High power ytterbium doped fiber laser has important application value in industry, scientific research, national defense and other fields. However, with the continuous improvement of the output power, the aging problem of the laser has become increasingly prominent, which has become one of the key bottlenecks limiting the further improvement of the power and stability of the fiber laser. This paper reviews the latest research progress in aging of high-power ytterbium doped fiber lasers by domestic and foreign research institutions, mainly covering the photon darkening effect (PD), radiation-induced darkening effect (RD), and the nonlinear effects caused by aging, and focuses on the formation mechanism, damage phenomenon and suppression methods of these effects.

In this work, we propose and demonstrate a novel approach to suppressing stimulated Raman scattering in an oscillating–amplifying integrated fiber laser (OAIFL) by changing the spectral bandwidth of the output-coupler fiber Bragg gratings (OC-FBGs). The reflectance bandwidth of the fiber Bragg grating (FBG) in the oscillating section was systematically investigated as a critical parameter for SRS mitigation. Three types of long-period FBGs with distinct reflectance bandwidths (1.2 nm, 1.3 nm, and 2 nm) were comparatively studied as output couplers. The experimental results demonstrated a direct correlation between FBG bandwidth and SRS suppression efficiency, with the configuration of the OC-FBG with a 2 nm bandwidth achieving optimal suppression performance. Concurrently, the output power was enhanced to 5.02 kW with improved power scalability. And excellent beam quality was obtained with M2 < 1.3. Remarkably, in the architecture of this laser, increasing the bandwidth of the output couplers in the oscillating section had a relatively minor effect on the optical-to-optical (O-O) efficiency, which reached up to 78%. Additionally, this modification also reduced the 3 dB bandwidth of the laser output, thereby achieving a beam output with enhanced monochromaticity.

In this study, we experimentally investigate spectral beam combining based on four long-wave infrared quantum cascade lasers (QCLs) with three dichroic mirrors. The coating curves of the dichroic mirrors were finely designed according to the output spectrum of the four adopted QCLs, whose central wavelength locates in 7.5 mu m, 8.3 mu m, 9.0 mu m and 10.2 mu m, respectively. At room temperature the highest combined power reaches as high as 2.39 W, corresponding to a combining efficiency of 83.0 %, and meanwhile, the combined beam keeps a high beam quality with average M2 2 of 1.78. To the best of our knowledge, this is the highest output power among spectral beam combining for QCLs. Due to the advantage of wide spectral range, high power, high beam quality and compact size, this demonstration may meet the demands of medical diagnosis, remote sensing, free-space optical communication and military application.

We establish a spectral beam combing structure with two distinct diffraction gratings. A theoretical analysis of the beam quality degradation of this beam combining system is given. A six-channel spectral beam combining experiment is constructed based on conical diffraction structure by transmission and reflection gratings. Over 19 kW combined power is achieved with a combining efficiency of about 92%. The six incident fiber amplifiers, ranging from 1040 nm to 1082 nm, can each deliver a 3.5 kW output power laser with about 60 GHz 3 dB linewidth. Both transmission and reflection diffraction gratings, with different grating periods (1000lines/mm, 1170lines/mm), are employed in this work. The combined beam quality factor is controlled to be M2 similar to 2 by effective dispersion compensation. To the best of our knowledge, this is the first time to demonstrate a high power beam combination by two gratings with different types and periods, which verifies the dispersion capability of this structure and provides an alternative approach for high power beam combining.

Narrow linewidth fiber lasers, based on the multi -longitudinal -mode oscillator seed source, have obvious advantages in engineering applications and space -limited loading platforms. Additionally, they are considered ideal sub -modules for high -power spectral combinations. The time domain of this type of seed is unstable due to the self -pulse effect, causing significant spectral broadening and stimulated Raman scattering effects during the amplification process, which limits their further improvement in output power and affects the purity of laser spectra. In this paper, we introduce four commonly used narrow linewidth seeds. The mechanism and suppression methods of the self -pulse effect in multi -longitudinal mode oscillator seeds are analyzed. Critical technologies essential for the optimization and relevant progress of the multi -longitudinalmode oscillator seed source and amplifier stages are discussed in detail. A future development outlook is also presented. This paper serves as a useful reference for the design of narrow linewidth fiber lasers based on the

In this study, we experimentally investigate high-power laser beam combining based on dichroic mirrors. Three-channel 4 kW nearly single mode fiber lasers with central wavelengths of 1059, 1075, and 1090 nm are combined to a single beam. The combined power reaches 11. 34 kW with a combining efficiency of 95%. Compared with the sub beam, the beam quality of the combined laser shows gradual degradation as the output power increases and the surface temperature of the dichroic mirror rises. When the full power is reached, the beam quality degrades to M(2)x=2. 941 and M(2)y= 3. 183 in both directions. The reasons that affect the combining efficiency and beam quality are analyzed. The effect of substrate thickness of the dichroic mirror on the degradation of beam quality is experimentally studied. This provides an important reference for further optimizing the combined beam quality.

To improve the radiation resistance of Yb-doped fiber lasers, we investigate the influence of pre-radiation and photo-bleaching on the gamma-radiated laser’s performance. When the gamma radiation dose is within 10 krad(Si) with a radiation dose rate less than 0.4 rad(Si)/s, compared to the output power of a non-pre-radiated Yb-doped fiber laser, the pre-radiation technique could enhance the radiation resistance against gamma-ray. However, the mode instability threshold was decreased, which was caused by the cumulated radiation-induced attenuation of pre-radiation and radiation. Based on an electronic probe micro-analyzer, the Yb-doped active fiber was Yb-doped aluminophosphosilicate ternary fiber; therefore, the radiated defects were mainly hole-related defects. A laser diode centered at 532 nm was chosen as the photo-bleaching laser source, which could recover 45.2% of the radiated-induced attenuation and increase the mode instability threshold. This work demonstrates the influence of pre-radiation and photo-bleaching on the radiation resistance against the gamma-ray of Yb-doped fiber lasers, which are of significance in the design and fabrication of related fiber lasers.

高功率掺镱光纤激光器在空间环境中的应用日益增多,但掺镱光纤材料在空间辐照条件下会产生色心效应,导致损耗增加,影响光纤器件以及激光器整机的性能,从而给高功率光纤激光器在空间环境的长期稳定工作带来隐患.从空间辐照对高功率光纤激光器性能的影响机理、抑制方法和研究进展等3个方面进行介绍.首先介绍了空间辐照对高功率掺镱光纤激光器中关键光学器件、放大级热负载、非线性效应等方面的影响分析,其次介绍了抑制辐照效应的典型方法及其在高功率掺镱光纤激光器中的可行性分析,最后介绍了国内外典型的高功率掺镱光纤激光器的辐照影响及抑制的研究成果,并展望了未来发展趋势.

The disabled glue on valve surfaces is known to reduce aircraft durability and performance. In this paper, glue contaminants were removed from 2Cr13 stainless valves by dry-type laser processing with a cold air gun and compared with the chemical soaking method. The laser-processed surface was examined by white-light interferometer, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometer, hardness tester, and metallographic microscopy. The substrate surface became a little smoother but also had deeper dips due to laser thermal melting. After laser degumming, the new constituent was found in the laser-irradiated region and analyzed as FeCr0.29Ni0.16C0.06, since the ratio of chemical compositions changed. Based on our simulation and experiments, the temperature of the workpiece was effectively controlled by the cold air gun, and its physical properties, including hardness and metallographic structure, were hardly changed. It was shown that laser degumming provides an alternative method for metal valve cleaning.

Yb-doped aluminophosphosilicate fiber was fabricated by the combination system of chelate precursor doping technique and the modified chemical vapor deposition system. The technical details of the fabrication process were optimized to ensure the same elemental concentration ratio of Al/P. The capability of this fiber for the beam combining application was investigated based on a narrow linewidth fiber laser system. This fiber presented the output power of 1783 W with a slope efficiency of 83.7 % and a 20 dB root-mean-square linewidth of 0.244 nm with no nonlinear effects in the laser spectrum. Near-diffraction-limited beam quality was also observed with a M2 factor less than 1.27. In conclusion, this fiber presented an attractive laser performance for beam combination through the comprehensive optimization of fabrication technique and narrow linewidth laser system.

激光合束技术是获得数十千瓦至百千瓦功率激光的有效技术路径,是实现满足激光武器系统需求的激光光源关键技术.但在实际应用中,振动、温变、材料强激光吸收等因素都会对光束指向产生影响,从而降低各路激光的重合度,导致合束效果变差,光束指向的闭环反馈控制是解决上述问题、提高合束激光器及合束系统环境适应能力的关键.分析了指向偏差对合束效果的影响规律,介绍了指向控制技术的基本原理、关键技术和研究现状,给出了三种常见的指向控制器件工作的优缺点,并对指向控制技术发展趋势进行了展望.

We demonstrate the influence of the thermal blooming effect on the far-field beam quality in a seven-channel spectral beam combining system. Stimulated Raman scattering in the incident narrow-linewidth fiber amplifier is verified to be the dominant factor that induces thermal blooming in the beam combining system. When the power density of Raman light reaches only 180W/cm2, the peak intensity of the far-field beam reduces severely and the beam distribution profile spreads. We reveal that H2O content in the atmosphere has a positive relationship with the thermal blooming effect and study the influence of the humidity on the thermal blooming effect. The influence of the optical path length on the thermal blooming effect is also revealed. The result shows that the focusing property of the far-field beam degrades gradually as the optical path length increases from 100 to 450 mm. The results are conducive to optimize the beam quality of spectral beam combining.

In this paper, laser surface treatment of Al alloy was studied by comparison of sandblasting and laser ablation. The effects of laser spot distribution on surface roughness, contact angle, chemical composition and shear strength of Al alloy were analyzed. The experimental results showed that the bonding performance of Al alloy are promoted by controlling the laser spot spacing. When laser spot spacing was smaller than the size of the laser spot, micro–nano composite structures were induced by multiple laser pulses, which would improve shear strength by increasing the contact area between Al alloy and adhesive. Using laser surface treatment, the adhesion properties on Al alloy can be promoted.

文中介绍了小型化光纤激光器的热仿真分析和优化设计方法.首先对光纤激光器的热损耗进行了分析,然后依据热力学相关理论,基于ANSYS Icepak软件,对光纤激光器进行了建模和仿真分析.针对小型化光纤激光器小尺寸流道的特点,进行了水冷板结构的仿真分析和散热优化,设计了2kW级的小型化、轻量化光纤激光器,并开展了实验验证.结果表明,在实现了工作波长为1080 nm,最大功率为2.2 kW的连续激光输出时,热耗器件安装位置处的最高温度为32.1℃,且光学参数正常.实验结果与仿真结果相符,光纤激光器的整体温度得到了明显改善.文中的仿真和优化设计可为小型化、轻量化光纤激光器的冷却设计提供重要参考.

点火通路损耗检测精度是激光点火系统的一个重要指标,其在很大程度上决定着点火系统状态判断的准确性.针对激光点火系统损耗检测精度随温度变化的问题,对不同温度条件下激光点火系统的点火通路损耗检测精度进行了分析.分析结果表明,探测器暗电流、运放输入偏置电流和输入失调电压等均会影响检测精度,且检测偏差随温度升高而增大.建立了点火通路损耗检测温度误差模型,在-40℃～75℃范围内,采用温度误差模型进行补偿后,火工品发火前的损耗检测偏差(峰峰值)从0.62dB减小为0.16dB,火工品发火后的损耗检测偏差(峰峰值)从1.45dB减小为0.30dB,提高了损耗检测的精度,为判断是否具备发火条件及发火状态提供了有效支撑.

Objective Spectral beam combining (SBC) is an effective method to achieve a high-power, high beam quality fiber laser. In the SBC system, multi-channel incident lasers are arranged spatially and are combined into a single laser beam via an optical element. The transmitted laser power density in the SBC system is very high due to the high power and small beam diameter. In this case, the thermal blooming effect becomes a nonnegligible factor that influences the far-field beam quality. In addition, a narrow linewidth is required in SBC to eliminate the dispersion effect. As a result, nonlinear effects are easy to stimulate, e. g., stimulated Brillouin scattering ( SBS) and stimulated Raman scattering (SRS), which generates a new wavelength laser. The new wavelength laser may cause enhanced atmospheric absorption and degrade the far-field beam quality. Atmospheric thermal blooming of highpower laser propagation has been studied extensively in the outer path (optical path in atmosphere) and inner path (optical path in the launching system). However, relevant studies of the inside optical path of a high-power laser have not been sufficiently thorough. Therefore, in this paper, the influence of thermal blooming on far-field beam quality in a high-power spectral beam combining system is studied. SRS in the incident narrow linewidth fiber amplifier is verified to be the dominant factor that induces thermal blooming in the beam combining system. In addition, N2 injection into the combining system essentially eliminates the influence of thermal blooming on far-field beam quality, which can be considered an efficient suppression method. s A three-channel spectral beam combining system is constructed with central wavelengths of 1064, 1072, and 1084 nm, respectively. Each incident laser can deliver 2 kW power. Taking the SRS effect into consideration, we employ 1400 W and 1800 W laser power in this experiment. First, the far-field beam patterns of each incident laser at 1400 W and 1800 W are tested. Then, the far-field beam patterns of the three -channel combined beam at different power are measured. By analyzing the measured results, the causing factor of thermal blooming in SBS system is confirmed. Then, the relationship between the optical path length and thermal blooming effect is investigated by adjusting the beam splitter position of a 1084 nm laser. Finally, suppression of the thermal blooming effect by N2 injection is verified. Results and Discussions When the power of each incident laser increases from 1400 W to 1800 W, apparent degradation is observed in the far-field beam pattern [Fig. 5( a) (c)]. The peak intensity degrades severely, and the beam distribution disperses badly, which reduces the laser' s focusing property. For the combined beam, when the power reaches 2000 W to 3800 W, no obvious beam quality degradation is observed [ Fig. 5( d)]. The results demonstrate that the 1 ttm signal laser does not cause obvious thermal blooming effect in the SBC system. The thermal blooming effect of the incident laser at 1800 W can be attributed to the SRS light. When the incident laser power is 1800 W, the SRS is measured as 100 W. In addition, the SRS wavelength covers from 1. 1 won to 1.3 won for the 1 ttm signal laser, which is in the strong absorption band of the H2O molecule in atmosphere. Thus, air in the beam propagation path is heated to cause the thermal blooming effect. We found that optical path length has direct influence on the thermal blooming effect. When the optical path length increases from 100 mm to 450 mm, the thermal blooming effect becomes increasingly significant (Fig. 6). The far-field beam patterns of the 1084 nm laser at 1400 W and 1800 W after N2 injection are measured ( Fig. 7). The peak intensity increases significantly from 1400 W to 1800 W, and no beam quality degradation is observed, which means that the thermal blooming effect did not occur. This result demonstrates that N2 injection can be an effective method to eliminate the thermal blooming effect in the SBC system. Conclusions In this paper, we investigate the thermal blooming effect in an SBC system. By comparing the farfield beam patterns of a sub-beam and combined beam with identical power density, stimulated Raman scattering in the incident narrow linewidth fiber amplifier is verified as the dominant factor that induces thermal blooming in the SBC system. When the power density of Raman light reaches 180 W/cm2, the peak intensity of the far-field beam is reduced significantly, and the energy spreads. The influence of optical path length on thermal blooming is investigated. The focusing property of the far-field beam degrades gradually and finally spreads as the length increases from 100 mm to 450 mm. By injecting N2 into the combining system to reduce H2O content, the thermal blooming effect is effectively suppressed. The results presented in this paper are expected to facilitate optimization of the beam quality of high-power spectral beam combining.

In this paper, a nanosecond fiber pulse laser is used to carry out the experimental study on laser weight removal of ZL205A aluminum alloy gyro rotor. By optimizing the process parameters of laser weight removal, better surface morphology was obtained. The effects of surface roughness, metallographic structure and hardness of samples before and after laser deweighting were analyzed. The experimental results show that the laser weight removal does not affect the matrix properties of ZL205A aluminum alloy. The laser de-weight technology is suitable for the balance of ZL205A aluminum alloy gyro rotor.

This paper utilizes a nanosecond pulse fiber laser to conduct rubber removal experiments on rubber laminated metal valves. The influence on surface roughness, metallographic structure and hardness of samples before and after different laser cleaning conditions are analyzed. Experimental results show that the laser has no significant effect on the substrate situation of the rubber laminated valves when it is immersed in water or sprayed with water. Through thermal simulation, the surface temperature when using wet-type laser cleaning is lower than that of using dry-type laser cleaning, and there is no significant effect on the substrate. Therefore, wet-type laser cleaning is appropriate for rubber laminated metal valves.

为了满足某驾驶操作舱对爆炸冲击波的防护,设计了防爆舱结构,选用了多种防护材料,数值计算了爆炸参数和结构强度,完成了防爆舱在距离爆炸点9 m处12 kg三硝基甲苯(trinitrotoluene,TNT)裸装药的爆炸试验,重点测试了防爆驾驶舱内外的声压、内部噪声及操作人员座椅处的3个方向的振动加速度曲线.结果表明:舱内脉冲噪声峰值最大为135.1 dB;压力峰值为882.5 Pa,持续时间约为1472 ms;座椅处3个方向的振动加速度最大为15.41g,持续时间为0.23 s;均在相关标准安全限制内,满足对等效重量为12 kg TNT及以下爆炸物在9 m处的爆炸冲击波的有效防护,验证了该防爆舱的可靠和安全.

In this work, we study the precision cutting technology of LiNbO3 which is belonged to brittle materials and difficult to machine. By using a femtosecond laser, we explore the influence of wavelengths on the cutting quality, the surface and cross-section morphology of the specimens were examined by optical microscopy and white light interferometer, the size of the slit width and cutting chipping, roughness have been measured. Subsequently, two optimization processing solutions have been designed to cut LiNbO3 with high quality and high reproducibility, the thermal effect and chipping have been reduced obviously. At last, the complete cut through the plate of LiNbO3 has been achieved.