Record SHG achieved under high pressure - Dr. Wenge Yang

Recently, new research from a team of scientists led by Dr. Wenge Yang from HPSTAR and Prof. Xin Wang from the State Key Laboratory of Superhard Materials at Jilin University, has set a new record in second-harmonic generation (SHG) intensity, reaching up to 28 times that of the commercial SHG material KDP crystal. Additionally, the team developed a high-pressure fitting strategy based on single-crystal angle-resolved SHG polarization intensity, which overcomes the limitations of the traditional Kurtz powder test method and is applicable to various experimental environments, offering important insights for the design of advanced nonlinear optical devices and the calibration of intrinsic SHG efficiency under high pressure. The study, published in the Journal of the American Chemical Society, provides a deep understanding of the pressure-induced nonlinear optical property enhancement in SHG material. The first authors of the work are Qu Jia, a jointly graduate student of HPSTAR and Jilin University, and Yiming Wang, a PhD graduate student of HPSTAR.

SHG (Second-harmonic generation) is a nonlinear optical phenomenon where two photons combine to form a new photon with double the energy. This effect occurs across a variety of fields, including optics, radio waves, magnetohydrodynamics, and even in the middle atmosphere. Enhancing SHG conversion efficiency has long been a major challenge in both fundamental research and industrial applications. In nonlinear optical crystals, the SHG intensity is primarily determined by the material's second-order nonlinear susceptibility, with lattice distortion playing a crucial role in enhancing this nonlinear response.

In recent years, halide perovskites have emerged as a promising system for investigating nonlinear optical properties. Thanks to their unique photoelectric characteristics and highly tunable crystal and electronic structures, these materials exhibit outstanding nonlinear responses, making them ideal candidates for the development of next-generation optoelectronic devices.

The SHG response of CGC under ambient pressure exhibits a considerable intensity, with 9.1 times greater than that of the classic KDP crystal (@1030 nm). Upon compression, the SHG intensity further increased by approximately ∼3 times, setting a record for the highest SHG intensity under high pressure.

Capiton：(a) Experimental high-pressure setup. Pressure is generated by two opposite diamond anvils. Gasket with a central hole is placed between two anvils to provide a chamber for sample and pressure transmitting medium. (b) SHG spectra of KDP at ambient pressure (black solid line) and CGC at different pressures with 1030 nm pump laser during compression. (c) Double-frequency coefficient deff of powder measurement and the second-order nonlinear tensor components of single-crystal at different pressures. (d) Pressure-modulated SHG performance showing a remarkable enhancement on CGC.

The team cross- validated the consistency of CGC's SHG intensity through both high-pressure single-crystal angle-resolved polarization measurements and powder averaged characterization. The dome-like evolution of CGC's SHG with pressure can be reasonably explained by the structural distortion of the [GeCl₆] octahedron and the influence of ns² lone pair electrons. Further band structure calculations and electron localization function (ELF) analysis revealed that, as pressure increases, the activity of the Ge²⁺ lone pair electron state and a large reduction in band gap, plays a crucial role in the SHG enhancement.

This research not only deepens our understanding of the nonlinear optical response mechanism of halide perovskites but also demonstrates the unique advantages of pressure in regulating and enhancing nonlinear optical performance. Additionally, the comprehensive research method they proposed is expected to provide guidance for the design and application of new optical modulation and optical switching materials.

近日，北京高压科学研究中心（HPSTAR）的杨文革课题组与吉林大学超硬材料国家重点实验室的王欣团队合作，实现了高下二次谐波(SHG)强度的新记录，高达商用SHG材料KDP晶体的28倍。此外，该团队设计了一种基于单晶角分辨SHG极化强度的高压拟合策略，可以克服传统Kurtz粉末测试方法的局限性，且可适用于多种测试场景。该研究有望为先进非线性光学器件设计与高压SHG本征效率的标定提供参考。相关结果以“Origin of Pressure-Induced Nonlinear Optical Property Enhancement in CsGeCl₃ Perovskite: [GeCl₆] Octahedron Distortion and Band Gap Closing”为题，发表于《Journal of the American Chemical Society》上。