Full Current Model for Terahertz Wave Generation from Femtosecond Laser Filament Under External Electric Fields
Hui Yuchen, and Zhao Jiayu
In this work, we propose a full current model in order to interpret the mechanism of terahertz (THz) wave generation from single-color femtosecond laser filamentation under transverse and longitudinal direct current fields. The model consists of two processes, i.e., oscillation of the microscopic plasma current and radiation of the macro current transmission line. Both processes are combined to describe the terahertz (THz) radiation characteristics such as terahertz wave enhancement and spatial distribution evolution. Compared with the well-known transition-Cherenkov radiation theory, the proposed full current model can achieve phase matching under the condition of equal light speed, and has a clearer physical picture and simpler formulas. Moreover, it can reproduce the experimental results well.
  • Jan. 17, 2022
  • Acta Optica Sinica
  • Vol.42 Issue, 1 0114002 (2022)
  • DOI:10.3788/AOS202242.0114002
Near-optimal intense and powerful terahertz source by optical rectification in lithium niobate crystal
L. Guiramand, J. E. Nkeck, X. Ropagnol, T. Ozaki, and F. Blanchard
  • Jan. 11, 2022
  • Photonics Research
  • Vol.10 Issue, 2 02000340 (2022)
  • DOI:10.1364/PRJ.428418
Point Cloud Registration Method Based on Dual Quaternion Description of Line-Planar Feature Constraints
Li Raobo, Yuan Xiping, Gan Shu, Bi Rui, Gao Sha, and Guo Yan
In view of the spatial feature correlation of adjacent station clouds collected by ground three-dimensional laser scanners, and a large number of line-planar features in urban buildings, a point cloud registration method based on line-planar feature constraints described by dual quaternion is proposed. This method not only uses dual quaternion to describe spatial transformation parameters, but also takes into account the scale factor. The objective function of spatial similarity transformation is constructed according to the geometric relationship between line-planar, as well as the intersection point and angle caused by the intersection of line-planar as registration constraints. The adjustment model is constructed by using the least square criterion to calculate the relevant parameters of spatial similarity transformation. In order to avoid the problem of iterative non-convergence caused by inappropriate initial values, the Levenberg-Marquardt method is applied to the solution of the adjustment model. Finally, the correctness and feasibility of the method are analyzed by experiments. The results show that the registration accuracy of the proposed method is higher than that of the point cloud registration method considering only linear of planar feature constraints, and the adjustment model solved by Levenberg-Marquardt method can converge correctly under any given initial value.
  • Dec. 29, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 2 0214003 (2022)
  • DOI:10.3788/AOS202242.0214003
Wide Angle Array Detection Technology for High Power Density Laser
Guan Wenlu, Tan Fengfu, Hou Zaihong, Luo Jie, Qin Laian, He Feng, Zhang Silong, and Wu Yi
In order to improve the detector array target laser power density measurement range and incident angle tolerance, starting from the protective sampling attenuation structure, based on the theory of total reflection and transmission scattering, we design a protective sampling structure composed by gold-plated copper base panel, fiber optic sampling, and scattering attenuation. At the same time, the designed structure is applied to detector array target system. Through thermal analysis of laser irradiation target, ray tracing simulation, and laser point-by-point scanning experiment, the anti-laser damage ability, angle characteristics, and channel response consistency of the system are analyzed and tested. The results show that the protective sampling attenuation structure can withstand long time irradiation of high power density laser. When the incidence angle ranges from 0° to 30°, the deviation of measured angle characteristic coefficient with respect to normal incidence is less than 4% after cosine correction. The standard deviation of response inconsistency among channel units all less than 2%.
  • Dec. 29, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 2 0214002 (2022)
  • DOI:10.3788/AOS202242.0214002
Transmission Characteristics of Blue-green Laser Through Two-Dimensional Dynamic Sea Surface-Bubble Layer
Wang Mingjun, Wang Yuhang, Chen Dan, Zhang Jialin, and Li Jianqing
In order to study the transmission characteristics of blue-green laser across the the air-sea cross-medium, the downlink transmission model of blue-green laser through the sea surface-bubble layer is developed based on Kirchhoff approximation, Mie theory, and Beer theory for the air-sea cross-medium interface and the the subsurface bubble layer. The factors such as the fluctuation of sea surface height affected by wind speed, the change of bubble concentration in seawater, the mixing of clean bubbles and thin film-covered bubbles in seawater are fully considered. The relationship among the transmittance of blue-green laser passing through the sea surface-bubble layer, wind speed, the transmission depth in seawater, and the angle between receiving plane and transmitting plane is calculated numerically. The results show that the transmittance of the blue-green laser passing through the air-sea interface and the seawater mainly depends on the wind speed and the laser transmission depth in the seawater. With the increase of wind speed, the sea surface roughness and the concentration of bubbles in the upper ocean increase, and the laser transmittance decreases. Compared with seawater, the effect of bubble layer on laser transmittance decreases with the increase of depth. For bubbles with radii greater than 10 μm, the covering of the protein film has little effect on the attenuation of the blue-green laser.
  • Dec. 29, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 2 0214001 (2022)
  • DOI:10.3788/AOS202242.0214001
Morphology Prediction of Coaxial Powder Feeding Multichannel Laser Cladding Layer Based on Response Surface
Liang Wanxu, Yang Yong, Jin Kang, Qi Kang, Xiong Li, Liu Yi, and Dai Longjie
In this study, the influences of different process parameters, such as the laser power, scanning speed, overlap rate, and distance from the cladding head to the substrate, on the morphological characteristics of the cladding layer, such as the average height of the cladding layer, average substrate melt depth, average dilution rate, and average surface height difference, were explored. Moreover, the prediction of the coating morphology was achieved. An entire factor experiment was designed and the mathematical model between the coating morphology and process parameters was constructed based on the response surface analysis method. The predicted results were compared with the experimental data. Results show that the scanning speed, laser power, distance between the cladding head to the substrate most significantly affect the average height of the cladding layer, average substrate melt depth, and average dilution rate, respectively. Furthermore, the average surface height difference is mostly affected by the scanning speed. The average relative errors of the average height of the cladding layer, average substrate melt depth, average dilution rate, and average surface height difference are 10.09%, 4.96%, 8.83%, and 8.34%, with the Radjust2 (goodness of fit) of 0.8971, 0.9251, 0.9240, and 0.8545, respectively.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 1 0114012 (2022)
  • DOI:10.3788/LOP202259.0114012
Q-Switched Mode-Locked Thin-Disk Tm∶ZBLAN Laser
Zhang Mingxia, Zhou Long, Ling Weijun, Yuan Zhen, Wang Wenting, Xue Jingwen, Wang Chong, Du Xiaojuan, and Dong Zhong
In this study, we have achieved novel continuous and passive Q-switched mode-locked operation in a Tm‍‍∶‍ZBLAN laser using a special crystal design. When the laser is in continuous operation, the maximum output power of 254, 296, and 230 mW is obtained using 1.5%, 3%, and 5% output mirrors, respectively. We use a 1.5% output mirror and transmission-type GaAs-SESAM as a mode-locking element to achieve a mode-locking operation. The absorbed pump threshold is as low as 131 mW. When the absorption pump power is greater than 1.09 W, a stable Q-switched mode-locking operation is achieved. The maximum output power is 98 mW, the pulse width of the Q-switched envelope is 6 μs, the repetition frequency is 19.23 kHz, the repetition frequency of the pulse under the Q-switched envelope is 102 MHz, and the pulse width is about 800 ps. The maximum single-pulse energy is 0.96 nJ.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 1 0114011 (2022)
  • DOI:10.3788/LOP202259.0114011
High-Aspect Ratio Blind Cutting of Ultra-Thin Ceramic by Nanosecond Ultraviolet Laser
Chen Xinghua, Li Wenyuan, Rong Youmin, and Huang Yu
Alumina ceramics have high thermal conductivity, good heat dissipation, and a small dielectric constant. It is a common substrate material used in mobile communication and integrated electronics; however, its high hardness and brittleness make it crack easily during conventional machining. In this study, we utilized a nanosecond ultraviolet laser to study the blind cutting process of an ultra-thin ceramic plate. Moreover, we analyzed the slit width and depth variations by controlling the three main processing parameters of the nanosecond laser, which were laser repetition frequency, scanning speed, and repetition times. The experimental results show that as the laser repetition frequency increases, the slit width increases and remains unchanged, and the slit depth first increases and then decreases. As the scanning speed decreases and the number of repetition times increases, the slit depth first increases and then decreases, and the slit width slightly fluctuates. With the slit depth-width ratio as the index, we obtain the following conclusions through an orthogonal experiment: the maximum depth-width ratio of single-pass multiple scanning in the blind cutting process of the ultra-thin ceramic substrate is 4.0137, and the optimal laser parameter combination is 40 kHz laser frequency, 0.07 m/s scanning speed, and 25 repetition times.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 1 0114010 (2022)
  • DOI:10.3788/LOP202259.0114010
Surface Quality and Mechanical Properties of 316L Stainless Steel Manufactured by Powder Feeding Laser Additive and Milling Subtractive Hybrid Manufacturing
Chen Feng, Song Changhui, Yang Yongqiang, Wei Hongming, and Zhou Heng
To investigate the surface quality and mechanical properties of parts produced by powder feeding laser additive and milling subtractive hybrid manufacturing technology, using 316L stainless steel as the research object, we manufactured the samples by the alternate "additive-subtractive-additive-subtractive" cycle and tested the surface roughness, microhardness, and mechanical properties of the samples. The findings demonstrate that the surface roughness of the samples produced by the powder feeding laser additive and milling subtractive hybrid manufacturing decreases with increasing milling speed and increases with increasing feed per tooth. The powder feeding laser additive and milling subtractive hybrid-manufactured samples have lower surface roughness than the substrate sample prepared by the traditional process and have higher microhardness than additive-manufactured and forged parts. The tensile and yield strengths of powder feeding laser additive and milling subtractive hybrid-manufactured samples increase by 5% and 60.5%, respectively, compared with the additive-manufactured sample. However, their elongation rate after breaking reduces. The powder feeding laser additive and milling subtractive hybrid manufacturing technology can produce parts with high surface quality and good mechanical properties and can be directly applied to manufacture parts, such as 316L stainless steel tire molds. This method combines the features of additive manufacturing's high material utilization and degree of freedom with subtractive manufacturing's high precision and surface quality to produce parts with complex structures as well as high shape accuracy and surface quality.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 1 0114009 (2022)
  • DOI:10.3788/LOP202259.0114009
Study on Driving Circuit of Narrow Pulse Width and Large Current Semiconductor Laser
Du Jianyan, Zhao Yiqiang, Ye Mao, Lin Yuanqi, and Zheng Xiaoxiao
Laser radar is widely used in unmanned driving, surveying, and mapping, etc. In order to reduce power consumption, cost, and volume, pulsed semiconductor laser has become the first choice of laser drive circuit. Under this background, an optimal design of narrow pulse and large current semiconductor laser drive circuit is completed with inductor as energy storage element. Based on the working principle of the driving circuit in detail, the influence relationship between the value of the energy storage inductor and the power consumption of the circuit is emphatically studied. The driving circuit simulation model was established by using ORCAD PSPICE simulation software, and the main factors affecting the pulse width, peak value, and wave oscillation of the pulse current were summarized. The test results show that the power loss of the energy storage inductor is 59 mW, the pulse width of the driving circuit is 3.8 ns, the rising edge is 3.5 ns, the falling edge is 3.7 ns, the peak current is 132 A, and the peak optical power of the laser output is about 326 W at 10 kHz.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 1 0114008 (2022)
  • DOI:10.3788/LOP202259.0114008