摘要
高重复频率、高功率、高时间对比度的飞秒激光器,凭借极高的峰值功率与优异的时间分辨率,为阿秒科学、强场物理及高能粒子加速等前沿研究提供了重要技术支撑。然而,在提升平均功率的过程中,寄生脉冲干扰与噪声累积常导致时间对比度显著下降。针对这一问题,构建了一套基于克尔透镜锁模(KLM)振荡器与多通放大的飞秒激光系统:以重复频率为32.75 MHz、平均功率为46.9 W的KLM碟片振荡器作为种子光,将其注入36通放大系统后,实现了平均功率为304 W、脉冲宽度为567 fs、单脉冲能量为9.1μJ的激光输出。该系统连续运行1 h的功率均方根(RMS)波动小于0.6%,横向光束质量因子M和纵向光束质量因子M_(y)^(2)分别为1.15和1.16。值得注意的是,功率放大后该系统有效抑制了皮秒脉冲基底的产生,在1.1 ns时间窗口内,主脉冲与前后沿脉冲的时间对比度达99.85%,为高功率超快激光在强场相互作用等研究领域中的应用提供了强有力的技术平台。
Objective Femtosecond lasers combining high repetition rates,high average power,and excellent temporal contrast are indispensable tools for cutting-edge scientific research,including attosecond science,strong-field physics,and high-energy particle acceleration.Furthermore,their capability to deliver extremely high peak power with exceptional temporal resolution makes them ideally suited for precision laser-matter interactions.However,scaling the average power in the femtosecond regime presents substantial challenges,including parasitic pulses and amplified spontaneous emission(ASE)noise interference,which compromise temporal contrast and limit efficacy in high-precision applications such as transparent material processing,nanostructuring,and strong-field experiments.To address these constraints,we develop a high-performance Yb∶YAG thin-disk system,incorporating a Kerr-lensmode-locking(KLM)oscillator coupled with a quasi-collimated multi-pass amplification architecture.This configuration simultaneously achieves high average output powers,ultra-short pulse durations,and high repetition rates.It also effectively suppresses the generation of picosecond pedestals on the leading and trailing edges of the main pulse after power amplification while preserving beam quality,thereby enhancing the performance of femtosecond laser systems for precision scientific applications.Methods The experimental setup consists of two main stages:a KLM Yb∶YAG thin-disk oscillator and a thin-disk multi-passamplifier(TDMPA)(Fig.1).The oscillator adopts a Z-shaped cavity with an optical path length of~4.5 m,corresponding to a repetition rate of~33 MHz.Its home-made laser head integrates a high-performance Yb∶YAG thin disk.Under stable mode-lockingoperation,the seed laser delivers an average power of 46.9 W,with a pulse width of 410 fs,a spectral bandwidth of 2 nm,and a redshifted spectral center at 1030.6 nm.For power scaling,the collimated seed laser is injected into the TDMPA,which employs a quasi-collimated 36-pass configuration.Thirty-six high-reflectivity mirrors(reflectivity is R>99.99%@1030 nm)are mounted on adjustable water-cooled copper bases,enabling 18 round trips through the thin disk.The Yb∶YAG thin disk has a thickness of 100μm,a diameter of 20 mm,and a radius of curvature of~40 m.Its front surface features an anti-reflection(AR)coating(R<0.1%@969 nm and 1030 nm),while the rear surface is equipped with a high-reflection(HR)coating(R>99.9%@969 nm and 1030 nm)and bonded to a diamond heat sink.Optimized positions of the thin disk and mirrors result in a single-pass distance of 700 mm and a total optical path length of 25.2 m(Fig.1).The seed laser is collimated,and its diameter is adjusted via a telescope system before being injected into the multi-pass amplification system.The seed laser exits after 18 round trips[Fig.2(a)].Calculations based on the transfer matrix indicate that the diameter of the seed beam varies periodically without forming strong focal points throughout the entire transmission process[Fig.2(b)].Results and Discussions The seed laser is injected into the 36-pass amplifier,and its beam spot achieves uniform overlap on the thin disk after 18 superpositions[Fig.3(a)].Following multi-pass absorption,the seed power is reduced to 23 W.As the pump power increases,the amplifier output power grows linearly,while the optical-to-optical conversion efficiency improves steadily[Fig.3(b)].At a pump power of 810 W,the amplifier delivers a maximum average output power of 306 W without saturation,corresponding to a conversion efficiency of 32%and a single-pulse energy of 9.1μJ at a repetition rate of 32.75 MHz.Spectral evolution shows an initial broadening from 2.0 nm to 2.3 nm,followed by narrowing to 1.7 nm at the maximum power due to gain narrowing,accompanied by a slight blue shift.Temporally,the 410 fs seed pulses are compressed to 370 fs via the positive dispersion of the disk but broaden to 567 fs at the maximum output due to enhanced gain narrowing.The beam quality factors remain excellent,with M_(x)^(2)=1.15 and M_(y)^(2)=1.16 at the maximum output power of 306 W.The far-field intensity profile maintains a clean Gaussian shape,confirming the effectiveness of the quasi-collimated multi-pass geometry in preserving spatial coherence.Long-term stability measurements show a normalized root-mean-square(RMS)deviation of below 0.6%over 60 min for both the seed and amplified output,indicating excellent thermal management and mechanical stability.The beam pointing stability of the multi-pass amplifier is tested over 2 h(Fig.5).The RMS value of the beam position deviation in the horizontal direction is 42.37μm,and that in the vertical direction is 70.09μm.For a beam with a size of 2.3 mm×2.5 mm at the 1/e^(2) intensity level,the calculated RMS pointing stability is 1.84%in the horizontal direction and 2.80%in the vertical direction.These results indicate stable beam pointing under moderate vibration and temperature fluctuations.In future work,a beam pointing stabilization module will be integrated to further enhance the long-term pointing stability of the amplifier system.The temporal contrast is further evaluated using a third-order autocorrelator.For the seed laser with a pulse duration of 410 fs,the ratio of the main pulse intensity to the ASE signal intensity within a 1.1 ns temporal window is approximately 10⁷;after amplification,this ratio decreases to the order of 10⁶due to slight ASE accumulation.Despite this reduction,over 99.8%of the pulse energy remains confined to the main peak,with no evidence of picosecond-scale pedestal formation.The amplified pulses therefore maintain excellent temporal contrast at an average power of 306 W,confirming the system ability to deliver high-power femtosecond pulses suitable for precision applications.Conclusions We demonstrate a high-power femtosecond laser system based on a home-made Yb∶YAG thin-disk module,integrating KLM with a 36-pass quasi-collimated TDMPA.The system delivers an average output power of 306 W at a repetition rate of 32.75 MHz,with a pulse duration of 567 fs and a single-pulse energy of 9.1μJ.Excellent long-term stability is achieved,with a RMS deviation of less than 0.6%over 1 h continuous operation.Within a 1 ns temporal window,no picosecond-scale pedestal is observed,and the temporal contrast reaches 99.85%.The measured beam quality factors(M_(x)^(2)=1.15,M_(y)^(2)=1.16)confirm that both power scalability and pulse quality are well preserved.These results verify the feasibility of simultaneously achieving high repetition rates,high power,and high temporal contrast in a femtosecond thin-disk laser platform.Future work will focus on further optimizing the amplifier design and implementing temporal pulse shaping strategies to enhance both power scaling and temporal contrast,thereby pushing the frontiers of high-power ultrafast laser technology.
作者
和星宇
徐思志
刘星
李云
陈俊展
高瑜博
吴宠昊
赵俊清
郭春雨
吕启涛
阮双琛
He Xingyu;Xu Sizhi;Liu Xing;Li Yun;Chen Junzhan;Gao Yubo;Wu Chonghao;Zhao Junqing;Guo Chunyu;LüQitao;Ruan Shuangchen(Shenzhen Key Laboratory of Laser Engineering,College of Physics and Optoelectronic Engineering,Shenzhen University,Shenzhen 518060,Guangdong,China;Key Laboratory of Advanced Optical Precision Manufacturing Technology of Guangdong Higher Education Institutes,Sino-German College of Intelligent Manufacturing,Shenzhen Technology University,Shenzhen 518118,Guangdong,China;Han’s Laser Technology Industry Group Co.,Ltd.,Shenzhen 518103,Guangdong,China)
出处
《中国激光》
北大核心
2025年第23期327-333,共7页
Chinese Journal of Lasers
基金
国家重点研发计划(2022YFB3605800)
国家自然科学基金(62105225,62275174,61975136,61935014)
深圳市科技重大专项(KJZD20240903100205008)
深圳市高等院校稳定支持计划(20220719104008001,20220718173849001)
深圳市新引进高端人才财政补助科研启动项目(GDRC202106)
深圳技术大学研究生校企合作研究基金(20243108010001)。
关键词
克尔透镜锁模
碟片多通放大
高时间对比度
高功率飞秒激光
Kerr lens mode locking
thin-disk multi-pass amplification
high temporal contrast
high power femtosecond laser
