The period (\(\wedge \)) of nanograting in sapphire varied from 320 to 398 nm with increasing the laser fluence, which is similar to the change trend of period of the near-subwavelength ripples previously observed on the material surface (\(0.4<\wedge / \lambda <1\)) (Huang et al. in ACS Nano 3:4062, 2009). The result shows that the interference of the incident laser with the plasma could take place at the high-excited state of internal modified interface and leads to a spatial modulation of the local energy (fluence) distribution. The initial plasma–laser interference and the subsequent nanocrack-assisted plasma–laser coupling were used to explain the growth of nanograting what we have observed experimentally. Using a finite-difference time-domain method, we simulated the redistribution of laser fluence about the nanocracks, which derived from the pre-induced periodic refractive index changes in the focal volume after the acid etching. The experimental result and theoretical simulation can be in good agreement. In addition, we realized the erasing and rewriting of nanograting by using two beams of orthogonally polarized femtosecond laser pulses. This study can provide new proof for the physical mechanism of laser-induced nanograting and offer a reference for the fabrication of nanodevices in the substrate of sapphire.

蓝宝石中纳米光栅的周期（\（\ wedge \））从320到398 nm随激光能量密度的增加而变化，这类似于先前在材料表面观察到的近亚波长波纹的周期变化趋势（\（ 0.4 <\ wedge / \ lambda <1 \）（Huang等人，ACS Nano 3：4062，2009）。结果表明，入射激光对等离子体的干扰可能发生在内部修饰界面的高激发状态，并导致局部能量（注量）分布的空间调制。最初的等离子体-激光干扰和随后的纳米裂纹辅助等离子体-激光耦合被用来解释我们在实验中观察到的纳米光栅的生长。使用有限差分时域方法，我们模拟了纳米密度裂纹周围激光能量密度的重新分布，该分布是由酸蚀刻后焦点体积中的预诱导周期性折射率变化得出的。实验结果与理论模拟吻合良好。此外，我们通过使用两束正交偏振的飞秒激光脉冲实现了纳米光栅的擦除和重写。这项研究可以为激光诱导纳米光栅的物理机理提供新的证据，并为在蓝宝石衬底上制造纳米器件提供参考。