Publication database

The increasing demand for miniaturized and high-performance consumer electronics has driven advancements in packaging solutions, including the transition to glass interposers. One of the critical aspects of the development is the fabrication of high-density through-glass vias (TGVs). This article presents the formation of TGVs in various glass substrates using an industrial femtosecond laser FemtoLux 30 operating in different operation modes – single-pulse, MHz burst, GHz burst and MHz+GHz burst modes. By employing burst mode and advanced machining methods such as bottom-up milling – TGVs fabrication is possible. With specific parameter sets TGVs with aspect ratios exceeding 1:80 was achieved, with drilling times as low as 350 ms. Additionally, to address current challenges in making electric traces on substrates, it introduces Selective Surface Activation Induced by Laser (SSAIL) as a unique complementary metallization technology, enabling direct copper deposition on different materials like ceramic, plastics and most importantly – glass, for complete packaging workflows. The findings demonstrate the potential of the FemtoLux femtosecond laser as a high-throughput and precise solution not only for TGV fabrication, but also for Selective Surface Activation Induced by Laser (SSAIL) based metallization - supporting next-generation semiconductor advanced packaging solutions.

As lasers expand further into industrial, research, medical, and military applications, end users are placing increased scrutiny on system cooling requirements. All lasers require a form of thermal management. The appropriate method depends on both the laser design and its operating environment: If the heat load fluctuates, for example, a user must account for both the laser’s range and rate of change.

Regardless of scale and power, overheating can lead to efficiency losses, wavelength drift, and shortened operating lifetime. Low-power lasers operating in stable environments with broad temperature tolerances can often rely on simple air cooling. On the other hand, higher-power systems, or those with tight tolerances, require more advanced methods. Today, system wall-plug efficiencies range from 0.1% to nearly 80%, and power levels can span from milliwatts in measurement and marking applications to multiple kilowatts in heavy manufacturing. Cooling design is therefore not a peripheral consideration. Instead, it is a critical factor that is central to ensuring reliability and performance across all systems and applications.

Intra-volume glass scribing for cutting is one of the most advanced applications of nondiffractive laser beams. However, ever-growing requirements from the industry for complexity, miniaturization, and quality of fabricated parts have pushed the technology forward. Most of the methods developed to improve glass scribing rely on spatial and temporal pulsed beam shaping. As another degree of freedom to manipulate light, polarization has received little attention so far. In this work, we investigate the effect of linear and circular polarizations on the volumetric modification and scribing of soda-lime glass using a zero-order Bessel beam in the MHz burst regime. We demonstrate that at a certain burst energy, transverse microcracks align with the linear polarization orientation. Furthermore, we show that the polarization state affects the modified glass separation, processing speed, efficiency, and quality.

The growing demand for flexible, high-quality fabrication of free-form micro-optics drives the development of laser-based fabrication techniques for both the shape formation and surface polishing of optical elements. In this paper, we performed a thorough and systematic study on fused silica glass ablation using 10 ps and 320 fs duration pulses. Ablation processes for both pulse durations were optimized based on the measurements of the removed material layer thickness and surface roughness, and by analyzing the topographies of ablated cavities to remove material layers as thin as possible with minimum surface damage. Our findings demonstrate higher process resolution and surface quality for femtosecond pulses. Ablation of pre-roughened glass reduced the minimal removable glass layer thickness well below the 1 μm mark for both pulse durations, improving the process resolution. The minimal removable glass layer thickness was 14 times smaller for the femtosecond pulses, with up to 4.5 times lower surface roughness compared to samples processed with picosecond pulses. On the other hand, results revealed faster glass removal rates with picosecond pulses. In the end, arrays of microlenses were fabricated with both pulse durations and subsequently polished with a CO2 laser. Results revealed higher performance of microlenses fabricated with femtosecond pulses, providing better focusing capabilities and lesser beam scattering. Finally, this study demonstrated the successful fabrication of free-form optical elements with femtosecond and picosecond pulses, demonstrating the versatility and the potential of laser-based techniques.

Utilisation of high-power ultrafast laser for ablation-based industrial processes such as milling, drilling or cutting requires high production rates and superior quality. In this paper, we demonstrate highly efficient, rapid and high-quality laser micro-machining of three industrial metals (aluminium, copper, and stainless steel). Our proposed optimisation methods of pulse energy division in time result in simultaneous enhancement of ablation efficiency (volume per energy) and ablation rate (volume per time) while maintaining a focused laser beam on the target surface and high resolution. A high-tech femtosecond burst laser, producing laser pulses of τ = 350 fs duration and intra-burst repetition rates of f_P = 50 MHz, was employed in the experiments. Due to the utilisation of bursts, material removal efficiency and removal rate were increased by 18.0 %, 44.5 %, and 37.0 % for aluminium, copper, and stainless steel if compared with the best performance of single-pulses. In addition to the high processing rate, processing by burst mode resulted in lower surface roughness. This technique is believed to be a solution enabling extremely high femtosecond laser powers for precise microfabrication.

Laser polishing offers numerous advantages, one of which is the convenience of using the same system for the
whole manufacturing process. In this work, an ultrashort pulse laser operating in a GHz burst regime was used to polish
stainless steel. The aim was to minimise surface roughness, characterised by the average roughness parameter R_a. Different
laser processing parameters (average laser power, number of pulses per burst, scanning speed, hatch size) were varied to polish
samples that were covered in laser-induced periodic surface structures (LIPSS). Thermal effects, such as melt layer formation,
were noticed and discussed. It was demonstrated that LIPSS can be erased and the initial surface roughness of 73 nm was
reduced to 41 nm using 100 pulses per burst and burst fluence of F_B = 0.15 J/cm².

The cutting quality and strength of strips cut with femtosecond-duration pulses were investigated for different thicknesses of borosilicate glass plates. The laser pulse duration was 350 fs, and cutting was performed in two environments: ambient air and water. When cutting in water, a thin flowing layer of water was formed at the front surface of the glass plate by spraying water mist next to a laser ablation zone. The energy of pulses greatly exceeded the critical self-focusing threshold in water, creating conditions favorable for laser beam filament formation. Laser cutting parameters were individually optimized for different glass thicknesses (110–550 µm). The results revealed that laser cutting of borosilicate glass in water is favorable for thicker glass (300–550 µm) thanks to higher cutting quality, higher effective cutting speed, and characteristic strength. On the other hand, cutting ultrathin glass plates (110 µm thickness) demonstrated almost identical performance and cutting quality results in both environments. In this paper, we studied cut-edge defect widths, cut-sidewall roughness, cutting throughput, characteristic strength, and band-like damage formed at the back surface of laser-cut glass strips.

Water-assisted ultrashort laser pulse processing of semiconductor materials is a promising technique to diminish heat accumulation and improve process quality. In this study, we investigate femtosecond laser ablation of deep trenches in GaAs, an important optoelectronic material, using water and ambient air environments at different laser processing regimes. We perform a comprehensive analysis of ablated trenches, including surface morphological analysis, atomic-resolution transmission electron microscopy imaging, elemental mapping, photoluminescence, and Raman spectroscopy. The findings demonstrate that GaAs ablation efficiency is enhanced in a water environment while heat-accumulation-related damage is reduced. Raman spectroscopy reveals a decrease in the broad feature associated with amorphous GaAs surface layers during water-assisted laser processing, suggesting that a higher material quality in deep trenches can be achieved using a water environment.

The laser synthesis and processing of colloids represents a group of scalable and “green” synthesis methods of crystalline metal oxides, that have recently made encouraging progresses in preparing amorphous as well as defect-rich nanoparticles. The relevant conditions and mechanisms that allow the design of amorphous metal oxides (AMOs) remain unknown. Consequently, in this work the synthesis of Fe-based partially amorphous oxide nanoparticles (NPs) by pulsed laser ablation in water was studied. Furthermore, both laser pulse duration and the number of laser pulse in pulsed laser fragmentation in liquid (LFL) allow a precise control of amorphization of AMOs in water. Hereby, a high-fluence nanosecond-LFL provides a significantly higher amorphization rate, whereas picosecond-LFL always presents minor fractions of crystalline α-Fe even with a higher specific energy input and laser intensity. Consequently, the laser fluence required for the repeated melting and quenching of NP appears to be the decisive parameter to control amorphization. During laser synthesis and processing of colloids, the amorphization of AMOs appears to be linked to the apparent size reduction effect, while a complete full amorphization of AMOs may be attributed to the stronger oxidation effects. This work will stimulate future studies using laser-generated AMO NPs for further functional purposes.

A new versatile patent-pending technology enabling new operation regimes and a unique set of features in the industrialgrade 30 W-level average power femtosecond hybrid laser is introduced in this work. The developed technology, based on the use of an all-in-fiber active fiber loop (AFL), enabled to form GHz bursts of ultrashort laser pulses with any desired pulse repetition rate and any number of pulses in a burst with identical intra-burst pulse separation. Furthermore, the AFL allowed to tune pulse duration from a few hundred femtoseconds to picoseconds and even up to the nanosecond range.