实验研究了掺镱大模场面积光子晶体光纤(LMA PCF)飞秒激光二级放大系统。振荡级和预放基于双包层保偏大模场面积光子晶体光纤,主放大级基于7芯大模场面积光子晶体光纤。7个纤芯六角排布,总的模场面积高达5000 μm2,有效降低了光纤中的非线性。而且各个纤芯之间离散分布,热应力等问题也得到了缓解。当抽运功率较小时,输出的模式为多个超模的叠加。在高功率抽运下,获得了平坦的同相位超模输出,对应远场具有很好的高斯分布。获得了重复频率1 MHz,平均功率24 W的激光放大输出。经光栅对压缩后,脉冲宽度为110 fs,对应的峰值功率达到150 MW。

A ytterbium-doped large mode area photonic crystal fiber (LMA PCF) femtosecond laser dual-stage amplifier is experimentally studied.Single polarization LMA PCFs are used in the oscillator and pre-amplifier,while a 7-core LMA PCF is used in the main-amplifier.The seven cores are arranged in array type with a mode field area up to 5000 μm2 which effectively suppress the nonlinearity in the fiber.In addition,the heat and stress induced beam distortions are reduced because the cores are discrete distributed.At low pump power,the output features a complex beam profile resulting from a superposition of several supermodes.Flat in-phase supermode and Gaussian-shaped far-field distribution are realized under high pump power.Average power of 24 W laser pulses at a repetition rate of 1 MHz are obtained.The pulses duration can be compressed to 110 fs with peak power up to 150 MW.