Dynamics of a dispersion-tuned swept-fiber laser
Duidui Li, Guolu Yin, Ligang Huang, Lei Gao, Laiyang Dang, Zeheng Zhang, Jingsheng Huang, Huafeng Lu, and Tao Zhu
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.
  • May. 19, 2023
  • Photonics Research
  • Vol. 11, Issue 6, 999 (2023)
  • DOI:10.1364/PRJ.484911
Hundredfold increase of stimulated Brillouin-scattering bandwidth in whispering-gallery mode resonators | Editors' Pick
Guoping Lin, Jingyi Tian, Tang Sun, Qinghai Song, and Yanne K. Chembo
Backward stimulated Brillouin scattering (SBS) is widely exploited for various applications in optics and optoelectronics. It typically features a narrow gain bandwidth of a few tens of megahertz in fluoride crystals. Here we report a hundredfold increase of SBS bandwidth in whispering-gallery mode resonators. The crystalline orientation results in a large variation of the acoustic phase velocity upon propagation along the periphery, from which a broad Brillouin gain is formed. Over 2.5 GHz wide Brillouin gain profile is theoretically found and experimentally validated. SBS phenomena with Brillouin shift frequencies ranging from 11.73 to 14.47 GHz in ultrahigh QZ-cut magnesium fluoride cavities pumped at the telecommunication wavelength are demonstrated. Furthermore, the Brillouin–Kerr comb in this device is demonstrated. Over 400 comb lines spanning across a spectral window of 120 nm are observed. Our finding paves a new way for tailoring and harnessing the Brillouin gain in crystals.
  • May. 16, 2023
  • Photonics Research
  • Vol. 11, Issue 6, 917 (2023)
  • DOI:10.1364/PRJ.484727
Microstructure and Mechanical Properties of Laser Welded Inconel690 Nickel-Based Alloy/SUS304 Stainless Steel Joints
Jiasen Huang, Chuang Cai, Zhijie Liu, Hanping Wang, Jia Xie, Jie Yu, and Yonghong Liu
ObjectiveAt present, the Inconel690 nickel-based alloy and SUS304 stainless steel are widely used in nuclear power, aerospace, and petrochemical fields owing to their excellent performance in thermal strength, corrosion resistance, and specific strength. Compared with traditional welding methods, laser welding is characterized by higher energy density, smaller welding deformation, and a narrower heat-affected zone. Compared with laser welding, laser welding with filler wire achieves the purpose of changing the metal composition of weld seams and thereby improving the mechanical properties of the welded joints. Different materials have different laser absorptivity, linear expansion coefficients, specific heat capacity, thermal conductivity, and microstructure evolution during solidification. These factors further affect the performance of the welded joints of dissimilar materials. The current research on stainless steel and nickel-based super-alloys mainly focuses on the mechanical properties of the welded joints under the influence of precipitates. In this study, laser welding and laser welding with filler wire are carried out under different heat inputs, and mechanical properties are investigated.MethodsThe thickness of the SUS304 and Inconel690 used in this experiment is 4.5 mm. Inconel ERNiCrFe-7A is used as the filler wire. The welding equipment used in this study is a 10 kW TRUMPF lasers TruDisk 10002. In addition, 99.99% pure argon gas is used as the shielding gas with a gas flow rate of 25 L/min. After welding, the ZEISS Axio Observer A1m metallurgical microscope is used to observe the surface morphology, and energy dispersive spectroscopy is employed to test the precipitates in the weld seams. The CMT4303 electronic universal testing machine is applied to test the tensile strength of the welded joints. The HVS-30 Vickers hardness tester is utilized to test the microhardness of the welded joints.Results and DiscussionsThe cross-sections of the welded joints are in the typical goblet shape with no crack defects. In the weld zone S2 (1.5 kJ/cm), many white particles are observed near the grain boundary, and they can be further confirmed as a titanium-containing phase. After the ERNiCrFe-7A filler wire is added, an irregularly shaped white precipitated phase is observed in the weld seam, and it can be determined as a chromium-rich phase. The X-ray diffraction (XRD) results suggest that this chromium-rich phase is Cr0.19Fe0.7Ni0.11 phase. The tensile strength of S2 (1.5 kJ/cm) is 9.7% higher than that of S1 (2.6 kJ/cm). After the filler wire is added, the tensile strength of S3 (1.5 kJ/cm) is 683 MPa, which is 16.2% higher than that of S1 (2.6 kJ/cm). Owing to the decrease in heat input, the grain size in the weld seam becomes smaller, which improves the plastic toughness and average hardness of the weld seam. When the heat input are 2.6 kJ/cm and 1.5 kJ/cm, the average hardness of the weld seam are 176.8 HV and 190.4 HV, respectively. After the filler wire is added, the average hardness of the weld seam in weld zone S1 (2.6 kJ/cm) is 216.7 HV.ConclusionsIn this study, laser butt welding of Inconel690 nickel-based alloy and SUS304 stainless steel is carried out. The influences of heat input and filler metal on the microstructure and mechanical properties of joints are studied. The results indicate that the cross-section of the weld seam is in the classical goblet shape after laser welding. The weld width of S1 (2.6 kJ/cm) is larger than that of S2 (1.5 kJ/cm). As the heat input increases, the grain size in the weld seam becomes larger. A titanium-containing phase is diffusively distributed in the weld seams of all welded joints. After the ERNiCrFe-7A filler wire is added, a chromium-rich phase appears, and it is speculated to be Cr0.19Fe0.7Ni0.11 phase according to the XRD results. The grain size of S2 (1.5 kJ/cm) is 40% smaller than that of S1 (2.6 kJ/cm), and the mechanical properties of the joints are improved.
  • May. 25, 2023
  • Acta Optica Sinica
  • Vol. 43, Issue 10, 1014001 (2023)
  • DOI:10.3788/AOS222151
Effect of Laser Remelting Path on Residual Stress and Surface Quality of Remanufactured Coatings
Jiasheng Wang, and Linsen Shu
The influence mechanism of the laser remelting path on the residual stress and surface quality of the cladding layer was studied by combining numerical simulation and experiment to further improve the surface quality of the remanufactured alloy layer and its comprehensive mechanical properties. First, the laser cladding and remelting models were established using the Simufact Welding software platform, and the variation laws of the temperature field and stress field during the remelting process were simulated and studied under three different scanning paths, respectively. Subsequently, the laser remelting process experiment was performed, and the residual stress and surface morphology of the remanufactured alloy layer were detected and analyzed using an X-ray residual stress detector and a Keyence ultra-depth-of-field microscope. The simulation results show that the temperature gradient of each point on the workpiece's surface during the remelting process is significantly lower than that during the cladding process. The workpiece's maximum residual stress before remelting is 269.59 MPa. The residual stress of the workpiece is significantly reduced after laser remelting, and the residual stress value of the workpiece under the L1-type-remelting path is the smallest, which is only about half of the stress value before remelting. Furthermore, the residual stress test results and the numerical deviation of the simulation calculation are both within 10%, which proves the simulation calculation's accuracy. Laser remelting can effectively reduce the surface roughness of the cladding layer, according to three dimensional extraction of the surface morphology of the alloy layer.
  • Apr. 10, 2023
  • Laser & Optoelectronics Progress
  • Vol. 60, Issue 7, 0714010 (2023)
  • DOI:10.3788/LOP220895
Research and Analysis of Instability of Reflective Infrared Laser Trigger Device
Chuanyu Zheng, Hong'e Luo, Jinlang Gu, Zhen He, and Tao Zhang
In this study, the instability phenomenon of an infrared trigger device that has operated for a long period of time is examined on the basis of working principle of the device and by means of experimental monitoring and analysis. The threshold current, Ith(T), of the infrared laser, which is the source of the infrared laser triggering device, increases after the infrared trigger device works for a long time owing to heat accumulation. In contrast, the output current, Iout(T), of the constant current source decreases with the increase in temperature. When Iout(T)<Ith(T), the infrared laser cannot emit the laser normally, and the output power becomes unstable; this leads to the instability of the infrared trigger. Upon increasing the output current of the constant current source to 1.44 times the maximum threshold current, that is, beyond 640 mA to make Iout(T)>Ith(T), the infrared laser can be guaranteed to be in a stable luminous state within the range of temperature change, and the infrared trigger device is therefore in a stable working state. After a long period of power-on operation experiment, the infrared trigger worked stably and did not trigger the signal by mistake, indicating that its instability problem is effectively addressed. The findings of this study have important engineering application value in improving the stability of infrared trigger devices.
  • Apr. 10, 2023
  • Laser & Optoelectronics Progress
  • Vol. 60, Issue 7, 0714009 (2023)
  • DOI:10.3788/LOP220610
Effect of Energy Density on Microstructure and Mechanical Properties of Hydrogen Resistant Steel HR-2 Selective Laser Melting Parts
Ningzhao Liu, Guowei Wang, Yu Qin, Kaijia Wang, and Xianfeng Shen
An HR-2 hydrogen embrittlement resistant stainless steel was subjected to selective laser melting process testing performed at different levels of volume energy density. The microstructure and properties of the formed parts were characterized. The results revealed that, for a certain range of volume energy density values, the density, microhardness, tensile strength, and elongation of the parts increased with increasing volume energy density. At the maximum energy density of 113.3 J/mm3, the maximum density of the formed part, corresponding tensile strength, yield strength, elongation after fracture, and reduction in area were 99.9%, 765.5 MPa, 634 MPa, 44.0%, and 61%, respectively. These values satisfy the performance requirements of HR-2 forging specified in the GJB 5724 standard. The printed structure of HR-2 is composed of columnar crystals, with equiaxed grains inthe XY plane and columnar grains in the YZ plane. In the XY plane, the grain size increases first and then decreases with the increase of bulk energy density. This is the combined effect of poor fusion pores caused by insufficient heat input, the increase of undercooling caused by the decrease of scanning speed, and the increase of the proportion of remelting zone caused by the decrease of scanning spacing on grain size.
  • Apr. 10, 2023
  • Laser & Optoelectronics Progress
  • Vol. 60, Issue 7, 0714008 (2023)
  • DOI:10.3788/LOP220477
Study on AlSi10Mg Alloy with Complex Flow Channels by Laser Powder Bed Fusion
Xiaogang Zhu, Anping Dong, Lingyu Cheng, Jing Sun, Zhengwu Liu, and Lijie Guo
The specimens with straight channels and the product with complex channels were manufactured by laser powder bed fusion. The results showed that when the diameter of the channel was less than 2 mm, the remaining powder inside the channels could not be removed completely due to the shrinkage of the flow channels after fabricated. In addition, the forming quality of the top surface of the circular channels became worse, with the increase of the diameter while the forming quality and dimensional accuracy for ridge shape channels still kept better with the increase of the size of the section, since the inclination angle of the inner surface was a fixed value. Meanwhile, the semi-melted powder particles adhered to the upper region of the flow channels caused by the deep penetration of the laser into the powder in the non-forming region could be removed by abrasive flow machining, high pressure airflow or water. The test results of the laser powder bed melting product with complex flow channels indicated that there were no defects such as crack or remaining powder by X-ray and computed tomography test. And the pressure test suggested that the product with complex flow channels was not damaged or leaked when the pressure reached 2 MPa for 5 min. Finally, the processes “design-form-test” were successfully established for the products with complex flow channels.
  • Apr. 10, 2023
  • Laser & Optoelectronics Progress
  • Vol. 60, Issue 7, 0714006 (2023)
  • DOI:10.3788/LOP220455
Pulse Characteristics of Quasi Continuous-Wave Pumped Yb∶KYW/Cr4+∶YAG Q-Switched Laser
Nihui Zhang, Mingjie Yao, Wenqi Ge, and Hongbo Zhang
A theoretical investigation of the influence of pump parameters of quasi-continuous-wave laser-diode (LD) pumped Yb∶KYW/Cr4+∶YAG laser on pulse characteristics based on passively Q-switched rate equations is presented. Through numerical calculation, the relationship between the characteristics of Q-switched pulse delay, pulse width, sub-pulse sequence, and pump rate is analyzed to obtain the optimal pump-light duty cycle and effectively reduce the thermal effect caused by continuous-wave pump. Furthermore, the high-repetition-rate LD pump source is used in the experiment, and the accurate locking and control of output characteristics such as repetition rate, pulse delay, and the number of pulse trains of the passively Q-switched laser are realized by adjusting the pump parameters. When the duty cycles of 15.6-W pump power are 6.5%, 8%, and 9.65%, stable outputs of single pulse, double pulse, and triple pulse, respectively, are obtained, and the coupling resonance of pump pulse and laser pulse is improved. The experimental results are in agreement with the theoretical calculation.
  • Apr. 10, 2023
  • Laser & Optoelectronics Progress
  • Vol. 60, Issue 7, 0714003 (2023)
  • DOI:10.3788/LOP220459
Experimental Study on Femtosecond Laser Cutting Quartz Devices with Complex Shapes
Fanyan Zeng, Guangfu Zhou, You Wang, Chaofan Yan, and Yutang Dai
A femtosecond laser micromachining experiment was carried out on a quartz sheet to cut and separate devices with complex shapes from a quartz single crystal wafer. The relationship between the ablation aperture square and laser parameters was studied experimentally at high repetition frequencies of 50 kHz, 100 kHz, and 200 kHz. The etching thresholds of pure quartz at the corresponding repetition frequencies were 3.73 J/cm2, 3.45 J/cm2, and 3.2 J/cm2, respectively. The effects of femtosecond laser pulse energy, scanning speed, and other processing parameters on the cutting quality of microgrooves were studied. The laser pulse energy could change the surface morphology of the machined microgroove significantly. In addition, the machining effect was the best when the scanning speed was approximately 3.5 mm/s. Finally, using optimized process parameters, the resonant tuning fork devices with complex shapes were cut out on a 0.45 mm thick quartz wafer, which generally meets the expected quality requirements.
  • Apr. 10, 2023
  • Laser & Optoelectronics Progress
  • Vol. 60, Issue 7, 0714002 (2023)
  • DOI:10.3788/LOP220506
Polarized Dual-Peak Radiation Mechanism and Energy-Band Characteristics of InGaAs Self-Fit Well-Cluster Composite Structure
Qingnan Yu, Ke Li, Xinyu Wang, Jian Wu, Jianwei Zhang, Zijian Liu, Jiatong Xing, Ling Liao, Huixian Ji, Qing Wang, and Hui Li
ObjectiveIn this paper, a novel, highly-strained InGaAs/GaAs self-fit well-cluster composite (WCC) quantum structure was investigated. The WCC structure differs from the conventional InGaAs/GaAs quantum-well structure, which exhibits considerable potential for numerous laser applications. Presently, the conventional quantum well exhibits a quasirectangle well structure, wherein each well consists of a fixed amount of indium and a single strain type in the material system. The WCC structure with variable indium content and thickness in an InxGa1-xAs/GaAs system can yield remarkable results, thereby facilitating the development of new laser types. This structure is associated with the indium-rich cluster (IRC) effect, wherein the IRCs were typically regarded as defects to be avoided for the conventional InGaAs quantum-well structure; hence, its special optical characteristics remain neglected. The migration of the indium atoms to the WCC structure would reduce the indium content in the corresponding InGaAs regions, consequently generating normal and indium-deficient InxGa1-xAs regions with hybrid strain types in the InGaAs material and aid in the production of special polarized spectra with dual peaks. Therefore, it is crucial to reveal the underlying corresponding luminescence mechanism between dual peaks in different polarized spectra and multiple InxGa1-xAs materials. This work offers new avenues for the development of new types of devices.MethodsFirst, the InGaAs-based WCC quantum structure was developed via metal-organic chemical vapor-phase deposition. To generate the IRC effect by sufficient strain accumulation, the In0.17Ga0.83As/GaAs/GaAsP0.08 material system was designed as a periodic gain structure (Fig.1). The thickness of the In0.17Ga0.83As layer was designed to be 10 nm, because an InGaAs layer thinner than 10 nm is insufficient to obtain the IRC effect. Second, the luminescence mechanism of the WCC structure was studied by coating the WCC sample at a transmittance of T=99.99% at the dual facets to avoid the end reflection. Third, the polarized photoluminescence (PL) spectra in transverse electric (TE) and transverse magnetic (TM) modes were measured using a linear polarizer under varying carrier densities (N) in the range of3.6×1017-4.8×1017 cm-3. The special bimodal feature was observed in both TE- and TM-polarized PL spectra (Fig.2), which could be associated with the emissions from normal and indium-deficient In0.12Ga0.88As regions with varying band gaps. To analyze the different strain types, the lattice constant a(x) of the InxGa1-xAs material was obtained. Subsequently, the hybrid strain types in normal and indium-deficient InxGa1-xAs were obtained. The compressive and tensile strain occurred in the In0.17Ga0.83As and In0.12Ga0.88As layers, respectively. Further, according to the transition matrix element theory, the PL spectrum in TE polarization was primarily associated with the electron-hole recombination between the first conduction (C1) and heavy hole (HH1) subbands, whereas that in TM polarization was associated with the electron-hole recombination between C1 and light hole (LH1) subbands. Moreover, in the compressively-strained In0.17Ga0.83As layer, the HH1 subband lies above the LH1 subband. Conversely, the HH1 subband lies below the LH1 subband in the tensile-strained In0.12Ga0.88As layer. Finally, the underlying luminescence mechanism of the polarized spectra with dual peaks was revealed according to the above analysis.Results and DiscussionsThe TE- and TM-polarized PL spectra (Fig.2) reveal the special bimodal features, and they are marked using letters A and B, and C and D, which correspond to 1.27 eV and 1.33 eV and 1.35 eV and 1.31 eV, respectively. GaAs, In0.17Ga0.83As, and In0.12Ga0.88As yield lattice constant values of 5.65325, 5.72215, and 5.7019 ?, respectively. Accordingly, the In0.17Ga0.83As layer is subject to compressive strain such that the HH1 subband lies above the LH1 subband. Meanwhile, tensile strain is noted in the In0.12Ga0.88As layer such that the HH1 subband falls below the LH1 subband. According to the transition matrix element theory, the main peaks, which are marked by A and C in both TE and TM spectral curves (Fig.2), are attributed to the compressively-strained In0.17Ga0.83As layer; the corresponding TE photon energy is less than the TM photon energy. Meanwhile, the subpeaks marked by B and D (Fig.2) are attributed to the tensile-strained In0.12Ga0.88As region; the corresponding TE photon energy exceeds the TM photon energy. Moreover, the characteristics of the hybrid energy band of the InGaAs self-fit WCC quantum structure are obtained (Fig.3). For the compressively-strained In0.17Ga0.83As layer, the energy intervals from C1 to HH1 and LH1 bands are 1.27 eV and 1.35 eV, which correspond to the photon energy at peaks A and C, respectively. In the case of the tensile-strained In0.12Ga0.88As material, the energy intervals from C1 to HH1 and LH1 bands are 1.33 eV and 1.31 eV, which correspond to the photon energy at peaks B and D, respectively.ConclusionsIn this paper, a novel, highly-strained InGaAs/GaAs self-fit WCC quantum structure is investigated based on the IRC effect. The measured spectra in TE and TM polarizations reveal special features with dual peaks, which are attributed to the combination of different emissions produced by the normal and indium-deficient InGaAs active regions. According to the transition matrix element theory, the corresponding luminescence mechanism between the dual peaks in polarized spectra and InGaAs material with different indium content is revealed. Furthermore, the band characteristics associated with the conduction subband C1 and valence subbands of heavy holes HH1 and light holes LH1 are determined to reveal the underlying luminescence mechanism. The special WCC structure demonstrates a hybrid strain distribution, which indicates the simultaneous existence of compressive and tensile strains. The results of this study can greatly enhance the performance of InGaAs-based WCC-tunable lasers.
  • May. 25, 2023
  • Acta Optica Sinica
  • Vol. 43, Issue 10, 1014006 (2023)
  • DOI:10.3788/AOS222184