The Galvanized steel sheet is used as the automotive body material, and the evaporation of zinc into the weld seam will cause welding defects during the laser welding process. The multi-point laser beam has great development potential in automobile industry, because it can effectively reduce the integration of the galvanized layer into the weld seam during welding. In this paper, a panda-shaped three-point beam (panda beam) is proposed to replace the original single beam used in welding and three methods to realize the panda beam have been discussed. The beam splitting of the diffraction grating is performed, and the three, five and four beam-splitting ratio Daman gratings are obtained but with relatively high energy loss. Additionally, based on the theory of grating diffraction, a panda beam has been obtained by splitting the 4kW incident laser through the Bragg grating. The single front beam radius is 0.6mm with a power of 1.1261kW, and the distance between the two front beams is 3.8mm. The radius of the main beam is 1mm with a power of 1.7168kW, and the distance from the front beam to the main beam is 9.7mm. Lastly, based on the beam splitting theory of geometric optics, the multi-point beam and the panda beam are realized by the ridge reflector with an energy loss of 14.09%, which shows the great advantage of laser beam splitter compared with multi-light source structure in practical application. When welding with the panda beam, two functions of zinc coating and solder melting are carried out respectively, which can avoid zinc vapor entering the molten pool and improve the welding quality
As a mid-infrared laser with large magnification and high beam quality, carbon dioxide lasers are often used as intermediate amplifiers in picosecond terawatt laser systems. With the combination of gas discharge and optical pump, the gain spectrum in 10μm can be greatly improved. In this paper, a numerical model is set up to describe the laser amplification and kinetic processes, based on six-temperature level structure, in hybrid pump CO2 laser amplifier system. The influences of the pump power and its amplification results compared with conventional CO2 laser are simulated and discussed. Such a hybrid pump CO2 laser amplifier is very promising in improving output pulse quality by reducing the pulse split.
KEYWORDS: Simulation of CCA and DLA aggregates, Semiconductor lasers, Diffraction, Diffraction gratings, Laser systems engineering, Reflectors, Output couplers, Optical engineering, Collimation, Collimators
An efficient spectral beam combining (SBC) system for diode lasers with compressed spectral interval is proposed and demonstrated experimentally. This structure consists of a transmission grating and a reflector paralleled to the grating, which can make the beam diffracted twice by only one transmission grating. The advantage of this configuration is that it compresses the spectral interval of the output beam into half compared to the traditional single-grating setup and improves the utilization rate of the grating element compared to the previous double grating system. The experimental results demonstrate that the spectral intervals of a 3-emitter diode laser array (DLA) and a 5-emitter DLA with traditional single-grating structure are 4.36 and 4.69 nm, respectively. In the modified system, the spectral intervals of the same DLA with 3 and 5 emitters are 2.15 and 2.35 nm, respectively, which shows that this method can compress the spectrum interval effectively and will be promising for a practical SBC system.
A Nd : YAG / Cr4 + : YAG composite crystal passively Q-switched laser with high-output pulse energy is studied both theoretically and experimentally. According to the characteristics of flash lamp pump, the rate equations of nonuniform pump are established. The pulse interval, pulse energy, and pulse width of the output pulse train are analyzed accurately by nonuniform pump. The experimental parameters are optimized by numerical simulation, with Cr4 + : YAG saturable absorber initial transmittance of 14%, output coupling mirror reflectivity of 30%, and cavity length of 9.7 cm. Under the same conditions, the maximum static energy is 954.34 mJ without Q-switch. An output pulse train with four pulses can be obtained at the same pump condition in experimental study. The four pulses energy are 156.5, 151, 149.74, and 145.76 mJ in turn with corresponding intervals of 20.81, 24.16, and 46.03 μs. The average pulse width is 5.72 ns. The Q-switch efficiency is 63.2%. The energy of the four pulses decreases, the pulse interval increases, and the pulse width is basically unchanged. The nonuniform pump theoretical and experimental results are in good agreement.
Ultrafast fiber laser has been widely used for spreading the extensive industrial applications and exploring the optics nonlinear dynamics. Here, we report a bidirectional fiber laser passively mode-locked by nonlinear polarization rotation (NPR) technique, supporting the emission of multi-state solitons. For the first time to the best of our knowledge, a Φ-shape auxiliary cavity based on chirped fiber Bragg grating (CFBG) is proposed to simultaneously introduce large anomalous and normal dispersion into the lasing oscillator. As a result, different dispersion distributions are achieved intra-cavity, respectively corresponding to counter propagating directions. Thus, conventional soliton (CS) and dissipative soliton (DS) are respectively generated in clockwise and counter-clockwise propagating directions. The results could benefit multifunctional ultrafast fiber laser system, which is potentially set for many practical applications as well as the study of soliton dynamics.
High power transverse flow CO2 laser was used to scan the brazing alloy and diamond grits, the paper studied the influence of laser power on brazing layer combination performance and diamond grits thermal damage, analyzed the thermal damage mechanism of laser brazed diamond and combination mechanism of brazing layer and diamond grits. The research result showed that laser power is one of factors for diamond thermal damage, under high laser energy input, oxidation took place between diamond grits and oxygen outside, diamond would be oxidized all along on the condition of branch gas pressure about free equation until the balance established between diamond and oxide, during this process, diamond grits would be carbonized or burn out and gasify.
As a novel cw hybrid laser, the lasing wavelengths lie in the near-IR range and for in the transparency window of the terrestrial atmosphere, diode pumped metastable rare gas lasers (DPRGLs) can be considered as a beam conversion system that produces a high-quality laser beam by passing a diode laser with poor beam quality through the rare gases medium at room temperature. In this paper, a numerical model is set up to describe the kinetic processes and the laser amplification, based the five-level structure, in DPRGL amplifier (DPRGA) system. Influences of the pump power and the cell length on the output laser are simulated and discussed. Such a master oscillator power amplifier (MOPA) system is very promising in achieving high output power for low power DPRGL radiation.
Polarization selective devices are commonly utilized as rear mirrors to generate high power cylindrical vector (CV) beams in the resonators. The modes of these polarization sensitive resonators are very significant for the generation and application of CV beams. Upon the scalar eigenvector method, a vectorial eigenvector method (VEM) was used to compute the CV modes of polarization-selective resonators. Then, different polarization dependent resonators were simulated with the VEM. We can find that both mode TE01* and mode TEM00 are the eigen modes of polarization sensitive symmetric confocal sphere resonator and when Rte=0.99 and Rtm=0.93, TE01* most possibly appears in the cavity with polarization sensitivity due to its lowest loss. In addition, the VEM was used to guide our design of a 45-degree three-fold cavity structure for high power radially polarized laser. The axicon mirrors with azimuthal polarization selection and four λ/4 phase shifters are used to obtain the output of radially polarized light.
A practical plane-cone resonator for the high-power, transverse-flow CO2 laser has been designed. The output characteristics of the plane-cone resonator are researched experimentally and compared with a traditional plane-concave resonator. The output mode is an approximate TEM03 mode with a resonator length of 3 m and an equivalent aperture radius of 30 mm. The beam divergence angles of the plane-concave resonator and the plane-cone resonator are 2.6 and 2.1 mrad, respectively. In the experiments that studied the misalignment characteristics, the miss rates of the output beam are 16% and 8%, respectively, when the misaligned angles of the output mirrors are both 0.41 mrad. Also, the miss rates are 20% and 5%, respectively, when the misaligned angles of the reflectors are both 0.41 mrad. The results indicate that this plane-cone resonator has a better anti-misaligned stability than plane-concave resonators.
A positive branch unstable-waveguide hybrid resonator has been designed for a RF-excited slab CO2 laser of 100 W level. The output beam mode and the propagation characteristics in the two directions of unstable and waveguide were investigated by numerical and experimental methods. The results show that the output beam was collimated in the unstable direction, and was an approximate fundamental mode in the waveguide direction with a divergence angle of 12 mrad. The output power decreased by 50% with the misaligned angle of the tail mirror of 1.5 mrad, and was close to 0 with the misaligned angle more than 3 mrad.
The output beam characteristics of a toric concave mirror laser resonator are discussed. The experiments of the toric concave mirror laser resonator, the plane-concave stable resonator, and the parallel plane resonator with the same Fresnel number of 17.25 are done on HUST2000 high-power transverse flow CO2 laser. The output laser beam of 1820 W with a doughnutlike distribution, the output laser beam of 1860 W with a Laguerre-Gaussian (LG) transverse electromagnetic modes (TEM)60 distribution and the laser beam of 1000 W with are approximate LG TEM30 distribution are obtained, respectively, at the same discharge current of 5 A. The scanning welding test on 316L stainless steel shows that the output beam of the toric concave mirror laser resonator can used for deep penetration laser welding, the welding depth is >2.4 mm at a velocity of 1 m/min, whereas that of other two resonators cannot be used for deep-penetration laser welding because of low beam quality or low output power. This resonator can be used in the laser with a large transverse gain size to improve beam quality greatly without sacrificing the output power.
Aiming at the 3kW transverse flow CO2 laser, a hybrid power system and its compatibility with pin-to-flat discharge
structure has been studied in the paper, CW/pulse output laser has been obtained. The DC high voltage output consists of
switching power supply and main transformer, and three-phase SCR power supply is replaced by switching power
supply. The pulse parameters are frequency from 0Hz to 1kHz, duty ratio from 0% to 100%. The pulse waveform of
discharge voltage and discharge current are measured. The results show that row resistances have been moved, pin
resistances have been reduced to 10kΩ. When the pressure P is 8.45kPa, the highest efficiency of electric-photo
conversion of laser is up to 14.8%.The laser output power can be modulated in the state of continuous and pulse at
arrange of 3kW. Then particular laser cladding is performed on the airplane engine blade, the laser cladding crack
produced in continuous state is solved, and the heat-affected zone of laser cladding is also narrowed.
Aiming to the special high power CO2 laser surface treatment, the paper developed the integrated control system based
on S7-200 PLC of transverse flow CO2 laser. The selection of key technology and components, detection and control of
signals, integrated control of complete circuit, technology of human machine interface and process control of system
have been researched. Double closed loop power control system was realized, so that the stability of the laser power was
in ±2%. Also, the giving power can be controlled by the laser controller or by the processing machine, thus, the users
can control the laser more efficiently when processing. A series of experiments have been performed on 5kW transverse
flow CO2 laser, the output laser power was stable at discharge current of 9A for 8 hours, and the maximal power was
5.42 kW. The new type of transverse flow CO2 Laser with Integrated Control System has been applied for special laser
cladding with power-modulating on the metallic surface of the oil industry production.
By means of the Collins formula and finite-element method, diffraction integral equation of the square resonator with
spherical mirrors is transformed to the finite-element matrix equation, mode-fields of the square aperture resonator is
calculated. Experiment with square aperture resonator is done on HUST2000 high power transverse flow CO2 laser. The
results show that a square multi-mode beam with uniform comparatively intensity appeares in near field distribution.
Laser quenching on 45# steel is done by using the square multi-mode beam and general circle beam. The hardened case
caused by the square multi-mode beam is more uniform than general circle beam.
According to the mode and focus characteristic of the laser beam, a laser focus mirror is developed based on the designing principle and method of analytical function non-spherical focus mirror(ANSFM), its designing and focus characteristic is analyzed systematically. The result indicated: With this design technique, numerous iterations and experienced parameters are not needed, comparing with the designing of high order multinomial non-spherical focus mirrors(HONSFM). Once the focal length f ,diameter D and refraction index n of mirror material are known, the analytical non-spherical focus mirror can be obtained accurately and fast. The designed mirror has flat surface and large machine tolerance, which makes it easy to be manufactured and tested. The focusing spot diameter(FSD) of the designed mirror is φ11.4μm for a parallel beam. The experimental results show that FSDANSFMHONSFM
A series of technological parameters in controlling plasma in deep penetration CO2 laser welding at an arrange of power level from 1 kW to 5 kW were investigated by using a precise declined-blow system by which the gas-assisting pressure and nozzle position can be precisely adjusted for various gas species and laser power levels. The mechanism of plasma-control by assist gas was also clarified on the basis of pressure measurement of assist gas, estimation of metallic vapor pressure in the cavity, and monitoring of plasma brightness by using phototransistors. It was found that the effect of assist gas on penetration depth can be divided three regions with the change of the assist gas pressure. No matter what gas species were used, only is the gas pressure slightly higher than the vapor pressure, plasma can be suppressed by forcing the vapor to flow away from the incidental laser beam along the cavity rear wall, then optimum weld beads can be obtained.