United States

In this study, we develop mid-infrared (MIR) waveguides and beamsplitters for applications such as spectroscopy, chemical sensing, and remote sensing using ultrafast laser inscription (ULI) within chalcogenide glass IG2 (Ge33As12Se55). MIR photonic integrated circuits (PICs) enable compact and efficient optical layouts. IG2 glass is ideal for MIR PICs because of its broad transparency window, low absorption, and compatibility with atmospheric windows at 3-5 and 8-12 µm.&lt;br&gt;
The waveguiding properties at 1.064 µm (Near-IR) and 4.55 µm (MIR) were investigated by examining the effects of inscription parameters and geometries, particularly the impact of pulse energy and the number of layers for a multi-scan strategy on the mode confinement and the morphology the waveguide cross-section. We determine that higher pulse energy or a higher number of layers is required to achieve guided modes at the longer wavelength. For example, for the single-layer configuration, the threshold pulse energy that enables the guided modes at the 1.064 and 4.55-µm wavelength is 3 and 6 nJ, respectively. Mode confinement at MIR was further achieved at 6nJ when two or more vertical layers were applied, achieving a minimum propagation loss of 1.8 dB/cm with a four-layer configuration. Waveguides with cross-sections larger than two layers exhibited higher-order modes at MIR in addition to the fundamental mode. We further demonstrate MIR 1x4 beamsplitters, achieving uniform splitting ratios of over 96 %. Our results highlight the potential of ULI-inscribed IG2 waveguides and beamsplitters for developing mid-infrared photonic devices and integrated circuits.

ICALEO 2023

Mid-IR Waveguide Beamsplitters in IG2 Glass by Ultrafast Laser Inscription

femtosecond laser writing

mid-ir waveguides

mid-ir integrated photonics

ultrafast laser inscription

In this study, we develop mid-infrared (MIR) waveguides and beamsplitters for applications such as spectroscopy, chemical sensing, and remote sensing using ultrafast laser inscription (ULI) within chalcogenide glass IG2 (Ge33As12Se55). MIR photonic integrated circuits (PICs) enable compact and efficient optical layouts. IG2 glass is ideal for MIR PICs because of its broad transparency window, low absorption, and compatibility with atmospheric windows at 3-5 and 8-12 µm. 
The waveguiding properties at 1.064 µm (Near-IR) and 4.55 µm (MIR) were investigated by examining the effects of inscription parameters and geometries, particularly the impact of pulse energy and the number of layers for a multi-scan strategy on the mode confinement and the morphology the waveguide cross-section. We determine that higher pulse energy or a higher number of layers is required to achieve guided modes at the longer wavelength. For example, for the single-layer configuration, the threshold pulse energy that enables the guided modes at the 1.064 and 4.55-µm wavelength is 3 and 6 nJ, respectively. Mode confinement at MIR was further achieved at 6nJ when two or more vertical layers were applied, achieving a minimum propagation loss of 1.8 dB/cm with a four-layer configuration. Waveguides with cross-sections larger than two layers exhibited higher-order modes at MIR in addition to the fundamental mode. We further demonstrate MIR 1x4 beamsplitters, achieving uniform splitting ratios of over 96 %. Our results highlight the potential of ULI-inscribed IG2 waveguides and beamsplitters for developing mid-infrared photonic devices and integrated circuits.

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. 

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**Klaus Löffler **  
ICALEO General Chair   
Managing Director, Precitec GmbH

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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.

Ultrashort pulse (USP) lasers, with pulse widths measured in femtosecond to picosecond, are widely used for machining or cutting materials of all kinds.&nbsp; Today’s newest USP lasers offer high output power (&gt;100W), with high pulse energy and high pulse repetition rate.&nbsp;&nbsp; When machining or marking metals, which have low ablation threshold and high thermal conductivity, low pulse energy and high pulse repetition rate typically give the best results.&nbsp; In contrast, when processing materials such as glass or polymers which can have high ablation threshold and low thermal conductivity, it is best to use high laser pulse energy and low pulse repetition rate. &nbsp;However, regardless of the material being processed, when total output power of the laser exceeds about 50W, thermal damage to the processing material (HAZ) can easily occur.&nbsp; Spreading laser power distribution across the target material becomes critical.&nbsp; This is typically achieved using higher scan speed, split beam processing, diffractive optics, or a combination of these. We discuss methods currently being used to effectively distribute &gt;100W laser power across a processing surface, to utilize the full power capacity of today’s USP lasers, and we present experimental results achieved with our newest 140W HyperRapid picosecond laser, and 150W Monaco femtosecond laser.

Laser Processing with femtosecond and picosecond at 150W

Additive manufacturing (AM) has revolutionized the production of complex geometries with superior properties compared to traditional manufacturing methods. However, the high roughness and poor wettability of as-produced surfaces of AM parts limit their suitability for certain applications. To address this, we present a maskless laser-assisted surface functionalization method to improve the wettability of metal 3D printed parts. 
This study explores the potential of combining metal AM with surface wettability patterning, a promising technique in fluid-related fields. Large area AlSi10Mg parts were fabricated using laser powder bed fusion (L-PBF), followed by an innovative laser-assisted functionalization (LAF) method to achieve patterned wetting surfaces. The LAF method consists of laser texturing and chemical modification steps, and two strategies were demonstrated to fabricate different types of wettability patterns. Strategy I produces two types of superhydrophobicity, while Strategy II creates a superhydrophobic-superhydrophilic patterned surface. The study demonstrates the simplicity, robustness, and feasibility of the process, and analyzes the processing mechanism, surface topography, and surface chemistry. The integration of surface wettability patterning and 3D-printing can optimize components to enhance performance and efficiency by creating intricate fluid flow pathways. Overall, this work highlights the potential of combining metal AM with surface wettability patterning, providing a pathway to produce high-performance parts with tailored wettability properties. This research has significant implications for fluid-related industries such as aerospace, automotive, and energy, as it offers unparalleled design freedom and the ability to create complex geometries.

Surface Wettability Patterning of Metal Additive Manufactured Parts via Laser-assisted Functionalization

In this study, the application of the ABA cladding strategy to coaxial wire-based cladding processes is investigated. Individual weld seams (A) are first welded on the substrate and additional weld seams (B) are deposited into the intermediate spaces in the second step. Thereby two different seam geometries are present in the cladding. Unidirectional AAA and ABA claddings are generated using laser hot-wire cladding and analyzed with respect to the quality criteria height, waviness, degree of dilution and defects. Three different welding parameter sets are used to consider the effect of the contact angle on the applicability of the ABA cladding strategy. 
 
When the same process parameters and seam-to-seam offsets are used for the ABA cladding as for the AAA cladding, the B weld seams are higher than the A weld seams and an uneven ridged cladding surface is present. Two approaches to solving this problem are considered. The cross-sectional area of the B weld seams is reduced by adjusting the welding speeds or an increase of the seam-to-seam offset. Both measures result in a significant reduction in waviness of 30% to 58% compared to the AAA cladding. However, lack of fusion defects occur more frequently after deposition of the B weld seams. It was therefore necessary to adjust the process parameters for weld seam B.

Application of the ABA Cladding Technique to a Wire Based Laser Cladding Process

This study examines the impact of wobble movement on a LASER beam's behavior while moving over an AISI 316L stainless steel sample of 1.2 mm thickness. The LASER beam oscillatory movement is superimposed on linear movement using a 400 W fiber LASER installed on an experimental bench equipped with a scanner and worktable. Mathematical modeling estimates instantaneous beam speed values, predicting thermal influence on weld bead aspects. Micro-welding experiments use autogenous modeling with lateral beam oscillation. Two forms of overlapping transverse wobble are tested: one with a circular path and the other describing a path like the mathematical symbol “infinity.” Correlations are evidenced between the parameters used and results obtained in the micro-welds, including penetration and width of the beads. Results show that the frequency of movement in a circle and in “infinity” for frequencies from 200 to 400 Hz has no significant influence on the result. Increasing the amplitude of the wobble movement from 0.5 to 2 mm significantly influences the width and depth of the strands generated. The wobble technique is effective in preventing discontinuities in the process such as porosity. A bead obtained with 300 W, 50 mm/s, 0.5 mm overlapping wobble movement, and 300 Hz circular rotation frequency showed the highest relationship between width and depth.

Effect of Wobble Parameters on Micro-Welding Bead Formation of AISI 316L Stainless Steel

Some traditional technologies, such as die-sinking EDM or Milling, are being pushed to their limits by the increasing complexity of machined components. In order to be able to tackle the manufacturing challenges related, new strategies and new technologies are often required. This is even truer in the field of micromachining, specifically when it comes to the production of micro cavities or of the smallest geometries that are crucial to the mass production of electronic or medical devices. 
As an example, the conventional method of producing mold inserts for electronic components in the fiercely competitive industry of moldmaking includes milling, wire-cutting EDM, or die-sinking EDM. Numerous electrodes must be produced for these multi-step processes, which can each take a significant amount of setup time, machining time, and operator expertise. 
Lasers can now be used in electronic components manufacturers in instead of, or in addition to, conventional subtractive techniques. The results of internal moldmaking or micromachining operations carried out by OEMs can be improved by the combination of technologies. Lasers can help create a process that is far faster than using traditional methods while also being more productive and profitable. 
In this presentation, Mark Keirstead, GF Sales Manager for Advanced Manufacturing Tools, would present how laser is revolutionizing the manufacturing chain through the review of numerous case studies.

Revoulutionize the Machining Process of Micro Components with Laser Technology: Case Studies

Most future industrial applications of USP lasers require high processing quality, but also higher throughput and productivity, for example with higher average powers and more advanced processing strategies. We provide a description of a built-in functionality enabling synchronization of multiple mechanical (rotary and linear) and optical axis to enhanced engraving and texturing operation over 3D surfaces. Thanks to a closed loop regulation of the scanner over the mechanical axis encoder, the energy distribution is maintained constant and homogeneous during machining. The functionality is fully integrated into LASEA KYLA® and LS-CAM software allowing us to easily generate complex machining with multiple input formats (DXF, STL, Greyscale). Thanks to the simultaneous and synchronized motion between mechanical and optical axis, large machining areas can be processed without discontinuities in the pattern, which are known, for instance, to impact the quality and the final product performance. This processing method also optimize the thermal management of laser machining compared to more conventional sequential positioning methods. This important aspect paves the way for increased productivity thanks to the increase of laser power and scanning speeds in industry. We provide a new solution for optimized cycle time and machining quality, demonstrated onto parts with a revolutionary geometry.

Advanced Synchronisation For Laser Engraving Of Complex Design

Laser Processing at the micrometer and below resolution is becoming more and more prominent driving the requirements of the equipment used for these processes to achieve more demanding specifications. Two-photon polymerization (2PP), selective laser etching of glass, and laser micromachining are several emerging processes that fall into this category. They rely on ultrafast lasers in the femtosecond pulse width regime focused with high numerical or high N/A focusing optics to achieve sub-micrometer spot size. The small spot size enables impressive processing resolution on the order of 150 cubic nanometers but it also creates real challenges for positioning a beam so small and allowing that beam to make large enough parts for practical applications. 
 
This challenge can be overcome by the use of high-dynamic laser scan heads that leverage galvanometer servo motors and precision linear motors to extend the scanning range beyond a fixed field of view. Combining the motion of the scanner motors and physical linear motors in a seamless fashion where the processing speed of the laser on the linear axes is shared between the scanner and the linear motor involves advanced motion control features to execute properly. Controller features known as Infinite Field of View (IFOV) combined with Position Synchronized Output (PSO) allow for large parts with nanometer precision to be created. A detailed technical overview of how these features work within a motion controller and what benefit they have on the aforementioned processes will be discussed. Additionally, application examples will be shared.

Laser Processing Macro Size Components With Sub-Micrometer Feature SIze & Precision

Laser-assisted double wire welding with nontransferred arc uses an electric arc to melt two welding wires fed towards each other. The molten material drips onto the substrate, where it is joined to the substrate without undercuts by means of oscillated laser radiation. The process offers the possibility of creating structures with high deposition rates (8,4&nbsp;kg/h), but faces challenges fulfilling the requirements for surface properties and geometric accuracy. One approach to meet the requirements is to confine the final seam geometry by applying the melt into a mold. Such a confinement can be a wall previously applied by a process with higher geometric accuracy. An investigation of this approach was carried out by studying the deposition of mild steel weld beads within two confining structures, in this case a groove. A particular interest in the evaluation is the connection of the weld bead to the base material in the corners, the bottom surface and the side surface of the groove. In a first step, weld beads are deposited in 12&nbsp;mm wide grooves in a mild steel substrate with variable laser beam oscillation amplitudes of 10&nbsp;mm to 13&nbsp;mm. In a second step, several layers are deposited with variable welding speeds. The oscillation amplitude that generates the best connection in the corners is 13&nbsp;mm. Bonding on the bottom and side surfaces could be achieved with all parameter sets. When applying several layers, the best lateral connection in the groove was produced with a welding speed of 200&nbsp;mm/min.

Welding Between Confinements as a New approach for high deposition rate Additive Manufacturing with laser-assised double-wire welding with nontransferred arc

Additive Manufacturing (AM) has become widely adopted in various industries with Laser AM being the most popular technology for metallic materials. Laser-wire DED (Directed Energy Deposition) is becoming an interesting additive manufacturing method for building large freeform structures that are not constrained by the printing machine dimensions. However, the WAAM process (Wire Arc Additive Manufacturing) is currently more widely used with several high-profile applications, such as bridges, pressure vessels, tanks, and barrels, due to its basic origins in MIG welding. The opportunities for these wire-DED process variants are immense in terms of reduced manufacturing complexity, costs, lead times, and tooling requirements, with more design flexibility. This conference paper discusses feature development testing for 3D printing 30in diameter compressor casings, comparing the advantages and disadvantages between the wire-arc and wire-laser process variants of wire-DED. Using aluminum 5XXX series alloy wire, demonstration test pieces were produced with features including stiffening ribs and local reinforcements. The quality of the printed development test pieces was assessed by radiographic inspections, metallurgical assessments, and dimensional scans. Further demonstrations could include split casings, ports, lugs, and other features that can be integrated as one single part instead of many, simplifying the supply chain with potentially significant gains in productivity.

A comparison of Wire-Laser and Wire-arc Directed Energy Deposition Processes

Laser welding is crucial in the manufacturing of e-mobility components, especially for parts made of copper and aluminum. However, welding these materials poses significant challenges due to their high reflectivity and thermal conductivity, leading to insufficient penetration depth and reduced mechanical properties. Beam shaping offers a promising solution to overcome these challenges by modifying the laser beam's spatial intensity distribution. The use of beam-shaping optics can significantly enhance the welding process by controlling the energy distribution and improving the weld's quality. 
In this study, we demonstrate the successful welding of aluminum battery cases and copper busbars using beam shaping with multi-plane light conversion. Multi-plane light conversion is a novel technique that enables the creation of complex intensity profiles by redirecting the laser beam through multiple planes of phase modulators. Our results show that beam shaping significantly improves the weld quality by reducing spatters and pores, and enhances the mechanical properties of the weld. The multi-plane light conversion technique offers an additional degree of freedom in shaping the intensity profile, enabling further optimization of the weld's quality, and present a higher depth of field enabling a more robust process. 
The successful welding of copper and aluminum components using beam shaping offers a promising solution for the reliable and efficient manufacturing of e-mobility components.

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Mid-IR Waveguide Beamsplitters in IG2 Glass by Ultrafast Laser Inscription

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Laser Processing with femtosecond and picosecond at 150W