TOPTEC Research Center, Institute of Plasma Physics of the Czech Academy of Sciences, Za Slovankou 1782/3, 182 00, Prague, Czech Republic.
Technical University of Liberec, Faculty of Mechatronics, Informatics and Interdisciplinary Studies, Studentská 1402/2, 461 17, Liberec, Czech Republic.
Sci Rep. 2023 May 29;13(1):8658. doi: 10.1038/s41598-023-35593-8.
Strong second harmonic generation (SHG) in silicon nitride has been extensively studied-among others, in terms of laser-induced SHG enhancement in SiN waveguides. This enhancement has been ascribed to the all-optical poling induced by the coherent photogalvanic effect. Yet, an analogous process for SiN thin films has not been reported. Our article reports on the observation of laser-induced threefold SHG enhancement in SiN thin films. The observed enhancement has many features similar to all-optical poling, such as highly nonlinear power dependence, cumulative effect, or connection to the SiN-Si interface. However, identical experiments for low-oxygen silicon oxynitride thin films lead to complex behavior, including laser-induced SHG reduction. Following a thorough experimental study, including the effects of repetition rate or pulse length, the observed results were ascribed to heat-induced SHG variation. In addition to revealing a new mechanism of laser-induced SHG variation, our results also provide a means to identify this mechanism.
氮化硅中的强二次谐波产生（SHG）已经得到了广泛的研究——例如，在 SiN 波导中的激光诱导 SHG 增强方面。这种增强归因于相干光电离效应引起的全光极化。然而，类似的 SiN 薄膜过程尚未有报道。我们的文章报道了在 SiN 薄膜中观察到的激光诱导三倍 SHG 增强。观察到的增强具有许多与全光极化相似的特征，例如高度非线性的功率依赖性、累积效应或与 SiN-Si 界面的连接。然而，对于低氧氮化硅薄膜的相同实验导致了复杂的行为，包括激光诱导的 SHG 减少。在进行了彻底的实验研究，包括重复率或脉冲长度的影响后，观察到的结果归因于热诱导的 SHG 变化。除了揭示激光诱导 SHG 变化的新机制外，我们的结果还提供了一种识别该机制的方法。
