United States

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&amp;nbsp; repetition rate of the laser, but he onset of thermal accumulation in the material limits this approach.&lt;br&gt;
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 mm&lt;sup&gt;3&lt;/sup&gt;/min/W), and the crucial role of the pulse overlap.

ICALEO 2023

GHz Long Burst for Femtosecond Laser Processing Optimization

ghz bursts

miocro-processing

ultrafast laser

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.

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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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.

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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.

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.

Ultrashort Pulsed Lasers and New Laser Wavelengths for Improved Battery Manufacturing

Laser welding is a key enabling technology the transition towards electric mobility, enabling joints with elevated electrical and mechanical properties. In the production of battery packs, cell to busbar connections are challenging due to the strict tolerances and zero-fault policy. Hence, it is of great interest to investigate how beam shaping techniques may be exploited to enhance the electro-mechanical properties as well as improve material processability. Industrial laser systems often provide the possibility to oscillate dynamically the beam or redistribute the power in multi-core fibers. Although contemporary equipment enables elevated flexibility in terms of power redistribution, further studies are required to indicate the most adequate solution for the production of high performance batteries. 
Within the present investigation, both in-source beam shaping and beam oscillation have been exploited to perform 0.2-0.2 mm Ni-plated steel welds in lap joint configuration, representative of typical cell to busbar connections. An experimental campaign allowed to define process feasibility conditions where partial penetration welds could be achieved by means of in-source beam shaping. Hence, dynamic beam oscillation was explored to perform the connections. In the subset of feasible conditions, the mechanical strength was determined via tensile tests alongside electrical resistance measurements. In-situ high speed videography allowed to disclose the process dynamics. Linear welds with a Gaussian beam profile enabled joints with the highest productivity at constant electro-mechanical properties. Spatter formation due to keyhole instabilities could be avoided by redistributing the emission power via multi-core fibers whilst dynamic oscillation did not provide significant benefits.

Effect of In-Source Beam Shaping and Laser Beam Oscillation on the Electro-Mechanical Properties of Ni-Plated Steel Joints for E-Vehicle Battery Manufacturing

We discuss laser micromachining as a means of fabricating dielectric-based electrospray thrusters that use ionic liquid propellants for nanosatellite propulsion applications. Because of their small size, nanosats typically lack means of propulsion, which limits their lifetimes and mission scopes and is problematic for deorbit at end of life. Electrospray thrusters, however, can be very compact, using electric potentials to accelerate and eject ionic matter, thereby achieving high specific impulse. Traditional fabrication methods involve numerous steps, including lithography and/or chemical etching, resulting in microscale emitter structures that protrude from a substrate and can easily be damaged during assembly and/or launch. This format also requires a separate, detached grid electrode that serves as an extraction grid needed to induce ionic emission of propellant from the emitters. Our fabrication approach uses Bessel-beam laser micromachining to form embedded, micron-diameter capillaries up to several hundred microns long through a transparent glass substrate, without chemical etching. One surface of the glass is coated with a transparent conductive layer that serves as an integrated extraction electrode and which needs no alignment. Further laser machining with Gaussian-beam, water-assisted cavitation is used to excavate cylindrical electrospray cavities in this surface around each capillary, to catch errant propellant and prevent shorting while optimizing the capillary emitter-extractor separation distance. The resulting array of capillary emitters and cavities with integrated extractor comprises an electrospray emitter chip that forms the core of an electrospray thruster, and provides the potential to achieve significantly lower onset voltages than traditional electrospray thruster designs.

Laser Microfabrication for Ionic Propulsion Systems

Liquid immersion is used in laser machining to cool and remove debris from samples.&nbsp; The use of fluid media such as water, oils, or air for machining is well researched; however, the application of low-vapor-pressure fluids, such as ionic liquids, for laser micromachining has not been researched in depth.&nbsp; Ionic liquids are electrically neutral salts that are liquid at room temperature.&nbsp; These liquids tend to have low vapor pressure, which impacts a fluid’s ability to vaporize and cavitate during laser machining.&nbsp; Fluids with high vapor pressures, on the other hand, can be considered volatile and easily vaporize with minimal added energy.&nbsp; This paper discusses the effects of various immersion fluids on laser micromachining.&nbsp; &nbsp;Different immersion media were tested on a borosilicate glass cover slip using ultrafast (300 fs) laser pulses focused by a high numerical aperture (NA 1.2) immersion lens.&nbsp; For each immersion fluid, rectangular arrays of holes were machined with single, well-separated pulses, where the cover slip was translated laterally and stepped axially to change the focal position and bracketing the glass surface with positions both above (in the fluid) and below it (in the glass).&nbsp; The machined samples were then replicated with polymer imprint lithography, and both the substrate and replica were imaged using optical and scanning electron microscopies.&nbsp; The results suggest that fluids with lower vapor pressures, like ionic liquids, can expand the usable machining focal range, while also reducing the diameter of the holes and perhaps even mitigating collateral surface damage.

Fluid-Immersion Laser Micromachining Using Ionic Liquids

In this study, laser doping of n-type 4H-SiC with boron for mid-wave infrared (MWIR) optical properties is reported. A novel doping technique based on a pulsed Nd:YAG laser (1064 nm) for doping silicon carbide (SiC) was developed. An aqueous boric acid (H 3 BO 3 ) solution was utilized as a precursor to facilitate p-type doping in 4H-SiC. FTIR spectrometry was used to characterize the optical properties of the as-received and boron-doped samples within the MWIR range. The boron dopant created an acceptor energy level at (E v + 0.29 eV) within the bandgap of 4H-SiC, corresponding to 4.3 µm wavelength. Upon absorption of photons of this wavelength by the boron-doped 4H-SiC, the electron densities in valence and acceptor energy levels were altered, resulting in a change in the refraction index of the 4H-SiC substrate. A theoretical heat transfer model was devised to establish a correlation between laser processing parameters and various other factors that impact the effectiveness of the laser doping process. These factors include the laser-substrate interaction time, minimum dopant diffusion time, dopant concentration in precursor solution and dopant concentration diffused into the substrate. To ensure a thorough analysis, a comprehensive investigation was carried out on the as-received and boron-doped samples, encompassing a careful examination of their optical properties for the MWIR wavelength range. The laser doping process resulted in a notable decrease in the refraction index from 2.873 to 2.517. Our experimental results aligned with the theoretical model developed for selecting the laser processing parameters, affirming its success.

Laser Doping of N-Type 4H-SiC With Boron Using Solution Precursor for MWIR Optical Properties

As emerging of IoT devices, the ICs should be fast. To fulfill the fast performance, 3D ICs has been adopted. A 3D IC has relatively shorter connection electrode than conventional 2D ICs. And it is achieved by interposer. A interposer has via holes which are filled with conducting materials. In previous studies, various researchers have been suggested glass interposer, so called through glass via (TGV). Since glass has low electric permittivity, thus it is suitable for interposer. Also, glass can match its thermal expansion coefficient with silicon and it can suppress a warpage of wafer. Therefore, we have been studying of TGV for last few years. There are many methods which can generate via holes in the glass. Among them, recently, selective laser etching is emerging as a good candidate for mass production. It consists with two steps for generating TGV. Which is laser local modification and chemical etching. With previous study, we could enhance a process speed with Bessel beam shaping and picosecond interval pulses. In this study, we are focused on chemical etching process. In order to enhance the etching rate, 4 different etchants are tested. Which is HF, KOH, NaOH, and NH4F. Each etchant has its own optimal etching conditions, such as temperature and molar concentration. Here, we compare their etching results. The main criteria of comparison is selectivity. In our study, NH4F shows the best selectivity. Thus, we claim that NH4F can be a good candidate etchant for mass production of Glass interposer.

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

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Next from ICALEO 2023

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

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