of alternating layers of silver-decorated silica glass nanoparticles and pure silica glass. The samples are fabricated using aerosol techniques and electron-beam dielectric coating, resulting in a bulk-like material with symmetry-breaking induced by the porosity of the alternating layers. The second-order nonlinear response increases with the number of layers. Further, by determining the components of the second-order susceptibility tensor of the samples, we show that the structural properties of the samples are well maintained as the sample thickness is increased. Our results form an important baseline for any further optimization of these types of structures, which can be fabricated using very straightforward methods.

Ordered multilayer silica-metal nanocomposites for second-order nonlinear optics

We use aerosol synthesis to fabricate ordered metal-silica nanocomposites consisting of alternating layers of pure silica and silica nanoparticles decorated with silver nanodots. These multilayer structures preserve the narrow plasmon resonance of the nanodots even for high optical densities and allow second-harmonic generation due to spontaneous symmetry breaking arising from the interfaces between silica and nanoparticle layers. Our concept opens up perspectives for complex structures for advanced optical applications.

Metamaterials with Tailorable Nonlinear Optical Properties

Second-order nonlinear processes such as second-harmonic generation (SHG) require noncentrosymmetric structures. The development of second-order metamaterials, however, has been hampered by symmetry breaking due to sample defects and shape distortions. The resulting outcomes can be interpreted in terms of effective higher-multipole (magnetic and quadrupole) effects that strongly modify the radiative properties of the samples.

Ways to optimize the second-harmonic response from metamaterials

Metamaterials consisting of metal nanoparticles offer the possibility to engineer the nonlinear optical properties by varying their plasmonic resonances. The resonances depend on the size, shape, and dielectric environment of the particles as well as their mutual ordering. We show several ways of controlling and optimizing the second-harmonic response of plasmonic metamaterials.

Second-Order Nonlinear Optical Properties of Plasmonic Nanostructures

We review our work on second-order nonlinear optical properties of plasmonic nanostructures. In order to achieve the required non-centrosymmetry of the structures, our samples consist of arrays of L-shaped nanoparticles and T-shaped nanodimers. The samples are investigated by polarization-dependent second-harmonic generation to address the tensorial nonlinear response. We show that the response can be strongly modified by symmetry-breaking defects and other deviations of the samples from ideal. Nonlinear sources localized to defects can also give rise to higher-multipolar emission. The defect problem is overcome with a recent and significant improvement in sample quality, allowing the dipole limit of the nonlinear response to be reached. This achievement opens the path towards plasmonic metamaterials with tailorable nonlinear properties. As a demonstration of this possibility, we modify the nonlinear response by the mutual arrangement of the L-shaped particles in the array. We will also summarize our numerical boundary-element method to describe the nonlinear response of nanoparticles.

Reaching the dipole limit in second-harmonic generation from gold nanoparticles

Second-harmonic generation from arrays of gold nanoparticles exhibits interference between electric-dipole and higher multipole (magnetic-dipole and electric-quadrupoles) effects. We show that improved sample quality suppresses the role of higher multipole effects in second-harmonic generation from L-shaped gold nanoparticles, thereby opening the possibility of reaching the pure dipole limit. This is a prerequisite for nonlinear metamaterials with tailorable properties.

Suppression of multipole effects in second-harmonic generation from L-shaped gold nanoparticles

Plasmon resonances of metal nanoparticles can lead to strong local electromagnetic fields near the particles and thus enhance their optical response. Nanoscale variations in the local fields can also enable magnetic dipoles and electric quadrupoles to contribute to the optical responses [1]. Very small nanoscale features, such as defects, can also support their own plasmonic modes and thereby modify optical responses [2]. We have earlier observed interference between electric dipoles and higher multipoles in second-harmonic generation (SHG) from arrays of metal nanoparticles [3] and interpreted this in terms of the local defect modes [4]. In this paper, we confirm this interpretation and show that the effect of higher multipoles in SHG is almost completely suppressed when new samples with significantly improved quality are used. Furthermore, we show that the overall SHG response from the new samples is about an order of magnitude higher than from the earlier samples.

Effective Medium Multipolar Tensor Analysis of Second-Harmonic Generation from Metal Nanoparticles

Second-order nonlinear optical effects are electric-dipole-forbidden in centrosymmetric materials, but become allowed through magnetic-dipole and electric-quadrupole effects. Furthermore, such higher multipole effects can play a role also in the response of non-centrosymmetric materials, as demonstrated for second-harmonic generation (SHG) from chiral thin films of organic molecules and from metal nanostructures. For nanostructured materials, higher multipole effects can occur due to elementary light-matter interactions or due to field retardation across nanoparticles. For SHG from metal nanostructures, the latter mechanism was operative and associated with nanoscale defects, which attract strong local fields. The evidence of multipolar SHG emission was obtained from the different radiative properties of the various multipolar sources. The goal of the present work is to perform a more comprehensive multipolar analysis of SHG from arrays of L-shaped metal nanoparticles. In particular, we seek evidence of the presence of multipole interactions also at the fundamental frequency by performing detailed polarization measurements of the SHG response and relying on the different transformation properties of the various multipolar interactions for SHG emitted in the transmitted and reflected directions and for the fundamental beam incident on the metal or substrate side of the sample.

Finite Difference Beam Propagation Method Applied to Photonic Crystal Fibres

University of Nottingham (UoN) and National Institute of Telecommunications (NIT) in Warsaw have a well established cooperation in the field of the numerical methods for the modelling of the photonic structures in the framework of COST Pll project. Both research groups are using frequency domain Finite-Difference Beam Propagation Method (FD-BPM) for the calculations. The algorithm developed at the University of Nottingham is a semi-vectorial, real distance ADI (Alternating Direction Implicit) Pade(l,l) algorithm with the Perfectly Matched Layers (PML) boundary conditions. Program developed at the NIT is a full-vectorial, real distance paraxial algorithm with the Transparent Boundary Conditions (TBC). This paper presents some of the results obtained in UoN and NIT and describes the disadvantages of the FD-BPM methods applied to Photonic Crystal Fibres (PCF).