摘要
基于窄线宽皮秒种子源和三级主振荡光纤放大系统,搭建了一台高峰值功率的皮秒脉冲光纤激光器,并基于该激光器研究了不同信号光功率对最终输出信号拉曼抑制比的影响。该激光器采用可饱和吸收镜进行锁模,窄线宽种子经过三级放大后,输出激光的中心波长为1064.2 nm,3 dB线宽为0.4 nm,平均功率为103 W,重复频率为29 MHz,脉冲宽度为32.4 ps,斜率效率为72.8%,峰值功率达到109.6 kW,拉曼抑制比为35 dB,偏振消光比为15 dB,光束质量因子M^(2)约为1.11。其功率的进一步提升受限于受激拉曼散射效应。该激光器结构紧凑,性能优异,可应用于材料冷加工、精密测距和光谱学等领域。
Objective Narrow-linewidth picosecond fiber lasers concurrently exhibit advantages such as high peak power and high spectral purity,and have been widely used in the fields of nonlinear frequency conversion,cold processing of materials,precise ranging,and ultrafast spectroscopy.Taking nonlinear frequency conversion as an example,obtaining blue-green laser output based on frequency doubling of the 1μm band laser is a highly mature technical approach.Owing to the matching characteristics of the frequency doubling crystal,to achieve a relatively high frequency doubling conversion efficiency,the 1μm band laser as the fundamental frequency light often demands high peak power,narrow linewidth,and high brightness.At present,the master oscillator power amplifier(MOPA)configuration is typically employed to realize narrow-linewidth,high-brightness,and high-peak-power picosecond pulsed fiber lasers.Nevertheless,the laser output generated by this MOPA structure is restricted by amplified spontaneous emission(ASE)and stimulated Raman scattering(SRS).Super-large mode area gain fiber is commonly utilized to suppress SRS for achieving laser output with higher peak power.However,this often results in deterioration of beam quality.Conventional few-mode fiber laser can achieve laser output near the diffraction limit,but cannot simultaneously achieve high average power and high pulse energy.Incorporating the merits of the above-mentioned two types of fiber laser,this paper proposes a picosecond pulsed fiber laser simultaneously achieving high peak power and high brightness picosecond pulsed laser output.Methods The experimental system is shown in Fig.1.The picosecond pulsed fiber laser is composed of an oscillator seed and a three-stage amplification structure.The narrow-linewidth picosecond pulsed seed source is a linear cavity semiconductor saturable absorber mirror(SESAM)mode-locked fiber oscillator operating at 1064 nm,whose structure is shown in Fig.2.A 976 nm semiconductor laser diode(LD)pumps a single-clad polarization-maintaining ytterbium-doped active fiber with a core absorption of 250 dB/m through a 976/1064 nm wavelength division multiplexer(WDM).A SESAM with a modulation depth of 32%and a relaxation time of 3 ps is used as the high-reflection mirror to form the resonant cavity.When the saturable absorber is in the saturated state,the signal light passes through the saturable absorber completely and is reflected by the end mirror with nearly 100%reflection to ensure the stability of the oscillation system.To reduce the mode-locking threshold,a fiber Bragg grating(FBG)with a 3 dB bandwidth of 0.1 nm,a center wavelength of 1064.2 nm,and a reflectivity of 70%is used as the coupling grating at the output end of the oscillator system.The seed light is amplified in the main amplification system after passing through two pre-amplification stages.The gain fiber in the main amplification stage has a core diameter of 30μm,a cladding absorption of 7.2 dB/m at 976 nm,a core numerical aperture of 0.06,an inner cladding diameter of 250μm,and a cladding numerical aperture of 0.46.This experiment explores the influence of the properties of the signal light injected into the main amplification system on the final output laser power and Raman suppression ratio.Results and Discussions The output power of the secondary preamplifier is controlled at 1.5 W.In the main amplification system,the length of the gain fiber is 2.3 m,and the fiber length of the passive devices such as cladding power stripper(CPS)and quartz block head(QBH)at the back end is optimized to 1.5 m.When the pump power is increased to 140 W,the maximum output power is 103 W,with a slope efficiency of 72.8%.The output results are shown in Fig.5.Figure 5(a)shows the variation of the output laser power with the pump power.Figure 5(b)shows the output spectrum at the maximum output power of 103 W.At this time,due to the influence of the self-phase modulation(SPM)effect,the output spectrum is significantly broadened,as shown in the inset in Fig.5(b).The SRS suppression ratio is 35 dB,and the polarization extinction ratio is 15 dB.Further power amplification is limited by the SRS effect.Figure 5(c)shows a schematic diagram of the final output pulse duration,which is broadened to 32.4 ps,with a repetition rate of 29 MHz and a 3 dB spectral width of 0.42 nm.The beam quality and beam waist profile at the maximum output power measured by the beam quality analyzer are shown in Fig.5(d),with a beam quality factor M^(2) of 1.11(transverse beam quality factor M 2 x=1.13 and longitudinal beam quality factor M 2 y=1.09).Conclusions This paper discusses a narrow-linewidth picosecond pulsed fiber laser with a MOPA structure.The mode-locked seed source built independently by SESAM is amplified through three stages to achieve high peak-power laser output.The experiment investigates the influence of the injection power of the main amplification stage on the Raman threshold of the final output signal during the picosecond pulse amplification process.The main amplification system adopts high-absorption polarization-maintaining gain fibers.By optimizing the output power of the secondary pre-amplification and the system structure,a laser output with a central wavelength of 1064.2 nm,an average power of 103 W,a repetition rate of 29 MHz,a pulse duration of 32.4 ps,and a peak power of 110.9 kW is achieved.At this time,the Raman suppression ratio is 35 dB,the polarization extinction ratio is 15 dB,and the M^(2) is 1.11.Further power enhancement is limited by the SRS effect.
作者
程俊杰
陈默
舒畅
罗永辉
李海清
彭景刚
邢颍滨
戴能利
李进延
Cheng Junjie;Chen Mo;Shu Chang;Luo Yonghui;Li Haiqing;Peng Jinggang;Xing Yingbin;Dai Nengli;Li Jinyan(Wuhan National Laboratory for Optoelectronics,Huazhong University of Science and Technology,Wuhan 430074,Hubei,China)
出处
《中国激光》
北大核心
2025年第11期55-61,共7页
Chinese Journal of Lasers
基金
国家重点研发计划(2023YFB4604500)。
关键词
光纤激光器
窄线宽
皮秒脉冲
主振荡功率放大
高功率激光
fiber lasers
narrow linewidth
picosecond pulse
main oscillation power amplification
high power laser
