High-power fiber laser welding has proven to be the most effective high-speed automatic welding technology. It is generally believed that the keyhole structure contains a large amount of welding quality information. Its behavior and instability are one of the causes of welding quality defects, especially the porosity. In this paper, we propose a fast-online detection method for high-power fiber laser welding. In view of the characteristics that the behavior and stability of the keyhole have an important impact on the welding quality, the real-time image of the keyhole is taken during the welding process, and the image is binarized through the adaptive threshold selection, and the maximum connecting area is selected to quickly get the contour of the keyhole. By combining the global convexity of the keyhole contour with the local angularity on the micro level, the support vector machine model is trained as the input data. Experiments show that the classifier has high accuracy. The combination of these features can characterize the pore defects, quickly and real-time find potential pores, reduce the cost and time of later detection, and explain abnormal metal flows in and out of keyholes when defects occur.
Laser Direct Part Marking (DPM) technology is a marking technology that has proved to be feasible in the industrial environment, and can be highly automated and environmentally friendly. It has become the preferred method for completing product marking in industrial product traceability. In this paper, MOPA laser marking system with flexible control and wide adjustment range of laser parameters is used for experiment. According to ISO/IEC TR 29158 bar code technology standards, the influence of laser processing parameters(such as laser peak power, laser pulse energy, laser power, filling space, scan speed, etc.) on the quality (such as symbol level, symbol contrast, print growth, etc.)of laser direct marking DM symbol is studied. By optimizing the laser processing parameters, high-quality DM symbol on the surface of AL2024 is realized.
A portable laser-induced fluorescence detector based on module design, which includes an excitation source of 405nm fibre-coupled stable spectra diode laser,a fluorescence collection module based on a fibre fluorescence optical fibre probe with an improved confocal optical arrangement,a fluorescence analysis module of Mini Fiber Grating Spectrometer. The advantages of the detector is compact, small size, low cost, high sensitivity, easy to operate.The performance of the detector is evaluated by fluorescein sodium. Water Raman peak S / N is 935.67. LOD of fluorescein sodium was 1.9×10-11g/L.Correlation of the fluorescence intensity was 0.9998 with the concentration from 10-10 to 10-12 g/L, the linear dynamic range was over 3 order. RSD of the fluorescence wavelength and intensity repeatability was 0.14% and 3.36% respectively. It is concluded that the 405nm LIFD has highly sensitivity,good repeatability,a wide linear range.
A novel high average power double slab laser with hybrid resonator is presented. By analyzing and simulating thermal distribution of the face-pumped slab medium, it is found that the thermal distortion of wave front caused by the non-uniform temperature distribution of the laser gain media can be self-corrected in this structure. According to the analysis of the slab thermal distribution, a hybrid resonator is presented. Using a plane-wave or k-space expansion together with the fast Fourier transform, mode patterns, power outputs from the laser are calculated. Far-field characteristic and beam quality of these modes are discussed. And besides, by comparing the properties of off-axis hybrid resonator with the on-axis hybrid resonator's, the off-axis hybrid resonator can produce better quality beam.
A novel scheme of the face-pumped double-slab Nd:YAG slab medium cooled by liquid with different temperatures on both sides is proposed. In this structure the thermal distortion of wavefront caused by the non-uniform temperature distribution in the laser gain media can be self-compensated. According to the running mode, the model of the slab medium’s temperature distribution and stress are presented. The analytic solutions for the model are derived. Furthermore, the numerical simulations with pulse pumping energy of 10J and repetition frequencies of 500Hz and 1000Hz are calculated for Nd:YAG laser medium. The simulation results show that the temperature gradient remains the approximative linearity, and the heat stress is in the range of stress extremes. Then the absorption coefficient is also discussed. The result indicates that the doped concentration cannot be too larger for the high repetition frequency laser. It has been prove that high repetition frequency, high average output power of the order of kW of Nd:YAG slab laser with high laser beam quality can be achieved in this structure.