角膜屈光手术用飞秒脉冲光纤激光器

Femtosecond fiber laser for femtosecond LASIK

目的 搭建脉冲宽度小于200 fs,单脉冲能量大于50 nJ的低重复频率飞秒光纤激光器;利用光学扩束和聚焦实现该激光器在猪眼角膜上爆破打孔的实验效果.方法 实验研究.采用具有超长保偏光纤的放大自相似结构的环形腔激光器作为种子源;采用预压缩-放大-二次压缩的结构对种子源输出的信号光进行放大和整形,实现高于参数水平的锁模激光输出;采用透镜组对激光进行扩束;采用不同数值孔径的平场物镜对扩束后的激光进行聚焦,并且设计平场物镜的焦点在角膜组织内部,实现猪眼角膜爆破打孔实验.结果 激光器实现了19.1 MHz、109 fs、1.4 W、73.2 nJ的锁模激光输出.在将锁模激光经过透镜组进行5倍扩束以后,采用数值孔径为0.2的平场物镜对激光进行聚焦,聚焦点在猪眼角膜组织上打出的爆破孔孔径为45～75 μm;采用数值孔径为0.5的平场物镜对激光进行聚焦,聚焦点在猪眼角膜组织上打出的爆破孔孔径约为30 μm.结论 在低重复频率的放大自相似结构的环形腔激光器中引入保偏光纤能有效地提高激光器的稳定性;预压缩-放大-二次压缩的放大整形结构可实现高质量的脉冲压缩放大效果;利用扩束镜和高数值孔径的平场物镜可实现高质量的眼角膜组织爆破打孔.

Objective To build a low repetition rate femtosecond fiber laser with its pulse width narrower than 200 fs and pulse energy bigger than 50 nJ and realize making blasting holes on pig cornea by optical expanding and focusing femtosecond laser.Methods Experimental study.Introducing very long polarization maintaining fiber into the ring cavity,the mode-locking fiber laser under the similariton amplifier scheme was used to be the oscillator.The signal laser was amplified and compressed by propagating it through the construction of pre-chirp,amplifier and de-chirp to realize outputting high quality pulse train.The high power fiber laser was expanded by the lens group.The expanded laser beam was focused into the pig cornea by the plane objective with different numerical aperture （NA） to realize making high quality blasting holes.Results This laser facility realized outputing a very stable 19.1 MHz,109 fs,1.4 W,73.2 nJ mode-locking fiber laser.After five fold expansion,the laser beam was focused into the pig cornea by the NA=0.2 plane objective to get blasting holes whose aperture were 45～75 μm.Focusing the laser beam into the pig cornea by the NA=0.5 plane objective,the aperture of the blasting holes were about 30 μm.Conclusion Introducing very long Polarization Maintaining fiber into the similariton amplifier ring cavity can improve stability effectively.The construction of pre-chirp,amplifier and de-chirp can use the nonlinear affects to depress the third order dispersion to realize high quality amplify and compression.After expanded by lens group,using higher NA plane objective to focus the expanded laser beam into the cornea can realize making higher quality blasting holes.