Proposal for a high brightness γ-ray source at the SXFEL

High brightness γ-rays produced by laser Compton scattering(LCS) are ideal probes for the study of nucleon and nuclear structure. We propose such a γ-ray source using the backscattering of a laser from the bright electron beam produced by the linac of the Shanghai Soft X-ray Free-electron Laser(SXFEL) test facility at the Shanghai Institute of Applied Physics(SINAP). The performance is optimized through theoretical analysis and benchmarked with 4D Monte-Carlo simulations. The peak brightness of the source is expected to be larger than2 × 1022photons/(mm2mrad2s 0.1%BW) and photon energy ranges from 3.7 Me V to 38.9 Me V. Its performance, compared to Extreme Light Infrastructure-Nuclear Physics(ELI-NP), and the Shanghai Laser-Electron Gamma-ray Source(SLEGS), is given. The potential for basic and applied research is also briefly outlined.

High-power compact continuous-wave Fe:ZnSe laser at 4μm with>50%overall conversion efficiency

We report on a compact,high-efficiency mid-infrared continuous-wave(CW)Fe:ZnSe laser pumped by a 2.9μm fiber laser under liquid nitrogen cooling.A maximum output power of 5.5 W and a slope efficiency of up to 66.3%with respect to the launched pump power were obtained.The overall optical-to-optical(OTO)conversion efficiency,calculated from the output of the 2.9μm fiber laser to the 4μm laser,was as high as~54.5%.The OTO efficiency and the slope efficiency are,to the best of our knowledge,the highest ever reported in Fe:ZnSe lasers.A rate-equation-based numerical model of CW operation was established,and the simulation agreed well with the experiment,identifying the routes used in the experiment for such high efficiency.

High-brightness all-fiber Raman lasers directly pumped by multimode laser diodes

High-brightness fiber laser sources usually utilize active rare-earth-doped fibers cladding-pumped by multimode laser diodes(LDs), but they operate in limited wavelength ranges. Singlemode-passive-fiber based Raman lasers are able to operate at almost any wavelength being pumped by high-power fiber lasers. One of the interesting possibilities is to directly pump graded-index(GRIN) multimode passive fibers by available high-power multimode LDs at 915–940 nm,thus achieving high-power Raman lasing in the wavelength range of 950–1000 nm, which is problematic for rare-earthdoped fiber lasers. Here we review the latest results on the development of all-fiber high-brightness LD-pumped sources based on GRIN fiber with in-fiber Bragg gratings(FBGs). The mode-selection properties of FBGs inscribed by fs pulses supported by the Raman clean-up effect result in efficient conversion of multimode pump into a high-quality output beam at 9 xx nm. GRIN fibers with core diameters 62.5, 85 and 100 μm are compared. Further scaling capabilities and potential applications of such sources are discussed.

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.

Novel types of photonic band crystal high power and high brightness semiconductor lasers

A novel type of high power edge-emitting semiconductor laser （SL） with extended vertical photonic band crystal （PBC） waveguide was reviewed. Simulations predict narrow beam divergence, resulting from the thick PBC waveguide, to be independent of realistic variations of the growth parameters. Narrow ridge lasers fabricated along the simulations indeed demonstrate superior output power, narrow beam divergence, circular beam profile, excellent beam quality and very low astigmatism. Efficient fiber coupling decisive for most applications was thus eased. Stability of the laser under a wide range of operating temperature was demonstrated. Ultrashort pulses with few ps of duration at GHz repetition rates were generated by passively mode locking the lasers.

Overview of ytterbium based transparent ceramics for diode pumped high energy solid-state lasers

Development of high energy laser sources with nanosecond pulses at several hertz values for repetition rate has been very attractive in recent years due to their great potential for practical applications. With the recent advancement in fabricating large size laser quality transparent ceramics, diode pumped solid-state laser generating pulse energy of 100 J at 10 Hz has been recently realized at HiLASE center using Yb:YAG ceramic with Cr:YAG cladding. This review discusses Yb based high energy lasers, specific laser geometries for efficient thermal management and the role of transparent ceramics in such diode pumped high-energy-class solid-state lasers around the world.

10 W近衍射极限输出的高效率窄线宽主控振荡放大半导体激光器

为研制近衍射极限的高功率半导体激光器,采用了片上光栅、窄脊型波导、锥形放大器一体集成的主控放大(Master Oscillator Power-Amplifier,MOPA)技术路线,以长度为8 mm、脊型宽度为3μm的波导为单模种子源,配合长度为7 mm、全角为3.3°的锥形放大器,实现了功率10.3 W、慢轴光束质量M^(2)(1/e^(2))因子=1.06,3 d B线宽40 pm,工作电光效率50.5%的半导体激光输出,并采用片上电致加热光栅调谐技术,实现了中心波长在4 nm范围内连续可调。

激光照明用荧光材料的研究进展

半导体激光器具有亮度高、传输距离远等优点,特别适用于特殊照明领域(如激光车灯、投影显示等)。简述激光照明的实现方式以及目前存在的主要问题,重点综述稀土、半导体、碳点3种荧光材料在激光照明中的研究进展。稀土作为目前最常用的激光照明用荧光材料,主要有稀土荧光粉、荧光陶瓷、荧光玻璃3种形式,具有光热稳定性高等优点,但资源不可再生和价格昂贵等限制了其进一步应用;半导体荧光材料主要有以CdSe和ZnS为代表的第二代半导体量子点材料、以SiC和AlN为代表的第三代半导体材料和钙钛矿材料,第二代半导体量子点材料和第三代半导体材料具有发光效率高、性能稳定等优点,但受限于成本和工艺,钙钛矿材料具有带隙可调、可获得稳定的自发辐射等优点,但含有毒性元素且对环境的高度敏感性导致其稳定性较差;碳点荧光材料具有发光波长可调、低毒性等优点,主要有光转换材料和增益介质2种形式,但目前在激光下的热稳定性欠缺。最后,对未来激光照明用荧光材料的发展前景进行展望。

激光加速质子束空间电荷力研究

激光加速器可以输出具有独特品质的质子束,例如μm尺寸、ps脉冲长度和高峰值电流。强流粒子束的空间电荷力效应较强,对面向应用的束流传输提出了挑战。通过二维PIC模拟研究了激光加速后与质子速度接近的电子的影响。采用椭球模型估算空间电荷力的影响,比较不同电荷分布的差异。结果表明每束团质子数超过1010后空间电荷力显著影响质子束传输,甚至严重破坏束流品质。空间电荷力的影响在20 ps后显著减弱,离开靶约1.2 mm。

高功率高亮度半导体激光器合束进展

半导体激光器体积小、效率高,但单元输出功率低、光束质量差限制了其应用。介绍了提升半导体激光器功率及光束质量的最新进展,对各种技术途径和实验结果进行了综述报道,并具体介绍了中国科学院长春光学精密机械与物理研究所近年来在高亮度半导体激光器芯片及合束方面取得的进展。

百瓦级高亮度光纤耦合半导体激光模块的研制

用3只976 nm半导体激光短列阵作为子模块,研制出连续工作的百瓦级高亮度光纤耦合模块。首先,利用光束转换器将每个半导体激光短列阵进行光束整形;然后采用空间复用技术将3个半导体激光短列阵在光参数积小的方向上叠加,并利用倒置伽利略望远镜作为扩束器进一步压缩发散角;最后利用优化结构的透镜组将激光聚焦到芯径200μm,数值孔径为0.22的光纤中。测量结果显示:聚焦后激光的发散角为24.8°,焦平面的光斑尺寸为175.2μm;耦合后测量光纤出光功率可达107 W,对应亮度为2.23 MW/(cm2.sr),达到了国内利用列阵进行光纤耦合的领先水平;在工作电流为52.5 A时,电光转换效率为43.1%,远高于全固态等激光器;最后测量本模块在不同驱动电流时的光谱,并以此计算出模块的热阻为1.29 K/W,说明它的散热性能良好。结果表明,本光纤耦合模块适合应用于泵浦光纤激光器、医疗和激光加工等领域。

高亮度半导体激光阵列光纤耦合模块

利用2只915 nm半导体激光短列阵作为子模块,设计并研制出连续输出的高亮度光纤耦合模块。首先对每个半导体激光短列阵进行光束整形,从而提高它的光束质量;然后采用空间复用技术将这两个半导体激光短列阵出射的激光在光参数积小的方向上叠加,并利用偏振复用技术进一步提高光束质量;最后利用单片非球面透镜将激光聚焦到芯径为100μm、数值孔径为0.22的光纤中。测量结果显示:在工作电流为52.5A时,聚焦镜焦平面的光斑尺寸为105.4μm;耦合后测量光纤出光功率可达72.6 W,对应亮度为6.08 MW/(cm2.sr),模块的电光转换效率为42.2%。最后测量了模块在不同驱动电流时的光谱,证明该模块的散热性能良好。

高亮度锥形半导体激光器

介绍了由双量子阱非对称波导结构外延片刻蚀成的带有脊形波导结构的锥形半导体激光器。该激光器有效抑制了p型区域对激光的影响,减小了半导体激光快轴方向的发散角,同时采用脊形结构和锥形结构的组合获得了高亮度激光。实验中,在电流7 A时获得了中心波长963 nm、连续功率4.026 W的激光输出。测得慢轴方向和快轴方向激光光束参数乘积分别为1.593 mm·mrad和0.668 mm·mrad。

高亮度固体激光器技术发展研究

激光推进、激光传能等重大科研方向对高亮度固体激光器技术提出了重大需求,使得相关研究持续成为国际关注焦点。本文阐述了高亮度固体激光器技术的宏观需求,梳理国内外的技术研究现状并总结发展趋势,凝练技术进一步发展所面临的问题;据此完成高亮度固体激光器的关键技术分析,并结合国情提出未来发展建议。板条激光器和光纤激光器由于具有突出优点成为研究热点,在单台激光器输出功率不断提升的同时,可配合光束合成方法来实现高亮度激光输出。研究表明,应着重推动新型激光材料、高端半导体激光泵浦源、高精度封装工艺、自适应光束控制、光束合成关键器件等方面的技术攻关,尽快形成核心技术体系;科学布局以表层增益板条激光器技术为代表的、具有良好发展潜力的固体激光器技术研究课题,加强共用基础技术研究与积淀,为未来固体激光器输出亮度、转换效率、功率质量比的持续提升奠定坚实基础。

850nm高亮度近衍射极限锥形半导体激光器(英文)

制备了具有低红暴优势的850 nm大功率高亮度锥形半导体激光器,获得了近衍射极限的激光输出。当连续输出功率为200 mW时,光束质量因子M2仅为1.7,亮度高达16.3 MW.cm-2.sr-1;当功率提高到1 W时,M2因子和亮度仍分别达到2.8和9.9 MW.cm-2.sr-1。此外,研究了锥形激光器的功率、光谱、远场分布等特性,并分析了不同脊形波导长度对锥形激光器自聚焦现象的影响。

光泽金属的激光精密刻蚀实验研究

采用266nm或355nm的紫外激光器可以对微小的金属薄膜器件直接进行激光精密加工。但是,目前紫外激光器的输出功率普遍较低,以至于还不能对大幅面、深尺度的光泽金属进行激光加工。为了克服光泽金属对大功率固体激光器输出的1064nm激光的高反射率和散热快问题,采用了优化谐振腔和扫描聚焦系统的光学方法,实现了激光单模运转,功率密度达到了1.592×109W/cm2,由此也使得加工工件通过原子吸收激光能量的方式改变为通过金属中的自由电子的等离子体激射来吸收激光能量。在平均功率为50W、重复频率为500Hz、焦斑直径小于20μm、脉冲宽度为80ns、切割速度为10mm/s的加工条件下,对厚度为10mm的大尺寸紫铜板直接进行了激光精密刻蚀实验,切割的槽宽和槽深均为100±10μm;槽间距为300±15μm,均达到了初始设计的指标要求。

激光精密刻蚀技术在硅太阳电池制备工艺中的应用

依据光学谐振腔的图解分析与设计方法,对以Nd:YAG固体激光器作光源的激光切割机进行了设计改进,实现了高亮度激光输出.并利用该设备对硅太阳电池进行了激光精密切割试验,使埋栅太阳电池电极槽达到了平均宽度为150±5μm,槽深100±10μm的设计指标.在发射结卷包太阳电池所用的硅衬底片上进行激光精密穿孔,目前最小孔径为20μm.通过应用激光精密刻蚀技术,现将埋栅太阳电池光电转换效率提高到了21%,接近该领域的世界先进水平.

半导体激光器侧向模式控制技术的研究进展

高功率半导体激光器在固体或光纤激光器泵浦、材料加工、激光雷达、空间通讯及国防等领域具有重大需求,但传统器件面临发散角大、光束质量差、亮度低的难题,限制了其直接应用。宽区半导体激光器具有输出功率和转换效率高的优点,但其侧向模式受多种物理效应的影响,高电流下激射模式数很大,导致远场宽度随电流增大迅速展宽,光束质量非常差,成为制约半导体激光亮度提高的关键瓶颈难题。因此,需要对半导体激光器的侧向模式进行控制。本文首先从半导体激光器的侧向模式影响机制出发,分析了其侧向模式特性及光场分布与器件结构的关联关系;接着,介绍了目前主要的侧向模式控制技术,通过抑制高阶模式及侧向远场展宽,实现光束质量的改善及激光亮度的提升。采用先进的侧向模式控制技术,可从芯片层次发展新型的高亮度半导体激光器,有利于拓展半导体激光器应用领域及降低应用成本,具有重要的研究意义。

808nm准连续半导体激光迭阵偏振耦合技术

利用激光偏振原理将两束同一波长不同偏振态的激光束耦合以获得更高功率输出,是目前国际研究的热点之一。通过激光偏振及偏振转换元件的理论分析,给出了偏振耦合技术的实验原理、装置及关键技术,并通过实验将20%占空比准连续808 nm两半导体激光迭阵进行耦合。自行设计光学系统对光束进行扩束、聚焦,实现输出光斑2 mm×2 mm,效率达60%。

高亮度半导体激光器的研制

针对高功率光纤激光器对高亮度、高功率光纤耦合半导体激光器的需求,研制了一种多单管半导体激光器,通过光束精密调试及空间和偏振合束等技术实现了高亮度、高功率光纤耦合输出。针对光纤芯径105μm,数值孔径0.22的光纤,研制了包含14只大功率单管的高亮度半导体激光器,并测试了其光电特性。实验结果表明:在工作电流为12A时,光纤的输出功率可达120W,对应亮度为9.1MW/(cm^2·sr),电光效率45%。