使用飞秒激光, 采用激光直写技术在有机玻璃(PMMA)内部写出折射率变化(Δn)的光学结构, 制备得到了体光栅, 将一组体光栅置于室温, 另一组进行退火处理。通过试验对比两组样品, 探索了退火处理对Δn的影响机理。试验结果表明：退火未对光学结构的物理尺寸造成明显影响, 但造成了拉曼光谱中1640 cm-1拉曼峰强度的增加, 对应于Δn的增大; 飞秒激光在PMMA内产生的折射率变化的光学结构不够稳定, Δn随时间的延长会缓慢增大, 退火处理会加快Δn的增大。

An optical structure with refractive index change (Δn) is written out inside polymethyl methacrylate (PMMA) by a femtosecond laser with laser direct writing technique, and the volume gratings are fabricated. One group of volume gratings is kept at room temperature, and the other group is annealed. By the experimental comparison between the two groups, the effect mechanism of annealing on Δn is explored. The experimental results show that, there exists no obvious difference in feature size of optical structure caused by annealing, and the intensity of Raman peak at 1640 cm-1 is increased as a consequence of annealing, which corresponds to the increase of Δn. Meanwhile, optical structures with refractive index change inside PMMA induced by femtosecond lasers are not stable. The Δn value increases slowly with the increase of time, and annealing treatment can accelerate this increase.