Optical Second Harmonic Generation in Anisotropic Multilayers with Complete Multireflection of Linear and Nonlinear Waves using #SHAARP.ml Package

TL;DR

This paper introduces SHAARP(ml), an open-source tool for accurately analyzing second harmonic generation in complex multilayer anisotropic structures without common approximations, validated through experimental benchmarking.

Contribution

The paper presents SHAARP(ml), a novel open-source package that provides exact analytical solutions for SHG in multilayer anisotropic systems, avoiding typical approximations.

Findings

Accurately models SHG in multilayer structures with multiple reflections.

Benchmarked results show high agreement with experimental data.

Enables precise material property evaluation without simplifying assumptions.

Abstract

Optical second harmonic generation (SHG) is a nonlinear optical effect widely used for nonlinear optical microscopy and laser frequency conversion. Closed-form analytical solution of the nonlinear optical responses is essential for evaluating the optical responses of new materials whose optical properties are unknown a priori. A recent open-source code, SHAARP(si), can provide such closed form solutions for crystals with arbitrary symmetries, orientations, and anisotropic properties at a single interface. However, optical components are often in the form of slabs, thin films on substrates, and multilayer heterostructures with multiple reflections of both the fundamental and up to ten different SHG waves at each interface, adding significant complexity. Many approximations have therefore been employed in the existing analytical approaches, such as slowly varying approximation, weak reflection of the nonlinear polarization, transparent medium, high crystallographic symmetry, Kleinman symmetry, easy crystal orientation along a high-symmetry direction, phase matching conditions and negligible interference among nonlinear waves, which may lead to large errors in the reported material properties. To avoid these approximations, we have developed an open-source package named Second Harmonic Analysis of Anisotropic Rotational Polarimetry in Multilayers (SHAARP(ml)). The reliability and accuracy are established by experimentally benchmarking with both the SHG polarimetry and Maker fringes predicted from the package using standard materials.