Tirole Romain, Vezzoli Stefano, Saxena Dhruv, Yang Shu, Raziman T V, Galiffi Emanuele, Maier Stefan A, Pendry John B, Sapienza Riccardo
Blackett Laboratory, Department of Physics, Imperial College London, London, SW7 2BW, UK.
Photonics Initiative, Advanced Science Research Center, City University of New York, 85 St. Nicholas Terrace, 10031, New York, NY, USA.
Nat Commun. 2024 Sep 5;15(1):7752. doi: 10.1038/s41467-024-51588-z.
Time-varying metamaterials rely on large and fast changes of the linear permittivity. Beyond the linear terms, however, the effect of a non-perturbative modulation of the medium on harmonic generation remains largely unexplored. In this work, we study second harmonic generation at an optically pumped time-varying interface between air and a 310 nm Indium Tin Oxide film. We observe a modulation contrast at the second harmonic wavelength up to 93% for a pump intensity of 100 GW/cm, leading to large frequency broadening and shift. We experimentally demonstrate that a significant contribution to the enhancement comes from the temporal modulation of the second order nonlinear susceptibility. Moreover, we show the frequency-modulated spectra resulting from single and double-slit time diffraction could be exploited for enhanced optical computing and sensing, enabling broadband time-varying effects on the harmonic signal and extending the application of Epsilon-Near-Zero materials to the visible range.
时变超材料依赖于线性介电常数的大幅快速变化。然而，除了线性项之外，介质的非微扰调制对谐波产生的影响在很大程度上仍未得到探索。在这项工作中，我们研究了在光泵浦的空气与310纳米氧化铟锡薄膜的时变界面处的二次谐波产生。对于100 GW/cm的泵浦强度，我们在二次谐波波长处观察到高达93%的调制对比度，导致大幅的频率展宽和频移。我们通过实验证明，对增强有显著贡献的是二阶非线性极化率的时间调制。此外，我们表明，单缝和双缝时间衍射产生的调频光谱可用于增强光学计算和传感，实现对谐波信号的宽带时变效应，并将近零介电常数材料的应用扩展到可见光范围。
