5 kW全光纤结构1018 nm激光合成

光纤激光同带抽运方案具有泵浦亮度高、量子亏损小等优势,有着巨大的功率提升潜力,是近年来国际上的研究热点。1018 nm光纤激光可作为高功率掺镱光纤激光器的高效同带抽运源,但是单个1018 nm光纤激光器输出功率有限,光束合成是突破这一局限的重要方案。基于19台单模1018 nm光纤激光器和一个191光纤功率合束器,搭建了一套全光纤结构激光合成系统,实现了5 kW的1018 nm合成激光输出。     

基于公共环形腔耦合的光纤激光器相干合成技术

 为提高光纤激光器无源自调整相干合成阵列的效率、稳定性和可扩展性,提出了基于公共光纤环形腔耦合与单模光纤滤波的光纤激光器相干合成方案。将多个2×2的光纤耦合器分别插入各单元激光器的谐振腔,利用耦合器余下的端口,两两相连构成公共环形耦合腔。采用单模光纤滤波技术,提高了各输出激光束之间相位锁定的稳定性。利用该方案在实验上实现了三路光纤激光器的被动锁相输出,实验测得的远场干涉光斑、输出功率及光谱均表明该方案适于构建性能较好的光纤激光器相干合成阵列。     

2.14kW级联泵浦光纤放大器

利用大模场掺镱光纤搭建了1018nm高功率光纤激光器,获得了476 W的最高输出功率。利用6台高亮度1018nm光纤激光器泵浦掺镱光纤,搭建了全光纤结构的级联泵浦光纤放大器,实现了2.14kW的最高输出功率,输出功率随泵浦功率线性增长,整体斜率效率为86.9%,M2因子为1.9。     

两光子晶体光纤激光器相干锁定的实验研究

利用自成像腔技术进行光子晶体光纤(PCF)激光器光束相干合成的实验研究,实现了两光子晶体光纤激光器的相位锁定.在不使用滤波器的情况下,实验仍能观测到清晰的下涉图样,且在高功率输出状态以及环境噪声情况下干涉图样仍可保持稳定,表明具有单模大模场特性的光子晶体光纤在实现光束相干合成方面比传统的双包层光纤(DCF)有明显的优越性.实验还表明耦合输出镜的反射率对相干输出功率有一定影响,当反射镜的反射率分别为5%,10%和15%时,两台激光器相干输出斜率效率分别为63.8%,61.6%和60.2%.在抽运功率为150 W和耦合输出镜的反射率为5%时,获得95.8 W的最大相干功率输出,相干功率合成效率为90.2%.实验中无任何热光效应产生,有望利用该方法获得更高的相干输出功率.     

两光纤激光器相干合成的实验研究

利用迈氏腔技术,进行了光子晶体光纤(PCF)激光器相干合成的实验研究,实现了两光子晶体光纤激光器的相位锁定,获得了功率为47W的相干输出.解释了在迈氏腔的两个输出光路上分别实现相干相长和相干相消的物理机理.实验结果表明,合成激光光谱较单台PCF激光器的激光光谱有显著的改善,波长带宽小于5nm. 关键词： 光子晶体光纤 相位锁定 迈氏腔 光纤激光器     

单频窄线宽分布布拉格反射光纤激光器研究

分析了单频窄线宽分布布拉格反射（DBR）光纤激光器的单模工作条件,在此基础上算出单模工作区域,制作了一个单频窄线宽分布布拉格反射光纤激光器。该激光器在波长为975.5nm的半导体激光器抽动下,在1556.91nm波长处。当抽运功率为55.35mW时输出功率可达1.43mW,频宽小于1.2MHz(受测量仪器分辨率限制）。经测量,该输出激光是稳定的单纵模输出。     

子激光器功率差对光纤激光器相干组束的影响

设计了由两支光纤激光器通过耦合器组成的迈克尔逊腔型光纤激光器阵列,实现了相干合成输出,相干合成功率与完全相干合成的理论值偏差约9％。研究了子激光器功率差对低损耗端口相干合成特性的影响。结果表明：当子光纤激光器功率差减小时,耦合效率增大,理论与实验偏差减小,泵浦效率增大,输出功率增大,光谱中心波长基本不变;子激光器功率越大,子激光器功率差对以上物理量的影响越小。     

高功率光纤激光的时间部分相干性对相干合成的影响

 将多个光纤激光器的输出光束进行相干合成是获得高功率、高光束质量激光的有效途径。利用准部分相干光(PPCB)模型，计算了高功率光纤激光器阵列发出的部分相干光在远场的能量分布，分析了激光的时间部分相干性对相干合成的影响。计算结果表明，随着单根激光器输出光束线宽的增大，远场光斑的图样基本保持不变，但峰值功率和Strehl比随之减小。对于采用的算例，要保证远场光斑的Strehl比大于0.8，单根光纤激光器的线宽不能超过5 nm。     

光纤复合环形腔单模激光器的研究

单模光纤激光器在光通讯和光传感中具有广阔的应用前景。分析了复合腔光纤激光器的构成及单模的实现特点,提出了一种新颖的光纤复合环形腔激光器结构,并对其进行了实验研究。该激光器使用了波长为980nm的半导体激光器作为泵浦源。三个腔长均为2m,彼此之间的腔长差为1～2mm的光纤环形滤波器与主谐振腔构成复合腔。此激光器在波长为1562nm处得到了线宽小于0.1nm的单模激光输出,输出的光功率可达到1mW。该激光器的阈值为5mW,斜率效率为4%。     

两路关联光纤激光器互注入锁相实验

基于角锥互注入锁相相干合成方案,利用光纤Bragg光栅（R=85％@1064nm）作为两路光纤激光器的共用腔镜,实现了两路光纤激光器相关联,进一步提高了激光的互注入能量。采用外腔结构,较容易实现了两路光纤激光器的能量互注入锁相。在实验上观察到了远场清晰稳定的干涉条纹（可见度超过0．8）,获得了功率合成效率约为80％的线偏振相干激光输出。     

利用全光纤结构Michelson腔实现两路高功率双包层光纤激光器相干合成

Michelson腔技术是实现激光相干合成的有效方案. 利用Michelson腔技术, 实现了全光纤结构下的两路光纤激光器的相干合成, 获得了功率为11.75 W, 效率为95.76%的相干输出. 实验研究了相干合成效率与激光腔长差的关系以及抽运对称性对相干合成效率的影响. 实验表明相干合成效率极易受激光腔长差的影响, 不同腔长差下相干合成效率差异可达18%以上, 且存在最佳腔长差; 抽运对称性对相干合成效率的影响在2%以内.     

Efficient single-mode operation of a standing-wave dye laser

The selection of a single longitudinal mode of a dye laser can be achieved with double or triple Michelson reflectors instead of Fabry-Perot etalons inside the laser cavity. These systems can be adapted to commercial multimode dye lasers. They provide a high efficiency and a good geometrical quality of the output beam. With a 7 watt pump power (λ=514.5 nm line of the Ar⁺ laser), a tunable output power of 1 watt was obtained at the peak of R6G, in the main output beam; the total single-mode power, including the auxiliary output beams, exceeded 1.4 watt. These results correspond to efficiencies of 14% and 20%, respectively (24% and 30% slope efficiencies). We discuss in the text why these efficiencies are comparable to those of ring lasers. In the infrared, with a 4.5 watt pump power (red lines of a Kr⁺ laser), 250 mW of single-mode output power in the main output beam was obtained at 780 nm with Oxazine 750.     

Efficient improvement of laser beam quality by coherent combining in an improved Michelson cavity

The efficient improvement of laser beam quality is demonstrated by coherent combining of two Nd:YVO4 lasers in an improved Michelson cavity. When the two lasers are separately operated with beam qualities of M(x)2 = 1.74 and M(y)2 = 1.34 for laser 1 and M(x)2 = 1.53 and M(y)2 = 1.39 for laser 2, by coherent combining of the two lasers, a single beam output exceeding 2 W with a nearly perfect TEM00 mode (M(x)2 = 1.08, M(y)2 = 1.04) is obtained. Moreover, it can withstand environmental perturbations with no change in beam quality or output power and has the potential for scaling to much higher output power with high beam quality by coherent addition of multiple lasers in this configuration.     

Experimental study of phase-locking of two photonic crystal fiber lasers

Two photonic crystal fiber (PCF) lasers are phase-locked by using self-imaging resonator techniques. Obvious and steady interference strips are observed even without using spatial filter in high power operation, which demonstrates the advantages of pure single-mode PCF lasers in coherent beam combining. The maximum coherent output power of 95.8 W is obtained with coupling efficiency of 90.2%.     

Local-cooled watt-level Nd-doped phosphate single-mode fiber laser

Efficient and stable continuous-wave (CW) laser operation at 1053 nm in a Nd-doped phosphate single-mode fiber (Nd:PSMF) has been demonstrated experimentally. The fiber laser consisted of a 21 cm Nd:PSMF placed in a F-P cavity formed by high reflector butt-coupled to coupling end of the fiber and Fresnel reflection of the other end facet. An output power of 1.42 W and a slope efficiency of 34.1% (18.4%) with respect to absorbed pump power (incident pump power) were obtained with 808 nm diode pumping. An increment as much as 9.7 and 15.0% in slope efficiency of the input coupling efficiency and the output power, respectively, were obtained by using a local-cooling design provided by watered sealing the coupling point. The repeatable results indicate that the design, featuring fluid sealing the coupling point of the fiber laser, which was capable of offering an effective alleviation of thermal effects and an elevation of the quality of the laser cavity, could be expected to be a convenient and effective scheme to improve the performance characteristics of the non-silica fiber lasers and the high power fiber lasers, generally in free-space coupling configuration.     

High power single-mode cw dye laser with Michelson mode selector

The application of a Michelson mode selector for high power single-mode operation of a cw dye laser is reported. By employing the selector for compensation of spatial hole burning effects in a standing-wave cavity, a tunable single-mode output power of 1 W has been obtained at 590 nm. A double Michelson selector has also been applied with the spatial hole burning taken into account.