High beam quality broad-area diode lasers by spectral beam combining with double filters

A modified spectral beam combining(SBC) approach based on double asymmetrical filters was proposed. By using this scheme, the high-order lateral modes at the edge of the far-field pattern can be suppressed in the external cavity, and the beam quality in the slow-axis direction was improved from 16.1 to 13.4 compared to the conventional SBC. In the meanwhile, the electrical-to-optical efficiency from the modified SBC was more than 40% with an output power of 34.1 W, which is similar to that of the conventional SBC.     

外腔两束光纤激光频谱组束的实验研究

报道了外腔2个大模面积双包层Er3+/Yb3+共掺光纤激光器频谱组束的实验结果,获得了最大功率为0.80 W、组束效率高达82.5%的组束激光输出。演示和分析了光纤末端放置位置的改变、光栅的旋转对输出光谱和组束效率的影响,结果表明:当光纤末端距系统轴的位置超过某一定值时,输出光谱呈现多模;当光栅与水平面所成角度减小时,组束效率逐渐增大。     

外腔两束光纤激光频谱组束的实验研究

报道了外腔2个大模面积双包层Er3+/Yb3+共掺光纤激光器频谱组束的实验结果,获得了最大功率为0.80 W、组束效率高达82.5%的组束激光输出。演示和分析了光纤末端放置位置的改变、光栅的旋转对输出光谱和组束效率的影响,结果表明：当光纤末端距系统轴的位置超过某一定值时,输出光谱呈现多模;当光栅与水平面所成角度减小时,组束效率逐渐增大。     

大模面积双包层光纤激光频谱组束的实验效果

基于透射体布拉格光栅频谱组束的设计方案,采用半导体激光器作为泵浦源,以大模面积双包层Er3+/Yb3+共掺光纤为增益介质,报道了两束光纤激光频谱组束的实验结果。在两束光纤激光输出功率分别为0.39和0.53 W、光栅实际衍射效率不到60%的情况下,实现了组束功率为0.64 W、绝对组束效率高达69.6%的组束激光输出,并分析了实验过程中影响组束效率的因素。     

大模面积双包层光纤激光频谱组束的实验效果

基于透射体布拉格光栅频谱组束的设计方案,采用半导体激光器作为泵浦源,以大模面积双包层Er3+/Yb3+共掺光纤为增益介质,报道了两束光纤激光频谱组束的实验结果。在两束光纤激光输出功率分别为0.39和0.53 W、光栅实际衍射效率不到60%的情况下,实现了组束功率为0.64 W、绝对组束效率高达69.6%的组束激光输出,并分析了实验过程中影响组束效率的因素。     

光纤激光器频谱组束的理论研究

 建立了由光纤激光器阵列、薄透镜和衍射光栅组成的频谱叠加理论模型,基于高斯光束的变换和衍射理论,推导出远场光强分布的关系式,探讨了系统参量的优化设计并进行了数值模拟。结果表明：当中心波长激光器的-1级干涉主极大与槽面衍射主极大重合、零级干涉主极大刚好落在槽面衍射的+1级零值极小上、其它波长激光器的-1级干涉主极大与中心波长激光器的槽面衍射主极大重合时,输出光束的衍射效率较高;当光栅平面法线与薄透镜光轴的夹角为衍射光栅槽形角的一半时,输出光束的半角宽度较小。     

光纤激光器频谱组束的理论研究

建立了由光纤激光器阵列、薄透镜和衍射光栅组成的频谱叠加理论模型,基于高斯光束的变换和衍射理论,推导出远场光强分布的关系式,探讨了系统参量的优化设计并进行了数值模拟。结果表明：当中心波长激光器的-1级干涉主极大与槽面衍射主极大重合、零级干涉主极大刚好落在槽面衍射的+1级零值极小上、其它波长激光器的-1级干涉主极大与中心波长激光器的槽面衍射主极大重合时,输出光束的衍射效率较高;当光栅平面法线与薄透镜光轴的夹角为衍射光栅槽形角的一半时,输出光束的半角宽度较小。     

Propagation characteristics of the Yb-doped fiber lasers after spectral beam combining by the VBGs

The propagation model for the spectral beam combining system of five Yb-doped fiber laser beams by the volume Bragg gratings (VBGs) has been built up. Considering the surface distortion by thermal effect, the intensity of an individual beam passing through the spectral beam combining system by the VBGs with deformation has been analyzed numerically and iteratively by using finite-different and sparse matrix methods, and the intensity of combined beam has been studied by the principle of incoherent superposition. Consequently, according to the intensity second-order moments method, the M²-factor of the combined beam has been calculated. The effects of deformation of the VBGs on the intensity, the combining efficiency, the M²-factor and the power in the bucket of the combined beam have been analyzed quantitatively. It can be shown that the effects of the deformation of the VBGs on the intensity distribution of combined beam become more and more obvious with the increasing of the deformation of the VBGs. The results show that the surface distortion of the VBGs due to high-power lasers dramatically degrades both the beam quality of the combined beam and the combining efficiency of the spectral beam combining system.     

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。     

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。     

Flat-top laser beam generated by coherent beam combining of Gaussian lasers

We present a fiat-top laser beam generation scheme using coherent beam combining of hexagonally arranged Gaussian lasers. To produce a beam with a flat-top profile, we optimize the amplitude and phase of each unit laser using the least-square method. Simulation results show that with 13 unit lasers, a beam with the flatness of less than 1% in the optimizing region can be achieved. The main lobe contains over 95% of the total power. The scheme requires no external beam shaping element and has the potential to be designed for high-power applications.     

利用频谱组束获取双光谱光源的实验研究

 针对激光多光谱探测对多色激光光源的需求,提出利用外腔频谱组束技术获取多光谱激光探测光源的方法。报道了外腔2个大模面积双包层Er3+/Yb3+共掺光纤激光器频谱组束的实验结果,获得了一种3dB线宽分别为29.3nm和11.52nm的可调谐双光谱激光探测光源。实验结果和理论分析表明：外腔频谱组束技术是一种获得多光谱激光光源的可行方法。     

体布拉格光栅用于高功率光谱组束的研究

使用透射型体布拉格光栅组束两束光纤激光,实现了856 W光谱组束输出。总的光谱组束效率为73.7%,组束光束的横向质量因子为7.9,纵向质量因子为2.7。研究结果显示,虽然体光栅的角色散严重影响衍射光束的光束质量,但其并不影响透射光束的光束特性。由于当前宽谱光纤激光器的输出功率远大于窄线宽输出,使用宽谱光纤激光器（光谱带宽超过4 nm）作为透射光束,能够在不降低组束效率和组束光束质量的前提下,有效提升使用体布拉格光栅进行光谱组束的总输出功率。     

体布拉格光栅用于高功率光谱组束的研究

使用透射型体布拉格光栅组束两束光纤激光,实现了856 W光谱组束输出。总的光谱组束效率为73.7%,组束光束的横向质量因子为7.9,纵向质量因子为2.7。研究结果显示,虽然体光栅的角色散严重影响衍射光束的光束质量,但其并不影响透射光束的光束特性。由于当前宽谱光纤激光器的输出功率远大于窄线宽输出,使用宽谱光纤激光器(光谱带宽超过4nm)作为透射光束,能够在不降低组束效率和组束光束质量的前提下,有效提升使用体布拉格光栅进行光谱组束的总输出功率。     

基于锥面衍射实现高效率双光栅光谱合成

分析了基于锥面衍射的双光栅光谱合成系统的可行性,设计了激光入射角为Littrow角附近的双多层介质膜（MLD）光栅光谱合成系统,开展了两路合成实验。当入射极角等于自准直入射角,入射方位角为6°时,光栅衍射效率近似等于光束自准直入射时的衍射效率。基于锥面衍射原理,对中心波长为1050.24 nm和1064.33 nm的两束光纤激光子束进行合成,入射极角为43.99°,测得合成效率为92.9%,较基于非锥面衍射的双光栅光谱合成系统的合成效率提高了8.8%;测得合成光斑光束质量M_x²＝1.204,M_y²＝1.467,与基于非锥面衍射的双光栅光谱合成系统输出光斑光束质量基本一致。     

Active coherent beam combining of diode lasers

We have demonstrated active coherent beam combination (CBC) of up to 218 semiconductor amplifiers with 38.5?W cw output using up to eleven one-dimensional 21-element individually addressable diode amplifier arrays operating at 960?nm. The amplifier array elements are slab-coupled-optical-waveguide semiconductor amplifiers (SCOWAs) set up in a master-oscillator-power-amplifier configuration. Diffractive optical elements divide the master-oscillator beam to seed multiple arrays of SCOWAs. A SCOWA was phase actuated by adjusting the drive current to each element and controlled using a stochastic-parallel-gradient-descent (SPGD) algorithm for the active CBC. The SPGD is a hill-climbing algorithm that maximizes on-axis intensity in the far field, providing phase locking without needing a reference beam.     

Wavelength beam combining of ytterbium fiber lasers

Wavelength beam combining of five ytterbium fiber lasers is demonstrated in a master-oscillator power-amplifier configuration at combined powers up to 6 W. The combined beam profile has an M2 value of 1.14, which is equal to that of an individual fiber. Beam steering in one dimension over 140 resolvable spots is also demonstrated.     

All-fiber coherent beam combining of fiber lasers

One half of a 2x2 fused taper single-mode fiber coupler is used for the all-fiber spatial and spectral beam combining of two fiber lasers.     

Beam combining of lasers with high spectral density using volume Bragg gratings

Incoherent combining of multiple laser beams with offset wavelengths into a single near-diffraction-limited beam is an effective solution to increasing energy brightness and scaling output power of high-power lasers. Volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass allow spectral beam combining with a remarkably high spectral density of channels. Spectral beam combining (SBC) of five channels within 1-2 nm bandwidth around 1064 and 1550 nm into a single near-diffraction-limited beam with absolute efficiency 92-94% is demonstrated. Scaling of this technique to multi-kW power level is discussed.