Enhanced Surface Second Harmonic Generation in Nanolaminates

TL;DR

This paper demonstrates that multilayer dielectric stacks significantly enhance surface second-harmonic generation due to increased surface area and broken symmetry, with experimental results aligning with theoretical predictions.

Contribution

It introduces a method to enhance surface SHG using periodic dielectric nanolaminates fabricated by PEALD, showing substantial SHG at large angles of incidence.

Findings

Surface SHG is substantially increased in multilayer stacks.

Experimental results agree with theoretical models.

Large angles of incidence (>20°) enhance SHG signals.

Abstract

Second-harmonic generation (SHG) is a second-order nonlinear optical process that is not allowed in media with inversion sym-metry. However, due to the broken symmetry at the surface, surface SHG still occurs, but is generally small. We experimentally investi-gate the surface SHG in periodic stacks of alternating, subwave-length dielectric layers, which have a large number of surfaces, thus enhancing surface SHG considerably. To this end, multilayer stacks of SiO2/TiO2 were grown by Plasma Enhanced Atomic Layer Deposition (PEALD) on fused silica substrates. With this technique individual layers of a thickness of less than 2 nm can be fabricated. We experimentally show that under large angles of incidence (> 20 degrees) there is substantial SHG, well beyond the level, which can be observed from simple interfaces. We perform this experiment for samples with different periods and thickness of SiO2/TiO2 and our results are in agreement with theoretical calculations.