United States

The ability to deliver high energy and high average power laser radiation through a flexible fiber is a key enabler for numerous processing applications. This provides better space management, direct delivery to the processing area and better serviceability. Silica fibers were successfully used to deliver signals in the near-infrared and visible spectra, but they suffer notably from high absorption in the UV region. Hollow-core fibers alleviates this issue as the mode of propagation minimally overlaps with the surrounding guiding microstructure. However, their power scaling was currently limited by two factors: beam quality/stability of available UV sources and power handling of the thin capillary microstructure, especially due to the limited control of the internal surface roughness.&lt;br&gt;
In this work we will present recent results achieved by the combination of a high beam quality UV nanosecond lasers and low-internal roughness hollow-core fibers to achieve efficient UV fiber delivery. After giving experimental characterizations of the improved hollow-core fiber, we will detail the characterization of the 343nm UV source, including beam stability measurements at full power and evolution of beam quality on a large range of parameters. Fiber delivery with power above 20W (150 µJ energy) and transmission above 90% will be presented. We will also present preliminary results achieved at 266 nm with output power of 20.5mW (20.5 µJ) and transmission efficiency above 90%.

ICALEO 2023

Fiber Delivery of UV Nanosecond Lasers using Hollow-Core Fibers

nanosecond lasers

fiber delivery system

hollow-core fibers

high-power uv lasers

high-power fiber lasers

The ability to deliver high energy and high average power laser radiation through a flexible fiber is a key enabler for numerous processing applications. This provides better space management, direct delivery to the processing area and better serviceability. Silica fibers were successfully used to deliver signals in the near-infrared and visible spectra, but they suffer notably from high absorption in the UV region. Hollow-core fibers alleviates this issue as the mode of propagation minimally overlaps with the surrounding guiding microstructure. However, their power scaling was currently limited by two factors: beam quality/stability of available UV sources and power handling of the thin capillary microstructure, especially due to the limited control of the internal surface roughness. 
In this work we will present recent results achieved by the combination of a high beam quality UV nanosecond lasers and low-internal roughness hollow-core fibers to achieve efficient UV fiber delivery. After giving experimental characterizations of the improved hollow-core fiber, we will detail the characterization of the 343nm UV source, including beam stability measurements at full power and evolution of beam quality on a large range of parameters. Fiber delivery with power above 20W (150 µJ energy) and transmission above 90% will be presented. We will also present preliminary results achieved at 266 nm with output power of 20.5mW (20.5 µJ) and transmission efficiency above 90%.

technical paper

**General Chair Welcome**

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Welcome to ICALEO® 2023!
	
We were excited to host the world’s leading international conference on Lasers and Electro-Optics in Chicago. The Laser has been shown to have the potential to revolutionize solutions for major global challenges like energy usage and supply, global warming, and CO2 footprint. Even the fusion energy breakthrough is based on laser technology. The conference, with peer-reviewed scientific and technical presentations, focused on the newest results in Micro Applications, Macro Applications, Additive Manufacturing, Beam Shaping and Frontiers in Laser Applications. Additionally, the Battery-Manufacturing Track gave an overview of the process combined with the newest advances in laser application results. 

The Business Session brought the business aspect and environment of the laser to the audience and the possibility to discuss with seasoned industry leaders from around the world. 

Whether this is the first time you are hearing about ICALEO or you are a longtime attendee, you will find something of interest, new ideas, and an excellent opportunity to network with other laser specialists worldwide. 

**Klaus Löffler **  
ICALEO General Chair   
Managing Director, Precitec GmbH

**What is ICALEO?**

ICALEO® brings together the brightest minds, seasoned professionals, and pioneering researchers from around the world. With a laser-focused agenda, ICALEO offers an exceptional platform to delve into the cutting-edge advancements, diverse applications, and transformative research that define lasers and electro-optics.

Participants will be immersed in a dynamic environment that fosters collaborative learning, networking, and idea exchange. Through engaging plenary presentations, technical sessions, an industry business panel, and networking events, attendees gain insights into the forefront of laser technology. From industrial applications to medical breakthroughs, additive manufacturing to materials processing, ICALEO covers the entire spectrum of laser-related disciplines. Moreover, the event serves as a launching pad for synergistic partnerships, paving the way for professionals to forge connections that shape the future of our industry.

Join us in Chicago and be part of an unparalleled gathering that challenges the boundaries of possibility within lasers and electro-optics. As we convene to share knowledge, explore innovations, and cultivate collaborations, ICALEO stands as a pivotal force driving the evolution of this transformative technology.

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ICALEO is tailor-made for professionals, researchers, academics, and enthusiasts who are deeply passionate about the world of lasers and electro-optics. If you're an industry trailblazer, an academic luminary, an aspiring expert, or a postgraduate student looking to dive into the latest developments and trends, this is an event you won't want to miss.

Industrial leaders seeking to stay ahead of the curve in their fields, engineers working on laser applications, and manufacturing experts interested in additive manufacturing and materials processing will find ICALEO to be an invaluable platform. Researchers and scientists exploring the forefront of laser technology, from fundamental principles to groundbreaking applications, will also discover a wealth of knowledge and networking opportunities.

Medical professionals investigating laser-based medical advancements, entrepreneurs seeking to innovate with lasers, educators aiming to stay updated with the latest in laser education, and policy makers shaping the industry's landscape are all essential attendees. Whether you're an established expert or a rising star, the 42nd annual ICALEO promises to offer a diverse ecosystem of expertise, connections, and knowledge sharing that caters to the laser and electro-optics communities.

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Please register for the ICALEO 2023 Conference to join the event.

ICALEO® brings together the brightest minds, seasoned professionals, and pioneering researchers from around the world. With a laser-focused agenda, ICALEO offers an exceptional platform to delve into the cutting-edge advancements, diverse applications, and transformative research that define lasers and electro-optics.

The railway industry has a high demand for lightweight structures in new trains. We present an overview of 20 years of progress in using laser-based manufacturing techniques to realize such structures, with the recent implementation of Additive Manufacturing (AM) enabling rapid advances. We show how AM-designs reduce car body weight by ~50% over conventional solutions. Moreover, the lifetime of rolling stock is scaling towards 50 years, creating a long-term demand for spare parts. AM offers a strategic solution, creating a digital warehouse, which produces parts only when needed, increasing resilience for the mobility industries.

Further advances in AM-techniques in lightweight manufacture are also being enabled by direct-diode laser technology. Kilowatts of optical power can now be efficiently generated in a compact module mounted on a lightweight process robot and delivered in a small spot onto the workpiece. New functions and operation modes are enabled, e.g. alternative wavelengths, with 780nm operation wavelength selected here, targeting the absorption maximum of aluminum. The 5-fold higher absorption over conventional 1060nm sources will shorten processing times, reduce energy consumption and minimize deformation.

Direct diode techniques are used to produce ultra-compact process heads that integrate laser source, simplified optics for imaging the optical output onto the work surface, and a wire-feed system. The resulting compact AM unit promises high flexibility and low cost and will enable complex shapes such as topology-optimized stiffening structures to be fabricated in limited accessibility environments typical for car body manufacturing. This will support the wide adoption of AM and raise sustainability.

Topology Optimized Lightweight Design through Additive Manufacturing: 780nm Laser Wire Deposition for Train Side Wall Structures

Hybrid Laser Arc Welding (HLAW) integrates the advantages of laser and arc welding, providing high process stability, high welding speed and penetration, narrow weld beads with a low heat input, low thermal distortion and good metallurgical properties. It is an outstanding joining process for medium and high thickness structural steels, being specially interesting for naval and offshore applications in which large panels must be 1G butt welded to manufacture larger flat panels. Although this technology has already provided appropriate results in terms of microstructure, weld morphology and static mechanical behaviour of HLAW butt joints, few studies have been yet reported regarding the fatigue behaviour. 
 
In the present research, HLAW process was applied to join 8 mm thick structural S355J2N steel under 1G configuration. Welding tests were performed at the Advance Laser Welding Center (CASOL) available at the University of Cadiz, Spain. Different experimental welding parameters were fitted to obtain sound butt welds. The welds were subjected to different quality control tests, including visual inspection, metallographic characterization, microhardness measurements, and tensile and fatigue tests. The HLAW tests were performed at higher welding rates in 1G configuration than previously reported for 8 mm thick steels. The present contribution reports novel fatigue results for these butt hybrid welds.

Laser Glass Deposition as an efficient Tool For the Production of Structural Components and Optical Systems

In this contribution, we investigate the influence of ambient atmosphere on the formation of laser-induced periodic surface structures (LIPSS) on the metal surface using 8 picosecond and 45 nanosecond pulses. We patterned the surface of AISI 216 stainless steel in air, nitrogen, and argon and observed that the properties of the fabricated LIPSS were affected by changing the beam scanning velocity and pulse fluence while keeping the pulse duration constant. The LIPSS phenomenon was found to be strongly dependent on the atmosphere surrounding the irradiation spot during fabrication. When patterned with picosecond pulses, the dependence was less pronounced and manifested itself mainly in the curvature of the fabricated ribs. The spatial period of the fins patterned with picosecond pulses was smaller in air than in nitrogen and argon atmospheres. On the other hand, periodic structures were observed with nanosecond pulses only when laser processing was performed in air, suggesting that the structures were related to surface oxidation. Further analysis using EDS, XPS, AFM, and FIB cross sections revealed that LIPSS obtained with nanosecond pulses on samples consisted mainly of periodic parallel ridges of accumulated oxides, while in the case of picosecond pulses LIPSS consisted of topographically modulated bulk material with an oxide layer deposited uniformly over the entire surface of the sample. The results suggest that the formation of stainless steel LIPSS is significantly influenced by the surrounding atmosphere and the pulse duration used for laser processing.

The Influence of Ambient Atmosphere on LIPSS Formation in Stainless Steel: A Comparison between Ps- And Ns-Pulse Processing

A fundamental understanding of ablation in different incidence angles is indispensable to expand the result to volume ablation where non-perpendicular irradiation exists. So far, no study with this orientation has been conducted in the category of volume laser machining. In this study, a nanosecond laser with different fluencies was utilized for single-point ablation experiments. The effect of incidence angles of 0°, 30° and, 60° on the ablation depth and the crater geometry was evaluated. Different laser pulse numbers are also considered. The results show that the ablation depth for the 0° and 30° angles is almost in the same range for the initial pulses, but afterward, the ablation depth for the incidence 30° drops considerably. As the number of incident pulses increases, the ablation depth first develops approximately linearly and then grows exponentially. By changing the incident from 0° to 60°, the affecting area changes as well. The affecting area could be categorized into two distinct areas: (1) ablation area (A.A) where the crater ablation depth rapidly increases for the first 20 pulses and then, as more incident pulses arrive, it does not grow anymore and reaches a plateau due to the increase in the ablation depth. The second area (2) is the heat-affected area (H.A.A) of the crater where no further ablation occurs, but due to heat accumulation, it becomes constantly bigger when more incident pulses strike the crater.

Tackling Micro-Processing Challenges with Beam Shaping

Femtosecond laser technology has opened a large variety of industrial applications. The short duration of the laser pulses enables material minimal collateral damages due to thermal effects, which makes possible to reach a high precision in micro-processiing. This is sometimes at the expense of industrial productivity, since a single femtosecond pulse will only remove a limited amount of matter. Increasing process throughput productivity can be achieved by increasing the&nbsp; repetition rate of the laser, but he onset of thermal accumulation in the material limits this approach. 
Femtosecond pulses with bursts of GHz repetition rate can significantly improve the ablation efficiency of femtosecond lasers. Freely adjustable bursts involve thermal and non-thermal ablation mechanisms. The long GHz bursts can remove very efficiently heated matter, with non-thermal ablation leading to a high-quality material processing. We report an experimental study on crystalline silicon line scribing with GHz burst regime of femtosecond pulses at 515 nm. The number of pulses per bursts varied from 50 ppb to 200 ppb. A second harmonic generation module was placed at the output of a 100 W femtosecond GHz laser to generate up to 50W of second harmonic (SHG,515nm) at 200 kHz. The results show the highest ablation efficiency obtained on silicon with fs pulses (more than 10 mm3/min/W), and the crucial role of the pulse overlap.

GHz Long Burst for Femtosecond Laser Processing Optimization

Micro-processing with ultra-short pulse lasers has become a vital tool in various industrial and scientific applications, such as surface texturing, surface treatment, metal drilling, glass drilling, and micro-welding. While these applications offer significant advantages over traditional processing methods, they also present unique challenges that must be overcome to take micro-processing to the next level. These challenges include improving process speed, enhancing process precision, and enabling easy integration of the laser into industrial applications. 
In this paper, we discuss how beam shaping can be used to tackle these challenges in various micro-processing applications. We describe how beam splitting, non-diffractive beams, top-hat shaping, and other original beam shapes such as U-shaped beams and triangular beams have been used to improve the process speed, precision, and integration of ultra-short pulse lasers into various micro-processing applications. We also discuss the challenges of fibering the laser for easy integration into industrial applications and describe how beam shaping can be used to overcome these challenges. 
In conclusion, this paper demonstrates how beam shaping can be used to tackle the unique challenges of micro-processing with ultra-short pulse lasers. With the appropriate beam shaping technology, we can significantly enhance the process speed, precision, and integration of ultra-short pulse lasers into various micro-processing applications.

Investigation of ns Single-Point Laser Ablation of Bronze under Different Incidence Angles and Pulses

Additive manufacturing processes have undergone significant development in regard to process management and reproducibility. Porosity, crack formation and similar defects can be reliably avoided through process control for a multitude of materials. This also applies to wire laser direct energy deposition (wire L-DED), which offers standardized feedstock material and direct controllable flow of mass. However, the process inherent microstructure remains fundamentally unaffected by parameter variations within typical process configurations. This microstructure is characterized by coarse columnar grains with a distinct fiber texture along the build direction. The underlying cause is the presence of a strong directional heat flux from the melt pool through the deposited material to the substrate. Consequently, as-built components demonstrate anisotropic mechanical properties with significantly lower tensile strength in build direction.&nbsp;One possible approach to inducing grain refinement and promoting the formation of an isotropic microstructure is the application of ultrasonic waves to the melt pool during solidification This lecture presents an approach to introducing ultrasonic waves to the wire L-DED process. An ultrasound system was developed, integrated in a laser wire deposition machine and a suitable process window has been established. A disruption of the highly directional solidification, resulting in a randomized texture as well as finer grains, has been confirmed by means of scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) (dm = 284,5 μm without ultrasound, dm = 130,4 μm with ultrasound).

Grain Size Manipulation by Wire Laser Direct Energy Deposition of 316L with Ultrasonic Assistance

Stainless steels are established in various fields with challenging environments, e.g. offshore, petrochemical, and automotive industries. The combination of high-performance properties and high-value added applications makes stainless steels attractive for Additive Manufacturing (AM). In powder-based AM processes such as Laser Directed Energy Deposition (DED-LB/M) typically pre-alloyed powders are used for part fabrication. By an innovative approach called in-situ alloying, the chemical composition of pre-alloyed powder can be adjusted by mixing it with an additional powder material. This allows the material properties to be flexibly and efficiently tailored for specific applications. In this work, a standard duplex stainless steel (DSS) is modified for the first time with elemental powders in order to systematically adjust the resulting phase formation, mechanical properties and corrosion resistance. For this, powder mixtures were generated consisting of pre-alloyed DSS 1.4462 and additions of pure chromium (+1.0 to +7.0 wt.-%) or nickel (+1.0 to +5.0 wt.-%) powder. Processing by means of DED-LB/M resulted in specimens (relative density &gt; 99.7 %) with ferrite-austenite phase ratios ranging from almost 10:90 % to 90:10 %. Increasing the Cr-content successively increased the ferrite percentage, resulting in higher material hardness, higher strength and resistance against pitting corrosion, but poor ductility and toughness compared to the unmodified DSS. In contrast, an increased Ni-content resulted in an increased austenite formation with lower hardness and strength, but increased ductility and toughness. This strategy was shown to add flexibility to powder-based AM processes by enabling an on-demand material design for stainless steels.

In-Situ Process Monitoring of Directed Energy Deposition Powder Flow to Detect Anomalies

Parts with complex geometry, elevated mechanical and corrosion resistance can be obtained by martensitic stainless steels (MSS) using additive manufacturing by laser directed energy deposition (AM L-DED) process. In this work, a proposed method was employed for choosing L-DED parameters based on design of experiments (DoE): Single beads, to define windows of powder feed rate, laser power, and travel speed; Single layers, to find the ideal hatch spacing for lateral bead overlapping; and Multilayer, to determine the ideal layer height for layer overlapping. Using the optimized parameters, AM L-DED samples were produced of AISI 410L MSS feedstock on AISI 410 MSS substrate. Microstructure, hardness, tensile strength, and impact toughness were evaluated in the as built and heat-treated conditions and compared to the AISI 410 substrate. Four heat-treatment routes were investigated: annealed (1050 °C for 90 min and water quenched), and annealed, water quenched and tempered at 300 °C, 450 °C, and 600 °C for 90 min, then air cooling. From results, as built samples showed the highest hardness, yield and ultimate tensile strength, but the lowest toughness. Ductility was progressively recovered with tempering temperature increase. Best compromise was seen in samples tempered at 600 °C that showed toughness improvement, keeping a tensile performance higher than AISI 410 substrate.

Influence of Post-processing Heat-Treatment on the Mechanical Performance of Aisi 410L Stainless Steel Manufactured by L-Ded Process

Batteries and other energy storage and energy transformation devices require a dedicated functionalisation of the subcomponents. From surface structuring to cutting and assembly of the different components, every single processing step should not influence the basic properties of the material and should even more increase the the characterics of the entire device. Ultrashort pulsed lasers provide technologies to optimize the electrical properties of the electrodes in batteries but also allow the modification of components in redox flow batteries and also in fuel cells. With micro and nano scaled structured electrodes based on ultra short ablation and modification the efficiency of batteries and electrolysers can be increased significantly. Especially in new types of batteries, like solid state batteries, short wavelengths in the UV provide the necessary power and physical properties to allow thin film modification an large scales. With ultra short pulsed lasers in the UV nano scaled modification of electrodes can be realized without influencing the electical properties of the electrodes without loosing active surface areas. With high power ultra short pulsed lasers and adapted beam guiding technologies large area surfaces can be processed. The presentation will show different approaches for the use of high power ultra short and UV lasers for the manufacturing of battery components.

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Topology Optimized Lightweight Design through Additive Manufacturing: 780nm Laser Wire Deposition for Train Side Wall Structures