Accurate determination of nonlinear refraction in ZnO and Au composite nanostructures

Sarah L Walden,Joseph F S Fernando,Matthew P Shortell,Esa A Jaatinen

doi:10.1364/ome.380344

Abstract

It is now well established that the nonlinear optical properties of ZnO nanoparticles can be significantly enhanced by coupling them to metallic nanoparticles. While the nonlinear absorption properties are well reported, there is large variation in the coefficients of nonlinear refraction reported in literature, largely due to simplifications made during the analysis of experimental z-scan data used to determine the coefficients. This work presents closed aperture z-scan theory which incorporates the effects of nonlinear absorption, thus providing a more accurate measure of the coefficient of nonlinear refraction. With this theory, it is shown that the coefficient of nonlinear refraction increases by an order of magnitude when ZnO is coupled to Au nanoparticles.

Highlights

Nonlinear refraction, known as the nonlinear Kerr effect, is a vital tool in the realization of optical information processing and all optical computing
To demonstrate the importance of including the nonlinear absorption coefficients into the numerical simulations of the closed aperture z-scan we present a direct comparison between the simulation fits and the results determined by dividing the closed aperture trace by the open aperture trace
This paper compared the nonlinear refraction properties of ZnO and ZnO-Au composite nanostructures using numerically simulated closed aperture z-scan traces which incorporates the effects of nonlinear absorption

Summary

Introduction

Known as the nonlinear Kerr effect, is a vital tool in the realization of optical information processing and all optical computing. There is large variation in the magnitude of the enhancement reported in these studies and, in particular, the nature of the specific absorption processes occurring This has largely been due to a lack of consideration of transient effects when determining nonlinear coefficients [5]. By incorporating the nonlinear absorption coefficients into the numerical simulations of the closed aperture z-scan, and comparing them to experimental data, more accurate coefficients of nonlinear refraction can be determined These results are compared with the simplified approach of dividing the closed aperture trace by the open aperture trace to demonstrate the importance of including significant nonlinear absorption processes into the theoretical treatment

Theory

Sample preparation and characterisation

Open aperture z-scan measurements

Closed aperture z-scan measurements

Conclusion