发表机构
School of Information Science and Technology, University of Science and Technology of China; Guilin Julian Technology Co., Ltd.; School of Electronic Engineering and Automation, Guilin University of Electronic Technology; School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology; Laboratory of Quantum Information, University of Science and Technology of China（中国科学技术大学信息科学与技术学院; 桂林朱利安科技有限公司; 桂林电子科技大学电子工程与自动化学院; 陕西科技大学化学与化工学院; 中国科学技术大学量子信息实验室）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究建立位移型铁电体中太赫兹调控光二次谐波产生的微观理论，揭示太赫兹驱动晶格畸变重构电子态以调制二次谐波响应的机制，为非平衡晶格动力学与超快非线性光学搭建微观桥梁。
AI 中文摘要
光二次谐波产生（SHG）是探测铁电有序性的有力手段，然而其微观起源与动态调控通常主要从对称性角度而非潜在电子过程来理解。本文中，我们建立了位移型铁电体中太赫兹（THz）调控光SHG的微观理论，在THz驱动的极性晶格畸变与由此产生的电子非线性光学响应之间建立直接联系。从完整的布洛赫带表象出发，我们表明破缺中心对称的晶格畸变会重构电子布洛赫波函数，修改光学偶极矩阵元，并激活在中心对称结构中被禁止的非线性光学路径。我们根据畸变诱导的电子态重构和光学跃迁矩阵元推导了二阶极化率，证明电子SHG极化率与极性畸变呈线性关系，即χ⁽²⁾(Q)∝Q，导致SHG强度与破缺中心对称的序参数呈二次关系。当极性模式被太赫兹电场相干驱动时，产生的随时间变化的晶格畸变会动态重构电子态，从而调制光学SHG响应，在主导阶满足I₂ω(t)∝|Q(t)|²。该框架将THz驱动的晶格动力学与负责光学SHG的电子带间过程区分开来，这在不存在低能载流子动力学的绝缘铁电体中尤为重要。我们的理论因此为非平衡极性晶格动力学与超快电子非线性光学之间提供了微观桥梁。
英文摘要
Optical second-harmonic generation (SHG) is a powerful probe of ferroelectric order, yet its microscopic origin and dynamical control are often understood primarily from symmetry considerations rather than from the underlying electronic processes. Here, we develop a microscopic theory of terahertz-controlled optical SHG in displacive ferroelectrics, establishing a direct connection between THz-driven polar lattice distortions and the resulting electronic nonlinear optical response. Starting from a complete Bloch-band representation, we show that an inversion-breaking lattice distortion reconstructs electronic Bloch wave functions, modifies optical dipole matrix elements, and activates nonlinear optical pathways that are forbidden in the centrosymmetric structure. We derive the second-order susceptibility in terms of the distortion-induced reconstruction of electronic states and optical transition matrix elements, and demonstrate that the electronic SHG susceptibility is linear in the polar distortion, $χ^{(2)}({\bf Q})\propto{\bf Q}$, leading to an SHG intensity quadratic in the inversion-breaking order parameter. When the polar mode is coherently driven by a terahertz electric field, the resulting time-dependent lattice distortion dynamically reconstructs the electronic states and thereby modulates the optical SHG response, with $I_{2ω}(t)\propto|{\bf Q}(t)|^2$ to leading order. This framework distinguishes the THz-driven lattice dynamics from the electronic interband processes responsible for optical SHG, which is particularly important in insulating ferroelectrics where low-energy carrier dynamics are absent. Our theory thus provides a microscopic bridge between nonequilibrium polar lattice dynamics and ultrafast electronic nonlinear optics.
