ALPhANOV (France)

In this work, investigations of the interaction between borosilicate glass and three laser regimes are presented: repetitive single pulse, MHz-burst, and GHz-burst. Experiments were carried out using an ultrafast industrial laser system and galvanometric scanning to inscribe bulk modifications inside borosilicate glass (N-BK7) samples. By varying pulse or burst energy and scanning velocity, we produced a wide range of in-volume modification morphologies. This approach enabled to classify modifications and establish processing maps for each regime. Results show that the single-pulse regime is more suited for generating large, defect-free bulk modifications with a teardrop shape, while the MHz-burst regime increases the probability of defect formation, including voids and local cracking. These defects become even more pronounced under GHz-burst irradiation, where the lower energy per pulse results in absorption mainly near the focal point, leading to crack formation. Overall, this work provides a comprehensive understanding of glass behavior under femtosecond laser irradiation and provides guidelines for selecting laser conditions suitable for transparent glass welding.

The switching transistors of an Integrated Circuit (IC) emit photons in a phenomenon known as photon emission. This emission allows for the observation of a circuit's activity and the reverseengineering of its internal components. Under certain conditions, the data being processed can be retrieved using a technique called Photon Emission Analysis (PEA). This paper demonstrates how PEA may be employed to reverse-engineer and retrieve data from the Flash memory embedded in Microcontroller Units (MCUs). It describes the constraints and limitations of PEA while offering a comprehensive explanation of the mechanisms governing light emission in ICs. Detailed insights are provided into the optical setup, sensors used, and operational nuances of embedded MCU memory. To capitalize on the information presented, various scenarios for reverse-engineering the Flash array of an MCU are demonstrated using Space-Resolved Photon Emission Analysis. Additionally, an attack scenario exploiting the memory architecture asserted during the characterization phase is presented, demonstrating how secret data stored in the Flash can be retrieved by an attacker with the equipment detailed in this work. • Security and privacy → Hardware attacks and countermeasures; Security in hardware; Hardware reverse engineering; • Hardware → Non-volatile memory.

In this contribution we show through via drillings in dielectrics by ultrafast laser top-down percussion drilling in GHzburst mode. We point out some limitations that occur during the drilling process and show how to overcome these. Finally, we obtained through vias of almost constant diameter in Sodalime glass, which might be of interest in the microelectronics industry for the fabrication of glass interposers.

Femtosecond (fs) laser technology is currently being considered in innovative fields such as osteotomy and treatment of hard tissue thanks to the achievable high resolution and ability to prevent tissue damage. In a previous study, suitable process parameters were obtained to achieve competitive ablation rates on pork femur processing. Nevertheless, a better control of thermal accumulation in the tissue during laser ablation could further improve the postoperative regeneration of the treated bone compared with conventional procedures and push forward the exploitation of such technology. This study presents methods for real time analyses of bone tissue temperature and composition during fs laser ablation and highlights the importance of implementing an efficient cooling method of bone tissue in order to achieve optimized results. Results show that it is possible to achieve a larger process window for bone tissue ablation where bone tissue temperature remains within the protein denaturation temperature in water-based processing environment. This is a key outcome towards a clinical exploitation of the presented technology, where higher process throughputs are necessary. The effects of process parameters and environments on bone tissue were confirmed by LIBS technique, which proved to be an efficient method by which to record real-time variation of bone tissue composition during laser irradiation.

In Li-ion batteries, ion diffusion kinetics represent a limitation to combine high capacity and a fast charging rate. To bypass this, textured electrodes have been demonstrated to increase the active surface, decrease the material tortuosity and accelerate the electrolyte wetting. Amongst the structuring technologies, ultrashort pulse laser processing may represent the key option enabling, at the same time, high precision, negligible material deterioration and high throughput. Here, we report a study on the structuring of electrodes with both holes and grooves reaching the metallic collector. Electrochemical models emphasize the importance of hole and line dimensions for the performances of the cell. We demonstrate that we can control the hole and line width by adjusting the applied fluence and the repetition rate. In addition, results show that it is possible to drill 65 µm-deep and ~15 µm-wide holes in nearly 100 µs resulting in up to 10,000 holes/s. To further reduce the takt time, bursts of 40 MHz pulses were also investigated. We show that bursts can reduce the takt time by a factor that increases with the average power and the burst length. Moreover, at comparable fluence, we show that bursts can shorten the process more than theoretically expected.

New industrial applications of femtosecond lasers are continuously emerging in various industrial sectors: health, production, energy, transport. Fiber delivery of femtosecond pulses and power is a key enabling technology for opening industrial application fields much wider: conventional micromachining stations typically based on ultrastable and ultraheavy granite tables are avoided and the femtosecond laser is coupled into a flexible light guide instead. Ultraprecise machining processes can such be displaced far from the femtosecond laser source and coupled to moving axes or robot systems. Here, we report on a femtosecond fiber delivery system for industrial applications. In a first demonstration, the delivery system is coupled to a Satsuma industrial femtosecond laser with average output power of more than 20 W and pulse energy up to 60 μJ. Polarization control allows addressing any kind of micromachining applications, also those sensitive to the polarization state incident on the workpiece. Coupling of the fiber delivery system to a robot system and the nanotexturing by LIPSS will be here reported. Comparisons of the obtained results with conventional micromachining applications using free beam propagation are drawn and future perspectives to higher laser powers and energies as well as to wavelength converted femtosecond pulses discussed.

Laser patterning of implant materials for bone tissue engineering purposes has shown to be a promising technique to control cell properties such as adhesion or differentiation, resulting in an enhanced osteointegration. However, the perspective of patterning the bone tissue side interface to generate microstructure effects has never been investigated. In the present study, three different laser-generated patterns were machined on the bone surface with the aim to identify the best surface morphology compatible with osteogenic-related cells recolonization. The laser patterned bone tissue was characterized by electron scanning microscopy and confocal microscopy in order to obtain a comprehensive picture of the bone surface morphology. Cortical bone patterning impact upon cell compatibility and cytoskeleton rearrangement to the patterned surfaces was performed with Stromal Cells from Apical Papilla (SCAPs). Results indicated that laser machining had no detrimental effect upon consecutively seeded cells metabolism. Orientation assays revealed that surface patterning characterized by larger hatch distances was correlated with a higher cell cytoskeletal conformation to the laser-machined patterns. For the first time, to our knowledge, bone is considered and assessed here as a potentially engineered-improvable biological interface. Further studies shall focus on in vivo implications of this direct patterning.

Today, glass and other similar dielectric materials are widely used in modern manufacturing. However, glass is a brittle and a heat sensitive material. Laser technology is used to process glass but quality and throughput are still a key issue. In the present paper, we investigate dual-wavelength double ultrashort laser pulses in order to control free electrons dynamics and subsequent ablation for fused silica processing, and further improve the understanding of this laser-material interaction. We used a high average power Yb-doped femtosecond laser source (100 W) with two optical lines exhibiting different pulse durations and wavelengths (500 fs at 515 nm; and 1 or 10 ps at 1030 nm) with various fluences and delays. The best configuration in terms of ablation efficiency is expected to take place when the green pulse first induces free electrons, followed by their heating by the red pulse. The obtained results are discussed in terms of optical transmission as well as ablated volume, and are compared with single pulse ablation. Our experimental results are supported by absorbed energy density calculations based on a model considering the two-color laser induced electron dynamics, including photoionization, laser heating of free electrons, and their recombination. We demonstrate that there is an optimal cooperating effect between the two sub-pulses for a 1-ps delay, nevertheless there is no beneficial effect in splitting the beam for optimizing fused silica ablation compared with the single-pulse green configuration.

In recent years, virtual reality headsets have become more accessible thanks to developments in technology. Educational applications for training in physics, and in particular in optics, can be found on the market today. We fully understand that these digital tools will never replace real world teaching, but they offer legitimate opportunities for learning by doing. In this presentation we will provide an overview of the opportunities offered by virtual reality in optics tuition at university and in continuing education.