Author Affiliations
Abstract
1 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
2 School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510640, China
We present a detailed theoretical and numerical analysis on the temporal-spectral-spatial evolution of a high-peak-power femtosecond laser pulse in two sets of systems: a pure lithium niobate (LN) plate and a periodically poled lithium niobate (PPLN) plate. We develop a modified unidimensional pulse propagation model that considers all the prominent linear and nonlinear processes and carried out the simulation process based on an improved split-step Fourier transformation method. We theoretically analyze the synergic action of the linear dispersion effect, the second-order nonlinearity (2nd-NL) second-harmonic generation (SHG) effect, and the third-order nonlinearity (3rd-NL) self-phase modulation (SPM) effect, and clarify the physical mechanism underlying the peculiar and diverse spectral broadening patterns previously reported in LN and PPLN thin plate experiments. Such analysis and discussion provides a deeper insight into the synergetic contribution of these linear and nonlinear effects brought about by the interaction of a femtosecond laser pulse with the LN nonlinear crystal and helps to draw a picture to fully understand these fruitful optical physical processes, phenomena, and laws.
Photonics Research
2024, 12(4): 774
Author Affiliations
Abstract
1 Chinese Academy of Sciences, Shanghai Institute of Optics and Fine Mechanics, State Key Laboratory of High Field Laser Physics, Shanghai, China
2 South China University of Technology, School of Physics and Optoelectronics, Guangzhou, China
A supercontinuum white laser with ultrabroad bandwidth, intense pulse energy, and high spectral flatness can be accomplished via synergic action of third-order nonlinearity (3rd-NL) and second-order nonlinearity. In this work, we employ an intense Ti:sapphire femtosecond laser with a pulse duration of 50 fs and pulse energy up to 4 mJ to ignite the supercontinuum white laser. Remarkably, we use water instead of the usual solid materials as the 3rd-NL medium exhibiting both strong self-phase modulation and stimulated Raman scattering effect to create a supercontinuum laser with significantly broadened bandwidth and avoid laser damage and destruction. Then the supercontinuum laser is injected into a water-embedded chirped periodically poled lithium niobate crystal that enables broadband and high-efficiency second-harmonic generation. The output white laser has a 10 dB bandwidth encompassing 413 to 907 nm, more than one octave, and a pulse energy of 0.6 mJ. This methodology would open up an efficient route to creating a long-lived, high-stability, and inexpensive white laser with intense pulse energy, high spectral flatness, and ultrabroad bandwidth for application to various areas of basic science and high technology.
intense white laser optical-damage-free water third-order nonlinearity second-order nonlinearity Advanced Photonics Nexus
2024, 3(1): 016008
Author Affiliations
Abstract
1 School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, China
2 Guangdong Jingqi Laser Technology Corporation Limited, Songshanhu, Dongguan 523808, China
3 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
4 State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China
Supercontinuum white laser with large bandwidth and high pulse energy would offer incredible versatility and opportunities for basic science and high technology applications. Here, we report the generation of high-efficiency 2.8-octave-spanning ultraviolet-visible-infrared (UV-Vis-IR) (with 350-2500 nm 25 dB bandwidth) supercontinuum white laser from a single chirped periodically poled lithium niobate (CPPLN) nonlinear crystal via synergic high-harmonic generation (HHG) and self-phase modulation (SPM). The CPPLN exhibits multiple controllable reciprocal-lattice bands to simultaneously support the quasi-phase matching (QPM) for simultaneous broadband 2nd-10th HHG via cascaded three-wave mixing against a broadband fundamental pump laser. Due to the efficient second-order nonlinearity (2nd-NL) up-conversion and significant 3rd-NL SPM effect both in the pump and HHG laser pulses, 350-2500 nm supercontinuum white laser is eventually obtained with 17 μJ per pulse under pump of 45 μJ per pulse mid-infrared femtosecond laser corresponding to an average high conversion efficiency of 37%. Our work opens up a route towards creating UV-Vis-IR all-spectrum white lasers through engineering the synergic action of HHG and SPM effects in nonlinear crystals for applications in ultrafast spectroscopy, single-shot remote sensing, biological imaging, and so on.
1 电子科技大学 电子薄膜与集成器件国家重点实验室, 成都 610054
2 电子科技大学 重庆微电子产业技术研究院, 重庆 401331
为了满足MHz以上频率的GaN半桥栅驱动系统的应用需求,提出了一种高速高可靠性低功耗的低FOM电平位移电路。串联可控正反馈电平位移电路通过仅在转换过程中减弱正反馈力度,实现了低传输延迟和高共模噪声抗扰能力,同时采用最小短脉冲电路设计以降低功耗。该电平位移电路基于0.5 μm 80 V高压(HV) CMOS工艺进行设计与仿真验证,结果表明,电路具有960 ps的传输延时、50 V/ns的共模噪声抗扰能力和0.024 ns/(μm·V)的FOM值。
电平位移电路 GaN半桥栅驱动 最小短脉冲 level shifter GaN half-bridge gate drive minimum short pulse
1 北京科技大学能源与环境工程学院，北京 100083
2 工业典型污染物资源化处理北京市重点研究室，北京 100083
柴油车尾气NOx后处理技术对冷启动阶段NOx净化效果较差，被动NOx吸附剂(PNA)应运而生。分别采用等体积浸渍法和离子交换法将1% Pd负载于m(Si)/m(Al)为11.5的ZSM-5分子筛，获得Pd/ZSM-5 PNA材料。考察反应气氛(有无O2和H2O)对2种不同Pd负载方式PNA吸附-释放NOx性能的影响。采用X射线衍射、N2吸附-脱附曲线测定、透射电子显微镜、原位漫反射Fourier变换红外光谱和NH3程序升温脱附手段，从Pd/ZSM-5结构性质，Pd物种形态和酸性质分析以上因素的影响作用机制，并进一步评价预处理气氛中O2作用。结果表明：反应气和预处理气氛存在O2及等体积浸渍法中存在更多NO活性吸附位点从而提高Pd/ZSM-5的NO吸附能力。此外，O2促进NOx低温(~200 ℃)释放，等体积浸渍法使释放温度降至430 ℃，有利于材料再生。H2O抑制了NO吸附，但可提高NOx高温释放能力。为设计高性能Pd/分子筛提供建议，具备高吸附-释放能力是开发高性能PNA的重要前提。
被动式 氮氧化物 吸附剂 分子筛 吸附-释放 passive nitrogen oxide adsorbent molecular sieve adsorption-release
光学 精密工程
2022, 30(14): 1749
华东交通大学信息工程学院，江西 南昌 330013
为降低真实毫米波辐射图像的模糊现象，提出了一种基于残差尺度递归网络（RSRN）的毫米波辐射图像盲去模糊方法。RSRN采用多级残差递归结构，在编码器-解码器网络结构中添加级联残差连接和多尺度循环连接。充分利用毫米波辐射图像多尺度特征信息可以提升模型性能，同时使网络的训练更加稳定。最后，通过端到端的方式对毫米波辐射图像进行去模糊。实验结果表明，与现有的图像去模糊方法相比，所提方法消除模糊的同时更好地保留了细节信息，并且呈现出较好的定性和定量结果。
图像处理 图像去模糊 编解码器 多尺度 深度学习 激光与光电子学进展
2022, 59(18): 1810011
1 吉林农业大学 信息技术学院，吉林长春308
2 吉林农业大学 工程技术学院，吉林长春130118
3 吉林大学 工程仿生教育部重点实验室，吉林长春10025
为了适应保护性耕作秸秆还田监测的技术需求，提出了一种改进的U-Net语义分割算法对秸秆覆盖率进行检测。首先，提出一种新的卷积模块代替原始U-Net框架中的卷积模块；其次，改进Inception结构，引入条纹池化和高效空间金字塔空洞卷积模块，形成新的Gception结构；最后，在模块中引入注意力机制。利用无人机采集田间地表图像，将改进的U-Net模型应用于自标注田间秸秆图像分割，与U-Net，PSP-Net，Link-Net，Res-Net，DSRA-Unet和DE-GWO算法进行对比实验，得到的平均交并比为80.05%，平均像素精确度为91.20%，覆盖率平均误差为0.80%。实验结果表明，改进U-Net模型的分割结果优于对比算法，能够保证特征提取的有效性和全局特征的完备性，有效剔除树影以及田内其他干扰因素。该模型适用于含有农机和树影等干扰的田间复杂场景，在大尺度图像中亦可获得较好的分割效果，可为大面积秸秆覆盖率检测提供技术支持。
秸秆图像 覆盖率检测 语义分割 U-Net模型 注意力机制 straw image coverage detection semantic segmentation U-net model attention mechanism
上海交通大学区域光纤通信网与新型光通信系统国家重点实验室，上海 200240
生物组织的吸收系数和散射系数与组织的生理状态相关，是检测人体健康状态的重要指标。当前双层生物组织模型的光学参数反演方案中，吸收系数和散射系数的预测精度受到上层组织厚度等参数的影响较大，限制了模型的实际应用范围。为此，提出一种对上层组织厚度等参数不敏感的吸收和散射系数反演方法。通过采集漫反射光信号的空间和时间分布信息，并利用卷积神经网络来反演双层生物组织的吸收系数和散射系数，在随机的上层组织厚度和折射率等参量下实现较高的吸收系数和散射系数反演精度。在仿真实验中，基于改进的蒙特卡罗模拟获得双层皮肤模型在不同空间探测位置处、不同时刻的漫反射光强信息，然后利用卷积神经网络实现对两层皮肤组织吸收系数和散射系数的预测。结果表明：在固定的上层组织厚度和折射率参数下，吸收系数和散射系数反演的平均相对误差均小于4%；而当上层组织厚度和折射率存在随机变化时，吸收系数和散射系数的平均相对误差仍小于8%。相较其他方法，所提的测量方案和反演算法进一步提升了反演精度和扩展了实际应用场景，为生物组织光学参数的无创测量提供了新思路。
激光与光电子学进展
2022, 59(6): 0617018
Author Affiliations
Abstract
1 State Key Laboratory of Advanced Communication Systems and Networks, Shanghai Jiao Tong University, Shanghai 200240, China
2 School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, China
3 e-mail: liuqingwen@sjtu.edu.cn
4 e-mail: zuyuanhe@sjtu.edu.cn
The miniaturization of the gyroscope is critical for spacecrafts, drones, wellbore surveys, etc. The resonant fiber-optic gyroscope (RFOG) is a competitive candidate due to its potential in both miniaturization and high resolution, while its actual performance is well below expectation because of laser-induced noise and complexity. Here we report the first navigation grade RFOG with a bias instability of 0.009°/h and an angle random walk of 0.0093°/. The results are realized using a fiber resonator with finesse of 63 containing 100-m long fiber. Compared with the traditional RFOGs using narrow-linewidth lasers, the key feature of the proposed RFOG is that it is driven with a broadband light source. A white-light multibeam interference method is proposed to detect the Sagnac effect, representing the simplest scheme of RFOG to date. The complexity caused by multiple feedback loops and coherent noise suppression in traditional RFOG scheme is avoided. The minimal scheme and simple modulation algorithm will also promote the on-chip waveguide gyroscope.
Photonics Research
2022, 10(2): 02000542
