Waterjet cutting and laser cutting are now widely used methods, and they’ve proven to be the most effective cutting solutions in the industry. However, the quest for even better cutting techniques continues—especially when it comes to processing precision metal components or cutting advanced materials. This has led to the development of a unique waterjet-laser cutting technology. With the emergence of new materials like carbon fiber-reinforced polymers and ceramic matrix composites, machining these innovative materials has become increasingly challenging. Both waterjet and laser cutting have their limitations, but to tackle these challenges head-on, waterjet-laser cutting technology was introduced. This hybrid method combines the precision of lasers with the power of a "thin" water jet. The water jet, much like a conventional optical fiber, precisely guides the laser beam during the cutting process. At the same time, the water jet continuously cools the cutting area and efficiently removes debris generated during the operation. When the laser beam is focused, it creates an intense energy stream that propels water forward through a pressurized chamber, concentrating into a fine nozzle. Finally, the laser beam exits the nozzle alongside the water flow. Notably, this water jet contains no abrasive particles—meaning the cutting action relies primarily on the laser itself. The water serves as a crucial medium: it helps direct the laser beam without causing dispersion, concentrates the laser’s energy for faster cutting, and also plays a key role in cooling the material and clearing away cuttings. From the nozzle all the way to the workpiece, the laser beam remains tightly confined within the water column, reflecting off its walls as it travels—a principle similar to how light is transmitted through optical fibers. Thanks to this unique mechanism, the laser beam can maintain its focus over distances of up to 10 cm, enabling clean, precise cuts without the need for additional focusing or distance adjustments. Initially developed for semiconductor wafer cutting, this technology has steadily evolved and expanded into various industries, including medical device manufacturing, watchmaking, gas and jet engine turbine blade production, mechanical processing of semiconductor equipment, and even the fabrication of ultra-hard tools. For manufacturers, waterjet-laser cutting offers significant advantages: it boosts production speed, accommodates a wider range of materials, delivers superior reliability, and ensures higher cutting quality—all while driving down overall costs. As more advanced materials continue to enter the market, the versatile and efficient features of waterjet-laser cutting will likely lead to even broader adoption across diverse industries.

It is well known that copper and its alloys are extremely challenging materials to weld, for the following reasons: Copper and its alloys have relatively high thermal conductivity, making it difficult to achieve melting. As a result, significant amounts of heat are required not only to compensate for heat dissipation but also to locally concentrate intense energy, which ultimately leads to thermal stresses and, in turn, defects such as warping or distortion. Additionally, dissolved oxygen tends to form oxides and porosity within the weld. Moreover, copper exhibits low absorption rates for laser beams—particularly when the laser wavelength exceeds 700 nm, where absorption drops below 3%. Auwal and colleagues previously conducted a comprehensive review on laser welding of copper alloys, thoroughly addressing the challenges associated with using these materials in engineering applications. ▲ Figure 1: The top image illustrates a schematic diagram of laser beam oscillation welding technology, while the bottom shows top and cross-sectional views of weld beads produced under varying laser power conditions. Welding parameters include: welding speed = 4.0 m/min, focal position = 0, rotation diameter = 1.0 mm, rotation frequency = 100 Hz, and beam path set as circular. The welding direction progresses from left to right. Copper and its alloys are notoriously difficult to weld due to their high thermal conductivity, which makes melting particularly challenging. To counteract this, substantial heat input is needed to offset heat loss and achieve localized, intense heating, often resulting in thermal stresses and subsequent deformation or other defects. Furthermore, dissolved oxygen readily forms oxides and gas porosity during the process. Another key issue is the material’s poor absorption of laser energy, especially at wavelengths above 700 nm, where absorption rates fall below 3%. Auwal and colleagues previously conducted a comprehensive review on laser welding of copper alloys, thoroughly addressing the challenges associated with using these materials in engineering applications. ▲ Figure 2: Top and cross-sectional views of weld beads obtained at different welding speeds. Laser parameters remain consistent: laser power = 4000 W, spot focus position = 0, beam oscillation diameter = 1.0 mm, beam oscillation frequency = 100 Hz, and beam path set as circular. Welding proceeds from left to right. Currently, most research on laser welding copper alloys has focused on pulsed laser spot welding. However, exploring the feasibility of continuous laser welding for thick copper plates could open up new possibilities for applications in heat exchangers, high-power wing converters, and equipment requiring excellent electrical and thermal conductivity. ▲ Figure 3: Schematic illustration (top view) of how the laser beam interacts with copper material during movement, with each color representing a single cycle T. To overcome the inherent welding challenges, various strategies have been developed to produce continuous, deep-penetration butt welds while effectively controlling welding defects, microstructure, residual stresses, and distortion. Among these approaches, laser beam oscillation—or "swinging"—has yet to be widely applied to copper laser welding, despite its successful implementation in welding aluminum alloys and titanium alloys, both of which are somewhat easier to join than copper alloys. ▲ Figure 4: Top and cross-sectional views of weld beads obtained under different laser spot focus positions. Welding parameters include: laser power = 4000 W, welding speed = 4.0 m/min, rotation diameter = 1.0 mm, rotation frequency = 100 Hz, and beam path set as circular. Welding proceeds from left to right. Laser beam oscillation expands the area of interaction between the laser beam and the material, increasing the weld width while simultaneously reducing the overall heat input required during the welding process. In highly reflective materials like copper alloys, beam oscillation helps elevate local material temperatures and enhances laser absorption efficiency. This results in improved energy utilization, as reflected energy is minimized during welding. Additionally, one of the key advantages of oscillating laser heads is their ability to precisely manage thermal gradients and maintain stable keyhole formation, leading to reduced welding defects and smoother weld surfaces. ▲ Figure 5: Top and cross-sectional views of weld beads obtained under varying laser beam oscillation rotation diameters. Laser parameters remain constant: laser power = 4000 W, welding speed = 3.0 m/min, spot focus position = 0, rotation frequency = 100 Hz, and beam path set as circular. Welding proceeds from left to right. The dynamic movement of the laser beam can take on diverse shapes, and variations in its oscillation patterns enable more effective temperature management throughout the welding process. This, in turn, ensures gentler heat input and cooling rates, as well as more gradual thermal gradients. Consequently, laser beam oscillation not only minimizes welding defects but also preserves the integrity of the post-weld microstructure—avoiding issues like those previously reported by Kraetzsch in Cu/Al dissimilar material welding, or those encountered by Wang et al. during Al alloy welding. ▲ Figure 6: Top and cross-sectional views of weld beads obtained using different beam trajectories. Laser parameters include: laser power = 4000 W, welding speed = 4.0 m/min, spot focus position = 0, and rotation diameter = 1.0 mm. Welding proceeds from left to right.Laser beam oscillation welding—specifically, beam oscillation technology—is now becoming increasingly feasible for a wider range of applications. Khodabakhshi and colleagues successfully demonstrated the use of beam oscillation to achieve dissimilar joining between aluminum and magnesium alloys. They observed that crack sensitivity could be effectively controlled under appropriate laser motion conditions. These findings were further validated by Shah, whose research confirmed that beam oscillation significantly enhances the quality of dissimilar material joints between aluminum and magnesium. Moreover, the formation of porosity during laser beam oscillation welding of Al-Mg alloys was also suppressed, providing additional evidence of the promising potential of this innovative technique in the welding process. Additionally, studies conducted by Jiang et al. and Li et al. revealed that grain refinement in the molten zone could be clearly observed when beam oscillation was employed. The intricate movement of the laser beam during oscillation allows precise control over both the peak temperature and thermal gradients within the material during welding. ▲Figure 7. Optical images of laser-welded copper alloy: (a) Macroscopic view of the weld joint; (b) Base material; (c) Heat-affected zone; (d) Molten zone Since laser oscillation welding remains an emerging technology, current applications are primarily focused on welding steel and aluminum. There is still a notable lack of understanding regarding its effectiveness for welding copper alloys. This study specifically investigates how beam oscillation parameters influence weld bead morphology and microstructure in laser welding of copper alloys, aiming to gain insights into how beam oscillation affects melt pool dynamics, weld bead geometry, cross-sectional features, and ultimately, the resulting microstructure. ▲Figure 8. (a) and (b) Schematic diagrams illustrating the beam oscillation (wobble) welding process; (c) Cross-section of the molten zone; (d) Comparison between the actual weld bead boundary and the theoretically predicted boundary ▲Figure 9. Simulation results showing velocity vector maps of the top surface of the molten pool at different beam oscillation frequencies, with the keyhole remaining stationary at the same position (test unit: m/s): (a) 30 Hz; (b) 50 Hz; (c) 70 Hz; (d) 90 Hz; (e) 0.50 mm; (f) 0.75 mm; (g) 1.00 mm; (h) 1.25 mm. (Material: SUS304 stainless steel) Key Research Findings Laser beam oscillation (wobble) technology has proven highly effective in welding copper alloys, yielding the following positive outcomes: When welding parameters are optimally adjusted, no defects such as porosity or cracking occur—critical factors that directly impact the performance and reliability of copper alloy components. Using a multimode fiber laser, defect-free welding of 1.5-mm-thick copper alloy sheets can be achieved under the following conditions: a welding speed ranging from 3.5 to 4 m/min, with a circular welding pattern characterized by a rotational diameter of 0.6–1 mm and a frequency of 100 Hz. Importantly, beam oscillation has a significant positive impact on the welding process, facilitating a transition from the keyhole mode to a more stable conduction-based welding regime. Without beam oscillation, samples exhibited numerous defects, including porosity, spatter, and voids, primarily due to the instability of the keyhole. Increasing the rotational diameter and frequency enhances overlap between adjacent weld beads, thereby reducing interaction time and diminishing the weld penetration depth. However, this approach also leads to fewer surface defects, such as spatter and surface voids. Notably, the asymmetrical nature of the welding process—caused by the rotating laser beam—results in incomplete fusion at the bottom of the weld, particularly at higher rotation frequencies. At higher welding speeds, while surface voids and spatter are minimized, the overall weld penetration depth decreases significantly. After testing various beam motion trajectories, it was determined that a circular motion path delivers the best results. Finally, unique microstructural features were identified within the molten zone of the weld, characterized by distinct circular bands formed along the solidification front under oscillating laser conditions. These circular patterns closely resemble the boundaries created by the interaction between the laser beam and the material. Due to the periodic oscillation effect, the laser beam spends more time interacting with the molten pool during each rotation cycle, allowing for extended exposure and enhanced heat transfer. As a result, partial melting occurs repeatedly during each rotation, leading to the formation of circular molten lines. Subsequent solidification then follows an epitaxial growth pattern, similar to what is observed in additive manufacturing processes involving copper alloys—but in this case, the phenomenon is actually attributed to the presence of Cu₂O phases.

Solid-state optical cooling of both liquids and solids can be achieved through a process known as anti-Stokes fluorescence. When certain materials are optically excited within an appropriate wavelength range, they emit fluorescence whose average energy exceeds that of the pump photons. This allows the material to extract energy in the form of phonons, leading to cooling without significant heat dissipation. Such phenomena are primarily observed by doping trivalent rare-earth elements into carefully selected crystalline or amorphous host matrices, designed to minimize detrimental heat-generation mechanisms that would otherwise overshadow the ASF cooling effect. The first solid-state cooling with temperatures as low as 91 K has been demonstrated in highly Yb³⁺-doped, purified YLiF₄ crystals via the anti-Stokes fluorescence mechanism. ASF cooling is particularly beneficial for high-power fiber-based lasers and amplifiers, where external coolers are typically used to dissipate heat from these devices. These coolers circulate air or water around the laser gain medium, but they often introduce thermal gradients and vibrations, increasing noise levels and degrading both the temporal coherence and spatial quality of the laser output beam. Alternatively, thermoelectric coolers based on the Peltier effect are employed, though while generally vibration-free, they tend to cool fibers asymmetrically, creating undesirable thermal gradients. In contrast, ASF cooling offers a compelling solution that sidesteps all these challenges entirely. Optical cooling of fibers also holds great potential for applications in cooled detectors, where it can significantly reduce thermal noise; in ultra-stable lasers, providing a temperature-controlled reference cavity; in reducing dark currents in spaceborne infrared and X-ray sensors; and even in localized cooling of microelectronic devices.  *Caption: Approximately 12 minutes after pumping began, the crystal temperature (blue line) reached 91 K, while the lid temperature remained steady at ~265 K.* To date, brief studies on ASF cooling in optical fibers have been conducted primarily in tellurite-based glasses, though most demonstrations have focused on fluoride hosts. For instance, Yb-doped ZBLANP fibers placed under vacuum reportedly exhibited a temperature drop of -65 K, while recently, Yb-doped ZBLAN fibers tested under ambient pressure showed a temperature reduction of about -0.65 K. Compared to traditional silica, fluoride glasses exhibit greater resistance to concentration quenching, enabling them to incorporate higher concentrations of non-quenched rare-earth ions. This translates into more ions—acting as heat engines—extracting heat per unit volume, thereby enhancing the overall cooling potential. However, practical applications of fluoride fibers remain limited compared to silica due to several key challenges. Most notably, fluoride fibers are fabricated by melting powdered materials and casting them into large glass blocks, from which the fibers are subsequently drawn. This manufacturing process results in impurity levels roughly one order of magnitude higher than those achieved using chemical vapor deposition techniques for producing quartz glass. Additionally, fluoride glasses are more brittle and significantly harder to polish, cut, and splice onto other fibers. They also suffer from lower optical damage thresholds, making it more challenging to inscribe reflective gratings within them, and their absorption and emission cross-sections are weaker. From a technical standpoint, developing silica compositions capable of supporting laser cooling remains crucial. The quartz fibers evaluated in this study were specifically engineered for low loss, aiming to mitigate absorptive heating, which scales linearly with pump power. Furthermore, since cooling efficiency increases proportionally with the number of heat-generating ions, the fibers were also optimized for high Yb³⁺ concentrations. However, as previously mentioned, this approach may come with some unintended side effects, such as enhanced concentration quenching and shortened non-radiative lifetimes. To counteract these issues, the silica core was doped with fluorine and aluminum oxide (Al₂O₃), which helps alleviate these adverse impacts.  *Caption: As temperature changes occur in the doped fiber and Fiber Bragg Grating (FBG), the resulting spectral shifts detected by the interrogation laser are tuned to one of the FBG’s resonance peaks.* The figure below illustrates an example of temperature measurements taken on fibers exposed to ambient air. The pump (represented by the solid red curve) remains off for 20 seconds before being abruptly switched on for another 40 seconds. Steady-state temperature changes are calculated as the difference between the average temperature during the initial 20-second period (typically well below 5 mK) and the average temperature recorded over the subsequent 20-second interval (shown here as two gray regions). To establish the relationship between temperature change per unit length and absorbed pump power, as depicted in Figure 4, a thermal power meter was utilized to measure the pump power delivered to the output end of the doped fiber. By combining these output power readings with known values for saturation power, small-signal absorption, and the distance between the FBG and the fiber’s output point, researchers were able to determine the amount of pump power absorbed per unit length at the specific measurement location.  Since Jennifer Knall of the University of California, along with her collaborators Magnus Engholm from Uppsala University, John Ballato from Clemson University, Martin Bernier and Tommy Boilard from Laval University, and Peter Dragic and Yu Nanjie from the University of Illinois at Urbana-Champaign, first achieved a breakthrough, researchers have since discovered two additional self-cooling quartz fiber components. Knall then used the top-performing candidate material to fabricate a cooling fiber amplifier, successfully amplifying a laser by more than 40 times while maintaining a consistently negative average temperature change along the length of the optical fiber. Although cooling tests demonstrated that laser cooling is indeed possible in silica, this type of fiber amplifier has now proven to be undeniably practical for real-world applications. Currently, researchers are able to extract about 4% of the energy injected into the fiber. While this efficiency is still relatively low—making it unlikely that the fiber could be used for high-power applications without first addressing this inefficiency—the findings open up exciting opportunities for low-power applications, such as ultra-precise metrology or advanced measurement science. --- ▲ Figure 5: Temperature changes in Fiber 1 as a function of pump power at three different wavelengths. To establish a new benchmark for ASF cooling in silica, the highest-performing fiber (Fiber 1) underwent more comprehensive characterization. Specifically, the relationship between temperature change and pump power was measured across two additional pump wavelengths: 1020 nm and 1040 nm. Since these parameters were constrained to remain consistent across all pump wavelengths, incorporating this extra data allowed for more accurate determination of absorption losses and critical quenching concentrations. As expected, when pumped at 1020 nm, the fiber heated up; however, at 1040 nm, the fiber exhibited its strongest cooling effect (Figure 3). At 1020 nm, while pump absorption was relatively high, the average energy difference between the pump photons and the emitted fluorescence photons was smaller. Consequently, due to concentration quenching and increased absorption losses, the extracted energy fell short of offsetting the heating effect. In contrast, at 1040 nm, the balance between pump absorption and the energy gap approached an optimal point, enabling the fiber to cool down to -70 mK at a pump power of 80 mW (corresponding to 170 mW/m of absorbed pump power). This represents twice the heat extraction rate per unit length compared to values previously reported in the literature. --- ▲ Graduate student Jenny Knall stands beside the experimental setup for the self-cooling fiber. A computer displays real-time measurements of the fiber’s temperature, which begins to drop immediately after Knall activates the laser pump. "As for how far we can take this technology," says Digonnet, "it ultimately depends on how much progress researchers can make in advancing materials science. And let’s just say, this is only the tip of the iceberg." **Source:** Jennifer Knall et al., "Laser Cooling in a Silica Optical Fiber at Atmospheric Pressure," *Optics Letters* (2020). DOI: 10.1364/OL.384658 **References:** S. D. Melgaard, A. R. Albrecht, M. P. Hehlen, and M. Sheik-Bahae, *Sci. Rep.* 6, 20380 (2016).

SemiNex has partnered with Futai Technology to introduce multi-junction semiconductor laser diodes featuring a safe wavelength range of 1310 nm to 1550 nm. These lasers deliver more than 20 times the photon count per second compared to 905nm LiDAR systems, while offering a detection range three times greater than that of 905nm technology. This innovative product line is set to accelerate the mass-market adoption of autonomous vehicles. Additionally, SemiNex’s new 1550nm multi-junction laser diode—available in an aperture width of 95μm—is capable of delivering up to 80W of power, making it more than three times more powerful than current laser diodes at this wavelength. Notably, these high-performance devices are now available in volume quantities.

Laser welding is a type of fusion welding that uses a laser beam as the primary heat source. The welding process works by exciting an active medium through a specific method, causing it to oscillate back and forth within the resonant cavity. This generates a beam of stimulated emission light, which, when it comes into contact with the workpiece, transfers its energy directly to the material. Once the temperature reaches the material’s melting point, welding can proceed.