Comparison of Small-Scale Actively and Passively Q-Switched Eye-Safe Intracavity Optical Parametric Oscillators at 1.57 μm

The first experimental comparison between the actively and passively Q-switched intracavity optical parametric oscillators (IOPOs) at 1.57μm driven by a small-scale diode-pumped Nd:YVO4 laser are thoroughly presented.It is found that the performances of the two types of IOPOs are complementary.The actively Q-switched IOPO features a shorter pulse duration,a higher peak power,and a superior power and pulse stability.However,in terms of compactness,operation threshold and conversion efficiency,passively Q-switched IOPOs are more attractive.It is further indicated that the passively Q-switched IOPO at 1.57 μm is a promising and cost-effective eye-safe laser source,especially at the low and moderate output levels.In addition,instructional improvement measures for the two types of IOPOs are also summarized.

Passively Q-switched diode-pumped Tm,Ho:LuVO4 laser with a black phosphorus saturable absorber

We presented a passively Q-switched(PQS) diode-pumped c-cut Tm, Ho:LuVO_4 laser with a black phosphorus saturable absorber for the first time.Under PQS mode, an average output power of 0.86 W and a peak power of 2.32 W were acquired from the Tm, Ho:LuVO4 laser with the pump power of 14.55 W, corresponding to a pulse width of 2.89 μs,a pulse repetition rate of 71.84 kHz, and a pulse energy of about 6.70 μJ.

Modelling of passively Q-switched lasers with intracavity Raman conversion

We present a model of passively Q-switched Raman lasers by utilizing the rate equations. The intracavity fun-damental photon density, Raman photon density and the initial population-inversion density of the gain medium are assumed to be of Gaussian spatial distributions. These rate equations are normalized by introducing some synthetic parameters and solved numerically, and a group of general curves are generated. Prom these curves we can understand the dependence of the Raman laser pulse characteristics on the parameters about the pumping, the gain medium, the Raman medium and the resonator. An illustrative calculation for a passively Q-switched Nd^3＋：GdVO4 self-Raman laser is presented to demonstrate the usage of the curves and related formulas.

Er^3+,Yb^3+:glass-Co^2+:MgAl2O4 diffusion bonded passively Q-switched laser

A Co^2＋：spinel passively Q-switched erbium-ytterbium-phosphate glass bonded laser pumped at 940 nm is reported.A pulse energy of 210 μJ, a peak power over 70 kW, and beam quality M-2 parameter of 1.2 are obtained under a pump power of 235 mW. An unbonded laser output experiment with the same dimension of the active material and the saturable absorber as the bonded laser output experiment is carried out. The reason why the output in the bonded laser is improved is determined.

Diode Pumped High Peak Power Quasi Q-Switched and Passively Q-Switched Nd:YVO₄Lasers at 1064 nm and 532 nm using Cr:YAG and KTP crystals

Diode end-pumped solid-state lasers have the potential to yield high quality laser beams with high efficiency for laser range finding and warning receiver applications as well as day and night military laser designation systems. In this paper we presents theoretical calculations using Advanced Dynamics Professional LASCAD software and experimental studies for a high power pigtailed fiber diode laser module of 8 W operating at 808 nm with a specially designed high efficiency cooling system, end pumped high-efficiency Nd:YVO4 laser of 3 × 3 × 10 mm rod and overall cavity length of 44 mm. To the best of our knowledge a self Q-switching effects was generated in Nd:YVO4 laser by changing the cavity dimensions and the position of the intracavity KTP crystal at certain regime of operation for the first time, in which the cavity length is reduced to be 30 mm and the distance between Nd:YVO4 rod and KTP crystal is only 1mm. Self Q-switched laser pulse at 532 nm with high peak power of 96 W, pulse width of 88 ns at FWHM and repetition rate of 400 kHz was achieved. Experimental studies of a passive Q-switched Nd:YVO4 laser using Cr:YAG crystal with three different transmissions of 30%, 40% and 70% were investigated. Passive Q-switched laser pulse at 1064 nm and narrow line width of less than 1.5 nm with highest peak power of nearly 18 kW, short pulse width of less than 4 ns at FWHM and higher repetition rate of 45 kHz using Cr:YAG with transmission of 30% was achieved for the first time.

Passively Q-Switched Erbium-Doped Fiber Laser Based on GeSe Saturable Absorber

GeSe nanosheets were prepared by ultrasonic-assisted liquid phase exfoliation (LPE), and the nonlinear saturated absorption performance was experimentally studied. The modulation depth and saturation intensity of the prepared GeSe saturable absorber (SA) were 15% and 1.44 MW/cm2, respectively. Using the saturated absorption characteristics of GeSe SA, a passively Q-switched erbium-doped fiber laser was systematically demonstrated. As the pump power increases, the pulse repetition frequency increases from 22.8 kHz to 77.59 kHz. The shortest pulse duration is 1.51 μs, and the corresponding pulse energy is 46.14 nJ. Experimental results show that GeSe nanosheets can be used as high-efficiency SA in fiber lasers. Our results will provide a useful reference for demonstrating pulsed fiber lasers based on GeSe equipment.

Recent Progresses on Passively Switched Mid-Infrared Fiber Lasers at 3 μm

We present the recent research progress of our group on mid-infrared pulsed fiber lasers at 3μm by passive switching. Three different kinds of saturable absorbers including semiconductor saturable absorber （SESAM）, Fe2＋：ZnSe crystal, topological insulator （TI） were used to perform the pulse generation, respectively. The temporal regimes of mode locking, Q-switching and Q-switching induced gain switching were gained. Some relative discussions and prospective efforts are proposed at the end of this paper.

A notion of passivity for switched systems with state-dependent switching

A passivity concept for switched systems with state-dependent switching is presented. Each subsystem has a storage function to describe the ＂energy＂ stored in the subsystem. The passivity property of a switched system is given in terms of multiple storage functions. Each storage function is allowed to grow on the ＂switched on＂ time sequence but the total growth is bounded by a certain function. Stability is inferred from passivity and asymptotic stability is achieved under further assumptions of a detectivity property of a local form and boundedness of the total change of some storage function on its inactive intervals. A state-dependent switching law that renders the system passive is also designed.

Cr^(4+):YAG as a Passive Q-Switch in a Diode-Pumped cw Nd:YVO_(4) Laser

The performance of a passively Q-switched all-solid-state Nd:YVO_(4) laser using Cr^(4+):YAG as saturable absorber is reported.Optimum coupling operation at 1064nm resulted in 70ns pulses at 40kHz repetition rates with average output power of 2.1 W.A quantitative theoretical description agrees well with the experimental results.

1514 nm eye-safe passively Q-switched self-optical parametric oscillator based on Nd3+-doped MgO:PPLN

We examined a 1514 nm eye-safe passively Q-switched self-optical parametric oscillator. The nonlinear crystal is an a-cut Nd:MgO:PPLN crystal, and the size of the crystal was 6 mm × 2 mm × 30 mm with 0.4 at.%Nd^3+ doped and a grating period of 29.8 μm. When the crystal absorbed 12.8 W, the output maximum singlepulse energy reached 39 μJ, and a pulse width of 6.1 ns at a repetition rate of 5.4 kHz was obtained.The peak power was 6 kW, giving a slope efficiency of 42%.

Enhanced nonlinear optical response of layered WSe1.4Te0.6 alloy in 1 μm passively Q-switched laser

Due to the composition-dependent properties of two-dimensional(2D)transition metal dichalcogenides(TMDs),alloying of existing dissimilar TMDs architecture is a novel and controllable route to tailor crystal structures with superior optical and optoelectronic properties.Here,we reported the hexagonal-phase WSe1.4Te0.6 alloy can enable great promise for enhanced saturable absorption response exceeding the parent component WSe2 and WTe2,with larger modulation depth and lower saturable intensity.These advantages allowed the 1064 nm passively Q-switched lasers based on WSe1.4Te0.6 to be more efficient,with pulse duration narrowed to 45%,and slope efficiency increased by 232%.Our findings highlighted the appropriate alloying of TMDs as an effective strategy for development of saturable absorbers.

双波长LD泵浦Nd^(3+)∶YAG免温控被动调Q激光器的研究

传统的固体激光器体积、重量大,功耗高,限制了其在空间受限设备中的应用。被动调Q的LD泵浦免温控固体激光器省去了复杂的温度控制装置,调Q机构简单,能够满足复杂温度环境的特殊应用场景的小型化、低功耗要求。提出了基于双波长LD泵浦实现宽温度范围免温控阈值自适应的1.06μm激光脉冲输出方法。基于Nd∶YAG晶体设计了角锥棱镜谐振腔,仿真分析了LD泵浦源到激光棒的面心距对热负载的影响,并确定4 mm的最佳面心距。数值分析了相同泵浦功率下-40~60℃温度范围内激光静态能量输出变化,以及不同初始透过率的可饱和吸收体对激光阈值脉宽的影响。计算结果表明在-37℃~60℃范围内,阈值脉宽都在200μs以下,阈值脉宽最低点达到了29.4μs。构建主波实时探测的阈值自适应调节装置并搭建实验系统,实验结果表明,在温度范围为-35~60℃时,阈值脉宽变化范围为40~180μs。采用激光腔体一体加工成型,应用轻量化的铝合金材料,实现工程化应用,体积83.5 mm×44 mm×29.5 mm,重量约为230 g。在23.8%初始透过率的饱和吸收体条件下实现单脉冲输出能量42 mJ,脉冲宽度5.2 ns。

基于RTP晶体的271 cm^(−1)拉曼频移五阶斯托克斯激光

报道了端面泵浦被动调Q激光驱动RbTiOPO4晶体拉曼实现271 cm^(−1)频移高阶斯托克斯激光输出。采用Nd:YAG与Cr4+:YAG键合设计来降低腔内的损耗,并使激光系统更紧凑,从而提升腔内光子功率密度,有利于拉曼频移向高阶斯托克斯激光转换。设计不同频移的一阶斯托克斯激光对应在不同腔内振荡,利用与基频光模式匹配的差异来抑制687 cm^(−1)频移的一阶斯托克斯激光,最终获得较纯的271 cm^(−1)频移的五阶斯托克斯激光输出。在泵浦功率8.1 W下,获得了平均输出功率230 mW的1244 nm波长激光,对应的脉冲宽度和重复频率分别为2.9 ns和11.7 kHz。1244 nm波段的激光正好与水中OH−1吸收峰对应,在地表植被和行星水含量的检测等领域有重要的应用。

主被动调Q-锁模Nd∶YAG激光器的实验研究

对脉冲氙灯泵浦的调Q-锁模Nd：YAG固体激光器进行了实验研究.比较和分析了声光主动锁模、Cr^4＋ ：YAG晶体被动调Q-锁模以及这两种机制联合锁模情况下Nd：YAG激光器的输出特性.在Cr^4＋ ：YAG晶体被动调Q-锁模时得到了深度80%以上的锁模输出,但是锁模不完全,且波形和能量稳定性低,脉宽为1.9～3.6 ns.而主被动联合锁模克服了这一缺点,可获得幅值和能量抖动小于±5%、锁模深度100%、脉宽小于650ps、能量近300mJ的超短脉冲输出.

基于无源控制的车用双管升压变换器研究

新能源汽车能处于正确的电压级别下安全可靠地运行,DC/DC变换器发挥着重要作用,针对其现有控制方法多为线性控制,难以应对负载与输入电压参数多变的情况的问题;在非线性控制既无源控制的基础上引入了PI阻抗反馈补偿环路的概念,提出了一种PI阻抗补偿无源控制策略。为证明其优越性,与现有方法进行了比较。并针对负载与输入电压参数变化情况进行了模拟仿真,结果表明,该策略在输入电压跌落8 V后,仅产生了2 V的波动;负载突变为初值的一半时,仅用了不到0.01 s便重新抬升至给定电压值。由仿真结果可得,该策略不仅响应速度快、不会产生超调现象,而且在负载和输入电压发生较大变化的情况下,仍能很好的抵御外部干扰并保持输出电压的稳定性和优秀的电压纹波抑制效果,具有良好的鲁棒性。

基于Ti3C2Tx-PVA被动调Q的低噪声556 nm腔内倍频黄绿光激光器

采用液相剥离法获得厚度约为3.2 nm、层数约为3至4层的碳化钛纳米片(Ti_(3)C_(2)T_(x)),结合旋涂法制备出Ti_(3)C_(2)T_(x)-聚乙烯醇(Ti_(3)C_(2)T_(x)-PVA)薄膜,并借助拉曼光谱、原子力显微镜和平衡双探测系统对Ti_(3)C_(2)T_(x)纳米片的物相组成、厚度及可饱和吸收性能进行了表征。将Ti_(3)C_(2)T_(x)-PVA薄膜作为可饱和吸收体应用于一种808 nm半导体激光二极管端面泵浦Nd∶YAG陶瓷/LBO腔内倍频的556 nm黄绿激光器中实现被动调Q。在分析布儒斯特偏振器和双折射晶体协同选频滤波机理的基础上,通过两者的协同使用,抑制了1116 nm和1123 nm处光谱腔内振荡并进一步压缩了1112 nm处p-偏振光的纵模个数。在5.1 W最高激光二极管泵浦功率下,获得了平均输出功率为86.2 mW、重复频率为745.8 kHz、脉冲宽度为46 ns的556 nm被动调Q脉冲黄绿激光输出。4 h内测得功率不稳定度和激光噪声仅为±0.39%和0.37%,光束质量评价因子为M2x=1.837和M^(2)^(y)=1.975。Ti_(3)C_(2)T_(x)-PVA薄膜被动调Q结合“布儒斯特偏振器+双折射晶体”协同选频滤波技术方案为开发高稳定性、低噪声脉冲黄绿激光提供有价值的参考。

LD泵浦被动调Q-Yb^(3+)∶YAG微晶片激光器的优化设计

从速率方程出发,理论分析了泵浦功率、输出镜反射率、Cr4+∶YAG的初始透过率和长度、Yb3+∶YAG的长度对调Q激光器的重复频率、脉冲宽度、平均输出功率、峰值功率、输出脉冲能量和单脉冲能量利用率的影响。依据理论结果设计了一个窄脉冲宽度、高峰值功率和脉冲能量的被动调Q-Yb3+∶YAG微晶片激光器。该激光器的脉冲宽度Δt=199 ps,峰值功率P m=1.04 MW,输出脉冲能量E=0.21 mJ。

基于器件复用的电流型软开关光伏全桥逆变器

提出了一种新颖的适用于分布式光伏的无源无损软开关全桥逆变器,用以减小逆变器高频开关的损耗。该电路保留了传统双降压全桥逆变器高效可靠的优点,在此基础上通过器件复用的方式,增加了无源无损吸收电路,并通过无源器件自身的谐振过程改善功率器件的开关状况实现软开关的功能,同时使无源无损吸收电路的能量得到有效转移,使得所提无源无损软开关全桥逆变器具有较高的可靠性。实验验证了所提无源无损吸收电路有效减小了开关损耗,提高了系统效率。

基于光开关阵列的灵活TWDM-PON系统研究

为了满足接入网日益增长的业务流量需求,解决当前因架构固定、资源维度有限而导致的不同无源光网络之间波长无法灵活分配的的问题,提出了一种将发射固定波长的激光器与光开关阵列组合的时分波分混合复用无源光网络结构。在这种新的系统结构中,下行波长资源被集中化处理,采用在局端配置光开关阵列的方法实现波长在不同网络之间的灵活调度,降低系统总体成本的同时能够用来解决负载平衡、流量“潮汐效应”、网络资源利用率低下等问题。通过理论分析和仿真实验验证了系统的可行性,得出该结构与传统无源光网络的兼容性、波长资源的共享性、系统低成本以及节能的特点。结果表明,在没有色散补偿的情况下,信号可以覆盖30 km的传输距离,同时服务512个用户。该研究可以为典型应用场景下的无源光网络部署提供参考。

一类切换时滞神经网络的有限时间无源性

为了研究切换拓扑下的时滞神经网络有限时间无源性,通过设计状态依赖型切换信号和控制器的方法,得到在切换拓扑下的时滞神经网络具有有限时间无源性的结论,进而得到有限时间镇定的结论。当2个时滞神经网络系统都具有有限时间无源性时,通过设计切换信号的方法,得到它们的反馈互联系统具有有限时间无源性的结论,通过数值例子验证定理结果的有效性。