In this work we apply second harmonic microscopy to the analysis of damage tracks inscribed by femtosecond laser irradiation in a Nd:YAG crystal. While second harmonic generation is not expected in the bulk of this centrosymmetric material, the 2D and 3D images obtained via second harmonic microscopy show that the induced micro-modification of the crystal structure leads to a localized generation of the nonlinear signal. The nature of this modification and its dependence on irradiation and detection parameters is discussed. These findings demonstrate the capability of second harmonic microscopy for the morphological analysis of written structures in Nd:YAG and open the door for the design and fabrication of new nonlinear structures to be integrated in novel photonic devices.

中文翻译：

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揭开飞秒激光微结构 Nd:YAG 晶体产生二次谐波的神秘面纱

在这项工作中，我们应用二次谐波显微镜来分析 Nd:YAG 晶体中飞秒激光照射刻出的损伤轨迹。虽然这种中心对称材料的主体不会产生二次谐波，但通过二次谐波显微镜获得的 2D 和 3D 图像表明，晶体结构的诱导微修改导致非线性信号的局部生成。讨论了这种修饰的性质及其对辐照和检测参数的依赖性。这些发现证明了二次谐波显微镜对 Nd:YAG 写入结构进行形态分析的能力，并为设计和制造集成到新型光子器件中的新型非线性结构打开了大门。