真空条件下激光诱导光纤损伤特性研究

Laser induced damage and fracture of optical fiber in vacuum chamber

实验研究并分析了调QNd:YAG脉冲激光诱导光纤损伤特性.设计了在真空条件下全石英光纤传输1064nm脉冲激光实验.通过将激光注入光纤端面气压降低到10—100Pa,光纤端面击穿阈值提高到大气环境下的1.85倍.结合光纤端面损伤形貌分析可知,光纤端面损伤主要是由于激光驻波场和烧蚀共同作用的结果,光纤端面或内部大量的缺陷降低了光纤抗激光损伤的能力.在真空条件下由于光纤端面光学击穿阈值的提高,激光诱导光纤损伤特性又表现出了另外一种损伤模式——光纤初始输入段损伤.它发生在光纤输入段附近,距离光纤输入端面为5—30mm之间,损伤形貌是长度为1—3mm的炸裂性损伤.通过理论和仿真分析,证明光纤初始输入段损伤是由于注入激光在光纤包层和纤芯界面处初次反射造成激光"聚焦"所引起.

The characteristics of Q-switched Nd： YAG laser induced damage to fused optical fibers has been investigated experimentally. A scheme of laser induced damage to optical fiber in a vacuum chamber was presented and carried out. With this scheme,the air pressures on the input face of optical fiber was reduced to 10—100 Pa,laser-induced breakdown on the optical fiber end face was significantly suppressed,the breakdown threshold increased to 1. 85 times that in the atmosphere. The damage morphology of optical fiber end face was analyzed,which was the result of the combined actions of laser pulses standing wave and ablation. The existence of a large number of defects on or under the fiber end face reduces the anti-laser-induced damage ability of the optical fibers. Under the vacuum condition,another damage mode——the fiber ＂entry＂segment damage occurred. This ＂entry＂segment damage mode occurred at 5—30 mm distances from the input end face of optical fiber,the blasting damage area was 1—3 mm long along the fiber core axis. That the initial reflection of laser beam at the interface of fiber cladding and core causes laser focusing which induced the entry damage,was proved by theory and simulations.