United States

Due to its exceptional dimensional stability in harsh thermal conditions and excellent mechanical and optical properties, Corning ultra-low expansion (ULE®) glass is the material of choice in many high-demanding fields such as aerospace, astronomy, and advanced optics. This material has recently attracted renewed attention with the advent of femtosecond laser technology, with a particular focus on the interaction of ultrafast pulses and the material itself. Phenomena like the formation of self-assembled nanogratings and their thermal stability as well as the darkening of laser-affected zones have then been characterized. This paper presents how to exploit femtosecond selective laser etching (SLE) techniques to manufacture truly three-dimensional (3D) components. To demonstrate the micron-scale accuracy and repeatability of this process from the mm- to the cm-size range, various devices are designed and fabricated: fiber hole arrays with different hole densities, sizes, orientations, and shapes; and fiber V-groove arrays. Additionally, a mechanical flexural fiber mount is presented as an example of how multiple functionalities can be monolithically integrated into a single piece of glass through SLE technology. An example of a passive alignment substrate for optical components is also shown. SLE technique represents a new advancement in the field of microscale manufacturing, enabling the scalable production of custom-designed ULE® glass structures with unprecedented precision and complexity, paving the way for the miniaturized integration of highly stable components.

ICALEO 2024

High Precision Microscale 3D Manufacturing of Ultra Low Expansion Glass by Femtosecond Selective Laser Etching

femtosecond selective laser etching

ultra low expansion glass

3d manufacturing

femtosecond laser

  #### Welcome to the 43rd annual ICALEO!

Attention laser enthusiasts, innovators, and industry leaders! Get ready to immerse yourself in the exciting world of lasers at the 43rd annual ICALEO conference. This year, we gathered in the iconic city of Hollywood, California, for cutting-edge technology, groundbreaking presentations, and unparalleled networking opportunities.
Whether you're a seasoned professional or new to the field of photonics, the 43rd annual ICALEO had something for everyone. 

#### General Chair Welcome Message

It is with immense joy and anticipation that I extend a warm welcome to each and every one of you as the General Chair of this year's ICALEO conference.

This year, we find ourselves in the iconic setting of Hollywood, serving as a fitting backdrop for the extraordinary developments in laser technology and applications unfolding in our community.

Our main sessions cover a diverse range of topics, from the intricacies of micro and nano processing to the transformative power of laser additive manufacturing. We will explore the frontiers of battery technology, delve into the intricate world of artificial intelligence, and witness the seamless integration of lasers into these realms.

For those joining us for the first time, we extend an especially heartfelt welcome. ICALEO is not just a conference; it's a convergence of minds, ideas, and innovations. Beyond the formal sessions, I encourage you to engage in informal exchanges. The spirit of discovery and camaraderie is as much a part of the ICALEO experience as the scheduled sessions.

Thank you for being a part of ICALEO 2024. Whether you are a returning participant or a first-time attendee, your presence adds immeasurable value to our vibrant community. May this conference be, this year again, a catalyst for inspiration, collaboration, and breakthroughs that will resonate in our community and beyond.

Eric Mottay<br>
Congress General Chair, ICALEO 2024


#### About LIA

The Laser Institute of America (LIA) is the professional society for laser applications and safety. Our mission is to foster lasers, laser applications, and laser safety worldwide. Serving the industrial, medical, research and government communities for over 50 years, LIA offers technical information, training and networking opportunities to laser users
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#### About LIA Conferences

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#### Program Tracks
Below is the list of all tracks that were on ICALEO 2024 Conference.

##### Laser Additive Manufacturing
* The Laser Additive Manufacturing (LAM) track is a forum to explore the latest innovations and research in laser-based additive manufacturing (LAM). The Laser Additive Manufacturing track focuses on diverse topics, including laser-based powder bed fusion (PBF-LB), directed energy deposition (DED), and other emerging techniques revolutionizing modern manufacturing processes. From materials science to process optimization, from design innovation to industrial implementation, this track connects researchers, engineers, and industry leaders to exchange insights and share breakthroughs in laser additive manufacturing.

##### Laser Materials Macroprocessing
* The Macroprocessing track comprises some of the most productive laser processing applications. Although these applications have been broadly adopted, researchers and industry are persistently innovating to provide new techniques and novel technologies to advance macro materials processing. The attendees will share and discuss those exciting achievements of their research with peers in these macroscopic specialized sessions.

##### Laser Materials Microprocessing
* The Microprocessing track will consist of papers and talks featuring a wide spectrum of applications and innovative equipment for materials processing in microscales with a strong focus on processes with Short and Ultrashort Pulsed Lasers. The presentations will introduce the latest and greatest advancements in their respective fields, presented by world-leading companies and research organizations. This year we will have talks around the headlines of “Beam shaping”, “Glass”, “Surface processing” and “Drilling” between other topics.

##### Frontiers in Laser Applications
* The Frontier in Laser Applications (FLA) track explores recent, cutting-edge applications of lasers, highlighting innovation at the transition of research and industry. The track has included presentations from a variety of fields: Novel 3-D Printing, Advanced Manufacturing, Laser Manufactured Devices, and Frontiers in Laser Processing. The sessions under the Frontier in Laser Application track promise to bring diverse and unique perspectives from real-world applications across laser manufacturing.

##### Laser in Battery Manufacturing
* Electrification is crucial to address global environmental challenges. The laser plays a key role in most manufacturing steps in battery production with all possible laser applications from ablation, structuring, welding, cutting, and marking. Further improvements in the batteries’ power densities, fast charging properties, and yield in battery production are related to photonics and, thus, lasers. We will hear and discuss the latest developments in research, development, and industrial applications. Join us for this year’s Battery Track.

##### Artifical Intelligence in Laser Processing
* The track ‘Artificial Intelligence in Laser Processing’ at ICALEO 2024 explores the fusion of AI and laser manufacturing. Discover cutting-edge research on optimizing laser processes and enhancing manufacturing efficiency. Explore AI’s diverse applications in parameter optimization, quality prediction, real-time process monitoring, and control. Join us to unlock the potential of AI-driven solutions revolutionizing laser materials processing, delivering unprecedented precision, productivity, and innovation.
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Attention laser enthusiasts, innovators, and industry leaders! Get ready to immerse yourself in the exciting world of lasers at the 43rd annual ICALEO conference. 

technical paper

The increasing demand for miniaturization in electronics has driven the need for advanced fabrication techniques capable of producing through-glass vias (TGVs) with high precision, minimal spacing, and low defect rates. Ultrafast laser-based methods, particularly laser drilling and selective laser etching (SLE), have emerged as critical technologies in the fabrication of TGVs for 3D microchip stacking. Glass offers superior electrical properties, such as reduced signal loss, improved thermal stability and mechanical strength compared to traditional materials like silicon. This study presents advancements in ultrafast laser drilling techniques for TGV fabrication. We demonstrate the feasibility of taper-free fabrication of high-aspect-ratio holes, addressing a common challenge in traditional ablation-based drilling methods. By controlling laser parameters and employing optimized processing strategies, we achieve uniform hole diameters below 100 um, reaching an aspect ratio of 1:20 without chemical etching. Our research focuses on process speed optimization to enhance fabrication efficiency. Moreover, we demonstrate a high aspect ratio and high-speed percussion drilling of through holes for the glass substrates thicker than 0.5 mm. The results were obtained using <200 uJ ultrashort pulses at 1030 nm wavelength (Jasper X0, Fluence, Poland). Our findings highlight the remarkable capabilities of ultrafast laser drilling for TGV fabrication for new microchip generation.

Advancements in Femtosecond Laser Drilling Techniques for Through-Glass Vias

Femtosecond laser processing is used in a wide range of  modern technology manufacturing. Its significance is particularly evident in sectors that demand high accuracy and minimal heat effects, like microelectronics, biomedical devices, and photonics. The field has recently seen ultraviolet (UV) wavelengths become a standard in laser processing as optical coatings have become resistant to prolonged exposure to UV radiation. These features have opened up exciting new avenues in both manufacturing and scientific research.

In this study, we explore the application of novel femtosecond laser that produces a flat-top intensity distribution, at a wavelength of 254 nm (4th harmonic of fundamental 1030 nm radiation). The 4th harmonic offers unique advantages in material processing due to its position in the direct absorption regime for multiple glass and polymer materials. Our experiments demonstrate the effective ablation of soda-lime glass using this specific wavelength.

A key feature of our methodology is the employment of a flat-top intensity distribution in the laser beam. Comparing to the conventional case of the Gaussian intensity distribution, a notable advantage is the consistent size of the damage patterns (craters) in both transverse directions, irrespective of variations in pulse energy or number of pulses impinged. This consistency is not achievable with traditional Gaussian distributions, making this approach more precise and predictable. In addition, the flat-top DUV laser source may be used for the removal of coatings on transparent substrates.

Processing of Transparent Glass Using a Femtosecond Duv Flat-Top Laser Source

The parameter space of beam shaping methods for laser driven processes is getting broader looking at spatial light modulators or coherent beam combining. While systems technology is improving, the knowledge on using beam shaping is mostly empirical driven and not - yet - based on a comprehensive understanding of causalities in the process physics. This presentation will, based on a comprehensive literature study, show some fundamental thoughts on how to connect beam shaping to process physics. To do so, laser deep welding is used as an example process, ready to be improved. In the presentation systems technology will be touched and compared. A process driven view on beam shaping will be developed and then connected to systems technology. Own research results will be used to underline the hypotheses given.

Beam Shaping vs. Feature Synchronous Energy Coupling

The laser energy absorption on the keyhole wall is decisive for the thermodynamic behavior and the resultant weld properties in the high-power laser beam welding process. Consequently, a realistic implementation of the effect of the laser radiation on the weld metal is crucial to obtain reliable and accurate simulation results. However, its highly transient nature on a microsecond scale makes the quantitative analysis challenging. In this paper, the influence of the relevant welding parameters, e.g. laser power, welding speed and focus position, on the laser energy absorption is studied statistically, namely in a time-averaged manner, by utilizing multi-physical modeling, in which the three-dimensional transient keyhole dynamics and thermo-fluid flow are calculated. The free surface is tracked by the volume-of-fluid algorithm. An advanced ray-tracing method based on a localized Level-Set strategy is employed to consider the underlying laser-material interactions, i.e. the multiple reflections and Fresnel absorption. The results show that the focus position has a remarkable effect on the time-averaged laser absorption, to which more attention should be paid. In contrast, the laser energy distribution regime is only slightly influenced by the welding speed in the studied parameter range between 1.5 m/min and 3 m/min. The comparison between the calculated results and the experimental measurements ensures the validity of the proposed model.

A Parametric Study of the Laser Energy Absorption in High-power Laser Beam Welding

Recent research has investigated in-situ process characterization for laser welding and Laser-based Powder Bed Fusion of Metals (PBF-LB/M) via a reflection measurement in the laser wavelength. These studies successfully identified the prevailing process regime and the formation of a vapor depression based on in-situ integrating sphere data. This approach has great potential to accelerate the process development by reducing the required ex-situ specimen testing. Unfortunately, the measurement with an integrating sphere does not allow its application as an in-line monitoring system without significantly restricting the process design because the integrating sphere is placed within the gas flow and limits the working area with its small aperture close to the process zone. Therefore, this work investigates directional reflection-based process monitoring in the laser wavelength for laser welding and PBF-LB/M of AISI 316L under insignificant restrictions to the system. For this, the changes in direction and intensity of the reflected laser radiation are monitored for bare plate experiments at various laser powers with photodiodes, which are fiber-coupled to parabolic dish collectors surrounding the working area. These experiments are conducted in a wide working area. It was found that a characteristic change in the reflection direction coincides with the threshold for vapor depression formation, which was previously identified with the integrating sphere. These results show great potential for in-line process monitoring because this novel measuring approach adds directional information to reflection monitoring while decreasing its impact on the process design.

In-Line Process Monitoring in Laser Welding and Powder Bed Fusion of Metals Using Directional Reflection Measurements

Directed energy deposition (DED) for additive manufacturing applications is commonly realized by the usage of industrial robots. The DED processing end effectors are usually mounted on industrial robot systems and can therefore be moved and oriented in up to many degrees of freedom. However, the design of the powder nozzle and the programming of the robot can limit the movement options. For this reason, translational movements, as with conventional 3D printers, are still common today. The end effector is usually guided vertically over the component surface. Although welding in forced position (PA) is preferred.

It may be necessary to tilt the end effector in order to gain advantages during processing due to the constrained position. This is particularly advantageous for overhang structures and is often realized with the help of a turn-tilt positioning table in combination with an industrial robot. However, this approach is in some cases not possible due to geometrical constrains. To extend applications in this direction, advanced methods for slicing the components and programming the robot movements are necessary. The main aspect of this work is the development, testing and evaluation of a multidimensional DED manufacturing approach. This is tested on a thin-walled component with defined overhang areas and compared with conventional approaches. Different strategies are assessed in terms of the geometrical match of the target geometry. Influences of strategies on the results are evaluated. It can be shown that multidimensional path planning approaches lead to a better match of the target geometry.

Influence of Robot-Guide Strategies on the Geometry of Directed Energy Deposition Components

To design future laser manufacturing processes for welding of copper materials, more and more high-end analysis methods are required. A fundamental process understanding by analyzing cause-and-effect relations of process dynamics using inline in situ diagnostics allows for an improved description of laser material interaction. Strategies for a reliable and robust welding process are derived from the findings. In this study, a four-step advanced methodical approach is presented and discussed. In the first step, a fundamental process description of the geometry of the vapor capillary and the formation of weld defects is developed. Therefore, welds on electrolytic tough pitch copper (Cu-ETP) and CuSn6 are carried out to analyze the temporal and spatial vapor capillary dynamics depending on laser power, welding speed, and focal diameter. This fundamental process understanding is transferred to the welding of copper pins in the form of I-pins. For this purpose, impurities and imperfections were applied to the pin surface to investigate the effects on the process result. As a third step, strategies by means of laser intensity distributions were adapted to compensate for imperfections in the welding process. Finally, a sensor vision system is adapted for ideal welding results. Investigations are based on in situ synchrotron analysis at Petra III, DESY in Hamburg. For the experiments, a TRUMPF TruDisk laser (100/400 μm fiber diameter), a TRUMPF TruFiber 6000P (50/100 μm fiber diameter), and a single-mode fiber laser (14 μm fiber diameter) were used. The focal diameter was adjusted with the optical system depending on the investigation.

A Development Workflow Based on In Situ Synchrotron Investigations to Optimize Laser-Processing of Copper Pins

In the realm of laser powder bed fusion, an emerging field with significant growth potential, we still find ourselves at a pioneering stage characterized by the intricate interplay between laser beam properties and their interaction with powdered material.  It is commonly assumed that a high-quality laser having a low M2 value would maintain a consistent M2 value uniformly across the build plate.  However, contrary to this assumption, variations do occur across the build plate, not due to fluctuations in the laser's M2 value, but rather due to alterations in the beam's geometry.  Even in scenarios where the F-theta lens or the 3-D galvo system operate at diffraction-limited conditions, the reality persists that a Gaussian beam with a low M2 value positioned at the nominal zero-zero point of the galvo system will inevitably lose its circular profile at positions beyond the zero-zero point.  At non-zero angles, the beam undergoes distortion, presenting itself to the powdered material as a conic section of the single-mode Gaussian beam.  Employing an innovative M2 measurement apparatus, we have quantified the M2 variation inherent in a fiber laser galvo scanning system across a scan field measuring 175mm x 175mm.  This understanding of the M2 variant holds significant promise in facilitating the stabilization of an optimal spot size.  Through dynamic focusing adjustments based on the powder bed's positional information, we can effectively compensate for the observed variance, thereby enhancing the overall performance and reliability of the laser powder bed fusion process.

M2 Projection Variant in Laser Powder Bed Fusion Systems

Smart-Alloying enables local modification of the chemical composition of metallic components within additive manufacturing processes. This new method represents an innovative process for localized grading of metallic materials in laser-based additive manufacturing. Smart-Alloying involves applying nanoparticulate alloying elements onto the surfaces of additive manufactured components in precise doses using suspensions. The method is shown here using a laser powder bed fusion (PBF-LB/M) as an example. By coating the base material powder and exposing it to the laser source, localized modifications in chemical composition and altered properties can be achieved. Using a chromium-rich ferritic stainless steel as an example, significant alterations in the fundamental microstructure are attained through localized re-alloying of carbon. Investigation utilizing FIB-SEM elucidate the evolution of increasing carbon content within the re-alloyed area. Next to the formation of chromium-rich carbides and ultrafine regions of needle-like martensite, retained austenite could be made visible. The completely renewed microstructure is then further modified using secondary exposures of the laser source. Under the influence of the subsequent melting process, there is an increasing distribution of the re-alloyed carbon, resulting in a completely new structure of a line-shaped duplex microstructure. The integration of secondary exposure introduces a completely novel aspect, offering the potential to merge localized grading via Smart-Alloying with targeted application of laser parameters.

Smart-Alloying for Tailored Microstructures in Laser-Based Metal Additive Manufacturing

The trajectory of metal additive manufacturing is transitioning from rapid prototyping towards on-demand and serial production. Consequently, the paramount objective remains the enhancement of additive manufacturing processes like laser-based powder bed fusion of metals (PBF-LB/M) to meet modern manufacturing needs and reduce environmental impact. Shielding gas flow significantly influences mechanical properties in PBF-LB/M by protecting metal from oxidation and removing process by-products from the powder melting zone. Accordingly, improper shielding gas flow distribution can result in poor part quality, excessive inert gas consumption, and contamination of the building chamber. Presently, a lack of consensus remains regarding which configuration of shielding gas supply is most appropriate in terms of process efficiency. This is the comprehensive investigation of a localized and vertically directed shielding gas flow and its effects on the properties of parts, also taking into account the reduction of inert gas consumption. In contrast to previous investigations, it is shown that enhanced surface roughness and relative density of the parts, as well as minimized contamination of the optics inside the building chamber is achieved through more efficient removal of metal plume particles from the processing zone by localized gas flow. Moreover, the developed computational fluid dynamics (CFD) simulation model enabled the efficient determination of particularly promising gas flow configurations. Furthemore, the validation of the simulation model is demonstrated in an experimental environment. Finally, by localizing shielding gas flow, energy consumption can be reduced by almost half.

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Advancements in Femtosecond Laser Drilling Techniques for Through-Glass Vias

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Processing of Transparent Glass Using a Femtosecond Duv Flat-Top Laser Source