Study and design of cladding power stripper for high power fiber laser systems

Heat handling has been a significant problem of the high power fiber laser systems as the output power increases rapidly.Cladding power stripper(CPS) which is used to deal with the unwanted optical power and light is required for higher cooling ability. So the methods of stripping the unwanted light attracted much attention recently, and the thermal effect is given. However, few investigations focus on the dissipation of the heat converted from the unwanted light. In this paper,an approach of active cooling for CPS is demonstrated. This is achieved by using microchannel cooling technology in heat sinking in CPS to improve the efficiency of heat exchange. In order to explain the mechanism of CPS the function of it and consistence of categories of the unwanted light are detailed firstly. Then microchannel heat sinking is proposed and verified by the heat exchange theory. At last, the design of the CPS with microchannel heat sinking is shown and following experiment is conducted. The final temperature of the device with 1000 W cladding power was demonstrated at last to verify the ability of heat distribution of the CPS component. This suggests that these CPSs can be used to stripe a thousand of watts of light in high power double cladding fiber lasers.

Fabrication of Tm-Doped Fibers for High Power and 121W Output All-Fiber Tm-Doped Fiber Laser

We fabricate the Tm-doped double cladding silica fiber by using the vapor-solution hybrid-doping method, then build up an all-fiber Tin-doped fiber laser which can provide the output power of up to 121 W, corresponding to a slope efficiency of 51% and an optical-optical efficiency of 48%. By using the domestic Tin-doped fiber, it is the first time a hundred-watt level output at 1915nm has been achieved, to the best of our knowledge. The thermal effect of Tm-doped fiber laser is also analyzed.

Experimental study of weld position detection based on keyhole infrared image during high power fiber laser welding

Keyhole is one of the important phenomena in high-power laser welding process. By studying the keyhole characteristic and detecting the seam offset during high-power fiber laser welding, an infrared sensitive high-speed camera arranged off-axis orientation of laser beam was applied to capture the dynamic thermal images of a molten pool. The 304 austenitic stainless steel plate butt joint welding experiment with laser power 10 kW was carried out. Through analyzing the keyhole infrared image, the weld position was calculated. Least squares method was used to determine the actual weld position. Image filtering technique was used to process the keyhole image, and the keyhole centroid coordinate were calculated. Also, least squares method was used to fit the keyhole centroid curve equation and establish a nonlinear continuous model which described the deviation between keyhole centroid and weld seam. The heat accumulation effect affected by the infrared radiation was analyzed to determine whether the laser beam focus spot deviated from the desired welding seam. Experimental results showed that the keyhole centroid has related to the seam offset, and can reflect the welding quality.

Efficient loading of ultracold sodium atoms in an optical dipole trap from a high power fiber laser

We report on a research of the loading of ultracold sodium atoms in an optical dipole trap,generated by two beams from a high power fiber laser.The effects of optical trap light power on atomic number,temperature and phase space density are experimentally investigated.A simple theory is proposed and it is in good accordance with the experimental results of the loaded atomic numbers.In a general estimation,an optimal value for each beam with a power of 9 W from the fiber laser is achieved.Our results provide a further understanding of the loading process of optical dipole trap and laid the foundation for generation of a sodium Bose–Einstein condensation with an optical dipole trap.

Numerical simulation of the molten pool character in high power fiber laser welding

A mathematical model was developed to describe moving laser welding by using the rotary Gauss body heat source model, and the effect of recoil pressure was taken into account. The formation of the long and narrow pool in high power fiber laser welding can be explained by the mathematical model （laser power： 10 kW, welding speed： 4 -20 m/min）. Numerical simulation was conducted by PHOENICS software. The results show that at high welding velocity the plasma accelerated the velocity of liquid metal around the keyhole which is the main reason for the formation of the long and narrow molten pool in high power laser welding.

Powerful 2 μm Silica Fiber Sources: A Review of Recent Progress and Prospects

A review on the progress of powerful 2 μm silica fiber sources in past decades is presented. We review the state-of-the-art records and representative achievements of 2 μm high-average-power continuous- wave, pulsed fiber lasers and amplifiers, and powerful superfluorescent sources. Challenges which limit the further power scaling of 2 μm silica fiber sources are discussed, including pumping brightness limitation, thermal problem and nonlinear effects. Potential and promising roadmaps to go beyond these limitations, like tandem pumping and beam combining, are discussed. Prospects of powerful 2 μm silica fiber sources are also presented in the end of paper.

Research on multi-kilowatts level tapered fiber bundle N × 1 pumping combiner for high power fiber laser

Pumping combiner is a kernel component of high power fiber laser （HPFL）. We demonstrate two types of tapered fiber bundle （TFB） end-pumping combiner able to combining multi-kilowatts of pumping laser. After the experimental test of coupling performance, the 3xl coupler is proved to have a power handling capacity of 2.11 kW with a coupling efficiency of 95.1%, and the 7× 1 coupler is capable of handling pumping power of 4.72 kW with a coupling efficiency of 99.4%. These two coupler have obtained the ability to be used in laser diodes （LDs） direct beam combining and the pumping coupling of multikilowatts level fiber lasers.

High power all-fiberized and narrow-bandwidth MOPA system by tandem pumping strategy for thermally induced mode instability suppression

An all-fiberized and narrow-bandwidth master oscillator power amplification(MOPA) system with record output power of 4 kW level and slope efficiency of 78% is demonstrated. Tandem pumping strategy is tentatively introduced into the narrow-bandwidth MOPA system for thermally induced mode instability(TMI) suppression. The stimulated Brillouin scattering(SBS) effect is balanced by simply using one-stage phase modulation technique. With different phase modulation signals, SBS limited output powers of 336 W, 1.2 kW and 3.94 kW are respectively achieved with spectral bandwidths accounting for 90% power of ～0.025, 0.17 and ～0.89 nm. Compared with our previous 976 nm pumping system, TMI threshold is overall boosted to be >5 times in which tandem pumping increases the TMI threshold of >3times. The beam quality(M～2 factor) of the output laser is well within 1.5 below the TMI threshold while it is ultimately saturated to be 1.86 with the influence of TMI at maximal output power. Except for SBS and TMI, stimulated Raman scattering(SRS) effect will be another challenge for further power scaling. In such a high power MOPA system, multidetrimental effects(SBS, SRS and TMI) will coexist and may be mutual-coupled, which could provide a well platform for further comprehensively investigating and optimizing the high power, narrow-bandwidth fiber amplifiers.

High power dual-wavelength tunable fiber laser in linear and ring cavity configurations

We describe and compare the performances of two crucial configurations for a tunable dual-wavelength fiber laser, namely, the linear and ring configurations. The performances of these two cavities and the tunability in the dual-wavelength output varied from 0.8 to 11.9 nm are characterized. The ring cavity provides a better performance, achieving an average output power of 0.5 dBm, with a power fluctuation of only 1.1 dB and a signal-to-noise ratio （SNR） of 66 dB. Moreover, the ring cavity has minimal or no background amplified spontaneous emission （ASE）.

152 W high-power blue diode laser operated at 447 nm

We demonstrate a high-power blue diode laser operated at 447 nm combining laser diodes using an optical fiber bundle. As many as 127 diode lasers at 447 nm were coupled into 400 μm/0.22 NA fibers using an aspherical lens group with different focus lengths. The bare fibers were mechanically bundled through high temperature ultraviolet adhesive after the coatings of the 127 fibers were stripped. The diameter of the fiber bundle was 6 mm. The total output power of such a bundle was 152 W with electro-optical conversion efficiency of 27.56%and the RMS power instability was less than ±1% within 3 h.

Researching the 915 nm high-power and high-brightness semiconductor laser single chip coupling module

Based on the high-speed development of the fiber laser in recent years, the development of researching 915 nm semiconductor laser as main pumping sources of the fiber laser is at a high speed. Because the beam quality of the laser diode is very poor, the 915 nm laser diode is generally based on optical fiber coupling module to output the laser. Using the beam-shaping and fiber-coupling technology to improve the quality of output beam light, we present a kind of high-power and high-brightness semiconductor laser module, which can output 13.22 W through the optical fiber. Based on 915 nm GaAs semiconductor laser diode which has output power of 13.91 W, we describe a thoroughly detailed procedure for reshaping the beam output from the semiconductor laser diode and coupling the beam into the optical fiber of which the core diameter is 105 μm and the numerical aperture is 0.18. We get 13.22 W from the output fiber of the module at 14.5 A, the coupling efficiency of the whole module is 95.03% and the brightness is 1.5 MW/cm2-str. The output power of the single chip semiconductor laser module achieves the advanced level in the domestic use.

5 kW-level single-mode fiber amplifier based on low-numerical-aperture fiber

A low-numerical-aperture(NA)concept enables large-mode-area fiber with better single-mode operation ability,which is beneficial for transverse mode instability and nonlinear effects suppression.In this contribution,we reported a high-power fiber amplifier based on a piece of self-developed large-mode-area low-NA fiber with a core NA of 0.049 and a core/inner cladding diameter of 25/400μm.The influence of the pump wavelength and fiber length on the power scaling potential of the fiber amplifier is systematically investigated.As a result,an output of 4.80 kW and a beam quality factor of~1.33 were finally obtained,which is the highest output power ever reported in a fiber amplifier exploiting the low-NA fiber.The results reveal that low-NA fibers have superiority in power scaling and beam quality maintenance at high power levels.

10kW级单纤泵浦耦合器件设计与实验研究

针对制约单纤系统向更高功率输出面临的泵浦光源亮度受限和有源光纤泵浦注入区域温度控制受限的问题,提出一种新型的端面泵浦耦合器件。通过扩大信号光纤的包层直径,有效提升了可注入光纤系统的泵浦功率,同时有效降低了有源光纤端面泵浦注入区域的温度。在实验中获得了9.95k W的泵浦激光注入,并在单纤系统中实现了6 k W的输出。该器件具备10 k W以上的泵浦耦合能力,具备应用于万瓦级单纤系统的潜力。

大功率激光入纤弯曲损耗机理研究

针对高功率激光入纤时对光纤弯曲处损耗增加的问题,设计了多种外界环境干扰下的测试系统,并分别在常温和高低温条件下测试了高功率激光对光纤的损伤规律,通过测试结果与理论分析相比对,揭示了高功率激光导致光纤弯曲处损耗的机理。提出在光纤弯曲处由于应力作用,在高功率激光注入时会产生局部高温,导致光纤内部出现微小损伤,从而改变纤芯与包层之间的折射率差,破坏原本的全反射条件,造成光纤损耗增加。研究结果表明,基于光纤的弯曲损耗理论以及上述热损伤理论建立的数值仿真模型可准确拟合实验测试结果,进而验证了所提出热损伤理论的合理性。而高低温测试条件加速了这一过程,导致光纤损耗增加速率高于常温下的测试结果。

工业用大功率固体激光加工系统

报道了一种符合工业应用的国产化大功率固体激光加工系统。大功率连续Nd∶YAG激光器采用对称放置方式四棒串接谐振腔,得到大于2100 W的稳定功率输出,光束参数积24 mm·mard,系统总光电转换效率达到3.5%;激光器的输出激光采用芯径600μm的光纤传输。对激光加工系统的关键问题进行了分析,包括大功率固体激光器在保证光束质量的条件下大功率输出、高效率光纤耦合输出、适应加工要求的控制系统等。研制的系统在实际应用中表明:加工系统稳定、可靠,操作方便,可与机械手、机床等外设联接,满足工业应用的要求。

高能光纤激光经准直系统后的光束质量研究

应用光线光学的理论,对透镜的几何像差、热非线性等因素对光纤激光光束质量的影响进行了分析和计算,给出了激光通过多透镜光学系统后,光束质量参数M2与系统参数的一般关系.研究了高能光纤激光通过准直系统后的光束质量.研究结果表明,随着激光功率的增大,经准直系统后光束的光束质量存在最佳值,其对应的激光功率与准直系统参数有关,为高能光纤激光准直系统的设计提供了参考.