Optical second harmonic generation in anisotropic multilayers with complete multireflection of linear and nonlinear waves using ♯SHAARP.ml package

• Published in: npj computational materials 2024-03, Vol.10 (1), p.64-15, Article 64
• Main Authors: Zu, Rui, Wang, Bo, He, Jingyang, Weber, Lincoln, Saha, Akash, Chen, Long-Qing, Gopalan, Venkatraman
• Format: Article
• Language: English
• Subjects: 639/301/119/996; 639/624/400/385; 639/766/400/385; Anisotropy; Approximation; Characterization and Evaluation of Materials; Chemistry and Materials Science; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Closed form solutions; Computational Intelligence; Crystal structure; Crystallography; Crystals; Exact solutions; ferroelectrics and multiferroics; Fourier analysis; Harmonic analysis; Heterostructures; Light microscopy; Material properties; MATERIALS SCIENCE; Mathematical analysis; Mathematical and Computational Engineering; Mathematical and Computational Physics; Mathematical Modeling and Industrial Mathematics; Multilayers; Nonlinear optics; Optical components; Optical materials; Optical microscopy; Optical properties; Optics; Phase matching; Polarimetry; Second harmonic generation; Source code; Substrates; Symmetry; Theoretical; Thin films
• ISSN: 2057-3960; 2057-3960
• DOI: 10.1038/s41524-024-01229-2

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 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 using standard and commonly used nonlinear optical materials as well as twisted 2-dimensional heterostructures.