Second-Harmonic Scattering-Defined Topological Classes for Nano-Objects

Abstract

Nano-object topology determination is a central question in nanoscience and remains a challenge to achieve in the absence of a supporting substrate and atomic resolution techniques. In this work, we demonstrate how second-harmonic scattering (SHS) is sensitive to the balance between the nano-object shape symmetry and size, thereby allowing for a SHS-defined topological definition. Although many data on nano-objects have been reported with this method so far, in most cases dispersed in liquid suspensions, no topological retrieval has been proposed. To reach this task, we have measured the second-harmonic scattered light from a series of representative nano-objects along two collection directions for well-defined polarization states. The experimental results are then recast within a general framework involving nonlinear emitting sources and the size as critical elements. This analysis leads to the classification of the nano-objects according to the topology defined by their SHS response.

Polarization-resolved second harmonic generation from LiNbO3 powders

“…Hence, within this context, polarizationresolved experiments have been performed in weakly scattering suspensions of metallic nanoparticles. In this case much can be retrieved from the nanoparticles, and in particular the fine details of the local and non-local origin of their SHG responses [6,7] as well as the competition between the roles of size and shape revealing the nanoparticles topology [8]. In scattering suspensions though, when linear optical scattering processes must be accounted for besides the nonlinear SHG events, this analysis also sheds some light on the problem of photon transport in random media and more precisely the transition from ballistic to multiple scattering regimes [9].…”

Gold-seeded Lithium Niobate Nanoparticles: Influence of Gold Surface Coverage on Second Harmonic Properties

“…Comparatively, the AuSeeds have a much larger D coefficient at 0.43 ( Table 3 ) and the reason for this is the surface origin of their response as gold is a centrosymmetric material. Their response is therefore highly three-dimensional and strongly dependent on their geometry [ 47 ]. For the LN@BPEI@AuSeeds samples, despite their very similar response to the bare LN NPs ( Table 3 ), a weak change in the depolarization ratio is observed, as a result of the weak surface contribution due to the AuSeeds.…”

PySHS : A Python Open Source Software For Second Harmonic Scattering

“…Two ways are implemented to perform the ISHS(𝛾, Π, Θ) calculation: the first way implemented in the SHS program of PySHS package explicitly computes ISHS according to equations (3)(4)(5)(6)(7)(8)(9). The second way implemented in the SHSlinear program, uses the approach detailed in these references 6,23,31 and in the HRS_Computing software 34 , approximates the exponential term in equation ( 5) by:…”

“…Taking the molecular hyperpolarizability, the position and orientation of each molecule in the supramolecular assembly as input parameters, the SHS and SHSlinear programs can compute the polarization resolved plot or the scattered angle plot. For the polarization plot, the outputs of the program are the coefficients 𝑎 Π Θ , 𝑏 Π Θ , 𝑐 Π Θ and 𝐼 2 Θ,Π , 𝐼 4 Θ,Π defined in this work 31 . Indeed, the SHS intensity exhibits the equivalent following dependencies with the input polarization angle 𝛾 :…”

“…Numerous models [25][26][27][28][29][30] have been developed to interpret experimental data and in particular angular distribution and polarization dependence of the second harmonic scattered light. The understanding of such variation allows the recovery of important properties about the symmetry 31 , the organization 9 and/or the correlation [5][6][7] of the nano-objects probed. Some of these models have also been implemented in software to compute the SHS intensity, in particular in the NLS_simulate software [32][33] or HRS_Computing software 34 .…”