Opt Lett. 2023 Apr 1;48(7):1954-1957. doi: 10.1364/OL.483894.
In this Letter, we report the first, to the best of our knowledge, femtosecond inscription of volume Bragg gratings (VBGs) directly inside phase-mask substrates. This approach showcases enhanced robustness as both the interference pattern generated by the phase mask and the writing medium are inherently bonded together. The technique is employed with 266-nm femtosecond pulses loosely focused by a 400-mm focal length cylindrical mirror inside fused-silica and fused-quartz phase-mask samples. Such a long focal length reduces the aberrations induced by the refractive-index mismatch at the air/glass interface which allows to inscribe a refractive-index modulation simultaneously over a glass depth reaching 1.5 mm. A decreasing gradient of the modulation amplitude from 5.9 × 10 at the surface to 1 × 10 at a 1.5-mm depth is observed. This technique has therefore the potential of increasing significantly the inscription depth of femtosecond-written VBGs.
在这封信件中，我们报告了我们所知的第一个在相位掩模衬底中直接进行飞秒激光写入体布拉格光栅（VBG）的案例。这种方法具有增强的稳定性，因为相位掩模产生的干涉图案和写入介质本质上是结合在一起的。该技术使用 266nm 飞秒脉冲，通过一个 400mm 焦距的圆柱形镜子在熔融硅和熔融石英相位掩模样品中进行非聚焦处理。这种长焦距可以减少由空气/玻璃界面折射率失配引起的像差，从而可以在玻璃深度达到 1.5mm 的范围内同时写入折射率调制。在从表面的 5.9×10 到 1.5mm 深度的 1×10 的调制幅度的递减梯度。因此，这种技术有可能显著增加飞秒写入 VBG 的写入深度。
