飞秒激光在LiNbO_3晶体上烧蚀衍射光栅

Diffraction Gratings Ablated on LiNbO_3 Crystal by Femtosecond Laser Pulses

利用脉冲宽度为50 fs,中心波长为800 nm,重复频率为1000 Hz的飞秒激光脉冲在LiNbO3晶体上烧蚀表面衍射光栅,采用632.8 nm的He-Ne激光测量不同光栅的衍射效率.在激光脉冲能量和光栅常数相同的情况下,烧蚀速率由20μm/s增大到200μm/s时,所加工光栅的1级衍射效率从1.7%增大到2.3%;如果光栅常数和烧蚀速率不变,将激光脉冲能量由70 nJ增大到110 nJ,所加工光栅的1级衍射效率从1.9%减小到1.3%;随着光栅常数的增大,在LiNbO3晶体上烧蚀光栅的各级衍射效率也随之增加.对实验结果进行理论分析表明,可以通过提高烧蚀速率、降低激光脉冲能量和增大光栅常数来提高飞秒激光加工光栅的衍射效率.

Surface diffraction gratings are written on LiNbO3 crystal by femtosecond laser pulses with the wavelength of 800 nm, pulse duration of 50 fs and repetition frequency of 1000 Hz. The diffraction efficiencies of the gratings ablated with various parameters are measured by He-Ne laser with the wavelength of 632.8 nm. The 1-order diffraction efficiencies of the gratings improve from 1.7% to 2.3% with the increase of ablation speed from 20 μm/s to 200 μm/s, and decrease from 1.9% to 1.3% with the increase of pulse energy from 70 nJ to 110 nJ, respectively. The experimental and theoretical results show that the diffraction efficiencies of gratings can be improved by increasing ablation speed and grating constant or decreasing pulse energy.