Lasers and Laser Optics|29 Article(s)
Experimental Investigation on High-order Transverse-mode of the Pr:YLF Laser by a Blue Laser-diode Off-axis Pumping
Feng-chen ZHANG, Chen-lin HUI, Qi-he SHU, Cai-hong HUANG, Dong-mei GONG, and Feng-jiang ZHUANG
The direct generation of the visible high-order transverse-mode laser was present by employing an off-axis pumping and cavity control in a diode end-pumped Pr:YLF laser. The detailed numerical analysis was proposed based on the intensity characteristic theory about the High-order Hermite-Gaussian (HG) beam and the coherent superposition of different HG amplitudes and phases. In our setup, a blue LD was served as an end-pumped source with a pump wavelength of 442 nm, and a compact plano-concave cavity was designed for lasing. For directly obtaining hollow and high-order HG mode 720 nm laser outputs, we manipulate the resonator of the Pr:YLF laser by employing an efficient off-axis diode-pumping. The experimental results confirmed that the high-order HG beams are generally consistent with the theoretical calculations. In this paper, we experimentally demonstrated an approach for generating the hollow and high-order (HG) mode 720 nm laser beams by manipulating laser modes inside the cavity. Further researches will focus on obtaining higher energy high-order transverse-mode laser outputs, and the method in this paper has potential in the fields of optical manipulation, optical micromachining, and optical communications.
Acta Photonica Sinica
  • Publication Date: Oct. 15, 2020
  • Vol. 49, Issue 10, 1014001 (2020)
Research on Fabrication and Optoelectronic Properties of Surface Modified Silicon by Ultrafast Laser Pulse
Yang YANG, Chao LI, and Ji-hong ZHAO
In order to extend the absorption edge of crystalline silicon to the near infrared band to meet the requirement of optical communication,the textured silicon was obtained by irradiation of nanosecond laser pulses. The surface morphology of modified silicon under irradiation with different laser fluence from 0.39 J/cm2 to 24 J/cm2 was investigated. Then, the optical properties including reflectance, transmittance, and absorptance of silicon samples by nanosecond laser irradiation with different laser fluence were measured. The results show that the absorptance below the bandgap of silicon enhances for all the textured silicon samples and it is up to 55% for near infrared light of 1 500 nm. Next, the thermal stability of infrared absorption for the textured silicon samples was investigated. The thermal annealing process at temperatures of 473~1 073 K can slightly reduce the absorptance below the bandgap of silicon and the magnitude of reduction only varied within 10%. Moreover, the dependence of reflectance, transmittance, and absorptance of modified silicon on the annealing temperature was studied on. Lastly, the crystal structures of modified silicon were determined by Raman spectroscope. After irradiation of nanosecond laser pulses, the crystalline silicon surface is disordered and amorphous or polycrystalline phases are formed. However, the crystal quality of textured silicon can be improved by post-thermal annealing process.
Acta Photonica Sinica
  • Publication Date: Oct. 15, 2020
  • Vol. 49, Issue 10, 1014002 (2020)
State-switchable Multi-wavelength and Dissipative Soliton Mode-locked Tm-doped Fiber Laser Based on a Combination of Nonlinear Amplifying Loop Mirror and Lyot Filter
Xiao-fa WANG, Jing-hui LIU, and Zeng-gao JIN
This paper demonstrates a state-switchable Tm-doped fiber laser based on nonlinear amplifying loop mirror and Lyot filter technique. By properly adjusting the polarization controller and pump power, the Tm-doped fiber laser can operate in multi-wavelength state and dissipative soliton mode-locked state, respectively. And two types of operating states can be switched to each other. For multi-wavelength state, 8 stable wavelength peaks are generated within half of peak power variation. For the dissipative soliton mode-locked state, the dissipative soliton with pulse energy as high as 41.49 nJ, the pulse duration of 2.4 ns, and the spectrum bandwidth of 29 nm is generated at the center wavelength of 1 996 nm. The switching between different operating states is due to the change in the function of the nonlinear amplifying loop mirror caused by the polarization controller.
Acta Photonica Sinica
  • Publication Date: Apr. 25, 2020
  • Vol. 49, Issue 4, 0414001 (2020)
Research on Heat Transfer Characteristics of Porous Foam Heat Sink for All Solid State Thin Disk Lasers
Rui LIU, Fa-quan GONG, Xiang LI, Long-hui DAI, Gang LI, and Yong TAN
The thermal lens effect of high-power all solid state thin disk lasers in operation can cause the laser output power to decrease and the beam quality to deteriorate. In this paper, focus on this problem, porous SiC foam and millimeter channels are introduced into the heat transfer heat sink of the thin disk laser and applied to all solid state thin disk laser. The finite element analysis software is used to optimize the structural model. And the simulation analysis indicates that, when the thickness of SiC is 2 mm, the porosity is 40% and the inlet pressure is 4 kg (0.4 MPa), the theoretical heat transfer coefficient is 1.51×105 W/m2·K, the experimental heat transfer coefficient is 1.45×105 W/m2·K, the results are similar to each other, which verifies the correctness of the theoretical model. Finally, the new heat sink is used to build a 24 multi-passes all solid state thin disk lasers experimental device based on Yb:YAG. The continuous laser output with output power of 393 W and wavelength of 1 030 nm is obtained, the optical-optical efficiency is 52% and the beam product parameter is 5.918 mm·mrad.
Acta Photonica Sinica
  • Publication Date: Apr. 25, 2020
  • Vol. 49, Issue 4, 0414002 (2020)
Calibration Method of 2D LIDAR and Camera Based on Indoor Structural Features
Lei ZHANG, Xiao-bin XU, Jia HE, Kai-yua ZHU, Min-zhou LUO, and Zhi-ying TAN
Aiming at the problem of LIDAR and camera data fusion, a calibration method of 2D LIDAR and color camera based on indoor structural features was proposed. According to the position relationship between the point and lines, pillar features of the indoor scene are used to derive the projection matrix equation between the 2D LIDAR and the camera coordinate systems. The Canny operator and Hough transform are employed to extract the line features of the corner image. Afterwards, the RANSAC method is used to fit the corner features from the point cloud. The projection matrix is solved by the singular value decomposition method. Finally, the calibration results are further optimized after removing the data with large reprojection errors. The experimental results show that the average reprojection error of the pillar feature point is reduced from 0.375 5 pixels to 0.045 9 pixels by adopting optimized projection matrix. Compared with the two-step calibration method, the algorithm proposed in this paper has a better reprojection effect. At the same time, this method does not require a specific calibration object, and can achieve high projection accuracy in less time.
Acta Photonica Sinica
  • Publication Date: Dec. 25, 2020
  • Vol. 49, Issue 12, 61 (2020)
Femtosecond Laser Ablation Characteristics of Gear Material 20CrMnTi
Xing-zu MING, Lei JIN, Yong-bo XIAO, Jia-jian LIN, Xian ZHOU, and Rui MING
The ablation mechanism of spiral bevel gear material 20CrMnTi and the ablation characteristics of tooth surface by monopulse femtosecond laser at different energy densities are studied. Considering the dynamic energy absorption effect of material and mutual coupling interaction of photon-electron-lattice system, the energy coupling model is established. The simulation results show that the energy density of ablated gear material is at least 67 mJ/cm2, and the material removal occurs in the area within the ablation depth 40 nm. Experimental results show that when the tooth surface temperature exceeds the vaporization temperature of gear material, a good ablative morphology of tooth surface can be maintained, and the variation value of roughness is less than 0.021 μm, which verifies the effectiveness of theoretical simulation. These results could provide a reference for improving the tooth surface quality of spiral bevel gear with micro-precise machining of femtosecond laser.
Acta Photonica Sinica
  • Publication Date: Dec. 25, 2020
  • Vol. 49, Issue 12, 73 (2020)
Experimental Research on Power-balanced Nd:YVO4/Nd:GdVO4 Dual-wavelength Laser
Meng-ying XIA, Miao HU, Hui-min ZHOU, Zheng-feng QIAN, Xue-fang ZHOU, Guo-wei YANG, Yang LU, and Mei-hua BI
The output characteristics of the power-balanced Nd:YVO4/Nd:GdVO4 Dual-Wavelength Laser (DWL) under different pumping conditions is investigated experimentally. The experimental results show for power-balanced Nd:YVO4/Nd:GdVO4 DWL, the heat sink temperature needs reduce when the pumping power increases, and the ratio of temperature decreasing versus pumping power increasing is 11.23 ℃/W. With the change of pumping power and heat sink temperature, the DWL wavelengths shift slightly. When the pumping power increases, the DWL left wavelength blue-shifting rate is 0.056 nm/W, and the right wavelength one is 0.054 nm/W. The result also found that the output power of the power-balanced DWL increases with the pumping power increasing. The fitted slope efficiency is 8.7%. When the pumping power is 5.58 W, the maximum output power reaches 115.7 mW.
Acta Photonica Sinica
  • Publication Date: Apr. 25, 2020
  • Vol. 49, Issue 4, 0414003 (2020)
Generation of Broadband Supercontinuum Source with Pulse Width of One Hundred Femtosecond
Zheng-yi LIU, Shuang-long LIU, Ai-wang HUANG, Wei LIU, and Dan-ni CHEN
A method of generating broadband supercontinuum pulses is proposed, and it is a prefer light source for coherent Raman spectroscopy.A 1 064 nm femtosecond laser was used to pump the normal dispersion photonic crystal fiber, and then a pair of gratings was used to compress the pulse. Then a supercontinuum light source with a pulse width of 178 fs and a spectral range of 760~1 300 nm was obtained.The temporary spectrum structure of the supercontinuum pulse was analyzed. The results demonstrated that its spectrum is basically linearly and smoothly distributed, but the pulse width reaches 1.43 ps, and the time delay between different spectral frequencies is quite large. Therefore, a pair of gratings is used for dispersion compensation. In addition, although increasing the power of pump light can increase the spectral broadening, it will also introduce higher-order dispersion, which will increase complexities to the following dispersion compensation. In the end, to verify the performance of the supercontinuum in Coherent Anti-stokes Raman Scattering (CARS), three-color CARS spectrum detection system was built using the supercontinuum, and the CARS spectrum of the benzonitrile solution was measured, and all vibration modes in the range of 3 200 cm-1 was obtained simultaneously.
Acta Photonica Sinica
  • Publication Date: Sep. 01, 2020
  • Vol. 49, Issue 9, 0914002 (2020)
Frequency-selecting Property of Fiber Laser Based on the Triple-ring Passive Resonators
Wenxiang CUI, Xuefang ZHOU, Miao HU, Meihua BI, Guowei YANG, and Tianshu WANG
Acta Photonica Sinica
  • Publication Date: Feb. 25, 2021
  • Vol. 50, Issue 2, 201 (2021)
Experimental Study on Dislocation Configuration and Grain Refinement of 690 High Strength Steel Treated by Laser Shock Processing
Yu-peng CAO, Cong YANG, Wei-dong SHI, Guo-ran HUA, Bin LI, and Rong LI
In order to study the relationship between dislocation configuration and grain refinement in materials treated by laser shock processing, 690 high-strength steel was impact-strengthened by pulsed laser. The scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy images of the sample treated by laser shock processing were obtained using scanning electron microscopy and transmission electron microscopy. The inverse fast Fourier transform was performed on the high resolution transmission electron microscopy image, and a grain refinement model of 690 high strength steel treated by laser shock processing was established from the perspective of dislocation configuration. The results show that after the 690 high-strength steel was loaded by laser shock with a power density of 5.09 GW/cm2, the internal dislocations of the material are proliferated and the surface grains are refined, with grain size ranging between 80 nm and 200 nm (cross section). The precipitation phase maintains a semi-coherent relationship with the matrix, and many defects such as edge dislocations, dislocation couples and extended dislocations are distributed in the matrix, among which the dislocation couples are formed by the screw dislocation motion with cut order. The geometrical dislocation interfaces' extension and intersection divides the original large crystal grains into fine grains, which consists of dislocations, extended dislocations, vacancies, etc.The grain refinement model of 690 high strength steel treated by laser shock processing can describe the grain refinement process dominated by the dislocation movement of 690 high strength steel.
Acta Photonica Sinica
  • Publication Date: Apr. 25, 2020
  • Vol. 49, Issue 4, 0414004 (2020)