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Dynamic characterization of beating sinusoidal wave oscillations in a thin-slice solid-state laser with coupled orthogonally polarized transverse modes
摘要： Dynamic characterization of self-induced beating sinusoidal wave (BSW) oscillations and related phenomena, which were previously explored in a thin-slice dual-polarization solid-state laser operating in the regime of incomplete mode-locking of orthogonally polarized transverse eigenmodes, namely, a quasi-locked state Otsuka (2018 Laser Phys. Lett. 15 075001), is performed in terms of the amplitude correlation coefficient and intensity circulation among various orthogonally polarized mode pairs. Polarization-dependent symmetry-breaking featuring a nonreciprocal intensity flow for different orthogonally polarized mode pairs operating in the BSW state are found. The singular state is hidden in a nonlinear system where a perfect mode-locked BSW state with a large amplitude correlation coefficient featuring reciprocal intensity flow is established for a transverse mode pair possessing particular polarization directions that are related to the intensity ratio of orthogonally polarized transverse eigenmodes. Self-organized chaos synchronization is shown to take place for such a single pair of transverse modes subjected to self-mixing modulations.
关键词： chaos synchronisation,transverse mode locking,beating sinusoidal wave (BSW) oscillation,dual-polarization laser
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Self-Healing Dynamically Controllable Micro-Comb
摘要： Micro-resonator-based frequency combs, or micro-combs, have gained considerable interest in recent years due to their many potential applications such as high-speed communication systems, spectroscopy and ultrafast optical clocks. Most micro-combs systems are based on laser pumped optical parametric oscillation and are typically non-self-starting, requiring a well-defined warm-up strategy involving smart control. An alternative approach to micro-combs is represented by the Filter-Driven Four-Wave Mixing (FD-FWM) laser, based on a nonlinear micro-resonator nested in a main amplifying fibre cavity. Although this system has demonstrated self-starting regimes, stable operation typically imposes a strict relation between the minimum free-spectral range (FSR) of the main-cavity and the Q-factor of the micro-resonator. The use of longer main-cavity fibre lengths (highly desirable for several positive features, such as a larger gain) results in unrecoverable unstable regimes, i.e. in super-mode instability, which arises from the existence of many oscillating main-cavity modes within each micro-resonator resonance. Here, we report a novel micro-comb scheme based on a three-cavitiy design shown in Fig. 1 (a). Our scheme exhibits the ability to spontaneously recover a set of unstable regimes in the FD-FWM laser. The basic concept is to introduce an intracavity periodic phase change via an additional short-loop fibre cavity, which effectively works as a low-Q, all-pass linear filter. Such a filter creates an irregular frequency-spacing among adjacent modes of the main-cavity loop, weakening the typical four-wave-mixing coupling between them. In sharp contrast to standard FD-FWM scheme, the system is tolerant to a significantly narrower spacing of the main-cavity modes. In the example, the total fibre length of the main-cavity is fixed to 20 metres, corresponding to a main-cavity FSR of 7.5 MHz - more than an order of magnitude lower than the micro-resonator bandwidth (~120MHz). This main-cavity FSR is generally very unstable at any pumping regime in the absence of the additional short-loop fibre cavity. An example of a stable mode-locking state with the properly chosen parameters is shown in Fig. 1(b)-(j). The experimental optical spectrum along with the corresponding intensity autocorrelation traces and RF spectrum are shown in Fig. 1 (b)-(d). A low background in the autocorrelation (AC) trace and a flat RF spectrum indicate the high stability of the generated micro-combs. A frequency comb-assisted spectroscopy is performed to accurately characterize resonances in the micro-cavity and the additional all-pass resonator filter, as well as the position of the oscillating comb lines (Fig. 1 (e)-(g)). The intra-cavity spectrum reveals that there is only a single longitudinal mode lasing within each micro-cavity resonance, regardless of the high modal density of the main cavity. Our analysis reveals that the introduced periodical spectral-phase modulation dominates the emergence of the oscillating modes.
关键词： Filter-Driven Four-Wave Mixing,micro-combs,frequency combs,optical parametric oscillation,micro-resonator
更新于2025-09-12 10:27:22
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Simulation of molten pool dynamics and stability analysis in laser buttonhole welding
摘要： Molten pool dynamics in laser buttonhole welding with wire feeding and laser beam oscillation were studied using computational fluid dynamics (CFD). The simulation results, such as temperature fields and molten pool velocities, were used to analyze the characteristics of molten pool dynamics. The dynamics in the rear part of the molten pool area were significantly reduced in comparison to those in the front when a buttonhole (a cavity in the molten pool) was present.
关键词： buttonhole welding,beam oscillation,laser welding,seam quality,numerical simulation
更新于2025-09-12 10:27:22
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Laser metal deposition of Ti-6Al-4V alloy with beam oscillation
摘要： One of the most prevalent problems of additive technologies is the improvement of process efficiency at the expense of increase in mass deposition rate and reduction of postprocessing time. Deposition rate can be improved by the modification of the shape and size of the molten pool through the optimization of laser beam power distribution. Time and cost of postprocessing depend on the surface roughness requirements and presence of macroscopic waviness. Beam oscillation can help to solve this problem. Laser metal deposition with linear beam oscillation was studied. Effects of numerous process parameters on pool shape and size was analysed by simulation. The heat conduction problem was solved analytically by Green’s function method. Temperature fields due to moving normally distributed strip heat sources were studied. It was established that on increasing the oscillation amplitude up to laser beam radius the heat flux of normally distributed strip heat source decrease rapidly to 53%. Greater the beam radius, the less effect of amplitude on the peak value of molten pool width and lower allowable oscillation amplitude. Microscopic examination revealed that beam oscillation promotes obtaining smooth wall surface without any macroscopic waviness.
关键词： surface waviness,titanium alloy,beam oscillation,temperature field,laser metal deposition
更新于2025-09-12 10:27:22
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Influence of oscillation frequency and focal diameter on weld pool geometry and temperature field in laser beam welding of high strength steels
摘要： As weld pool geometry and thermomechanical strains are known to affect formation of solidification cracks, the influence of a superimposed beam oscillation on these characteristics is investigated for this paper. In this context the effects of the oscillation frequency and focal diameter on the weld pool and temperature field are determined by means of infrared thermography. As a result an increase of the weld pool size for larger focal diameters and a more even shape of the seam edges for higher frequencies can be identified.
关键词： infrared thermography,beam oscillation,laser beam welding,solidification conditions,temperature field,weld pool geometry,high strength steels
更新于2025-09-12 10:27:22
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Influence of focal spot diameter and beam oscillation on the process efficiency of laser beam welding utilizing a direct diode laser
摘要： Costs of power consumption, efficiency improvement and a green image are increasing issues for automotive manufacturers. One possibility to reduce energy consumption is to increase process efficiency of the established laser beam welding. For this reason this contribution examines whether the laser output power of a direct diode laser can be reduced whilst keeping weld seam volumes constant. This is realized by a reduced spot diameter from initial 664 μm to 368 μm in combination with beam oscillation in order to generate blind seams in 22MnB5 and DC01 steel. It is shown that energy consumption can be reduced significantly.
关键词： Energy efficiency,Oscillation,Focal spot diameter,Direct-diode laser,Automotive
更新于2025-09-12 10:27:22
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Laser welding of hidden T-joints with lateral beam oscillation
摘要： Welded T-joints usually have one- or two-sided fillet welds which were carried out from the web-sheet side. However, accessibility to the joint from the web-sheet side is not always given for any construction. Therefore, T-joints sometimes have to be welded from the face-sheet side which can be very challenging. These so-called hidden T-joints require accurate positioning and fixing of the web-sheets. Flanges help to increase the process reliability, but they are no guarantee for defect-free welds especially in case of laser welding without filler metal. This study addresses the improvement of the process reliability for welding hidden T-joints from the face-sheet side. Therefore, two different methods were investigated: 1) lateral beam oscillation and 2) local thickening of the edge of the web-sheet. Welding experiments comprise both aluminum sheets (EN AW-1050) and uncoated DC01 steel sheets. The results demonstrate that the locally thickened edge of the web-sheet is beneficial to compensate misalignments of the travel path of the laser beam and of the positioning of the web-sheet. In contrast, beam oscillation only improved the steel weldments in terms of compensating misalignments. Best results were achieved for 1.8 mm oscillation width at 200 Hz.
关键词： laser welding,process controll,beam oscillation
更新于2025-09-12 10:27:22
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Real-time spatter detection in laser welding with beam oscillation
摘要： Spatter formation is a longstanding issue in laser welding. This research addresses this topic and proposes a machine vision algorithm executed on a graphics processing unit to detect spatters in real time. Using this approach, a control system detecting spatter at a rate of 1 kHz and with a resolution of 900 x 900 pixels was implemented. Based on an experimental series, it is shown that the variation of the process parameters has a significant influence on the formation of spatter. It was also possible to quantify the variance of the spatter formation for a given set of process parameters.
关键词： machine vision,beam oscillation,laser welding,spatter formation,graphics processing unit
更新于2025-09-12 10:27:22
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Effect of Laser Beam Oscillation on Laser Welding–Brazing of Ti/Al Dissimilar Metals
摘要： Ti4Al6V and 6061 Al dissimilar metals were butt welded by the laser oscillating welding method. The e?ects of laser o?set, oscillation frequency, and energy distribution on the formation, microstructure, and tensile properties of dissimilar metal joints are discussed in detail. The experimental results show that the Ti6Al4V was micro melted with a laser o?set of 1.1 mm, and a large number of intermetallic compounds (IMCs) were formed on the side of the Ti6Al4V. Additionally, there were some porosity defects in the fusion zone (FZ) due to an inappropriate laser oscillation frequency. When the laser o?set was increased to 1.2 mm, the IMC distribution was uniform and the thickness was controlled below 2 μm. The porosity defects in the FZ decreased and the tensile strength of the joints increased signi?cantly. The maximum value of tensile strength reached 173 MPa at a laser frequency of 28 Hz.
关键词： dissimilar metals,tensile properties,microstructure,laser beam oscillation,Ti/Al butt joint
更新于2025-09-12 10:27:22
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Light-fuelled freestyle self-oscillators
摘要： Self-oscillation is a phenomenon where an object sustains periodic motion upon non-periodic stimulus. It occurs commonly in nature, a few examples being heartbeat, sea waves and fluttering of leaves. Stimuli-responsive materials allow creating synthetic self-oscillators fuelled by different forms of energy, e.g. heat, light and chemicals, showing great potential for applications in power generation, autonomous mass transport, and self-propelled micro-robotics. However, most of the self-oscillators are based on bending deformation, thereby limiting their possibilities of being implemented in practical applications. Here, we report light-fuelled self-oscillators based on liquid crystal network actuators that can exhibit three basic oscillation modes: bending, twisting and contraction-expansion. We show that a time delay in material response dictates the self-oscillation dynamics, and realize a freestyle self-oscillator that combines numerous oscillation modes simultaneously by adjusting the excitation beam position. The results provide new insights into understanding of self-oscillation phenomenon and offer new designs for future self-propelling micro-robots.
关键词： Twisting,Bending,Micro-robotics,Contraction-expansion,Liquid crystal network actuators,Light-fuelled,Self-oscillation
更新于2025-09-12 10:27:22