相对论电子束在理想顺磁环境下能够以较高的注量率击中靶目标，但实际情况中由于受环境的影响，相对论电子束的传输方向可能会与地磁场呈小角度偏差，因此会受到地磁场的作用产生拉莫尔进动，影响电子束的到靶瞄准以及到靶注量。基于二维片状相对论电子束，分别对相对论电子束顺磁和偏离磁场3°角两种传输情况进行仿真模拟，通过模拟束团的传输过程，分析研究了顺磁环境下不同传输距离束团到靶率的变化规律，以及偏离磁场3°角时传输过程中注量率的变化规律，为相对论电子束到靶率的预估和靶目标的瞄准提供数据参考。

Epsilon-near-zero (ENZ) media were demonstrated to exhibit unprecedented strong nonlinear optical properties including giant second-harmonic generation (SHG) due to their field-enhancement effect. Here, on the contrary, we report the quenching of SHG by the ENZ media. We find that when a tiny nonlinear particle is placed very close to a subwavelength ENZ particle, the SHG from the nonlinear particle can be greatly suppressed. The SHG quenching effect originates from the extraordinary prohibition of electric fields occurring near the ENZ particle due to evanescent scattering waves, which is found to be universal in both isotropic and anisotropic ENZ particles, irrespective of their shapes. Based on this principle, we propose a kind of dynamically controllable optical metasurface exhibiting switchable SHG quenching effect. Our work enriches the understanding of optical nonlinearity with ENZ media and could find applications in optical switches and modulators.

In this paper, we studied the dynamics of a dispersion-tuned swept-fiber laser both experimentally and theoretically. By adding a dispersion compensation fiber and an electro-optic modulator in the laser cavity, an actively mode-locked laser was obtained by using intensity modulation, and wavelength sweeping was realized by changing the modulation frequency. Using a high-speed real-time oscilloscope, the dynamic behaviors of the swept laser were investigated during wavelength switching, static-sweeping cycle, and continuous sweeping, respectively. It was found that the laser generates relaxation oscillation at the start of the sweeping mode. The relaxation oscillation process lasted for about 0.7 ms, and then the laser started to operate stably. Due to the nonlinear effect, new wavelengths were generated in the relaxation oscillation process, which is not beneficial for applications. Fortunately, relaxation oscillation disappears if the laser starts up and operates in the continuous sweeping mode, and the good sweeping symmetry between the positive sweep and negative sweep increases the application potential of the laser. In addition, the instantaneous linewidth is almost the same as that in the static state. These results describe the characteristics of the laser from a new perspective and reveal, to the best our knowledge, the intensity dynamics of such lasers for the first time. This paper provides some new research basis for understanding the establishment process of dispersion-tuned swept-fiber lasers and their potential application in the future.

Ultra-high spectral purity lasers are of considerable research interests in numerous fields such as coherent optical communication, microwave photonics, distributed optical fiber sensing, gravitational wave detection, optical clock, and so on. Herein, to deeply purify laser spectrum with compact size under normal condition, we propose a novel and practical idea to effectively suppress the spontaneous radiation of the laser cavity through weak external distributed perturbation. Subsequently, a laser configuration consisting of a main lasing cavity and an external distributed feedback cavity is proposed. The feedback signal with continuous spatio-temporal phase transition controlled by a distributed feedback structure is injected into the main cavity, which can deeply suppress the coupling rate from the spontaneous radiation to the stimulated emission and extremely purify the laser spectrum. Eventually, an ultra-narrow linewidth on-chip laser system with a side mode suppression ratio greater than 80 dB, an output linewidth of 10 Hz, and a relative intensity noise less than -150 dB/Hz is successfully obtained under normal conditions. The proposed concept in this work provides a new perspective for extreme regulation of laser parameters by using weak external distributed perturbation, which can be valid for various gain-type lasers with wide wavelength bands.

Duecorresponding author guidelines for details."?> to the electronic bottleneck limited real-time measurement speed of common temporal-spectral detection and the particle-like nature of optical soliton enabled nonrepeatable transient behaviors, capturing the ultrafast laser pulses with unknown times of arrival and synchronously characterizing their temporal-spectral dynamic evolution is still a challenge. Here, using the Raman soliton frequency shift based temporal magnifier and dispersive Fourier transform based spectral analyzer, we demonstrate a self-synchronized, ultrafast temporal-spectral characterization system with a resolution of 160 fs and 0.05 nm, and a recording length above milliseconds. The synchronized nonlinear process makes it possible to image full-filled temporal sub-picosecond pulse trains regardless of their arrival times and without extra pump lasers and photoelectric conversion devices. To demonstrate the significance of this improvement, a buildup dynamic process of a soliton laser with a complex breakup and collisions of multisolitons is visually displayed in the spectral and temporal domains. The soliton dynamic evolution processes observed by our characterization system are in one-to-one correspondence with the numerical simulation results. We believe this work provides a new multidimensional technique to break the electronic bottleneck to gain additional insight into the dynamics of ultrafast lasers and nonlinear science.

Characterization of the state of polarization (SOP) of ultrafast laser emission is relevant in several application fields such as field manipulation, pulse shaping, testing of sample characteristics, and biomedical imaging. Nevertheless, since high-speed detection and wavelength-resolved measurements cannot be simultaneously achieved by commercial polarization analyzers, single-shot measurements of the wavelength-resolved SOP of ultrafast laser pulses have rarely been reported. Here, we propose a method for single-shot, wavelength-resolved SOP measurements that exploits the method of division-of-amplitude under far-field transformation. A large accumulated chromatic dispersion is utilized to time-stretch the laser pulses via dispersive Fourier transform, so that spectral information is mapped into a temporal waveform. By calibrating our test matrix with different wavelengths, wavelength-resolved SOP measurements are achieved, based on the division-of-amplitude approach, combined with high-speed opto-electronic processing. As a proof-of-concept demonstration, we reveal the complex wavelength-dependent SOP dynamics in the build-up of dissipative solitons. The experimental results show that the dissipative soliton exhibits far more complex wavelength-related polarization dynamics, which are not shown in single-shot spectrum measurement. Our method paves the way for single-shot measurement and intelligent control of ultrafast lasers with wavelength-resolved SOP structures, which could promote further investigations of polarization-related optical signal processing techniques, such as pulse shaping and hyperspectral polarization imaging.

卷烟主流烟气是卷烟燃烧时被人体吸食到体内的主要气体, 其减焦降害已成为全社会高度关注的问题。 在各种卷烟主流烟气组分中, 巴豆醛以其强烈的基因毒性, 成为国家规定的卷烟中七种主要有害指标物之一。 传统的巴豆醛分析方法大都采用高效液相色谱法等实验室分析方法, 需繁琐的样品前处理过程, 无法测量巴豆醛的实时浓度, 难以准确评估巴豆醛对人体健康的影响。 为了快速、 准确地检测卷烟主流烟气中的巴豆醛组分, 本研究搭建了一套可以直接与吸烟机耦合的傅里叶红外光谱分析系统(FTIR), 并创新性开发过采样数据驱动光谱分析方法(ODDSA), 从复杂、 变动的卷烟主流烟气中准确提取巴豆醛的光谱组分信息。 ODDSA方法从实验设计入手, 采用随机设计的思路尽可能模拟实际卷烟样品的分布范围, 以构建具备良好光谱数据结构的样品集。 在此基础上, 创新性地将高密度小波变换引入红外光谱数据的处理过程中, 以时/频双域过采样的方式提升了光谱解析分辨率, 进而降低了其他基质组分对巴豆醛光谱信息的干扰。 最后, 发展改良竞争自适应重加权采样方法, 从多倍冗余的高密度小波系数中准确提取待测物质的最佳变量组合, 由此构建高质量的巴豆醛光谱定量分析模型。 为了验证ODDSA方法的有效性, 实验中采集了15种典型市售卷烟品牌, 每个品牌在线采集8支样品的主流烟气红外光谱, 随后采用随机挑选的25个验证集样本对ODDSA方法进行验证。 结果表明, 检验集的线性拟合系数为0.971, 相对均方根误差为5.5%, 其预测精度能有效满足卷烟主流烟气中巴豆醛的在线分析需求, 并可拓展到环境二手烟气中其他组分的在线监测, 进而为吸烟与健康评估提供全新手段。