Versatile Raman fiber laser for sodium laser guide star

Robust high‐power narrow‐linewidth lasers at 589 nm are required for sodium laser guide star adaptive optics in astronomy. A high‐power 589 nm laser based on Raman fiber amplifier is reported here, which works in both continuous‐wave and pulsed formats. In the continuous‐wave case, the laser produces more than 50 W output. In the pulsed case, the same laser produces square‐shaped pulses with tunable repetition rate (500 Hz to 10 kHz) and duration (1 ms to 30 μs). The peak power is as high as 84 W and remains constant during the tuning. The laser also emits an adjustable sideband at 1.71 GHz away from the main laser frequency for better sodium excitation. The versatility of the laser offers much flexibility in laser guide star application.     

Recent progress in multi-wavelength fiber lasers:principles,status,and challenges

In recent years,multi-wavelength fiber lasers play a significant role in plenty of fields,ranging from optical communications to mechanical processing and laser biomedicine,owing to their high beam quality,low cost,and excellent heat dissipation properties.Benefitting from increasing maturity of optical elements,the multi-wavelength fiber laser has made rapid developments.In this review,we summarize and analyze diverse implementation methods covering continuous wave and pulsed fiber lasers at room temperature conditions:inserting an optical filter device and intensity-dependent loss structure in the resonant cavity,and applying ultrafast nonlinear optical response of materials and a dual-cavity structure.Finally,future challenges and perspectives of the multi-wavelength fiber laser are discussed and addressed.     

基于石墨烯可饱和吸收体的纳秒锁模掺铥光纤激光器

报道了一种基于石墨烯可饱和吸收体的纳秒锁模掺铥光纤激光器.该激光器采用环形腔结构,利用自制的三层石墨烯薄膜作为可饱和吸收体实现锁模.同时在腔内插入一个窄带光纤光栅,约束腔内起振的纵模数,适当调节抽运功率和偏振控制器的角度,得到了重复频率为3.8 MHz、脉宽在3.8—94.3 ns之间灵活可调的2μm纳秒锁模脉冲输出,整个脉宽调节范围超过90 ns.此外,由于获得的兆赫兹纳秒锁模脉冲时间带宽积在49—1119范围内,即存在强烈的啁啾,因而可作为2μm波段啁啾脉冲放大系统中的种子源使用.     

High-power pulsed diode-pumped Er:ZBLAN fiber laser

We report on the operation and performance of a gain-switched Er:ZBLAN fiber laser based on an active pulsed diode pump system. The produced laser pulses offer high peak powers while retaining the high average powers and efficiency of the cw regime. The measured pulse duration was about 300 ns and nearly independent of the pump repetition frequency. The maximum obtained 68 W of peak power is the highest reported, to our knowledge, for diode-pumped Er:ZBLAN fiber lasers, and the 2 W of average power at the repetition frequency of 100 kHz is 2 orders of magnitude higher than previously reported average power in a pulsed regime. The obtained slope efficiency was 34%.     

Synchronization and coherent addition of three pulsed fiber lasers by mutual injection and phase modulation

The coherent beam addition of pulsed fiber lasers is an effective way to improve the average power and the peak pulse power. We demonstrate a new architecture based on mutual injection and phase modulation to generate synchronous pulsed fiber lasers. Firstly, we realize the synchronization of the pulses of three fiber lasers using this technique. Secondly, coherent addition of three synchronous pulsed fiber lasers is obtained. Experimental results show that the three fiber lasers are phase locked and have good temporal and spatial coherence under mutual injection locking. This method can be extended to combine more beams.     

Yb-Bi pulsed fiber lasers

A new type of pulsed fiber laser is suggested and developed - Yb-Bi lasers. In such lasers the Yb fiber laser is Q-switched by use of a saturable absorber, a Bi-doped fiber placed in its own resonator, and pulsed lasing is obtained in both fiber lasers. Continous-wave diode-clad pumping of the Yb-Bi lasers at a 975 nm wavelength with power up to 16.5 W results in pulsed laser action in a spectral diapason of 1050-1200 nm with a maximum pulse energy of up to 100 microJ, an average power up to 7.5 W, and a repetition rate up to 100 kHz.     

Ultrafast fiber lasers for strong‐field physics experiments

The recent demonstration of rare‐earth‐doped fiber lasers with a continuous‐wave output power approaching the 10‐kW level with diffraction‐limited beam quality proves that fiber lasers constitute a scalable solid‐state laser concept in terms of average power. In order to generate high peak power pulses from a fiber several fundamental limitations have to be overcome. This can be achieved by novel experimental strategies and fiber designs that offer an enormous potential towards ultrafast laser systems combining high average powers (> kW) and high peak power (> GW). In this paper the challenges, achievements and perspectives of ultrashort pulse generation and amplification in fibers are reviewed. This kind of laser system will have a tremendous impact on strong‐field physics experiments, such as the generation of coherent light by high‐harmonic generation. So far, applications in the interesting EUV spectral range suffer from the very low photon count leading to nonrelevant integration times with highly sophisticated detection schemes. High repetition rate high average power fiber lasers can potentially solve this issue. First demonstrations of high repetition‐rate strong‐field physics experiments using novel fiber laser systems will be discussed.     

Synchronization and coherent combining of two pulsed fiber lasers

We demonstrate a scalable architecture for coherent combining of pulsed fiber lasers.A new method for generating synchronous pulsed fiber lasers by direct phase modulation is proposed and investigated.It is shown that phase modulated mutually coupled laser array can be a steady synchronous pulsed fiber laser source.The synchronous pulsed fiber lasers are coherently combined with an invariable phase difference of π in adjacent lasers.Neither active phase control nor polarization control is taken in our experiment.     

Transient behaviour of pulsed dye lasers

Some aspects of the transient behaviour of pulsed dye lasers are investigated both theoretically and experimentally. Relaxation oscillations induced in the output from a dye cell by an external reflector have been observed and explained, using a rate equation approximation to the physical situation in the dye cell. These oscillations are shown to play an important part in the generation of short laser pulses from long cavity dye lasers. Finally, it is proposed that 10 ps pulses can be obtained from conventional dye lasers pumped by 100 ps pulses from a high-pressure nitrogen laser.     

High power fiber lasers

In this review article, the development of the double cladding optical fiber for high power fiber lasers is reviewed. The main technology for high power fiber lasers, including laser diode beam shaping, fiber laser pumping techniques, and amplification systems, are discussed in detail. 1050 W CW output and 133 W pulsed output are obtained in Shanghai Institute of Optics and Fine Mechanics, China. Finally, the applications of fiber lasers in industry are also reviewed.     

High power fiber lasers

In this review article, the development of the double cladding optical fiber for high power fiber lasers is reviewed. The main technology for high power fiber lasers, including laser diode beam shaping, fiber laser pumping techniques, and amplification systems, are discussed in detail. 1050 W CW output and 133 W pulsed output are obtained in Shanghai Institute of Optics and Fine Mechanics, China. Finally, the applications of fiber lasers in industry are also reviewed.      

32 W百兆赫兹高重频可调谐单频激光光源

通过对连续种子光源的光强调制,并利用光纤放大器和固体介质放大器结合的混合放大方式,实现了百兆赫兹高重频可调谐单频激光光源。系统在基模输出条件下的最大输出功率为31.9 W,光束质量因子小于1.5,脉冲重复频率达到100 MHz,脉宽1 ns,测量得到的光束线宽小于0.8 GHz。实验结果验证了通过对连续光源进行光强调制获得高重频脉冲光源的可行性,并验证了混合放大方式是获得功率放大的一种有效手段。     

Mode-locked pulse generation from an all-FMF ring laser cavity

Experimental generation of stable mode-locked pulses and cylindrical vector beams(CVBs), from an all fewmode fiber(FMF) ring laser is first reported, to the best of our knowledge. In this laser, a section of few-mode erbium-doped fiber(FM-EDF) is used as the gain medium. The FM-EDF is pumped by 976 nm laser with LP11 mode, which is simultaneously converted and multiplexed through a homemade hybrid device, i.e., wavelength division multiplexing-mode selection coupler(WDM-MSC). All the components in our experiment are connected using FMF. The resulted CVB pulses have a spectral width of 0.33 nm with a repetition rate of 30.58 MHz under the pump power of 340 m W. Moreover, both azimuthally and radially polarized CVBs were achieved with a high purity of 95%. This mode-locked CVB fiber laser with an all FMF configuration opens the way to manipulate the transverse mode in mode-locked fiber lasers.     

Analysis of data transmission technique based on pulsed laser

Pulsed lasers are used mainly in lidar systems as sources of short and highly energetic light pulses. In data transmission systems continuous wave lasers are typically applied, however it is also possible to use pulsed lasers in such systems. Such approach seems to be especially reasonable for devices where a pulsed laser is applied anyway and executes another function (rangefinding). The article discusses a data transmission concept based on a pulsed laser technology. Advantages and limits of such a transmission method are described. Influence of individual transmission elements on the effective data transmission speed is analysed.     

高重复率脉冲放电金属蒸气激光中电泳对金属蒸气分布的影响

建立了一个理论模型描述了高重复率脉冲放电金属蒸气激光中的电泳动力学过程.得到了稳态和瞬态时金属蒸气密度扩散方程的解析表达式.分别计算了高重复率脉冲放电的He-Sr⁺和He-Cd⁺激光在不同时刻金属蒸气密度的轴向分布过程.结果表明，在放电开始后约2s内即可在阴极区建立起相当均匀的轴向金属蒸气密度分布，从而确保了电泳式金属蒸气激光的稳定输出特性. 关键词： 电泳 高重复率脉冲放电 轴向金属蒸气分布 金属蒸气激光     

高功率光纤激光器中ASE噪声的测量方法（英）

高峰值功率脉冲光纤激光器在激光雷达系统中有着广泛的应用。然而,光纤激光器中放大自发辐射噪声（ASE）严重影响了系统的探测性能。提出一种测量高峰值功率脉冲光纤激光器中ASE噪声的方法。在该方法中,首先对高峰值功率的激光脉冲衰减,然后在时域分别测量和计算ASE噪声和激光脉冲的相对能量。给出了光纤激光器在驱动电流分别为6 A,7 A和8 A时衰减后的ASE噪声廓线以及ASE噪声占激光脉冲能量的比例。     

Diffraction of pulsed laser radiation from an acoustic wave with frequency- and phase-shift keying

Bragg acoustooptic diffraction of nanosecond pulsed laser radiation from a frequency- and/or phase-keyed acoustic wave is studied experimentally and theoretically for exact synchronization of laser pulses and signal keying. It is shown that the diffraction field for short pulses is practically stationary and is determined by the positions of acoustic signal keying over signal aperture. The application of this type of signals for the formation of a multibeam diffraction pulsed radiation field is considered. A method is proposed for transforming the angular spectrum of laser radiation intensity from the initial Gaussian to a nearly rectangular spectrum. This may considerably increase the efficiency of high-power technological lasers used in material processing (laser cutting, welding, engraving, etc.), in which the action of radiation is of the thresh-old type in light intensity. The possibility of correcting the angular intensity distribution for a pulsed fiber laser, which increases the thermal efficiency of radiation from such a laser, is established experimentally.     

Dispersion-mode pulsed laser

A new self-consistency condition in pulsed lasers with strong intracavity dispersion imposes dispersion modes with specific cavity-length dependent pulse rates, utilizing pulse-train self-imaging properties of a temporal Talbot effect. We give an experimental demonstration of such a laser operation, using a long fiber cavity. We also demonstrate temporal Talbot imaging of a train of short pulses that propagate along large distances of dispersive fibers.     

皮秒光纤激光脉冲两个关键问题的研究

窄带耗散孤子锁模光纤激光器可以产生接近变换限制的皮秒脉冲，但受非线性相移的限制，输出脉冲重复频率不能通过增加腔长来降低，脉冲能量仅在0.1 nJ以下，严重制约着这类皮秒脉冲的实际应用。提出一种通过耦合器抽取腔内脉冲能量、抑制腔内非线性相移积累，进而允许增加腔长来降低窄带耗散孤子皮秒光纤激光脉冲重复频率的方法。运用该方法，成功地将激光器重复频率由35.2 MHz降低到了1.77 MHz，且脉冲时频特性保持不变。提出了一种基于级间FBG陷波滤波的抑制皮秒脉冲光纤放大中光谱展宽的方法。通过简单地使用级间陷波滤波器，既可窄化第一级光纤放大器后的输出脉冲谱宽，允许采用第二级光纤放大器进一步提升脉冲能量，而且，还可将脉冲重塑为近高斯形，利用高斯脉冲光谱展宽斜率小的特点，允许第二级光纤放大器将脉冲能量提升得更高。利用该方法，在RMS（均方值）谱宽保持0.4 nm以内的前提下，10 ps脉冲经标准单模光纤放大器后，能量可由0.2 nJ可提升到10 nJ以上。     

超短脉冲强激光与团簇的相互作用

超短脉冲强激光与团簇的相互作用已被证明能够产生能量高达ＭｅＶ量级的高能离子和中子以及非常强的Ｘ射线辐射。广阔好原子团簇在超短脉冲强激光场的作用下的加热、电离和膨胀等机制,对这种相互作用的深入研究可能会对激光核聚变和Ｘ射线激光等应用领域产生重大影响。