摘要
掺镱超快光纤激光器因光束质量好、输出功率高而被广泛应用于科学研究、工业加工、医疗诊断等领域.大模场面积的棒状光纤可以提供平均功率在百瓦量级的高能量飞秒脉冲输出,本文基于掺镱棒状光纤搭建了啁啾脉冲放大系统,详细研究脉冲输入功率对脉冲放大及压缩的影响.实验结果表明,在低放大功率下(＜160 W)增大输入功率可提升放大效率且脉冲压缩质量基本不受影响;当放大功率进一步增大时,需选择合适的输入功率避免积累过量非线性相位.该啁啾脉冲放大系统可将20 W圆偏光输入放大至305 W,压缩后产生平均功率为273 W、能量为273 μJ的264 fs脉冲,脉冲平均功率和峰值功率比Pedersen课题组(Pedersen M E,Johansen M M,Olesen A S,Michieletto M,Gaponenko M,Maack M D 2022 Opt.Lett.47 5172)结果约提升了一倍.
Abstract
Ytterbium-doped ultrafast fiber lasers are widely used in scientific research,industrial processing,medical diagnosis,and other fields due to their excellent beam quality and high power output.The larger mode area allows the fiber to transmit higher peak-pulse power.The commercial rod-type Ytterbium-doped fiber with a core diameter of 85 μm,produced by NKT in Denmark,can produce ultra-short pulses on the order of 100 watts and 100 microjoules.Based on this rod-type fiber,we construct a chirped-pulse amplification(CPA)system in which the high-efficiency transmission gratings and temperature-tunable chirped fiber Bragg grating(CFBG)are used to compensate for dispersion.We investigate the effect of power input on the amplified power and pulse compression quality,and find that higher power input slows down the gain saturation and improves amplification efficiency.At power inputs of 20 W and 30 W,we obtain power outputs of 305 W and 323 W respectively,with an amplification efficiency of about 80％.To reduce the accumulation of nonlinear phase shift,we use circular polarization amplification.At low power outputs(less than 160 W),the effect of nonlinear phase accumulation on the compressed pulse is negligible,and the increase in power input increases the amplification efficiency.When the power output exceeds 200 W,the cumulative increase of nonlinear phase shift reduces the pulse compression quality,which implies that the input power is appropriately reduced to the power range between 5 W and 20 W.With a power input of 20 W and pump power of 429 W,the power output can reach 305 W.After pulse is compressed by using a diffraction-grating pair,this rod-type fiber CPA system can deliver 1 MHz,264 fs pulses with 273 W in average power.These results provide an important experimental basis for optimizing the performance of high-power and high-energy ultrafast fiber lasers.
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