1 MHz repetition rate hollow fiber pulse compression to sub-100-fs duration at 100 W average power

We report on nonlinear pulse compression at very high average power. A high-power fiber chirped pulse amplification system based on a novel large pitch photonic crystal fiber delivers 700 fs pulses with 200 μJ pulse energy at a 1 MHz repetition rate, resulting in 200 W of average power. Subsequent spectral broadening in a xenon-filled hollow-core fiber and pulse compression with chirped mirrors is employed for pulse shortening and peak power enhancement. For the first time, to our knowledge, more than 100 W of average power are transmitted through a noble-gas-filled hollow fiber. After pulse compression of 81 fs, 93 μJ pulses are obtained at a 1 MHz repetition rate.     

High-power all-normal-dispersion femtosecond pulse generation from a Yb-doped large-mode-area microstructure fiber laser

We report on an all-normal-dispersion mode-locked fiber laser based on a large-mode-area Yb-doped microstructure fiber and using a high nonlinear modulation depth semiconductor saturable absorber mirror. The laser delivers 3.3 W of average output power with positively chirped 5.5 ps pulses at a center wavelength of 1033 nm. The pulse repetition rate is 46.4 MHz, which results in an energy per pulse of 71 nJ. These pulses are extracavity dechirped down to 516 fs by using bulk gratings. The average power of the dechirped pulses is 2.3 W, which corresponds to a peak power of more than 96 kW.     

135 W average-power femtosecond pulses at 520 nm from a frequency-doubled fiber laser system

We present a high-average-power femtosecond laser system at 520 nm central wavelength. The laser system delivers sub-500 fs pulses with 135 W average power at a pulse repetition rate of 5.25 MHz. Excellent beam quality is provided by high power fiber amplifiers and maintained during frequency doubling, resulting in a beam quality factor of M2<1.2. To our knowledge, the system presented here is the highest average power green laser source generating femtosecond pulses with diffraction-limited beam quality.     

High average and peak power femtosecond large-pitch photonic-crystal-fiber laser

We report on the generation of high-average-power and high-peak-power ultrashort pulses from a mode-locked fiber laser operating in the all-normal-dispersion regime. As gain medium, a large-mode-area ytterbium-doped large-pitch photonic-crystal fiber is used. The self-starting fiber laser delivers 27 W of average power at 50.57 MHz repetition rate, resulting in 534 nJ of pulse energy. The laser produces positively chirped 2 ps output pulses, which are compressed down to sub-100 fs, leading to pulse peak powers as high as 3.2 MW.     

66 W average power from a microjoule-class sub-100 fs fiber oscillator

Performance scaling of passively mode-locked ultrashort-pulse fiber oscillators in terms of average power, peak power, and pulse energy is demonstrated. A very-large-mode-area fiber laser in an all-positive group-velocity-dispersion ring cavity configuration with intracavity spectral filter, mode-locked by nonlinear polarization evolution, emits 66 W of average power at 76 MHz repetition rate, corresponding to 0.9 μJ pulse energy. The pulses are dechirped to 91 fs outside the cavity with an average power of 60 W remaining after the compressor. The generated pulse peak power is as high as 7 MW.     

高稳定性、高质量脉冲压缩飞秒光纤激光系统研究

报道了一款用于眼科手术的高稳定性、高质量脉冲压缩飞秒光纤主振荡功率放大系统. 振荡器采用混合腔方式增加了光纤双折射, 改善了非线性偏振旋转锁模在低重复频率下无法自启动的缺点, 提高了飞秒光纤激光器自启动锁模的稳定性. 研究了脉冲预啁啾与飞秒脉冲压缩质量的关系, 通过实验证明了光纤放大器的入射脉冲保持负的预啁啾状态可以得到最好的脉冲压缩结果. 实验最终实现了满足自启动锁模条件的重复频率19.4 MHz、平均功率1.2 W、脉冲宽度183 fs的激光脉冲, 目前这台激光器是国内首台具有自主知识产权并应用于动物角膜实验的飞秒光纤激光器.     

High-energy femtosecond photonic crystal fiber laser

We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15.5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1.9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber.     

基于多通单元的高能量耗散孤子锁模光纤振荡器

为了在有限抽运功率条件下探索基于大模场面积光 子晶体光纤的耗散孤子锁模振荡器的能量提升潜力, 本文利用多通单元将基于掺镱大模场面积光子晶体光纤锁模振荡器的腔长延展, 消除了有限抽运功率的限制, 使得该系统能够在较低平均功率水平下获得更高的单脉冲能量. 实验上构建了重复频率低至15.58 MHz的高能量光子晶体光纤锁模脉冲振荡器, 并通过分别使用6 nm带宽和12 nm带宽的两种不同带宽的光谱滤光片, 能够直接输出平均功率分别为3.73 W和4.9 W的啁啾脉冲, 对应单脉冲能量分别为239 nJ和314 nJ. 经过光栅对去啁啾后, 最窄脉冲宽度分别为56 fs和75 fs, 对应峰值功率均超过3 MW. 关键词： 多通单元 耗散孤子 飞秒 光纤激光器     

Ultrawide tunable Er soliton fiber laser amplified in Yb-doped fiber

A Raman-shifted and frequency-doubled high-power Er-fiber soliton laser for seeding an efficient high-power Yb fiber femtosecond amplifier is demonstrated. The Raman-shifted and frequency-doubled Er-soliton laser is tunable from 1.00 to 1.070microm and produces bandwidth-limited 24-pJ pulses at a repetition rate of 50 MHz with a FWHM pulse width of 170 fs at 1.040microm . The Yb(3+) amplifier has a slope efficiency of 52% and generates 3-ps linearly chirped pulses with an average power of 0.8 W at 1.05microm . After pulse compression, 74-fs bandwidth-limited pulses with an average power of 0.4 W and a pulse energy of 8 nJ are generated.     

90 W average power 100 microJ energy femtosecond fiber chirped-pulse amplification system

We report on an ytterbium-doped fiber based chirped-pulse amplification system delivering 100 microJ pulse energy at a repetition rate of 900 kHz, corresponding to an average power of 90 W. The emitted pulses are as short as 500 fs. To the best of our knowledge, this is the highest average power ever reported for high-energy femtosecond solid-state laser systems.     

基于光纤中超短脉冲非线性传输机理与特定光谱选择技术的多波长飞秒激光的产生

高集成、高可靠性宽调谐飞秒激光源在超快光谱学、量子光学及生物成像等研究与应用领域具有重要价值.如在生物多光子显微成像中,具有适中能量的宽调谐飞秒激光源不仅可满足多种生物组织荧光激发所需的峰值功率与激发波长,而且也可以显著提升非线性荧光产生效率、成像分辨率以及增大成像穿透深度.采用自主研发的高可靠性全保偏光纤飞秒激光器作为抽运源,基于低色散光纤中高峰值功率飞秒激光脉冲非线性传输引起的光谱加宽机制,本文开展了多波长全光纤飞秒激光产生技术研究.通过采用中心波长在980, 1000,1050, 1070与1100 nm的带通滤波片选择性地对单模光纤输出光谱中最左边与最右边光谱旁瓣进行滤波,在上述中心波长处分别可获得203, 195, 196, 187与194 fs的激光输出.本文提出的基于全光纤飞秒激光脉冲在单模光纤中非线性传输引起的光谱加宽机制与特定光谱选择技术的实验方案为高集成、高可靠性宽调谐飞秒激光源的实现提供了新的研究途径.     

全光纤高功率被动锁模掺铥光纤激光器

利用非线性光环形镜(NOLM)的可饱和吸收特性实现了可自启动的2μm全光纤高能量被动锁模掺铥光纤激光器。当泵浦功率大于3W时,激光器工作在连续或不稳定脉冲运转状态;泵浦功率达到4.69W后,输出为自启动锁模脉冲,重复频率4.26MHz,中心波长2 061.5nm,光谱半极大宽度18.1nm,平均输出功率8.8mW;继续增加泵浦功率到最大值7.56W,可以得到中心波长2 062.2nm、光谱半极大宽度17.1nm、斜率效率为6.2%、脉冲宽度和能量分别为424fs和65.6nJ的稳定锁模脉冲。这是目前已报道的在未经放大情况下脉冲能量最高的2μm锁模脉冲光纤激光器。     

Fiber based high repetition rate, high energy laser source applying chirped pulse amplification

We demonstrate the potential of a high-gain Yb-fiber amplifier system to provide ultrashort pulses with high energies. 100 μJ pulses generated at a repetition rate of 32 kHz exhibit nearly diffraction limited output (M²≈1.7) at a 1060 nm center wavelength. Using chirped pulse amplification, temporally streched laser pulses from a femtosecond oscillator could be compressed after amplification to subpicosecond pulse duration. The achievable intensities are high enough to create plasmas which can efficiently convert laser light to the extreme ultraviolet radiation. In a multimode Yb-doped fiber amplifier we obtained average powers of up to 22 W and single pulse energies up to 130 μJ.     

High-power Yb-fiber comb with feed-forward control of nonlinear-polarization-rotation mode-locking and large-mode-area fiber amplification

We report on a simple scheme to precisely control carrier-envelope phase of a nonlinear-polarization-rotation mode-locked self-started Yb-fiber laser system with an average output power of ～7 W and a pulse width of 130 fs. The offset frequency was locked to the repetition rate of ～64.5 MHz with a relative linewidth of ～1.4 MHz by using a self-referenced feed-forward scheme based on an acousto-optic frequency shifter. The phase noise and timing jitter were calculated to be 370 mrad and 120 as, respectively.     

Passive coherent combination of two ultrafast rod type fiber chirped pulse amplifiers

Using passive coherent beam combining of two ultrafast fiber amplifiers, we demonstrate the generation of high temporal quality 300 fs and 650 μJ pulses corresponding to 60 W of average power at a repetition rate of 92 kHz. Furthermore, at 2 MHz of repetition rate record coherent combining average powers of 135 W before and 105 W after compression are measured. A combining efficiency higher than 90% is maintained over the whole range of output powers and repetition rates investigated demonstrating the efficiency and robustness of the passive combining technique. The measured pulse-to-pulse relative power fluctuation at high energy is 2%, indicating that the system is essentially immune to environmental phase noise. We believe the passive combining method to be an attractive approach for compact multi-GW peak power femtosecond fiber-based sources.     

Passively mode locked femtosecond Tm:Sc2O3 laser at 2.1 μm

We report on the passive mode locking of a Tm3+:Sc2O3 laser at 2.1 μm using a semiconductor saturable absorber mirror based on InGaAsSb quantum wells. Transform-limited 218 fs pulses are generated with an average power of 210 mW. A maximum output power of 325 mW is produced during mode locking with the corresponding pulse duration of 246 fs at a pulse repetition frequency of 124.3 MHz. A Ti:sapphire laser is used as the pump source operating at 796 nm.     

Millijoule pulse energy high repetition rate femtosecond fiber chirped-pulse amplification system

We report on an ytterbium-doped fiber chirped-pulse amplification (CPA) system delivering millijoule level pulse energy at repetition rates above 100 kHz corresponding to an average power of more than 100 W. The compressed pulses are as short as 800 fs. As the main amplifier, an 80 microm core diameter short length photonic crystal fiber is employed, which allows the generation of pulse energies up to 1.45 mJ with a B-integral as low as 7 at a stretched pulse duration of 2 ns. A stretcher-compressor unit consisting of dielectric diffraction gratings is capable of handling the average power without beam and pulse quality distortions. To our knowledge, we present the highest pulse energy ever extracted from fiber based femtosecond laser systems, and a nearly 2 orders of magnitude higher repetition rate than in previously published millijoule-level fiber CPA systems.     

Passive picosecond and femtosecond mode-locking laser action of Yb<Superscript>3+</Superscript>:LuYSiO<Subscript>5</Subscript>

Efficient passive mode locking of a diode-pumped Yb³⁺:LuYSiO₅ (Yb:LYSO) laser is first demonstrated in experiment using a semiconductor saturable absorber mirror (SESAM), to the best of our knowledge. A stable pulse train with a repetition rate of 101 MHz is generated. The average output power of 2.13 W and the pulse duration of 3.9 ps. With a pair of SF10 uncoated prisms for dispersion compensation, we obtained pulses as short as 780 fs with center wavelength around 1042 nm, the average output power of 1.03 W and the peak power of 13.1 kW.     

Femtosecond fiber laser at 780 nm for two-photon autofluorescence imaging

We present an Er-doped fiber(Er:fiber)-based femtosecond laser at 780 nm with 256 MHz repetition rate, 191 fs pulse duration, and over 1 W average power. Apart from the careful third-order dispersion management, we introduce moderate self-phase modulation to broaden the output spectrum of the Er:fiber amplifier and achieve 193 fs pulse duration and 2.43 W average power. Over 40% frequency doubling efficiency is obtained by a periodically poled lithium niobate crystal. Delivering through a hollow-core photonic bandgap fiber, this robust laser becomes an ideal and convenient light source for two-photon autofluorescence imaging.     

基于非线性偏振旋转锁模的高功率光子晶体光纤飞秒激光振荡器

为了探索大模场面积光子晶体光纤锁模激光器在全正色散锁模域内的耗散孤子锁模机理, 以获得更大的单脉冲能量和更高的峰值功率, 本文搭建了以掺镱大模场面积光子晶体光纤作为增益介质的耗散孤子锁模激光器. 激光器使用环形腔结构, 利用非线性偏振旋转以及滤光片提供的耗散作用实现了稳定的锁模运转. 实验中, 从激光器振荡级直接获得了平均功率10 W, 重复频率49.09 MHz(对应202 nJ的单脉冲能量), 脉冲宽度为1.03 ps的稳定锁模脉冲输出, 经过腔外色散补偿得到的脉冲宽度为95.5 fs.