Publication database

Using laser-induced metal deposition technology, we demonstrate a cost-efficient and large-scalable method of transparent microscale metal electrode fabrication on glass. The novel electrodes are effective conductive layers, presenting a promising alternative to many electronic and electro-optic applications. This study discusses electrode formation and compares various designs. We analyzed the influence of femtosecond and picosecond laser pulse durations by varying the laser pulse duration and optimizing the repetition rate during laser processing. We found that picosecond pulses are more suitable for producing wider (about 31 μm) and higher (about 2 μm) electrodes. Meanwhile, femtosecond laser pulses are ideal for producing narrower (about 8 μm), lower (about 1 μm) electrodes. Furthermore, the optimized copper electrode design was tested in a multilayer smart window structure. It utilized a flexible conductive polymer, Poly(3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), in combination with the lithium perchlorate (LiClO₄) electrolyte. We demonstrated the importance of proper layer alignment for achieving optimal smart window performance. Our findings suggest that transparent microscale electrodes formed by laser-induced metal deposition could contribute to the development of more sustainable and cost-effective smart devices.

Laser micro-machining is a rapidly growing technique to create, manufacture and fabricate microstructures on different materials ranging from metals and ceramics to polymers. Micro- and nano-machining on different materials has been helpful and useful for various biomedical applications. This study focuses on the micro-machining of innovative barbed sutures using an ultrashort pulse laser, specifically a femtosecond (fs) laser system. Two bioresorbable polymeric materials, namely, catgut and poly (4-hydroxybutyrate) (P4HB), were studied and micro-machined using the femtosecond (fs) laser system. The optimized laser parameter was used to fabricate two different barb geometries, namely, straight and curved barbs. The mechanical properties were evaluated via tensile testing, and the anchoring performance was studied by means of a suture–tissue pull-out protocol using porcine dermis tissue which was harvested from the medial dorsal site. Along with the evaluation of the mechanical and anchoring properties, the thermal characteristics and degradation profiles were assessed and compared against mechanically cut barbed sutures using a flat blade. The mechanical properties of laser-fabricated barbed sutures were significantly improved when compared to the mechanical properties of the traditionally/mechanically cut barbed sutures, while there was not any significant difference in the anchoring properties of the barbed sutures fabricated through either of the fabrication techniques. Based on the differential scanning calorimetry (DSC) results for thermal transitions, there was no major impact on the inherent material properties due to the laser treatment. This was also observed in the degradation results, where both the mechanically cut and laser-fabricated barbed sutures exhibited similar profiles throughout the evaluation time period. It was concluded that switching the fabrication technique from mechanical cutting to laser fabrication would be beneficial in producing a more reproducible and consistent barb geometry with more precision and accuracy.

The clinical assessment of microvascular pathologies (in diabetes and in inflammatory skin diseases, for example) requires the visualization of superficial vascular anatomy. Photoacoustic tomography (PAT) scanners based on an all-optical Fabry–Perot ultrasound sensor can provide highly detailed 3D microvascular images, but minutes-long acquisition times have precluded their clinical use. Here we show that scan times can be reduced to a few seconds and even hundreds of milliseconds by parallelizing the optical architecture of the sensor readout, by using excitation lasers with high pulse-repetition frequencies and by exploiting compressed sensing. A PAT scanner with such fast acquisition minimizes motion-related artefacts and allows for the volumetric visualization of individual arterioles, venules, venous valves and millimetre-scale arteries and veins to depths approaching 15 mm, as well as for dynamic 3D images of time-varying tissue perfusion and other haemodynamic events. In exploratory case studies, we used the scanner to visualize and quantify microvascular changes associated with peripheral vascular disease, skin inflammation and rheumatoid arthritis. Fast all-optical PAT may prove useful in cardiovascular medicine, oncology, dermatology and rheumatology.

We reveal for the first time by experiments that within a narrow parameter regime, two cavitation bubbles with identical energy generated in anti-phase develop a supersonic jet. High-resolution numerical simulation shows a mechanism for jet amplification based on toroidal shock wave and bubble necking interaction. The micro-jet reaches velocities in excess of 1000 m/s. We demonstrate that potential flow approximation established for Worthington jets accurately predicts the evolution of the bubble gas-liquid interfaces.

Photoacoustic imaging offers high spatial resolution, imaging depth, and molecular information, emerging as a promising biomedical imaging modality. In particular, when using exogenous contrast, the advantages of photoacoustic imaging can be more effectively utilized in preclinical and clinical studies. We provide a novel approach to screen and identify efficient photoacoustic performance as contrast agents of the metals. To accomplish this, we introduce a novel figure of merit that quantifies the potential performance of contrast agents. As a result of the quantification, we discover that Ti nanodiscs outperform Pt nanodiscs in terms of photoacoustic ability, which shows a similar level to Au nanodiscs. We compare these results by performing a photoacoustic phantom imaging experiment. The photoacoustic performance of the three materials is compared by comparing the signal intensity of the materials measured on the photoacoustic image for various wavelengths. The imaging results further support our findings, demonstrating the superior performance of Ti nanodiscs as contrast agents.

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.

Photonic-based methods are crucial in biology and medicine due to their non-invasive nature, allowing remote measurements without affecting biological specimens. The study of diatoms using advanced photonic methods remains a relatively underexplored area, presenting significant opportunities for pioneering discoveries. This research provides a comprehensive analysis of marine diatoms, specifically Nitzschia sp., across varying salinity levels, integrating fluorescence lifetime imaging microscopy (FLIM), combined photoacoustic and fluorescence tomographies (PAFT), and ultrastructural examinations using transmission electron microscopy. Key findings include a systematic shift in the mean fluorescence lifetime from 570 ps at 20‰ to 940 ps at 80‰, indicating functional adaptations in chlorophyll molecules within light-harvesting complexes. At 60‰ salinity, anomalies are observed in the development of silica valves and polysaccharide layers, suggesting abnormalities in valve morphogenesis. Lipid droplets within the cells display a minimum diameter at 40‰, indicating metabolic adjustments to osmotic stress. The intensity of both fluorescence and photoacoustic signals increases with increasing salinity levels. These insights enhance understanding of the ecological implications of salinity stress on diatom communities and pave the way for future research on leveraging the unique adaptive mechanisms of microalgae for environmental monitoring and sustainable biotechnological applications.

A bendable electrode is an essential component of flexible electronics. The resistance stability against deformation is highly desired for practice. In this work, a bendable Cu electrode is fabricated by femtosecond laser direct writing (FsLDW), involving photothermal reduction of Cu ions and deposition of Cu on polyethylene terephthalate (PET) substrate. A highly conductive Cu electrode with a sheet resistance of 0.56 Ω·sq⁻¹ is obtained, which is improved by at least one order of magnitude over previous works. It is worth noting that the sheet resistance of the Cu electrode almost remains unchanged after 6000 downward bending cycles at a bending angle of 30° and shows a slight increase after 10 adhesion tests, demonstrating excellent bending stability and adhesive strength. The porous morphology of the deposited Cu may relieve bending stress, resulting in high deformation resistance. The temperature field simulation confirms sufficient heat accumulation during FsLDW for Cu ion reduction and PET surface melting, allowing for Cu embedding on the PET surface and improving adhesion between the Cu electrode and the substrate.

The flow around a bubble, precipitously expanding in a thin gap between flat walls, was found to have a peculiar feature: distinct fingering occurs at the bubble wall, which was observed through the ultra-high speed optical visualization. The effect is attributed to the reversal of the flow within boundary layers, which provokes the growth of instabilities at the inflection point and, when the surface tension is low enough (the local Weber number is high enough), leads to the fingering. In this paper, we show the high speed recordings of the fingering and model the evolution of the radial velocity to quantitatively confirm feasibility of the proposed instability mechanism.

Advancements in light engineering have led to the creation of pulsed laser sources capable of delivering high-repetition-rate, high-power few-cycle laser pulses across a wide spectral range, enabling exploration of many fascinating nonlinear processes occurring in all states of matter. High-harmonic generation, one such process, which converts the low-frequency photons of the driver laser field into soft x-rays, has revolutionized atomic, molecular, and optical physics, leading to progress in attosecond science and ultrafast optoelectronics. The Extreme Light Infrastructure, Attosecond Light Pulse Source (ELI ALPS) facility pioneers state-of-the-art tools for research in these areas. This paper outlines the design rationale, capabilities, and applications of plasma- and gas-based high-repetition-rate (1 kHz to 100 kHz) attosecond extreme ultraviolet (XUV) beamlines developed at ELI ALPS, highlighting their potential for advancing various research fields.