Franceschini Paolo, Tognazzi Andrea, Chernyak Anna M, Musorin Alexander I, Cino Alfonso C, Fedyanin Andrey A, De Angelis Costantino
Department of Information Engineering, University of Brescia, Via Branze 38, 25123, Brescia, Italy.
National Institute of Optics - National Research Council (INO-CNR), Via Branze 45, 25123, Brescia, Italy.
Nanophotonics. 2024 Jan 2;13(1):1-8. doi: 10.1515/nanoph-2023-0389. eCollection 2024 Jan.
Nanostructures proved to be versatile platforms to control the electromagnetic field at subwavelength scale. Indeed, high-quality-factors nanocavities have been used to boost and control nonlinear frequency generation by increasing the light-matter interaction. However, nonlinear processes are triggered by high-intensities, which are provided by ultrashort laser pulses with large bandwidth, which cannot be fully exploited in such devices. Time-varying optical systems allow one to overcome the time-bandwidth limit by modulating the cavity external coupling. Here we present a general treatment, based on coupled mode theory, to describe second harmonic generation in a doubly resonant cavity for which the quality-factor at the fundamental frequency is modulated in time. We identify the initial quality factor maximizing second harmonic efficiency when performing -boosting and we predict a theoretical energy conversion efficiency close to unity. Our results have direct impact on the design of next generation time-dependent metasurfaces to boost nonlinear frequency conversion of ultrashort laser pulses.
纳米结构被证明是在亚波长尺度上控制电磁场的通用平台。实际上，高品质因子的纳米腔已被用于通过增强光与物质的相互作用来促进和控制非线性频率产生。然而，非线性过程是由高强度触发的，而高强度是由具有大带宽的超短激光脉冲提供的，在这类器件中无法充分利用。时变光学系统允许通过调制腔的外部耦合来克服时间带宽限制。在此，我们基于耦合模理论给出一种通用处理方法，以描述在双共振腔中二次谐波产生的情况，其中基频的品质因子随时间调制。我们确定了在进行增强时使二次谐波效率最大化的初始品质因子，并预测理论能量转换效率接近100%。我们的结果对下一代随时间变化的超颖表面设计具有直接影响，以促进超短激光脉冲的非线性频率转换。
