Effect of the high-power electromagnetic pulses on the reactivity of the coal-water slurry in hot environment

An effect of the high-power electromagnetic pulses onto the droplet of coal-water slurry inside the furnace was investigated.In contrary to the previously investigated laser-induced fuel atomization that occurs at the room temperature,the pre-heated(to 400 K)slurry becomes dry enough to prevent the explosion-like steam formation.Thus,fuel does not atomize and the ignition does not accelerate.Furthermore,the absorption of several laser pulses leads to evident sintering of irradiated surface with following increase of the ignition delay time for up to 24%.Variation of the pulse energy in range 48-118 mJ(corresponding intensity up to 2.4 J·cm^-2)leads to certain variation of the increase of ignition delay.The strong pulsed overheating of the coal water slurry which does not initiate the fine atomization of the fuel generally makes its ignition longer.

A 40-GHz Colliding Pulse Mode-Locked Semiconductor Laser

A monolithically active-passive integrated colliding pulse mode-locked semiconductor laser is demonstrated in the InGaAsP//InP material system. The device is mode locked at the second harmonic passive mode-locking regime with a wide mode-locking range. Pulse trains with the repetition rate of 40 GHz, 3-dB rf line width of 25 kHz, the pulse width of 2.5 ps, and a nearly transform-limited time-bandwidth product of 0.53 are obtained.

Wavelength-Tunable Rectangular Pulses Generated from All-Fiber Mode-Locked Laser Based on Semiconductor Saturable Absorber Mirror

The wavelength-tunable rectangular mode-locking operation is demonstrated in an all-fiber laser based on semi- conductor saturable absorber mirror. As the dissipative soliton resonance signature, the pulse duration varies from 5SOps to 2.1 ns as a function o~ the increasing pump power. Correspondingly, the maximum pulse energy is 9.11 n3. Moreover, it is found that the wavelength tunable operation with a range of approximately 10 nm could be obtained by properly adjusting the polarization controllers. The characteristics of the rectangular pulses at different wavelengths are similar to each other. The demonstration of the wavelength tunable rectangular pulses would be beneficial to some applications for many fields such as spectroscopy and sensing research.

high-power laser;off-axis reflective exposure system;pulse compression grating;spatial frequency errors;specifications

The large-aperture pulse compression grating(PCG) is a critical component in generating an ultra-high-intensity, ultra-short-pulse laser;however, the size of the PCG manufactured by transmission holographic exposure is limited to large-scale high-quality materials. The reflective method is a potential way for solving the size limitation, but there is still no successful precedent due to the lack of scientific specifications and advanced processing technology of exposure mirrors. In this paper, an analytical model is developed to clarify the specifications of components, and advanced processing technology is adopted to control the spatial frequency errors. Hereafter, we have successfully fabricated a multilayer dielectric grating of 200 mm × 150 mm by using an off-axis reflective exposure system with Φ300 mm. This demonstration proves that PCGs can be manufactured by using the reflection holographic exposure method and shows the potential for manufacturing the meter-level gratings used in 100 petawatt class high-power lasers.

The Hyperbolic Two Temperature Semiconducting Thermoelastic Waves by Laser Pulses

A novel model of a hyperbolic two-temperature theory is investigated to study the propagation the thermoelastic waves on semiconductor materials.The governing equations are studied during the photo-excitation processes in the context of the photothermal theory.The outer surface of o semiconductor medium is illuminated by a laser pulse.The generalized photo-thermoelasticity theory in two dimensions(2D)deformation is used in many models(Lord–Shulman(LS),Green–Lindsay(GL)and the classical dynamical coupled theory(CD)).The combinations processes between the hyperbolic two-temperature theory and photo-thermoelasticity theory under the effect of laser pulses are obtained analytically.The harmonic wave technique is used to obtain the exact solutions of the main physical fields under investigation.The mechanical,thermal and recombination plasma loads are applied at the free surface of the medium to obtain the complete solutions of the basic physical fields.Some comparisons are made between the three thermoelastcity theories under the electrical effect of thermoelectric coupling parameter.The influence of hyperbolic two-temperature,two-temperature and one temperature parameters on the distributions of wave propagation of physical fields for semiconductor silicon(Si)medium is shown graphically and discussed.

Trends in ultrashort and ultrahigh power laser pulses based on optical parametric chirped pulse amplification

Since the proof-of-principle demonstration of optical parametric amplification to efficiently amplify chirped laser pulses in 1992, optical parametric chirped pulse amplification（OPCPA） became the most promising method for the amplification of broadband optical pulses. In the meantime, we are witnessing an exciting progress in the development of powerful and ultrashort pulse laser systems that employ chirped pulse parametric amplifiers. The output power and pulse duration of these systems have ranged from a few gigawatts to hundreds of terawatts with a potential of tens of petawatts power level. Meanwhile, the output pulse duration based on optical parametric amplification has entered the range of fewoptical-cycle field. In this paper, we overview the basic principles, trends in development, and current state of the ultrashort and laser systems based on OPCPA, respectively.

High-power femtosecond laser generation from an all-fiber linearly polarized chirped pulse amplifier

An all-fiber high-power linearly polarized chirped pulse amplification(CPA)system is experimentally demonstrated.Through stretching the pulse duration to a full width of approximately 2 ns with two cascaded chirped fiber Bragg gratings(CFBGs),a maximum average output power of 612 W is achieved from a high-gain Yb-doped fiber that has a core diameter of 20μm with a slope efficiency of approximately 68%at the repetition rate of 80 MHz.At the maximum output power,the polarization degree is 92.5%and the M^(2)factor of the output beam quality is approximately 1.29;the slight performance degradations are attributed to the thermal effects in the main amplifier.By optimizing the B-integral of the amplifier and finely adjusting the higher-order dispersion of one of the CFBGs,the pulse width is compressed to 863 fs at the highest power with a compression efficiency of 72%,corresponding to a maximum compressed average power of 440.6 W,single pulse energy of 5.5μJ and peak power of about 4.67 MW.To the best of our knowledge,this is the highest average power of a femtosecond laser directly generated from an all-fiber linearly polarized CPA system.

SESAM锁模全保偏皮秒脉冲光纤激光器输出特性

搭建了基于半导体可饱和吸收镜(SESAM)锁模的全保偏皮秒脉冲光纤激光器,对比分析了以多量子阱和体材料作为可饱和吸收层的SESAM对锁模激光器输出特性的影响。实验结果表明,多量子阱和体材料SESAM均可实现稳定的自启动锁模。随着量子阱周期数的增加,SESAM调制深度增大,激光器输出脉冲宽度变窄,具有更高的输出功率和更大的锁模区间。但量子阱周期数过高的SESAM具有较大非饱和损耗,使得相同泵浦功率下输出功率降低。在相同调制深度下,体材料SESAM的非饱和损耗偏大,降低了输出功率和光光转化效率,但对脉冲的窄化作用更显著。SESAM对输出脉冲的波长和光谱宽度无显著影响,主要受光纤布拉格光栅(FBG)控制。本文对SESAM的设计与选型具有一定指导意义。

一种多波长激光器的多模式驱动研究

介绍了一种多波长半导体激光器驱动系统的设计,该系统采用了压控电流源与PicoLAS模块混合驱动的方法,具有效率高、体积小、电路简单可靠、易于系统集成等优点,为半导体激光器的驱动设计提供了一种选择和参考。

一种纳秒级半导体激光器集成微模块

为提升半导体激光器在高重频下工作的稳定性,并满足模块高集成度的需求,研制了一款纳秒级半导体激光器集成微模块。该微模块包括半导体激光器芯片、装载激光器芯片的基板以及驱动电路。在基板侧面设计金属化过孔,将半导体激光器芯片的电极从基板侧面引出,实现了激光的垂直发射;采用球栅阵列(BGA)封装GaN HEMT和GaN驱动器,优化电路布局和半导体激光器的回流路径,减小寄生电感,实现了1 ns的发光脉冲宽度,工作重频达到了1 MHz;同时,发光脉冲信号的前沿抖动度小于60 ps,脉冲宽度抖动度小于200 ps,表明其具有较高的稳定性。最后,采用高透明、耐高温的灌封胶对该微模块实现集成化封装,整体尺寸仅为6mm×5mm×2.6mm。

基于SESAM的掺铥锁模光纤激光器研究

目的:研究基于半导体可饱和吸收镜的大能量被动锁模掺铥光纤激光器的输出特性。方法:利用半导体可饱和吸收镜作为锁模器件,分别采用光纤全反射镜和光纤光栅搭建全光纤结构的被动锁模掺铥光纤激光器。结果:在采用光纤全反镜结构中,在泵浦功率为900 mW时,获得了中心波长为1945 nm,重复频率为9.80 MHz,单脉冲能量为9.46 nJ的锁模脉冲输出。用光纤光栅替换光纤全反射镜,大大降低了锁模阈值。在泵浦光为210 mW时,获得了中心波长为1941.5 nm的稳定锁模脉冲输出,功率稳定性RMS小于1%。结论:本文所搭建的锁模光纤激光器单脉冲能量可以达到nJ量级且锁模稳定。

激光辐射波长和脉冲寿命对碲化镉熔化阈值的影响

碲化镉的相对分子量为240,密度为5.885 g/cm^(3),熔点为1092℃。碲化镉是一种Ⅱ-Ⅵ族的化合物半导体材料,属于直接带隙型,带隙宽度为1.56 eV。碲化镉是制造X射线、伽马射线和红外线探测器的基本材料。对碲化镉的特别关注主要是由于其大原子数和大的光电吸收截面。在基于CdTe的伽马辐射势垒探测器结构中,其表面的处理方法之一是纳秒激光照射,在某些情况下,纳秒激光照射可以在触点(Ag、In、Au)和势垒形成的技术处理阶段优化所需的表面参数。另一种方法是在脉冲激光照射下在碲化镉表面形成有序的纳米结构。对基于半导体及其结构的脉冲激光器,可根据其不同的脉冲持续时间τ_(p)和辐射波长λ将其分类。例如,红宝石激光器(λ=694 nm)、钕激光器(一次谐波1064 nm和两次谐波532 nm)、准分子KrF激光器(248 nm)和XeF激光器(351 nm)等,其脉冲持续时间分别为7、20、80、120 ns。这些激光器常被应用于表面修饰等领域。因此,往往有必要事先知道或至少估计在脉冲激光辐射下碲化镉表面的熔化温度和阈值,这取决于激光脉冲持续时间τ_(p)、辐射波长(光吸收系数α(λ))以及碲化镉表面本身的电物理参数,特别是表面重组率S和非平衡电荷载流子的寿命。这些参数取决于表面处理的方法和掺杂物的浓度。在上述情况下,实验研究是非常耗费人力和时间的,因此基于τ_(p)、α(λ)和碲化镉表面本身的电物理参数对融化阈值th和表面温度进行理论计算变得非常重要。本工作采用激光照射碲化镉,辐射波长为300~800 nm,脉冲持续时间为7~120 ns。为了以非破坏性的和有效的方法来管理接近表面层状态的CdTe,在T=80 K下进行了光致发光实验。为了监测熔化阈值,研究了由Acrorad公司制造和抛光的尺寸为5 mm×5 mm×0.5 mm的Cl补偿p-CdTe(111)单晶的光致发光光谱。经过研究发现,在激光脉冲寿命从7ns到1μs的范围内,CdTe熔化阈值明显取决于光吸收系数α(λ)。因为在脉冲寿命长于1μs的情况下,热扩散深度明显大于CdTe中的激光辐射穿透深度,并开始依赖于反射系数R(λ)。对于较短的激光脉冲长度τ_(p),当辐射波长λ变化时,熔化阈值会发生显著变化。同时,非平衡过剩载流子参数的变化(如表面重组速度S从10^(3)m/s增加到10^(5)m/s,还有扩散深度LD从0.4μm增加到2μm)会对CdTe熔化阈值产生至少25%的影响。而且红宝石激光的脉冲持续时间在(20±5)ns区间内的变化导致相对熔化阈值的变化(ΔIth/Ith)为35%。CdTe熔化阈值的计算值可以有效地被用于优化脉冲激光对晶体的表面处理与掺杂。

激光供电脉冲电场传感器设计

为应对高电压电力系统中瞬变电场强度的测量难题,并确保直流输电系统的安全稳定运行,本研究设计并构建了一种由激光光电池供电的脉冲电场传感器。该传感器包括激光光电池供电模块、电光信号转换模块和单极子天线。此外,还在设计中采用恒流源电路作为半导体激光器的供电系统,它能将特定波长的激光能量转换为电能,为传感器或其他负载提供远距离非接触式供能。为确保传感器的精确度,本研究开发了一套系统标定装置,用于在控制空间内产生标准测试电场,并通过部署的传感器阵列来测量产生的电场、磁场及被测物体内部的其他数据,实现对动态系统电场强度的即时校准。实验测试表明,所研制的脉冲电场传感器具有20kHz至500MHz的3 dB带宽,100V/m至60kV/mm的动态范围,125Ω的负载阻抗,优于10%的线性度,以及上升沿小于3.5ns的瞬态响应性能,验证了其在强电磁干扰环境下仍具备良好的快速响应速度。

Post-compression of high-energy,sub-picosecond laser pulses

The post-compression technique based on self-phase modulation of high-energy pulses leads to an increase in achievable peak power and intensity.Typically,the pulses considered in experiments have been less than 100 fs in duration.Here,the method is applied to the ELFIE laser system at the LULI facility,for a pulse of 7 J energy and an initial measured duration of 350 fs.A 5-mm-thick fused silica window and a 2 mm cyclic-olefin polymer were used as optical nonlinear materials.The 9 cm diameter beam was spectrally broadened to a bandwidth corresponding to 124 fs Fourier-limited pulse duration,and then it was partly post-compressed to 200 fs.After measuring the spatial spectra of the beam fluence,a uniform gain factor of 4 increase in the fluctuations over the studied range of frequencies is observed,due to small-scale self-focusing.

Nonlinear chirped pulse amplification for a 100-W-class GHz femtosecond all-fiber laser system at 1.5μm

In this work,we present a high-power,high-repetition-rate,all-fiber femtosecond laser system operating at 1.5μm.This all-fiber laser system can deliver femtosecond pulses at a fundamental repetition rate of 10.6 GHz with an average output power of 106.4 W–the highest average power reported so far from an all-fiber femtosecond laser at 1.5μm,to the best of our knowledge.By utilizing the soliton-effect-based pulse compression effect with optimized pre-chirping dispersion,the amplified pulses are compressed to 239 fs in an all-fiber configuration.Empowered by such a high-power ultrafast fiber laser system,we further explore the nonlinear interaction among transverse modes LP01,LP11 and LP21 that are expected to potentially exist in fiber laser systems using large-mode-area fibers.The intermodal modulational instability is theoretically investigated and subsequently identified in our experiments.Such a high-power all-fiber ultrafast laser without bulky free-space optics is anticipated to be a promising laser source for applications that specifically require compact and robust operation.

Passive Model-locking of 1.5μm InGaAsP Quantum Well Lasers

The generation of ultrashort optical pulse from passively mode-locked InGaAs/InGaAsPquantum well laser diodes is reported.The device consists of two segments:one is reversed-ly biased as a saturable absorber and the other is current forward injected as a gain segment.The optical pulse with 7.8ps duration at 26 GHz repetition rate has been measured from thepassively mode-locked laser with 1.625μm cavity length and 1.53μin emitting wavelength.Some simple descriptions of PMLD characteristics are also given.

大功率半导体激光器的高精度脉冲电源设计

为了满足大功率半导体激光器脉冲应用的实际需求,针对单脉冲内电流平顶下降问题和重复性情况下电流稳定性降低的问题,设计了一种多参数宽范围可调的高精度高稳定脉冲驱动电源。该电源以大功率场效应晶体管为核心,通过现场可编程门阵列产生的高精度时序波形来完成单脉冲内的上升沿调控和栅极控制电压补偿,通过微控制器结合电流采样的闭环控制方案实现重频运行下的电流高稳定输出。结果表明,在输出电流100 A、脉冲宽度400μs、重复频率1 kHz的最大功率输出驱动二极管负载时,驱动电流上升沿过冲幅度小于0.5%、单脉冲内电流衰减小于0.2%、重复率脉冲不稳定度小于0.1%;在同样输出条件下驱动半导体激光器,其在单脉冲内光功率过冲小于2%,重复光脉冲不稳定度小于0.2%。该研究有助于提高脉冲电源脉冲电流稳定性,对现有脉冲电源结构的改进具有一定的参考意义。

基于FPGA脉宽可调的窄脉冲激光器驱动电路设计

针对激光驱动电路纳秒脉冲宽度无法调节的问题,设计了一种新型的脉宽可调的窄脉冲激光驱动电路。利用FPGA和激光二极管的工作原理,设计并搭建半导体激光器驱动电路。电路采用高速MOSFET作为开关器件驱动激光二极管SPLPL90-3,并利用LTspice仿真软件分析激光驱动电路中电源电压、储能电容和阻尼电阻对驱动脉冲的影响,最终选择最佳的电路参数。当电源电压为150 V,储能电容为1 nF,阻尼电阻为2Ω时,最终输出激光二极管的电流为39.7 A,脉冲宽度6 ns,上升沿3 ns,满足了大电流纳秒脉冲半导体激光器驱动电路的设计要求。

矿用脉冲激光测距系统研究

激光测距是在光学高速发展的背景下出现的新型测距方式,被广泛应用于建筑、医学和煤矿井下等距离信息测量场景。针对目前煤矿井下顶底板移进量测量存在无法实时监测、测量精度低、使用不便等问题,设计了基于飞行时间测距原理的脉冲式激光测距系统,并对其系统方案、硬件电路等方面进行了研究。通过高功率半导体激光器、大电流激光驱动电路,发射高能量激光光束。采用ns级雪崩光电二极管,捕获经目标物反射的激光回波信号。利用时刻鉴别电路,计算脉冲激光的飞行时间,精确计算目标物距离。系统试验结果表明,所设计的脉冲激光测距系统体积小、精度高、实用性强,能够达到mm级的测量精度,充分满足煤矿井下的距离测量需求。

高密度封装垂直出射窄脉冲半导体激光模块

针对采用边发射半导体激光器芯片进行多线集成窄脉冲半导体激光模块设计时,存在激光器芯片的排布位置受限、排列密度受限及发射板光轴方向尺寸较大等问题,研制了高密度封装垂直出射窄脉冲半导体激光模块。首先分析了寄生参数对驱动能力的影响,通过减小寄生电感和寄生电阻以获得高峰值窄脉冲驱动电流;然后进行芯组设计,通过设计侧面金属化陶瓷载体,将激光器芯片电极从陶瓷载体侧面引出,该结构将激光器芯片出光方向旋转90°,实现了激光垂直板面出射和板面自由排布,同时极大地压缩了光轴方向尺寸;最后将芯组和驱动电路进行整体设计,在密集排列的同时兼顾关键电路的均匀布局,实现了16线激光器芯片0.7 mm间隔的高密度排布和垂直板面出光。测试结果显示,模块的单路峰值输出功率约为80 W,脉冲宽度约为6 ns,功率不一致性≤5%。