A cladding-pumping based power-scaled noise-like and dissipative soliton pulse fiber laser

We report a high-average-power noise-like pulse(NLP) and dissipative soliton(DS) pulse fiber laser. Average power as high as 4.8 W could be obtained at the fundamental mode-locked repetition rate. The NLP can also be transformed into a more powerful DS mode-locking state by optimizing the polarization and losses of intra-cavity pulses in the nonlinear polarization evolution regime. The operation mode between the NLP and DS can be switched, and the laser output performance in both modes has been studied. The main advantage of this work is switchable high-power operation between the NLP and DS. In comparison with conventional single-mode NLP fiber lasers, the multi-function high-power optical source will greatly push its application in supercontinuum generation, coherence tomography, and industrial processing.

Noise-like rectangular pulses in a mode-locked double-clad Er:Yb laser with a record pulse energy

Generation of noise-like rectangular pulse was investigated systematically in an Er–Yb co-doped fiber laser based on an intra-cavity coupler with different coupling ratios.When the coupling ratio was 5/95,stable mode-locked pulses could be obtained with the pulse packet duration tunable from 4.86 ns to 80 ns.The repetition frequency was 1.186 MHz with the output spectrum centered at 1.6μm.The average output power and single pulse energy reached a record 1.43 W and1.21μJ,respectively.Pulse characteristics under different coupling ratios(5/95,10/90,20/80,30/70,40/60)were also presented and discussed.

Multi-frame speckle reduction in OCT using supercontinuum pumped by noise-like pulses

In most coherent imaging modality,speckle noise is a major cause that blurs the boundary of tissues and degrades the image contrast.By utilizing the unique properties of supercontinuum(SC)generated by noise-like pulses(NLPs)and a simple multi-frame averaging technique,we achieved significant speckle reduction in spectral domain optical coherence tomography(SD-OCT).We quantitatively compared the speckle of our proposed method with those of conventional swept source OCT(SS-OCT)and SD-OCT based on commercial light sources.The experimental results show that SC pumped by NLPs combined with noncoherent averaging method achieves better denoising performance in terms of contrast to noise ratio(CNR).

Effect of Rectangle Wave Pulse Current on Solidification Structure of ZA27 Alloy

The effect of rectangle wave pulse current on solidification structure of ZA27 alloy was studied. The restdts show that the wave pattern relies on the frequency range of harmonic wave and the energy of pulse current within the frequency range of pulse current. Imposed pulse current could induce the solidification system to oscillate. The frequency range and the relevant energy distribution of pulse current exert an influence on the amount of atoms involved for forming critical nucleus, the surface states of dusters in melt, the oscillating state of melt on the surface of dusters, the active energy of atom diffusion , the frequnce response of the resonance of bulk melt and the absorbability of the solidification system to the external work. Rectangle wave pulse current involves rich harmonic waves ; the amplitudes of high order of harmonic waves are higher and reduce slowly, so it has a better effect on inoculation and modification.

Study on the transient radiation for apertures excited by rectangle pulse

The analytic representation of the transient radiation for an aperture excited by a rectangle pulse is obtained. It shows that the field duration and amplitude depend on the observation distance, the elevation angle, the pulse width of the rectangle pulse and the aperture size.

Stable watt-level mode-locked noise-like pulse from an all-PM fiber oscillator at 2 μm

We have experimentally presented a watt-level noise-like (NL) pulse mode-locked all-polarization-maintaining(PM) fiber laser centered at ~1995 nm, which can directly generate stable NL pulses with a maximum output power of ~1.017 W and pulse energy of ~0.61 μJ, representing the highest output power of mode-locked NL pulse at 2 μm from any fiber oscillators,to the best of our knowledge. The mode-locked NL pulse laser exhibits an excellent stability with a power fluctuation of~0.1% in 8 h of monitoring, and a signal-to-noise ratio of ~83 dB at a fundamental frequency of ~1.662 MHz. Moreover, the pulse envelope and coherence spike width of the NL pulse can be widely tuned from ~4.5 ns to ~16 ns, and ~364 fs to~323 fs, respectively, with the enhancement of the pump power. Such an all-PM fiber oscillator is the ideal seed source for the implementation of a high-power NL pulse laser and has potential valuable applications in mid-infrared spectroscopy and industrial processing.

Experimental studies of noise-like pulses in a dispersion-managed fiber laser

Based on an erbium.doped dispersion-managed fiber laser,the characteristics of noise-like pulses under different net cavity group velocity dispersions (GVDs) are experimentally investigated.Results show that the spec-tral bandwidth of noise-like pulse will increase as the net cavity GVD increases and attains maximum when the GVD is slightly positive.The effect of Raman scattering is enhanced due to the temporal width attains minimum.When the net cavity GVD increases continually and further into the positive region, the spectral width begins to decrease and the effect of Raman scattering is suppressed due to the positive dispersion.Our experimental results are in good agreement with the previous prediction of numerical simulation.

Stable noise-like pulse generation in all-PM mode-locked Tm-doped fiber laser based on NOLM

A stable noise-like(NL)mode-locked Tm-doped fiber laser(TDFL)relying on a nonlinear optical loop mirror(NOLM)was experimentally presented.Different from the previous NL mode-locked TDFL with NOLM,the entire polarization-maintaining(PM)fiber construction was utilized in our laser cavity,which makes the oscillator have a better resistance to environmental perturbations.The robust TDFL can deliver stable bound-state NL pulses with a pulse envelope tunable from〜14.1 ns to〜23.6 ns and maximum pulse energy of〜40.3 nj at a repetition rate of〜980.6 kHz.Meanwhile,the all-PM fiber laser shows good power stability[less than〜0.7%)and repeatability.

Noise-like pulse generation from a thulium-doped fiber laser using nonlinear polarization rotation with different net anomalous dispersion

A mode-locked thulium-doped fiber laser(TDFL) based on nonlinear polarization rotation(NPR) with different net anomalous dispersion is demonstrated. When the cavity dispersion is-1.425 ps^2, the noise-like(NL) pulse with coherence spike width of 406 fs and pulse energy of 12.342 nJ is generated at a center wavelength of 2003.2 nm with 3 dB spectral bandwidth of 23.20 nm. In the experimental period of 400 min, the 3 dB spectral bandwidth variation, the output power fluctuation, and the central wavelength shift are less than 0.06 nm, 0.04 d B, and0.4 nm, respectively, indicating that the NPR-based TDFL operating in the NL regime holds good long-term stability.

Noise-like pulse with a 690 fs pedestal generated from a nonlinear Yb-doped fiber amplification system

Noise-like pulses having a pedestal of 690 fs and a spike of 59.6 fs were generated in a nonlinear Yb-doped fiber amplification system. The seed source is a mode-locked Yb-doped fiber laser by nonlinear polarization rotation,and dissipative soliton pulses were obtained in it. Then, the dissipative soliton pulses passed through a 7.6 m dispersive fiber to enhance the dispersion and nonlinearity. Further on, the dissipative soliton pulses were launched into a Yb-doped fiber nonlinear amplifier, and stable noise-like pulses with a pedestal of 6.26 ps and a spike of 227 fs were achieved. Finally, by a grating pair, the pedestal and spike of the noise-like pulses were effectively compressed to 690 fs and 59.6 fs, respectively. To the best of our knowledge, this is the shortest pedestal demonstrated in noise-like pulses operating at 1 μm.

Vector soliton and noise-like pulse generation using a Ti3C2 MXene material in a fiber laser

We built a Tm:Ho co-doped fiber laser using a Ti3C2 MXene material as a saturable absorber(SA).The formation of vector solitons(VSs)and noise-like pulses(NLPs)was observed.The SA was prepared by dripping a Ti3C2 solution on a side-polished D-shaped fiber and then naturally vaporized.The VS is characterized by two coexisting sets of Kelly sidebands.By modulating the polarization controller in the fiber laser,NLPs with about 3.3 nm bandwidth can be switched from the VS.To the best of our knowledge,this is the first time that VSs have been generated in a fiber laser using a Ti3C2 MXene material as the SA.

80kV可调节高压脉冲方波脉冲电源的研制

研制了80kV可调节高压脉冲方波电源系统以对ZnO样品特性进行测试,实现电源输出脉宽、重复频率、运行时间可调。系统采用人工形成线、脉冲变压器加可调节负载电阻等技术路线,实现了高压方波脉冲的输出;采用高速数据I/O卡产生序列脉冲信号控制两个火花间隙开关的通断,对人工形成线形成的方波进行截尾,实现了输出方波宽度可调;利用Labview中的图形化控件,编写友好简洁的计算机控制界面;采用光电隔离、光纤传输和供电隔离等一系列措施,提高触发控制系统的抗干扰能力。实验结果表明,最终电源输出电压幅值超过80kV,输出方波脉冲宽度超过25μs,脉冲前沿小于0.7μs,并且输出电压幅值可调,脉冲宽度在输出范围内可连续调节。利用该电源对ZnO压敏电阻样品进行了测试,得到了较好的ZnO压敏电阻非线性伏安特性曲线。

方波脉冲电流对ZA27合金凝固组织的影响

研究了方波脉冲电流对ZA27合金凝固组织的影响。结果表明脉冲电流的波形关系到谐波的频域及能量在其频域上的分布。脉冲电流诱发凝固系统处于振荡状态,脉冲电流的谐波的频域及能量分布影响到形成临界晶核所需的原子数。团簇表面熔体的振荡状态及润湿状态,原子的扩散激活能和整体熔体对振荡频率的响应。方波脉冲电流具有丰富的谐波,其高次谐波所引起的振荡的振幅衰减较慢,因而具有较好的孕育变质作用效果。

方波 PEF 处理中负载失匹情况下波形的优化

为了解决脉冲方波PEF处理中由于负载与脉冲电源不匹配导致的波形严重畸变的问题,在已有工作的基础上,提出了基于波形优化网络的重塑方波的优化方案。该波形优化网络由电容和磁开关构成,通过理论分析,确定了优化网络中各个元件的参数。模拟仿真和实验表明:在负载严重失匹的情况下,加入波形优化网络,将波形由近似三角波转化成了较理想的方波,其脉冲上升时间减少到200 ns左右,同时方波的平顶部分也得到显著的改善;但优化后的脉冲宽度明显减小,实际应用中还应对脉宽予以补偿。

方波脉冲电流对Al-Cu合金凝固组织的影响

针对单极方波脉冲电流幅值对Al-Cu合金凝固组织的影响进行了试验研究。结果表明,脉冲电流对亚共晶Al-5Cu和过共晶Al-50Cu合金的凝固组织和初生相有明显细化作用,这主要是由于方波脉冲电流频域较宽,高次波的能量衰减较慢,对凝固系统所做的有效功值较高。由于电流及感生磁场的不均匀性而产生的磁场梯度漂移和磁力线曲率漂移,使得过共晶Al-50Cu合金中Al3+及Cu+离子沿磁场方向迁移,在脉冲电场作用下,促使初生相CuAl2沿磁场方向优势生长。

矩形波冲击下瓦楞纸板缓冲包装衬垫的冲击响应

以已有的瓦楞纸板本构模型为基础,建立动力学方程,通过数值计算方法,着重研究了瓦楞纸板在矩形波激励下阻尼系数及线性参量对瓦楞纸板缓冲包装系统冲击谱和破损边界的影响。

MV级近方波Marx发生器的设计

分析了Marx发生器与正弦振荡回路组合直接输出方波脉冲的近方波Marx发生器理论,并设计了一个该类型的方波发生器装置。其中,Marx发生器由16个充电电压为100kV、容值为40nF的电容器组成,采用正负充电的S型超前触发回路,正弦振荡回路由5个与Marx发生器同类型的电容器和1个0.5μH的电感组成。通过Spice模拟,在负载为100Ω时,输出脉冲电压为1.1MV,脉宽约300ns。提出了利用Marx发生器触发LC回路的方法,以解决Marx与LC回路的同步触发问题,使输出电压能够有效叠加。

矩形波冲击时瓦楞纸板衬垫破损边界曲线的研究

根据瓦楞纸板平压静态模型 ,建立了动力学方程。通过数值计算方法 ,研究瓦楞纸板在矩形波激励下的冲击响应 。

一种改进型的PCNN路面裂缝检测方法

路面病害的视觉自动检测一直是公路养护研究的热点问题,针对传统脉冲耦合神经网络(PCNN)在路面图像分割中的参数选择以及迭代中最佳分割结果的选择问题,提出通过简化脉冲耦合神经网络的模型,对关键参数自适应以及神经元点火条件的改进,以图中最大的裂缝作外接矩形,在迭代去噪过程中,外接矩形面积大大减小或矩形内部出现更多裂缝,表明出现过分割,利用该特征可以确定迭代中止,取上一次迭代结果,并用连通域分割去除细小噪声。通过受试者工作特征(ROC)曲线分析,该算法在裂缝检测上比基于最大熵的脉冲耦合神经网络分割算法提高8.4%,比基于灰度迭代阈值算法的脉冲耦合神经网络算法提高14.7%,提高了裂缝检测的准确率和抗噪性。

低压防雷器件响应时间测试

目前,对低压防雷器件(气体放电管、压敏电阻、暂态抑制二极管等)的响应时间的定义和测试方法尚未统一。为了使各器件对暂态过电压的响应能力在同一测试平台上具有可比性,选择上升时间在1ns左右的矩形脉冲发生器作为测试响应时间的设备,响应时间统一到IEC 61643-321对雪崩二极管响应时间的定义上来。分别对气体放电管、压敏电阻、暂态抑制二极管试品进行了响应时间测试,通过分析这些试品的响应特性,证实所提的响应时间测试方法可行。