实验研究了主动调Q掺镱光纤激光器(YDFL)中放大自发辐射(ASE)对调Q脉冲形成和演化的影响。结果表明,尾纤型声光调制器(AOM)打开过快和掺镜光纤(YDF)增益瞬态特性间的综合相互作用结果,使得注入至腔内的初始宽带ASE形成功率波动,并在腔内循环放大,导致输出脉冲呈多峰结构;而注入的宽带ASE因功率过高会导致YDF的增益自饱和效应,制约高增益的获取,使激光器难以获得调Q激光脉冲,输出脉冲主要为调Q的ASE脉冲;通过引入光纤布拉格光栅(FBG),可以有效抑制YDF中因ASE产生的增益饱和效应,YDF工作在高增益状态,有利于获得低阈值、窄脉宽和高峰值功率的调Q激光脉冲。引入FBG后,在160 mW抽运时,实验测得的调Q激光脉冲峰值功率和脉宽分别为40.7 W和30 ns。

The influences of amplified spontaneous emission (ASE) on the formation and evolution of pulses in actively Q-switched ytterbium-doped fiber laser (YDFL) are investigated experimentally. The experimental results show that the combined effect between the short switching time and the gain transient property of ytterbium-doped fiber (YDF) causes the initial ASE power fluctuation,which then forms the multi-peak structure in the output pulse after having been circulated and amplified in the cavity. Meanwhile,the high-level broadband ASE may give rise to the gain self-saturation effect in the YDF,making it difficult to form Q-switched laser pulses for the fiber laser. The output pulses may be eventually Q-switched ASE pulses,giving lower peak-power and larger pulse duration. By using fiber Bragg grating (FBG) to suppress the gain self-saturation effect,the gain supplied by the YDF can be greatly enhanced,making it easy for the laser to achieve the Q-switched laser pulse with low threshold,small duration,and high peak-power. When the YDFL with FBG is pumped with 160 mW,the Q-switched laser pulses with the peak power of 40.7 W and the duration of 30 ns are achieved.