Superior performance of a 2 kHz pulse Nd:YAG laser based on a gradient-doped crystal
Meng’en Wei, Tingqing Cheng, Renqin Dou, Qingli Zhang, and Haihe Jiang
Herein, we report a homemade new Nd:YAG crystal rod that contains a gradient dopant of 0.39–0.80 at.% Nd3+ from end to end, achieving superior performance of a 2 kHz Nd:YAG pulse laser at 1064 nm. The optical-to-optical conversion efficiency reached 53.8%, and the maximum output power of the laser was 24.2 W, enhanced by 35.9% compared with a uniform crystal rod with the same total concentration of Nd3+. Significantly, our experiments revealed that the gradient concentration crystal produced a relatively even pumping distribution along the rod axis, greatly reducing the temperature gradient as well as having a smaller thermal effect. The pump and thermal distribution smoothing obviously improved the features of laser oscillation and output.
  • Jun. 09, 2021
  • Photonics Research
  • Vol.9 Issue, 7 07001191 (2021)
  • DOI:10.1364/PRJ.424989
Simulation of Axial Focal Shift of Optical System Under High-Power Laser
Ding Wei, Wang Fei, Wang Mengjie, and Weng Ningzhi
In a high-power optical cutting system, the laser is focused by the optical system to generate heat, which causes the optical system components to undergo thermal deformation and change in refractive index, which changes the focal length of the lens and affects the processing effect. COMSOL software is used to model the optical system in a multi-physics field, the shape of the mirror and the change of refractive index under the action of continuous laser and quasi-continuous laser are obtained by simulation. The heated data of the lens is imported into ZEMAX for beam tracing, and the axial offset of the focal point of the optical system is calculated by simulation. The higher the power, the greater the focal shift; the larger the pulse width, the smaller the focal shift; the higher the repetition frequency, the smaller the focal shift. Finally, the focus shift is compensated by introducing the convection coefficient, and the position of the focus can be controlled by changing the convection coefficient. This research solves the problem of difficult measurement of the axial focus offset during high-power laser processing and provides a theoretical basis for the focus control of high-power laser cutting equipment.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114011 (2021)
  • DOI:10.3788/LOP202158.1114011
Design of Microstructure Fiber for Direct Down Laser Backlight of Liquid Crystal Displays
Shen Kaifeng, and Wu Zhangqiang
The scheme of an external semiconductor laser with built-in microstructure fiber is designed and studied to achieve fiber-side lighting. This scheme solves the problems associated with traditional direct down liquid crystal modules: these require a large number of light-emitting diode chips, and the volume of the built-in semiconductor laser scheme is too large. The effects of different depths, radii, and the number of microstructures on the optical field are simulated and analyzed. Light field with a peak illumination of 32650 lx, a horizontal viewing angle of 85°, and a vertical viewing angle of 84°33′35″ is obtained. These values meet the requirements of the liquid crystal display (LCD) industry for achieving a peak backlight illumination of 10000 lx, a horizontal viewing angle of 60°, and a vertical viewing angle of 50°. The proposed scheme provides a new method for applying semiconductor lasers in the field of LCD display.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114010 (2021)
  • DOI:10.3788/LOP202158.1114010
Parameters Optimization and Friction and Wear Properties for Laser Cladding Ni60AA Coating on 45 Steel Shaft Surface
Wu Jun, Zhu Dongdong, Yang Richu, Wu Siyu, Huang Yan, and Zhang Yuliang
To improve the service life of 45 steel shaft parts, we aim to study optimum process parameters of laser cladding Ni60AA coating on 45 steel shaft surface. The cladding process test of shaft surface was carried out with multi-pass spiral lap technology, namely, a Ni60AA alloy cladding layer was prepared on a 45 steel substrate. Based on the single variable method, the single factor cladding experiments were carried out on three process parameters, namely laser power, powder feeding rate and shaft speed. The thickness of cladding layer, dilution ratio and micro-hardness were selected as the evaluation indexes of coating quality. Based on the single factor experiment, the orthogonal experiment of three-factor and three-level was completed. The multi-objective comprehensive optimization of the process parameters was finished by the weight matrix method, and the microstructure and micro-hardness of the optimized cladding coating were analyzed. At the same time, friction and wear experiments were carried out at different working temperatures, and the friction coefficient,wear rate and wear scar morphology were analyzed and the feasibility of process optimization is verified. Powder feeding rate has the largest comprehensive influence ability, followed by laser power and shaft speed. The optimal parameters are laser power of 1400 W, powder feeding rate of 16.3 g/min, and shaft speed of 2.3 r/min. The thickness and micro-hardness of the cladding coating were increased by 3.49% and 2.8% respectively compared with those before optimization. When the test temperature is 35, 80 and 125 ℃, the average friction coefficient of the cladding coating is 28.5%, 21.1% and 11.8% lower than that of 45 steel and the wear rate of the cladding coating is 87.6%, 86.6% and 80.9% less than that of the substrate. Ni60AA cladding coating with high forming quality and significantly improved hardness and wear resistance can be obtained by optimizing the laser cladding process parameters.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114008 (2021)
  • DOI:10.3788/LOP202158.1114008
Yb Slab Laser Amplifier with a Laser Output of 7.13 kW, 2 Times Diffraction Limit
Wang Yanan, Zhou Tangjian, Shang Jianli, Li Mi, Wang Juntao, Wu Yingcheng, Shi Yong, He Ping, Gao Qingsong, and Wang Dan
The injection angles of Yb∶YAG slab are calculated and the configuration of laser amplification is optimized. The advantages of the reflective image transfer system are compared and analyzed, and the spherical aberration of the image transfer system is calculated. The results show that the spherical aberration is significantly decreased by the reflective image transfer system, which improves the beam quality of the amplified laser. Based on single Yb∶YAG slab, a three-passes master oscillator power amplifier system is developed at room temperature. By using the reflective image transfer system and matching the near-filed intensity between pump laser and seed laser, an output power of 7.13 kW and a beam quality of 2 times diffraction limit are achieved without the active optical correction system.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114007 (2021)
  • DOI:10.3788/LOP202158.1114007
Effects of Scanning Strategy on the Microstructure, Properties, and Residual Stress of TC4 Titanium Alloy Prepared by Laser Melting Deposition
Shan Qibo, Liu Chen, Yao Jing, Zhan Yu, and Liu Changsheng
In this paper, TC4 titanium alloys were prepared by laser melting deposition using different scanning strategies. The effects of scanning strategy on the microstructure and properties of TC4 titanium alloys were studied using optical microscopy, X-ray diffraction (XRD), scanning electron microscopy, and electronic universal material testing machine. In particular, the evolution and distribution of residual stress in the XOZ plane of the TC4 alloys were analyzed in detail using XRD. Results indicate that the scanning strategy affected the morphology of the basket microstructure, which in turn affected the mechanical properties of the TC4 alloys. The tensile and yield strengths of the TC4 specimen under the roundabout scanning strategy were the maximum (1251.7 MPa and 1250.0 MPa, respectively), while the tensile and yield strengths of the TC4 specimen under the unidirectional scanning strategy were the minimum (991.5 MPa and 1010.9 MPa, respectively). The residual stress varied substantially under different scanning strategies, with the test results of the partition roundabout scanning being distributed more uniformly. The order of the overall stress level of the specimens obtained using different scanning strategies was partition roundabout, reciprocating, roundabout, and unidirectional scanning.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114002 (2021)
  • DOI:10.3788/LOP202158.1114002
Influence of Misalignment on Properties of Focused Laser Beam by Large Aperture Off-Axis Parabolic Mirror
Zeng Xiahui
Based on the rigorous full vector diffraction theory, the influence of misalignment on the beam focusing characteristics of large aperture off-axis parabolic mirror (OAP) are analyzed in detail. The results show that the shape of the diffraction focal spot does not change after the translation or revolving of OAP around the z″ axis, but the center position of the focal spot shifts. The quantitative relationship between OAP’s three-dimensional translation and rotation deviation around z″ axis is obtained by using Rayleigh criterion. When OAP’s rotation deviation around x″ or y″ axis occurs, the appearance of astigmatism and coma will cause the shape of diffractive focal spot to change, and the peak intensity of the focal spot is greatly reduced. The relationship between the maximum rotation deviation angle and OAP off-axis parameters and beam parameters is discussed in detail. Therefore, understanding the influence mechanism and variation relationship of misalignment on beam focusing characteristics can provide a reliable theoretical basis for precise adjustment of OAP.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114006 (2021)
  • DOI:10.3788/LOP202158.1114006
Nonsynergistic Response in Laser Additive Manufacturing of Nickel-Based Superalloys Comprising the Constrained Structure of a Ductile Iron Surface
Lang Tiantian, and Pang Ming
In this study, an L-shaped model was designed to simulate the constraining structure of the laser additive strip sidewall of a valve seat to construct the constrained structure. The basic laser additive simulation model considers the changes in laser absorptivity, latent heat of phase change of the material, and heat exchange between the additive process and the external environment. Results show the existence of a competitive relationship between the laser energy density change and the energy input of the laser in space. When the effect of increasing the laser power and power density on the temperature rise is greater than the effect of increasing the speed and reducing the energy in the space on the temperature drop, the temperature of the additive layer increases. Because of the influence of the substrate structure asymmetry and the heat transfer and dissipation in the laser additive process, the depth of fusion between the additive layer and the bottom surface of the substrate is greater than the depth of fusion with the side surface and the cross section of the additive layer has a stepped-crescent shape. Furthermore, because of the combined effects of the hysteresis of heat conduction and rapid heating and cooling of the laser, with the increase in laser power and scanning speed, the cross-sectional profile of the additive layer gradually switches from a crescent to a platform shape.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114005 (2021)
  • DOI:10.3788/LOP202158.1114005
Copper-Steel Laser Welding Process under Two Laser Deflection Angles
Xu Aiming, Tang Chao, Li Zhouxuan, He Wei, Ye Cheng, and Wu Hao
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114004 (2021)
  • DOI:10.3788/LOP202158.1114004
<100 fs All-Fiber Bound Dissipative Soliton Passively Mode-Locked Laser
Zhong Min, Lin Xiaoping, Ruan Qiujun, Wang Hang, Hu Zhijie, Fu Yu, Huang Fengshan, Huang Liuping, Zhou Huili, and Luo Zhengqian
We report an all-fiber dissipative soliton passively mode-locked Er-doped fiber laser. By adjusting the pump power and the polarization states, we can obtain the two-soliton and three-soliton bound state dissipative solitons further. Utilizing anomalous dispersion fiber to compress the pulse duration of wide-bandwidth two-soliton bound dissipative solitons, compressed pulse width is fitted to 96 fs by hyperbolic secant, and the calculated time-bandwidth product is 0.324, indicating the near transform-limited pulse. The broadband spectrum is obtained thanks to the dispersion management in the cavity and high modulation depth (20%) of carbon nanotube (CNT) saturable absorber. On this basis, the dissipative soliton with the spectral width of 35 nm (center wavelength is 1.57 μm) is obtained, which is also the widest spectrum based on the dissipative soliton produced by CNT.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1114003 (2021)
  • DOI:10.3788/LOP202158.1114003