Tunable and Switchable Narrow Bandwidth Semiconductor-Saturable Absorber Mirror Mode-Locked Yb-Doped Fiber Laser Delivering Different Pulse Widths

The wavelength-tunable and switchable narrow bandwidth mode-locking operation is demonstrated in an all fiber laser based on semiconductor-saturable absorber mirror （SESAM）. Two narrow-band fiber Bragg gratings centered at 1029.9nm and 1032nm respectively with a polarization controller inserted between them are used to realize the wavelength switchable between 1029.9nm and 1032nm. The laser delivers different pulse widths of 7.5ps for 1030nm and 20ps for 1032nm. The maximum output power for both could reach -6.5mW at single pulse operation. The output wavelength couM be tuned to about 0.gnm intervals ranging from 1030.2nm to 1031.1 nm and from 1032.15nm to 1033.7nm with the temperature change of the fiber Bragg grating, respectively.

Radio-frequency compressed electron pulse-width characterization by cross-correlation between electron bunches and laser-induced plasma

A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images.This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 105 electron numbers.

太瓦飞秒脉冲激光峰值功率测量装置及测量不确定度分析

超短超强脉冲激光(飞秒强激光)具有极高的峰值功率,在激光惯性约束聚变、高能物理、激光微加工等领域具有广阔的应用前景。飞秒脉冲激光峰值功率是评价超短超强脉冲激光系统性能的重要参数。介绍了基于光谱相位相干直接电场重构法的太瓦量级飞秒脉冲激光峰值功率测量方法、测量装置组成和工作原理,搭建了一套太瓦量级的飞秒脉冲激光峰值功率测量装置,分析和讨论了影响太瓦激光峰值功率测量结果的测量不确定度分量来源和主要因素。测量峰值功率的重复性为2.9%,测量不确定度达到17.6%(k=2),有效解决了太瓦量级飞秒激光峰值功率测量问题。

基于空间光调制器的激光光束宽度调节装置

为了满足激光产业对光束宽度测量装置的溯源要求,提升激光光束宽度校准能力,针对400~700 nm波段的激光器不同光束宽度校准的需求,设计了一套基于空间光调制器的激光光束宽度可调节装置,用于光束质量分析仪或激光光斑测量仪的校准。实验结果表明该装置在0.1~5.0 mm的宽度范围连续可调;利用部分相干光束抗环境扰动能力强的特点,其短期稳定性达99.5%,长期稳定性达99.1%,优于参考激光器96.8%的短期稳定性和96.3%的长期稳定性。此外,基于空间光调制器优越的光束整形能力,该装置可将输入的非规则光束输出为高斯光束。

基于激光法的圆箔式热流传感器动态特性研究

为使圆箔式热通量传感器满足不断发展的高超声速风洞等极端环境中动态热通量监测需求,采用了大功率半导体激光器作为热通量源,搭建了热流动态标定平台,并对系统产生的激光束能量进行了测量分析,确保了后续实验的科学性与合理性。系统产生热流密度达每平方米兆瓦级别,脉冲激励宽度为毫秒级别。通过动态响应实验,研究了戈登计动态响应时间与激励激光参数的关系。结果表明,在一定范围内,时间常数与激光功率、脉冲宽度为负相关关系。当激光脉冲宽度小于传感器时间常数一个数量级附近时,可以被视为理想脉冲激励。同时还得到了激光参数与产生热通量的线性关系,证明了采用激光法进行测试标定的可行性。

小熔池激光沉积制造薄壁件沉积宽度的模型预测及试验研究

将激光沉积制造的热物理过程与薄壁件的几何特性相结合,基于层间沉积过程中的能量守恒关系建立了可以适配于小熔池激光沉积制造薄壁件沉积宽度的预测模型。该模型详细阐述了沉积宽度与激光功率、扫描速度与送粉速率之间的关系。利用Ti–6Al–4V(TC4)粉末沉积制备了多组样品来进行预测模型的验证,结果表明,该模型可以准确地预测不同工艺参数下薄壁件的沉积宽度,提高了试验参数匹配的准确性与效率,并为小熔池激光沉积制造工艺成形精度控制奠定了理论基础。

空间整形飞秒激光高效制备纳米光栅

针对常规物镜聚焦飞秒激光光斑较小,难以单次直写加工成型大面积纳米光栅结构的问题,提出了利用空间狭缝整形的飞秒激光脉冲直写方法。通过开展单晶硅表面纳米光栅结构对加工系统的参数依赖关系研究,获得入射整形飞秒激光能量密度8.00μJ/cm^(2)、扫描速度9 mm/s、狭缝宽度0.40 mm的优化条件。采用SEM、AFM等手段对光栅进行微观表征,结果表明,单次扫描所制备的纳米光栅结构具有极高的宽度(41.20μm),说明提出的方法可以显著提升一次成型大面积纳米光栅结构的制备效率。

高重频窄脉宽多波长激光器可靠性分析

本文对高重频窄脉宽多波长激光器的可靠性进行了分析及验证,建立了高重频窄脉宽多波长激光器的框图法模型。在初始设计阶段开展激光器的可靠性分析,定量计算了激光器各单元的可靠性结果,包括失效率λ和平均无故障工作时间(Mean Time Between Failure,MTBF),预计激光器整机的无故障工作时间为1798.8 h。为满足激光器的设计指标要求,通过选用高品质晶体、半导体激光器的Ⅰ级降额设计和电源控制的冗余设计,实现激光器的可靠性优化。经优化设计后,激光器整机的无故障工作时间达2260.9 h。搭建激光器整机对可靠性优化设计结果进行验证,验证结果表明:激光器无故障工作时间可达2400 h。

超宽调谐(2.6~5μm)中红外皮秒脉冲激光的研究

在超快脉冲激光中,超宽调谐通常应用于超连续谱产生、光谱分析和调制等多个领域。文章利用皮秒脉冲同步泵浦技术,搭建了一种基于MgO:PPLN晶体的“Z”形光参量振荡器,通过具有扇形周期极化的晶体在中红外波段产生了高功率、波长超宽调谐(2.6~5μm)的皮秒脉冲激光源输出。该振荡器由五镜一晶体组成,这五镜片的选择和精确调整是提高光参量振荡器输出性能的关键因素,采用波长为1.064μm的Nd:YVO_(4)皮秒脉冲激光源,选择周期在26~32μm可调谐的MgO:PPLN晶体,最大泵浦功率为15W时,2.66μm、3.44μm和4.99μm处获得了最大输出功率分别为3.41W、2.78W和0.52W的闲频光,相应的光-光转换效率分别为58%、55%、15%,测量到中红外光谱谱宽为2.37nm(2615nm)、Δλ=1.87nm(3687nm)、Δλ=1.30nm(4992nm),观察到在没有任何窄化光学元件条件下长脉冲随波长光谱谱宽具有线性变窄的过程。在2.6~4.5μm波段的激光输出功率均大于1W,实现了高功率,波长超宽调谐的中红外皮秒激光的连续输出。窄谱宽超宽调谐中红外皮秒脉冲激光为超快过程研究和应用领域提供了一种强大的工具。通过优化波长调谐范围和脉冲宽度能够满足不同领域对中红外激光的高要求,对推动相关领域的研究和发展至关重要。

基于ESP32的激光器控制系统设计

阐述针对激光退火设备中对多种类型激光器控制需求及安全保护,设计一套激光器控制系统。设计基于ESP32主控芯片,集成2.4GHz Wi-Fi和蓝牙双模的单芯片方案,采用台积电超低功耗的40nm工艺,具有超高的射频性能、稳定性、通用性和可靠性。Wi-Fi和蓝牙等通信传输功能,更加适配未来的工业互联网模式,同时主控芯片具有丰富的数字模拟输入输出接口资源以及丰富的I2C/SPI等总线通讯方式,适用于各种应用场景。

多波环形激光器密封钉焊接工艺优化

随着新能源汽车行业的发展,对动力电池焊接质量提出了更高要求。为解决铝合金电池密封钉采用传统激光焊接时出现的裂纹、气孔等缺陷问题,并提高生产效率,采用自主研发的多波环形光斑光纤激光器对2 mm厚的3003铝合金盖板和0.95 mm厚的密封钉进行焊接,研究了在一定焊接速度下内外环焊接功率、离焦量等主要工艺参数对焊缝成形的影响。试验结果表明,在40 mm/s焊接速度下,光纤(内环)功率500 W,半导体(外环)功率1 700 W,离焦量1.5 mm时,焊缝熔深达0.6 mm,熔宽1.2 mm,此时焊接效果最优,焊缝各位置熔深一致性高,焊接飞溅极小且无炸点、气孔、裂纹等缺陷。通过样品焊接试验,验证了该焊接工艺的稳定性和可靠性。

三维激光扫描技术在钢箱梁拼宽改造中的应用

为大幅扩大城市交通通行能力和缩短工程施工工期,桥梁拼宽改造项目是一种行之有效并逐渐广泛应用的方法。传统桥梁拼宽工程往往面临工程实体不规则、设计资料不完整以及桥梁变形等多重挑战,导致无法直接基于CAD设计文件进行精确的桥梁模型创建。为此,本文基于实际项目经验,采用桥梁点云数据采集、点云数据处理和逆向建模等方法进行重建现状桥三维模型,并通过偏差分析等手段进行拼接精度分析,从而提高桥梁拼宽改造工程质量控制精度和施工进度。此外,针对拼宽过程中可能出现的一期工程施工误差导致的钢箱梁无法精确对齐问题,本文进一步提出了利用点云和实景数字可执行文件实测实量的方法,实现了快速、高精度的测量。这种方法不仅提高了测量效率,而且其毫米级的测量精度完全满足桥梁拼接的精度要求,为高精度拼接提供了有力的数据支撑。

Temporal characteristic analysis of single event effects in pulse width modulator

In this paper,the nature and origin of single event effects(SEE) are studied by injecting laser pulses into different circuit blocks,combining with analysis to map pulse width modulators circuitry in the microchip die.A time-domain error-identification method is used in the temporal characteristic analysis of SEE.SEE signatures of different injection times are compared.More serious SEE are observed when the laser shot occurs on a rising edge of the device output for blocks of the error amplifier,current sense comparator,and T and SR latches.

Four distributed feedback laser array integrated with multimode-interference and semiconductor optical amplifier

Monolithic integration of four 1.55-μm-range InGaAsP/InP distributed feedback （DFB） lasers using varied ridge width with a 4 x 1-multimode-interference （MMI） optical combiner and a semiconductor optical amplifier （SOA） is demon- strated. The average output power and the threshold current are 1.8 mW and 35 mA, respectively, when the injection current of the SOA is 100 mA, with a side mode suppression ratio （SMSR） exceeding 40 dB. The four channels have a 1-nm average channel spacing and can operate separately or simultaneously.

宽光谱多参数激光告警探测研究

随着激光技术的发展,激光武器得到了快速发展,针对来袭激光的威胁,激光告警也成为目前各国发展的重点,不同的激光告警系统探测不同的参数,根据告警参数采取相应的躲避和反击措施;目前激光告警主要探测参数有来袭激光方位角、俯仰角、激光波长、激光脉冲宽度等,但现有激光告警系统无法实现多参数的同时探测,且光谱范围窄、视场小、探测俯仰角和方位角为相对角度、无法获得绝对来袭方向。为此本文提出宽光谱波段、大视场、多参数激光告警新方法,可实现450~1700 nm宽光谱来袭激光波长、绝对方位角、绝对俯仰角、脉冲宽度多参数的高精度综合测量,该方法主要由激光脉冲宽度测量、绝对角度及激光波长测量、控制及数据处理三大部分组成。其中脉冲宽度测量模块由光学镜头、多带通窄带滤光片、高速光电探测器组成,实现来袭脉冲激光的高速光电转换;绝对角度及激光波长测量模块由光栅、大视场宽波段消色差镜头、多带通窄带滤光片、宽波段面阵探测器、三维电子罗盘组成,通过一级和零级衍射光斑位置获得来袭激光波长、相对方位角和相对俯仰角信息,结合三维电子罗盘测得的方位角、俯仰角以及横滚角,进而获得来袭激光的三维绝对方位角和绝对俯仰角。多带通窄带滤光片主要是根据常用几个军用激光波长进行选通滤光,有效滤除背景光的影响,降低系统虚警、漏警。理论分析推导具体测量方法和参数,设计宽光谱多参数激光告警探测系统样机,并进行实验可行性验证。实验结果表明,该系统的方位角视场120°、俯仰角视场96°、角度测量精度优于1°、中心波长测量精度优于10 nm、脉宽测量精度优于3 ns。该技术将为海、陆、空、天领域对来袭激光的高精度多参数综合探测奠定基础,有望提高复杂战场的生存能力。

Effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier

The effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier is investigated theoretically and experimentally. The complex Ginzburg–Landau equation and adaptive split-step Fourier method are used to simulate the propagation of pulses with different pulse widths in the fiber amplifier, and the results show that a longer pulse is more profitable in near-infrared supercontinuum generation if the central wavelength of the input laser lies in the normal dispersion region of the gain fiber. A four-stage master oscillator power amplifier configuration is adopted and the output spectra under picosecond and nanosecond input pulses are compared with each other. The experimental results are in good accordance with the simulations which can provide some guidance for further optimization of the system.

Flexible pulses from carbon nanotubes mode-locked fiber laser

We demonstrate a flexible erbium-doped pulsed fiber laser which achieves the wavelength and pulse width tuning by adjusting an intracavity filter. The intracavity filter is flexible to achieve any of the different wavelengths and bandwidths in the tuning range. The wavelength and width of pulse can be tuned in a range of - 20 nm and from - 0.8 ps to 87 ps, respectively. The flexible pulsed fiber laser can be accurately controlled, which is insensitive to environmental disturbance.

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by using a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation （PA） spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is （34.8± 0.22） MHz. By analyzing other broadening mechanisms, a value of （32.02 ± 0.70） MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.

Development of the active flux in superalloy laser welding and the effect on the weld formation

In this study,adopting uniform design method established a mathematical model to prepare multi-element active flux. GH4169 superalloy plates were welded by the Nd: YAG laser equipment with the prepared active flux. The results show all kinds of fluxes increase the depth to width ratio and the multi-component systems are more significant. The largest increment of the weld depth to width ratio is 159%,obtained by using of the F12 series flux. It is proved that by using of the active flux to increase the depth to width ratio of micro laser welding is feasible.

基于光辐射压力的激光功率测量技术

随着激光应用领域的快速拓展,超高峰值功率、超窄脉宽逐渐成为未来激光行业的重点研究方向之一,这种激光的超高电场能量给高精度的激光功率测量提出了挑战。传统的激光功率测量方法,如光电法、热释电法、量热法等逐渐显露出不适用于上述激光功率测量的缺点,此外上述方法都难以实现实时、在线测量。为了克服以上困难,需要一种新型激光功率测量原理与方法。以美国国家标准与技术研究院为代表的机构提出了一种光辐射压力测量法,该方法使激光作用在高反射率的反射镜上,激光动量形成了光辐射压力,这个力可以采用多种力学传感方式进行计量。该方法不但能实现激光功率快速、准确测量,而且不影响激光能量传输,可以实现实时、在线的激光功率测量。系统回顾了国内外通过光辐射压力测量激光功率的基本原理和系统组成,光辐射压力测量激光功率的研究现状,并对该方法的发展方向进行了展望。