光纤激光器直接输出的高功率贝塞尔超短脉冲

构建了一种能够直接输出高功率贝塞尔超短脉冲的光纤激光放大器. 该方案基于在光纤端面特殊设计和制备的微型负轴锥镜, 针对常规超短脉冲光纤激光放大系统所设计, 不需要引入其他分立整形器件, 避免了目前基于轴锥透镜产生贝塞尔光束的通用方法所带来的额外烦琐准直工作, 极大简化了产生贝塞尔光束的方法. 其中的微型负轴锥镜由聚焦粒子束刻蚀法在一段掺镱大模场光子晶体光纤的端面制备, 它和光纤激光系统中的固有准直透镜构成了集成化的光束整形器件. 基于数值模拟结果成功搭建的系统与理论设计一致, 直接输出了在米量级具有高度准直无衍射特性的啁啾皮秒贝塞尔超短脉冲波包, 平均功率高达10.1 W, 对应脉冲能量178 nJ, 经过光栅对压缩后脉冲宽度可达140 fs. 关键词： 衍射 超短脉冲产生 光纤器件 光纤激光器     

反射镜热畸变对高能激光系统输出光束质量的影响

高能激光系统中,反射镜镜面热变形会使系统的输出光强和波前分布不均匀性加剧,从而导致输出光束质量的下降。建立了复杂镜面光线追迹的模型,使用Fresnel衍射公式和光线追迹的方法,研究了高能激光系统内通道不同数量22．5。反射镜对输出光束质量的影响。该方法和部分结果对高能激光系统激光器的优化设计,激光内通道冷却方式以及自适应光学校正能力设计参数的选取具有一定的参考价值。     

光纤光束传输系统

光纤光束传输系统ＯＤＣ－１００型光纤光束传输系统可为精密加工和其它材料管理传输激光功率。透境组件把激光功率耦合进１００－１００μｍ光纤中。光纤的尺寸由功率的大小及焦斑尺寸决定。聚焦透镜组件具有纤芯放大（４：１）功能且含有选定穿孔及对视频作视轴准直的光...     

基于光路自动准直的甲烷遥测技术

针对目前甲烷遥测装置因光学准直固定,在不同检测环境使用时不能进行动态调整的问题,在光路准直设计中引入了电控可变焦透镜,实现了光路自动准直。测试结果表明,针对不同的检测距离和辅助目标,通过改变电控可变焦透镜的驱动电流可实现快速变焦,在动态调节激光光束发散效果的同时可使遥测装置的接收光功率最大化,其接收光功率相比无变焦透镜接收光功率可提高1.7倍以上,同时可提高检测系统的信噪比。针对变焦透镜在遥测应用中出现的新问题,如重力效应引起的光束偏转效应,提出了形变模型,并进行了理论计算和仿真分析。使用甲烷气袋进行泄漏模拟测试,通过Allan方差分析得到:当积分时间为18 s时,极限标准差达到1.51×10^-6。对装置进行实地测量,测试距离为52.2 m,检测到楼道空气中存在4.95×10^-6浓度(体积分数)的甲烷气体。该研究展示了使用电控可变焦透镜实现光路自动准直和优化在气体泄漏遥测装置中的可行性与应用价值。     

高功率蓝光半导体激光加工光源EI北大核心CSCD

针对目前铜、金等金属材料加工的实际应用需求,开展了连续输出功率500 W的光纤耦合输出蓝光半导体激光加工光源研究。基于平面窗口TO封装的蓝光半导体激光单管器件,设计采用长后工作距的快轴准直镜和慢轴准直镜分别准直,获得低发散角、高光束质量的单元准直光束;结合二维空间合束、偏振合束和光纤耦合,将144个蓝光单管器件耦合进200μm/NA 0.22光纤,通过ZEMAX软件对半导体激光光路进行光线追踪模拟;并从实验上实现,3 A电流驱动下,200μm/NA 0.22光纤输出连续功率523 W,电光转换效率29%。该激光光源具有直接加工铜、金等材料的能力。     

高功率高效率光纤耦合半导体激光模块研制

采用光束整形和空间合束的方法,研制出高功率、高效率多阵列光纤耦合半导体激光模块。将波长为976nm连续工作的5个标准半导体阵列,通过对快轴进行准直和快慢轴光束旋转的方式进行光束整形,准直后进行空间合束,经耦合透镜聚焦,耦合入芯径400μm、数值孔径0.22的光纤。测量结果显示:光纤的出光功率最大可达到327 W,光纤耦合效率大于93.6%。     

异轴双半圆柱透镜准直半导体激光光束

运用光线追迹的方法,讨论了异轴双半圆柱透镜准直半导体激光光束的效率.数值模拟结果表明,异轴双半圆柱透镜可用于准直半导体激光光束,在最佳准直时,透镜材料的折射率允许高于2;当折射率在一定的范围内变化时,其准直效率随折射率的增大而提高.理论上可以将半导体激光器输出光束快轴方向的发散角压缩到0.1 mrad量级以下.     

光纤准直器高回波损耗的理论分析与研究

在高斯光束传输理论的基础上，利用矩阵光学 原理和高斯光束耦合理论得出了斜面耦合自聚焦透镜型光纤准直器的回波损耗的数学表达式。分析了发迹光纤准直器的参数而引起回波损耗变化的原因。实验结果与理论分析比较吻合。     

基于自适应桶中功率评价函数的光纤放大器相干合成实验研究

光纤激光光束合成技术被公认为是实现高亮度、高光束质量激光束的优秀方法, 而激光阵列间的倾斜像差是影响合成效果的重要因素. 针对当前光束合成中存在的倾斜校正量受限问题, 提出了基于自适应桶中功率(PIB)评价函数的倾斜控制策略. 搭建了两路2 W光纤放大器的相干合成实验平台, 利用自制的压电环光纤相位调制器和自适应光纤准直器分别实现锁相和倾斜像差校正, 验证了基于自适应PIB的倾斜控制策略的可行性, 并实现了相干合成. 关键词： 光纤激光阵列 倾斜控制 自适应桶中功率 相干合成     

光纤激光相控阵相干合成技术研究进展

主要介绍了近年来光纤激光相控阵相干合成技术的发展现状,总结了中国科学院光电技术研究所在这方面的最新研究成果,包括基于振幅调制的光纤激光相控阵相干合成能力优化、光纤激光相控阵实现收发一体相干合成、光纤激光相控阵的目标在回路相干合成、光纤激光相控阵在大气湍流下实现耦合接收光束的共相合束、基于多孔径波前探测的相干合成方法、基于自适应光纤准直器和微透镜阵列的光束大角度高精度连续寻址扫描等。以上研究工作将促进光纤激光相控阵技术朝向更多单元、更高功率、更远距离等方向演进,并推动其与激光大气传输、空间激光通信、自适应光学等理论和应用的结合与发展。     

Degradation of beam quality and depolarization of the laser beam in a step-index multimode optical fiber

The characteristics of a laser beam are altered during propagating through large-core multimode optical fibers. The distribution of modes excited by the input laser beam is modified by means of mode coupling on transmission through the fiber, leading to the degradation of beam quality and the depolarization of the delivered beam. The relationship between the beam quality factor (M²) of output beam from a large-core multimode fiber and the fiber length, as well as the relationship between the degree of polarization (V) of output beam from such a fiber and the fiber length, are introduced in this paper. When a laser beam was well launched into a large-core step-index multimode fiber, M² of the output beam was a compound tanh function of the fiber length. A linear polarization beam that well launched into such fiber suffered depolarization. The V of the output beam was an exponent function of fiber length. And the misalignment between beam axis and fiber axis made the beam quality degrade faster but made no difference of the utmost M² in the aligned and misaligned conditions. Also, the misalignment condition made the polarization of output beam degrade faster.     

Optical fiber cleaved at an angle by CO2 laser ablation: Application to micromachining

Laser ablation can be achieved by delivering short power pulse with durations much smaller than the heat diffusion time. In this investigation, we are collimating and magnifying a beam from a CO₂ laser with a Keplerian telescopic system. Then we study the quality of the cut performed by scanning the beam at a fast speed over an optical fiber just after focusing a well collimated CO₂ beam at λ=10.6 μm. It is found that the best results for cutting optical fibers depend upon both the time required in raising matter temperature to the vaporization point and the scanning speed of the CO₂ laser beam. Some aspects of the laser beam collimation before focusing is reviewed briefly and results for optical fibers being cleaved at low and fast speed under various conditions are also shown and discussed.     

Theoretical calculation of beam quality factor of large-mode-area fiber amplifiers

In order to evaluate a fiber amplifier’s output beam quality, we have explored the beam quality factor calculation. A theoretical beam quality factor calculation method is presented in this paper. The method bases on modal power decomposition, laser rate equations and Fourier diffraction theory. Through the rate equations, each modal power weight factor at the fiber output facet is obtained. By the modal power decomposition, the optical field at the fiber output facet is established. Finally, running Fourier transformation, the beam diverging state in free space and corresponding M ² parameter are obtained. The calculation process is verified with applying it to working out the beam M ² parameters of large-mode-area (LMA) fiber amplifier system under different conditions. The numerical results help us well know and predict the out beam property. Some obtained results are also accord with other reporting outcomes.     

Incoherent combination of fiber lasers using a collimating and focusing optical system in fiber-based laser fusion

The incoherent combination of fiber laser beams using a collimating and focusing optical system in fiber-based laser fusion is theoretically and numerically studied. The propagation of the fiber lasers passing through the optical system is analyzed by the ABCD law. The super-Gaussian fitting is performed to study the synthetic intensity profile near the focal spot quantitatively. The intensity profile of the combination beam is dependant on the defocusing distance, the number of the fibers, the separation of the fibers, and the beam expansion ratio of the collimating system.     

A highly efficient 5 kW peak power Nd:YAG laser with time-shared fiber optic beam delivery

Here, we report on the development of an efficient, high peak power lamp pumped Nd:YAG laser with time-shared fiber optic beam delivery. A maximum average output power of 270 W with 100 J maximum pulse energy and 5 kW peak power has been achieved with an electrical to laser conversion efficiency of 5.4%, which is on higher side for typical lamp pumped solid-state lasers. We have improved efficiency by spectral conversion and water flow optimization in the pump cavity, with a resulting beam quality comparable to commercial systems of similar power level. The resonator has been designed for stable operation from single-shot to 200 Hz repetition rate. A study of pulse-to-pulse laser energy stability for different resonator configurations has also been performed. The resonator was designed to achieve a good beam quality for the whole range of operation with a maximum beam parameter product of 15 mm mrad (M²45). A simple mechanism for time-shared fiber optic port selection has also been devised. Material processing applications such as cutting of stainless steel sheets up to 14 mm thickness and welding of metals such as carbon steel with weld depths up to 2 mm using the developed laser system has also been reported.     

半导体激光器光束准直系统的功率耦合效率

在长距离无线光通信中，接收点光功率密度与光束发散角平方呈反比关系，为了获得小的发散角和大的功率耦合效率，要求准直系统有较大的数值孔径(NA)，但数值孔径过大会增加像差，因此合理设计功率耦合效率与准直系统的数值孔径就非常重要。该文对半导体激光器光束准直系统中功率耦合效率进行了研究，给出了半导体激光器光束功率耦合效率与k(孔径半径与孔径处等效光束半径之比)的关系表达式，并结合激光器光束准直系统，给出了半导体激光器光束功率耦合效率与准直系统数值孔径的关系表达式。该研究结论对于半导体激光器光束准直系统设计具有参考作用。     

CW single transverse mode all-fiber Tm3+-doped silica fiber laser

The CW 25.6 W output power with a slope efficiency of 30.6% respected to the pump power from a CW single transverse mode all-fiber Tm³⁺-doped Silica Fiber Laser is reported. The all-fiber laser is made up by progressively splicing the pigtail fiber, matched FBG fiber and Tm fiber. The reflective FBG and Tm³⁺-doped fiber end Fresnel reflection build up the laser resonance cavity. Due to the multi-mode FBG as the reflective mirror, the output laser spectrum is multi-peaks at high output power, but the spectrum width is less than 2 nm at 1.94 μm. We estimate the beam quality to be M ² = 2.39, clearly indicating nearly diffraction-limited beam propagation.     

Tapered diode lasers and laser modules near 635nm with efficient fiber coupling for flying-spot display applications

Flying-spot displays require light sources in the red, green and blue with a high optical output power and nearly diffraction limited beams. In this paper we present experimental results of red-emitting, AlGaInP based, tapered diode lasers and their integration into diode laser modules. The laser modules emit a collimated, almost diffraction limited beam with an optical output power as high as 1W at a wavelength close to 635 nm. The tapered laser chips were designed with emphasis on achieving a good beam quality in vertical and lateral directions of a collimated beam. To test the suitability for flying-spot display applications, we performed fiber coupling experiments with a low mode number optical fiber with an etendue as low as 6 × 10^?6 mm² sr. A maximum transmission of 70% of the launched power behind the uncoated fiber as well as a usable power in excess of 580mW were measured.     

一种测量GaAs-GaAlAs行波激光放大器增益特性的实验方法

本文报导了一种测量光耦合效率η的新实验方法。这个方法是建立于p-n结短路光电流原理上的。本文推导出适合于行波激光放大器的光耦合效率的公式。短路光电流用一检流计测量,利用公式获得光耦合效率的实验值。利用实验所测光耦合效率,测量了行波激光放大器的增益随注入电流变化的规律,其结果和实验符合。另外本文还介绍了在脉冲注入电流条件下测行波半导体激光放大器增益的实验方法。     

Fiber-laser-based green-pumped continuous-wave singly-resonant optical parametric oscillator

Stable, high-power, second-harmonic-generation (SHG) of a compact CW Ytterbium (Yb) fiber laser at 1064 nm into the green and its use as a pump source for CW singly-resonant optical parametric oscillator (SRO) is demonstrated. Using a simple single-pass SHG configuration in MgO:sPPLT, as much as 9.6 W of single-frequency green radiation at 532 nm is generated from 30 W of fundamental power at a conversion efficiency of 32.7% in a Gaussian spatial profile with a beam quality factor of M ² < 1.3. Thermal effects have been investigated at different fundamental power levels and various thermal management schemes are employed to maximize the second-harmonic power. The green source is successfully deployed to pump a CW SRO tunable over 855–1408 nm, generating up to 2.1 W of idler at 1168 nm. The peak-to-peak idler power stability is better than 10.7% over 40 min, with beam quality factor M ² < 1.26 for the idler and M ² < 1.52 for the signal.