A Review of Beam Shaping Technology in Laser Welding Applications

 01 Introduction

Laser welding is widely used in fields such as aerospace and automotive manufacturing due to its high efficiency and precision. However, traditional Gaussian beams face challenges when meeting modern welding demands, particularly when processing high-reflectivity materials like aluminum and copper. The highly concentrated energy of a Gaussian beam can easily trigger keyhole instability and local overheating, leading to defects such as porosity and spatter. To overcome these limitations, beam shaping technology has emerged. By adjusting the power density distribution and shape of the laser beam (e.g., flat-top, ring, elliptical), this technology can effectively control molten pool dynamics, expand the process window, and significantly improve welding quality and stability. This article aims to comprehensively review beam shaping technology, bridging theory and practice to provide guidance for future industrial applications.

02 Full Text Overview

This article systematically reviews the research progress and application status of beam shaping technology in laser welding, focusing on beam morphology control methods, energy distribution characteristics, and their impact on physical welding processes. The structure is arranged as follows: First, the basic principles of laser welding and its application background in modern manufacturing are introduced, the limitations of traditional Gaussian beams are explained, and the research significance of beam shaping technology in improving welding stability and quality is highlighted. Second, beam shaping methods are systematically categorized, distinguishing between static and dynamic beam shaping techniques, with detailed introductions to the working principles and application characteristics of key optical devices such as diffractive optical elements (DOE), spatial light modulators (SLM), deformable mirrors (DM), and optical deflectors. Subsequently, from an application perspective, the mechanisms of different beam morphologies (Gaussian, elliptical, flat-top, ring, and multi-beam modes) in welding typical materials like aluminum alloys, copper alloys, and titanium alloys are summarized. The impact of beam energy distribution on molten pool behavior, keyhole stability, weld formation, and defect suppression is analyzed in depth. Finally, combined with recent development trends in multi-beam systems and dynamic beam laser technology, the application prospects of beam shaping in intelligent and adaptive laser welding are discussed, with suggestions for future research directions.

03 Application of Different Beam Shaping in Welding

3.1 Gaussian Beam

Figure 1 visually compares two technical routes. Figure (a) shows the non-contact mode proposed in this study, where the ultrasonic transducer moves with the nozzle to ensure constant energy input; Figure (b) shows the traditional contact mode where ultrasound is transmitted through the substrate. From the EBSD results of large-sized samples (f-h), it can be seen that the contact method (h) fails in the upper part of the sample, with grains coarsening into columnar crystals; while the non-contact method (f) maintains uniform fine equiaxed grains throughout the 100 mm height. Furthermore, the mechanical property data in Figure (i-k) shows that the non-contact method (LU) not only significantly improves strength but also has extremely low data dispersion, proving the high reliability of the process.

As laser processing technology has developed, Gaussian beams have become the most widely used beam mode in laser welding due to their excellent propagation characteristics and stable fundamental mode output. Their intensity distribution exhibits typical bell-shaped features, with high peak power density in the center, facilitating rapid material heating and large weld penetration depth. However, in the welding of high-reflectivity metals like aluminum alloys, excessive central energy density often leads to local overheating and violent evaporation, triggering keyhole instability, severe molten pool fluctuations, and the formation of defects such as porosity and spatter, thereby significantly limiting the process window and reducing weld quality.

To alleviate the adverse effects of uneven Gaussian beam energy distribution, researchers have proposed various improvement strategies such as quasi-Gaussian beams, beam oscillation, and Modulated Beam Welding (MBW). These methods redistribute laser energy in space or time, effectively reducing temperature gradients in the molten pool and stabilizing keyhole evolution while maintaining high penetration. Compared to traditional Gaussian Beam Welding (GBW), MBW typically exhibits lower porosity and more stable molten pool dynamics in aluminum alloy welding, as shown in Figure 1. Additionally, the periodic heat input introduced by MBW can reduce the weld cooling rate, helping to inhibit solidification crack formation and improve weld microstructure, further enhancing the overall quality of the welded joint.

Nevertheless, the inherent problems of excessive peak power density and uneven energy distribution in Gaussian beams remain key challenges in laser welding of high-reflectivity materials, providing important research directions for the subsequent development of beam shaping and energy control technologies.

Figure 1: (a) Schematic of Gaussian beam (b) Cross-sectional views of MBW and GBW welded specimens

 3.2 Elliptical Beam

Due to its asymmetrical energy distribution along the major and minor axes, the elliptical beam demonstrates superior process adaptability and stability compared to traditional circular Gaussian and flat-top beams in laser welding. Studies show that under deep penetration welding conditions, elliptical and rotating elliptical beams can significantly suppress spatter and widen the process window, especially in the welding of high-reflectivity materials like copper. By forming a wider remelting zone and more uniform evaporation behavior, the welding process becomes more stable. Compared to flat-top or circular Gaussian beams of the same minor axis size, the more concentrated energy input along the welding direction of an elliptical beam favors the formation of a wider weld with more stable penetration, thereby increasing adaptability to welding speed fluctuations. In the presence of assembly gaps, the elliptical beam, with its wider and more uniform molten pool morphology, can maintain stable welding under larger gap conditions, whereas traditional circular Gaussian beams are prone to molten pool shrinkage and bridging failure. Additionally, in titanium alloy welding, transverse elliptical beams can significantly broaden the molten pool front and smooth the transition of molten pool curvature, optimizing solidification behavior and improving weld formation quality. Figure 2 provides typical comparison results between elliptical beams and traditional circular beams in high-reflectivity material welding, intuitively demonstrating the comprehensive advantages of elliptical beams in molten pool stability, weld width, and process window expansion. Overall, the elliptical beam provides an efficient and engineering-potential beam shaping solution for enhancing welding stability, increasing gap adaptability, and regulating molten pool dynamics.

Figure 2: Top view of molten pools for beam shape C (Gaussian circular) and TE (Gaussian transverse elliptical) under different joint gap widths

 3.3 Flat-top Beam

Due to its nearly uniform energy distribution within the transverse cross-section, the flat-top beam can significantly improve heat input consistency in laser welding, effectively alleviating the severe temperature gradients and molten pool instability caused by the excessive central peak power density of Gaussian beams. The uniform power density allows the material to heat up more gently, facilitating the formation of stable keyhole structures and precise control of the heat-affected zone (HAZ), reducing the risk of local overheating while enhancing the controllability of the welding process. Compared to Gaussian beams, flat-top beams typically produce lower peak temperatures and shallower penetration, but their more stable energy deposition mechanism can significantly reduce keyhole oscillation amplitude and heat input fluctuations, thereby inhibiting keyhole collapse and porosity formation. In terms of spatter behavior, flat-top beam welding often exhibits high-frequency, low-amplitude molten pool oscillation characteristics, producing larger but lower-velocity spatter particles, and overall process stability is superior to Gaussian beams. Figure 3 shows typical comparison results of keyhole morphology and molten pool dynamic behavior under Gaussian and flat-top beam conditions, clearly indicating the advantages of flat-top beams in reducing oscillation amplitude, stabilizing keyhole structure, and controlling the heat-affected zone. Overall, flat-top beams are particularly suitable for application scenarios with high requirements for welding stability, heat input uniformity, and weld surface quality, although their relatively low peak power density also limits deep penetration welding capability to some extent.

Figure 3: Keyhole shapes under Gaussian and top-hat beam profiles. (b) Oscillation frequency and amplitude under Gaussian and top-hat beam conditions

 3.4 Dual-mode Beam

Dual-mode beam technology provides higher degrees of freedom for welding process stability and microstructural optimization by synergistically superimposing a central beam with a ring beam, allowing independent control of their power ratio and spatial distribution. Numerous studies have shown that compared to a single Gaussian beam or a pure ring beam, the dual-mode beam can significantly improve keyhole stability and molten pool flow behavior while maintaining high penetration. Its core mechanism lies in the "buffering" and redistribution of heat input from the ring beam to the central high-energy zone, effectively suppressing keyhole collapse, spatter, and porosity defects. In aluminum alloy welding, a reasonable core-ring power ratio is a key parameter for achieving high-quality welding, not only expanding the stable keyhole existence interval but also significantly reducing porosity and improving fusion efficiency. Additionally, by adjusting the ring beam power or introducing oscillation modes, the molten pool thermal cycle and solidification behavior can be further regulated, promoting grain refinement and reducing crack sensitivity. Figure 4 showcases the dual-mode beam welding process under different core-ring power ratios, intuitively demonstrating more stable keyhole and molten pool morphologies after optimizing power distribution, highlighting the engineering application advantages of dual-mode beams in high-stability laser welding. Overall, the dual-mode beam provides a highly promising beam shaping solution for low-defect, high-consistency, and high-performance laser welding.

Figure 4: Dual-mode 3 kW ring / 1.5 kW center laser welding process status. (a) Visualization of keyhole and molten pool. (b) Schematic of dual-mode 3 kW ring / 1.5 kW center aluminum laser welding. (c) Process stability diagram

04 Conclusion

1. Beam shaping technology has become one of the core driving forces in the modern laser welding field, marking a transition from coarse heat input to refined light-field regulation. Through precise manipulation of the laser focal spot shape and energy distribution, this technology has significantly enhanced welding process stability and weld formation quality. Currently, relying on advanced optical devices such as static Diffractive Optical Elements (DOE), dynamic Deformable Mirrors (DM), and Optical Phased Arrays (OPA), researchers can flexibly generate various complex spot modes including flat-top, elliptical, and ring beams. These customized beam profiles play a decisive role in optimizing heat input gradients, stabilizing molten pool flow, and improving keyhole dynamics, effectively suppressing common welding defects like porosity and spatter while ensuring uniform weld geometry and stable penetration. Notably, with breakthroughs in Coherent Beam Combining (CBC) and Direct Beam Combining (DBL) technologies, high-frequency beam modulation under high-power, single-mode, continuous-wave conditions has become a reality. This provides a new technical path for real-time matching of transient molten pool characteristics during welding, making microsecond-level process response possible under high-energy beams. Although challenges remain, the enormous potential of beam shaping technology in improving molten pool dynamics control precision and suppressing defects is unquestionable. Particularly in the field of ultrafast laser welding, Bessel beams generated by axicons or SLMs, with their long focal depth characteristics, can form filaments hundreds of microns long inside transparent materials, significantly improving focal depth tolerance and effectively solving the focus drift problem in complex curved surface welding.

2. Looking to the future, with the deep integration of photonics and artificial intelligence, beam shaping technology will experience explosive development in several dimensions:

1) Innovation in new optical materials and low-cost manufacturing processes: With progress in materials science, new optical materials with ultra-high damage thresholds, low scattering rates, and excellent thermal conductivity (such as diamond substrates, metasurface materials) will be introduced into high-power welding systems, providing a more solid hardware foundation for beam shaping. Simultaneously, as micro-nano manufacturing processes like nanoimprint mature, the manufacturing cost of high-performance optical elements is expected to decrease significantly, promoting their adoption in fields like automotive manufacturing and power batteries.

2) Deepening of multi-beam synergistic shaping technology: Future laser welding systems will no longer be limited to single-beam shaping but will shift toward multi-beam synergy. By precisely controlling the spatiotemporal interference or incoherent superposition of multiple laser beams, more flexible energy field distributions (such as dynamic power ratios between central and ring beams) can be constructed. This multi-beam technology can customize the thermal gradient of the molten pool according to the needs of different materials (e.g., high-reflectivity materials) and dissimilar material connections, achieving ultimate spatter suppression while significantly increasing welding efficiency.

3) Fusion of intelligence and adaptive closed-loop control systems: This is the most transformative development direction for beam shaping technology. Future beam shaping will evolve from "passive execution" to "active adaptation." By integrating machine learning (ML) algorithms and multi-sensor feedback mechanisms (e.g., molten pool vision monitoring, pyrometers, spectrum analysis), the welding system will build dynamic correlation models of "beam profile - molten pool state - weld quality." On one hand, deep learning networks can be used for inverse design of optical elements to quickly generate optimal phase maps that meet specific process requirements; on the other hand, a millisecond-level real-time closed-loop control system will be established to adjust beam shape and power distribution in real-time according to transient fluctuations in the molten pool, compensating for process instability. This "perception-decision-execution" integrated intelligent beam shaping technology will completely eliminate welding defects in complex industrial scenarios.

In summary, beam shaping technology is at a critical transition period from "auxiliary means" to "core process." It is not only a tool for transforming laser welding from coarse connection to precision manufacturing but also the cornerstone of the future intelligent manufacturing system. With breakthroughs in damage-resistant optical materials, falling costs of micro-nano manufacturing, and the implementation of data-driven intelligent control strategies, the synergistic effect of photonics and artificial intelligence will completely break traditional optical limitations, ushering in a new era of defect-free, adaptive, and highly efficient next-generation intelligent laser welding.

Original Link: https://doi.org/10.1007/s00170-026-17571-2

**--Cite the article published by 高能束加工技术 on April 22th, 2026, in the WeChat public account "High-Energy Beam Processing Technology and Applications."