We report resonantly enhanced and switchable third order nonlinearity in magnesium thin films. Utilizing an optical parametric oscillator as a tunable broadband light source, we find a highly wavelength dependent third harmonic conversion efficiency, exhibiting a 40- to 50-fold signal increase over the investigated wavelength range between 1300 and 1800 nm. We relate this unusually strong increase of the intrinsic magnesium material nonlinearity to resonant sp-interband transitions around 0.7 eV or 1770 nm in the fundamental wavelength range, multiplying their impact on the conversion efficiencies. Moreover, we make use of the drastic change in the optical properties of magnesium at the phase transition between metallic magnesium and dielectric magnesium hydride by in situ hydrogenation. We are able to cyclically switch the nonlinearity and the efficiency of the third harmonic conversion process. The time-dependence of the nonlinear signal is complex and is a consequence of several contributions, including the hydrogen concentration-dependent change in the intrinsic nonlinear susceptibility, the change in the surface morphology during hydrogenation and dehydrogenation, as well as the volume change of the material. While shedding new light on the structural and morphological changes in such magnesium thin films, we envision that the switchable and large resonant third-order nonlinearity in magnesium will find applications in nanostructured systems, unlocking additional degrees of freedom in design and implementation, such as wavelength dependency and switchable material nonlinearities.

中文翻译：

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镁薄膜中金属到绝缘体跃迁的可切换光学非线性

我们报告了镁薄膜共振增强和可切换的三阶非线性。利用光学参量振荡器作为可调宽带光源，我们发现了高度依赖于波长的三次谐波转换效率，在所研究的1300至1800 nm波长范围内，信号增加了40至50倍。我们将本征镁材料非线性度的这种异常强劲的增长与基本波长范围内大约0.7 eV或1770 nm处的共振sp-带间跃迁相关联，从而倍增了它们对转换效率的影响。此外，我们利用原位氢化技术在金属镁和氢化镁之间的相变中利用了镁光学性质的急剧变化。我们能够循环切换非线性和三次谐波转换过程的效率。非线性信号的时间依赖性是复杂的，并且是多种贡献的结果，包括固有非线性磁化率中氢浓度的变化，加氢和脱氢过程中表面形态的变化以及碳纳米管的体积变化。材料。尽管我们对这种镁薄膜的结构和形态变化有了新的了解，但我们设想镁中可切换的大共振三阶非线性将在纳米结构系统中找到应用，从而在设计和实现方面释放更多的自由度，例如波长依赖性和可切换的材料非线性。