近日，以色列理工学院Mordechai Segev团队研究了光子时间晶体中的二次谐波产生和非线性频率转换。该研究于2025年4月2日发表在《光：科学与应用》杂志上。

课题组研究了折射率随时间突变和周期性变化的光子时间晶体中二次谐波产生的非线性过程，并得到了该过程的相位匹配条件。结果发现，即使在没有相位匹配的情况下，二次谐波的产生也会大大增强，这取决于光子时间晶体动量隙中模式的指数增长。此外，在这些条件下，高阶谐波的级联以指数速度增长。该过程是稳健的，不需要相位匹配、谐振或阈值的存在，从调制中获取能量。

附：英文原文

Title: Second harmonic generation and nonlinear frequency conversion in photonic time-crystals

Author: Konforty, Noa, Cohen, Moshe-Ishay, Segal, Ohad, Plotnik, Yonatan, Shalaev, Vladimir M., Segev, Mordechai

Issue&Volume: 2025-04-02

Abstract: We study the nonlinear process of second harmonic generation in photonic time-crystals, materials with refractive index that varies abruptly and periodically in time, and obtain the phase matching condition for this process. We find conditions for which the second harmonic generation is highly enhanced even in the absence of phase matching, governed by the exponential growth of the modes residing in the momentum gap of the photonic time crystal. Additionally, under these conditions, a cascade of higher-order harmonics is generated at growing exponential rates. The process is robust, with no requirement for phase-matching, the presence of a resonance or a threshold, drawing energy from the modulation.

DOI: 10.1038/s41377-025-01788-z

Source: https://www.nature.com/articles/s41377-025-01788-z