Visible second-harmonic light generated from a self-organized centrosymmetric lattice of nanospheres

Abstract

We designed and fabricated a centrosymmetric material where one may be able to consider an efficient quadratic nonlinear interaction. We followed a solid phase-supported organic synthesis methodology to covalently bind a large number of highly nonlinear molecules to the surface of polystyrene nanospheres. Such chemically modified optically nonlinear latex spheres, when suspended in water, are seen to perfectly self-organize into a centrosymmetric lattice. Taking advantage of the nonlinear interaction located at the sphere-water interface and the photonic crystal properties of the fabricated material we were able to generate second-harmonic light visible to the naked eye.

Synthesis of Colloidal Photonic Crystals with High Nonlinear Optical Performance: Towards Efficient Second‐Harmonic Generation with Centrosymmetric Structures

“…With the position of the SH peak and in accordance to Refs. [1,2,[6][7][8][9] we estimated that the plane separation is around 203 nm which is in perfect agreement with the position of the Bragg dip in transmission shown in Figure 1. Indeed, the appearance of such narrow peaks is a confirmation that in both cases the covered polystyrene spheres are organized in a periodic lattice or CCA.…”

“…The resulting chemically modified CCAs takes advantage of the nonlinear interaction located at the sphere-water interface and their photonic crystal properties to produce-via second-harmonic generation-light visible to the naked eye. [2] The magnitude of this NLO response is the direct result of the high coverage of nanospheres surface with nonlinear chromophores, achieved with the new synthetic procedure. Furthermore, the broad applicability of this novel methodology, which could be used with the majority of organic and organometallic NLO chromophores described in the literature, suggests a new route to synthesize organic centrosymmetric structures with second-order NLO properties.…”

“…The lines shown in Figure 3 correspond to a theoretical fit obtained when a theoretical model that includes all 3D aspects of the interaction is used. [2] The advantages of chemically modified crystals over those having surface adsorption are evident: high coverage of the nanosphere surface can be achieved; the resultant systems are more thermally stable; and have the capability of displaying SHG several orders of magnitude higher. In fact, the second harmonic generated is visible to the naked eye as is shown in Figure 4a.…”

Nonlinear optics in spheres: from second harmonic scattering to quasi‐phase matched generation in whispering gallery modes

“…This tetrahedron could be linked to the second-order nonlinear response of the molecule. A weak, but visible to the naked eye, SH beam was generated from a 200 μm thick macroscopically centrosymmetric material [21]. Yet, molecular absorption, sphere size dispersion, and structural defects in the crystalline lattice proved to be limiting factors to reach quadratic growth of the SHG versus the colloidal crystal path length [22].…”

Light generation at the anomalous dispersion high energy range of a nonlinear opal film

“…Such hydroxyl group was covalently linked to the functional carboxylic acid groups present at the surface of the spheres [17]. The chemically modified spheres present a high coverage of their surface, estimated to be on the order of 70% [17,18]. After the reaction the sulfate groups remain unaltered preventing coagulation and also helping to maintain stability during the crystallization process of the opal.…”