United States

The laser peening is a surface treatment technology that improves the mechanical performance of metals. For instance, it has been utilized to increase the resistance of a metal to crack initiation, extend the fatigue life, and enhance the fatigue strength. These effects are imparted by shockwave generated by the expansion of laser-induced ablation plasma. Utilizing double-pulse laser ablation is one of the methods to improve a coupling of the laser beam with the plasma plume and target material. With double-pulse laser ablation, a target material is irradiated by two pulsed laser beams separated by a nanosecond inter-pulse delay time. It is reported that this irradiation method allows for a more effective energy delivery to the plasma plume and target material. In this study, double-pulse laser ablation has been adopted for laser peening. The experiments were performed by two Nd: YAG Q-switched pulsed lasers (wavelength: 532 nm) in water ambient. Austenitic stainless steel SUS316L was used as the target sample. The pulse durations of the first pulse and second pulse were 6 and 4 ns, respectively. Varying the inter-pulse delay time, the surface hardness on the sample after laser peening was evaluated. The results indicated that the surface hardness depends on the inter-pulse delay time. It is found that optimizing the inter-pulse delay time for a double-pulse laser enables enhancement of the laser peening effect.

ICALEO 2024

Double-Pulse Laser Peening as a Surface Enhancement Technology

surface enhancement

double pulse

laser peening

laser ablation

poster

  #### 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
from around the globe.

#### About LIA Conferences

The conferences of the Laser Institute of America are the town square of the laser community. A large and diverse group, laser professionals often find themselves disconnected from each other. LIA conferences, however, bring the university researcher, the business executive and the production floor user together under one roof for a unique and
rewarding networking opportunity.

#### 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. 

Sustainable and cost-effective long-term archival storage remains an unsolved problem.  The most widely used enterprise storage technologies today are magnetic (hard disk drives and tape). They use media that degrades over time and have a limited lifetime, which leads to inefficient, wasteful, and costly solutions for long-lived data. This talk presents Silica: an archival digital data storage solution, designed starting from application of laser material processing, through multiple layers of abstraction, to address the needs of the modern archival workload.  Silica can support a wide range of archival storage workloads and ushers in a new era of sustainable, cost-effective storage.

Project Silica: Application of Laser Material Processing to Archival Storage

Throughout Greg’s 30-plus year career in lasers he has continually seen how this amazing technology has overcome tremendous obstacles to revolutionize applications and industries. He will share from his personal experiences several encouraging and fun examples that will leave you feeling that lasers really are the star of the show!

“Lights, Camera, Laser Action!”

Pure copper has antimicrobial effect, and the development of pure copper coating technology for product surfaces is needed to prevent the spread of infections. To achieve high antimicrobial performance in coatings, it is essential to form a coating with high copper purity and minimal defects. In this study, we attempted to form a pure copper coating layer on a SS304 substrate using multi-beam directed energy deposition with blue diode lasers. In the coating layer formation process, multiple bead layers are overlapped to form a smooth surface and two different types of joining is conducted simultaneously: the similar material joining area with the remelted previous layer, and the dissimilar material joining area with the substrate. However, it was challenging to conduct this process for SS304 and pure copper, due to their significantly different thermal properties. Therefore, we varied the hatching distance to control the heat input to both joining areas and investigated the effect on the quality of the coating layer. The results showed that there is an optimal ratio of similar and dissimilar joining areas, at which a high-quality coating layer with few voids and low dilution is formed. Furthermore, antimicrobial tests showed that the pure copper coating layer formed in this study exhibited the antimicrobial performance equivalent to those of a pure copper plate.

Pure Copper Coating by Multi Beam Directed Energy Deposition With Blue Lasers for Antimicrobial Effect

The electrification of the mobility sector is vital to meet the targets for reducing greenhouse gas emissions. Besides battery-based mobility solutions, polymer electrolyte membrane fuel cells (PEMFCs) are a promising technology for electrifying drive trains, especially in heavy-duty applications, such as maritime or logistics. Bipolar plates, a key component of PEMFCs, can consist of two stainless-steel foils that must be welded to be gas-tight. In order to join the two metal foils, laser beam welding is the state-of-the-art technology. Current challenges include process instabilities at higher welding speeds, such as the humping effect, which can cause weld seam imperfections. Therefore, applying sensors for laser beam welding is a promising approach to monitor the welding process. AISI 316L foils were welded within the scope of this work with various process parameters using an adjustable ring mode laser beam source. Additionally, an optical microphone was used as a process monitoring system. By applying different parameter settings and due to the introduction of artificial faults, weld seam defects, such as a burn-through or a gap, were induced. After utilizing a noise reduction algorithm for the acoustic signals, numerous features in the time and frequency domain were extracted, with which multiple machine learning algorithms were trained and compared concerning their performance. A light gradient boosting machine was identified as a suitable machine learning model for the weld seam classification. Finally, a hyperparameter tuning was conducted, which resulted in a cross-validation accuracy of 94.78 %, depending on the quality categories considered.

Acoustic Process Monitoring During the Laser Beam Welding of Stainless-Steel Foils Using an Adjustable Ring Mode Laser Beam Source

In this paper, the necessity and theoretical analysis for Nanosecond-Scale Temperature Sensing Technology during Flat-Top Nanosecond Green Laser Annealing Process of Semiconductor Si-Wafer is overviewed. When a 532nm laser pulse with 10 ns or less pulse duration and several 100s mJ pulse energy is irradiated on the Si-wafer chip surface, the surface and internal temperature inside the chip is increased to several 100s or thousands quickly and cooled down during the next several 100s nanoseconds. The fastest commercial temperature sensor based on IR energy sensing has 40 us response time at which time the cooling process was already finished. So, the annealing process using 10 ns pulse laser annealing needs a proper method of ultrafast temperature measurement technology to understand the relationship between heated temperature and annealing quality which can make an impact on semiconductor chip performance. To resolve this issue, two-wavelength temperature measurement technology using fiber-guided sensing is selected among several technologies which is analyzed to know re-emission energy distribution from the Si-Chip and the captured energy into sensing fiber. Then, a proper focusing lens or lens set with optimum entrance pupil size to enhance the captured energy is determined. Then, a prototype setup for this two-tone temperature measurement is prepared and its performance is tried to compare with the results using a fast commercial temperature sensor.

Analysis of Nanosecond-Scale Temperature Sensing Technology for Flat-Top Nanosecond Green Laser Annealing Process of Semiconductor Si Wafers

Chromatic dispersion is a wavelength dependence of a group velocity of an optical fiber, and is an important fiber characteristic in fabricating pulse fiber lasers because it affects spectrum and pulse width. One of the chromatic dispersion measurement methods is a phase shift technique, which measures a relative phase shift between intensity-modulated lasers with different wavelengths. A disadvantage of this measurement method is that fiber lengths of several hundred meters or more are required to obtain high time resolution. Therefore, specialty fiber with short production lengths and amplification fiber that absorbs light of a specific wavelength, used for pulse fiber lasers, is difficult to measure with the method.

This study aims to develop a chromatic dispersion measurement method that can evaluate specialty fiber and amplification fiber using a short fiber under test of a few meters. The measurement light source used is a broadband light of high brightness and fiber optics that we developed. The feature of this study is that the fiber under test constitutes a Fabry-Perot resonator using the Fresnel reflections at both endfaces of the fiber. Enables measurement with the short fiber under test because it is measured from a standing wave of the resonator. The wavelength dependence of reflection characteristics from the standing wave is measured to obtain a relative group delay. Chromatic dispersion can be obtained by measuring the group delay difference at different wavelengths. Also, the fiber under test is the resonator, therefore measurement can be done without connectors and end face polishing.

Development of Wavelength Dispersion Measurement Method Using Fresnel Reflection of Fiber Under Test at Both End Faces

Additive Manufacturing (AM) has revolutionized the production of high-performance components, particularly in industries like motorsport and aerospace. This study investigates the mechanical properties of AM-produced AlSi10Mg and introduces a novel Al2024-RAM2C alloy, designed to elevate the performance benchmarks of AM aluminum alloys in demanding environments. The Al2024-RAM2C alloy, formulated with patented RAM additions, showcases a suite of superior characteristics, including high tensile strength and enhanced fatigue resistance. However, the integration of this innovative alloy with AM processes necessitated meticulous parameter optimization efforts. Through comprehensive testing methodologies, the mechanical strength, impact toughness, and fatigue resistance in both axial and flexural bending loading of both AlSi10Mg and Al2024-RAM2C were carefully evaluated and further analyzed through FE-SEM microscopy. Results from these analyses revealed that while Al2024-RAM2C exhibited higher fatigue limits in axial loading and superior tensile strength, its impact toughness was significantly lower than that of AlSi10Mg. This comparative study clarifies the inherent strengths and limitations of the Al2024-RAM2C alloy relative to AlSi10Mg. The findings provide valuable insights into the performance characteristics of these materials, which can inform future developments in material design and manufacturing processes. This research contributes to the broader understanding of AM-enabled materials and their potential applications in producing lightweight, high-performance components for various industries.

Advanced Additive Manufacturing: Comparative Analysis of Mechanical Properties of AlSi10Mg and Al2024-RAM2C

Laser welding is widely used in the automotive industry to join various materials due to its advantages of minimal thermal deformation and high productivity, applied in different joint

configurations, such as T-fillet and single-lap. The tensile properties of these joints are crucial for the stability of vehicle bodies, prompting research into both experimental and analytical evaluations. In particular, to experimentally evaluate the tensile properties of single-lap joints, a load cell-based force and crosshead displacement are generally used. However, the reliability of crosshead displacement data is affected by machine compliance and the specimen's dimensions, resulting in low reliability of displacement-related tensile properties such as structural stiffness. This can lead to discrepancies between experimental results and numerical analysis, which are critical for evaluating vehicle stability. Therefore, this study introduces a novel numerical modeling method for predicting structural stiffness using crosshead displacement during tensile testing of single-lap joints. Additionally, it presents modeling techniques to enhance the computational efficiency of the numerical model. Laser welding was performed on two types of materials, SPFC 590 and A6061, to make single-lap joint specimens. To evaluate the structural stiffness of these specimens, lap-shear tensile test was conducted. A three-dimensional numerical model based on ABAQUS software was developed, and a modeling method involving the application of an elastic modulus in the numerical model was proposed to enhance the correlation with the structural stiffness derived from lap-shear tensile test. Furthermore, modeling techniques such as optimizing mesh size and element type were suggested to enhance the computational efficiency.

A study on numerical modeling method for predicting structural stiffness using crosshead displacement in laser welded joints

Ultra-short pulse laser machining has emerged as a transformative technology across various industries, including medical device fabrication, electronics manufacturing, and precision glass machining. With each technological leap in laser power, new industrial applications have become feasible. Yet, as the industry approaches the threshold of high-power ultra-short pulse lasers, such as kilowatt-scale femtosecond systems for advanced R&D, the challenge shifts from merely harnessing this power to utilizing it intelligently without sacrificing machining quality. This is crucial as many users currently underutilize their systems' capabilities due to quality degradation at higher power settings.

This presentation addresses the utilization of Multi-Plane Light Conversion (MPLC) technology to optimize and expand the capabilities of ultra-short pulse laser systems. MPLC technology, notable for its entirely reflective design, ensures durability under high power and enhances process efficiency. Its mode-cleaning feature provides stable and robust beam shaping, which is less susceptible to laser and environmental variations, making it ideal for precision applications. Additionally, MPLC allows for intricate, high-quality beam shaping with an extensive depth of field, significantly easing integration into existing systems.

We will discuss the application of MPLC in combining beam shaping with splitting functionalities, highlighting the flexibility of this approach. Specific adaptations, such as adjustable beam division pitch, shape alterations, and rotation capabilities, will be showcased alongside their impact on the quality of micro-machining processes, particularly in surface texturing. The results underscore substantial improvements in both the quality and throughput of machining processes.

Advancing Ultra-Short Pulse Laser Machining with MPLC Technology: Enhancing Micro-Processing Capabilities

Ultrafast laser surface structuring presents a compelling avenue for finely tuning material surface properties, such as coloration, wettability, tribological properties, etc. While nanoripples, the conventional laser-induced periodic surface structures, offer control over surface coloration, their effectiveness is limited to a narrow viewing angle. Addressing this limitation requires the development of techniques for generating alternative surface structures like nanobumps. Current methods for generating nanobumps, such as the double-pulse technique, are characterized by their complexity and high costs, posing significant challenges to widespread implementation. In this investigation, we introduce a novel approach for creating periodic nanobump structures through a straightforward double-scan method. This method involves subjecting the same surface to two consecutive laser scans with differing polarization directions.

Our study delves into the formation dynamics of these intriguing nanostructures, exploring the influence of laser parameters such as peak fluence, overlapping ratio, and polarization angle between scans. We propose and validate a formation mechanism to elucidate the observed phenomena. The resultant nanobump structures exhibit superior optical characteristics compared to nanoripples, particularly in terms of enhanced visibility across multiple viewing angles. By broadening the scope of achievable surface structures, our findings significantly expand the potential applications of ultrafast laser surface structuring. This research not only advances our understanding of laser-material interactions but also paves the way for the development of innovative surface engineering strategies with implications across diverse fields.

Double-Pulse Laser Peening as a Surface Enhancement Technology

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