Pump-probe microscopy (PPM) is a powerful technique for investigating laser-material interactions, such as the determination ofmaterial stiffness by means of the detection of Acoustic Waves (AWs). While detection of AWs in transparent media relies onrefractive index changes, AWs in scattering biological media, such as bone or dentin, are detected by monitoring the local waveinduced displacement in the surface speckle pattern. The resulting signal, which appears as noise in a difference image, is oftenfaint and difficult to distinguish from background intensity fluctuations.This study investigates the influence of surface topography on the detectability of AWs in scattering media using homogeneouscasein blocks as artificial reproducible phantom. Casein surfaces were systematically polished using polishing grits with grain sizesfrom 125 µm down to 1 µm, which results in a surface with optical quality of Sq ≈ 70 nm. The rough polishing of the surfaceresults in scattering of the pump beam, hindering the generation of AWs, and of the probe pulse, preventing the acquisition ofAW-related images and evaluation. With decreasing grain sizes, the surface became smoother and subsequently AW-related imagescould be recorded and evaluated. The most reliable AW detection was achieved on the surface polished with 5 µm-grit (Sq ≈ 250nm). Further polishing to an optical quality surface exhibited inconsistent and degraded images and measurements of AWs.These findings demonstrate that for scattering samples, a specific, moderate surface roughness (e.g., 5 µm) is superior to opticalquality in maximizing both pump-pulse energy transfer and the visibility of the wave-induced signal shift. This suggests that theoptimal sample preparation for PPM of scattering materials requires balancing roughness for speckle generation and for sufficientenergy coupling.

This article presents a novel fabrication route for miniaturized piezoelectric actuators that relies exclusively on processes based on femtosecond (fs) laser ablation. Previous work has already demonstrated that fs-lasers are uniquely suited for the fabrication of piezoelectric actuators based on PMN-PT, which are required for multiaxial strain-tuning of quantum dots (QDs) to enable, e.g. the generation of highly entangled photon pairs. Building on these foundations, the present work advances actuator performance and capabilities by introducing a local thinning strategy. This approach allows the realization of smaller devices, which in turn enables lower operating voltages, while simultaneously offering the possibility of integrating multiple quantum light sources on a single chip. The article provides a detailed description of the full fabrication chain, entirely based on fs-laser processing steps, from substrate thinning to metal layer structuring and final device definition. A particular focus is placed on the final cutting process, where the implementation of a third-harmonic ultraviolet (UV) fs-laser wavelength significantly improves edge quality and shape definition compared to the second harmonic (SH) wavelength used in previous work. The device fabricated through the combination of local thinning and UV-based cutting promises not only to enhance the efficiency of strain transfer but also to ensure the mechanical stability required for practical applications. These results establish fs-laser-based fabrication as a versatile and scalable method for next-generation piezoelectric actuators, paving the way for advanced strain-engineering approaches in semiconductor quantum optics and integrated quantum photonics.

Electronic textiles (e-textiles) offer promising capabilities in communication, energy storage, safety, comfort, and sensing. A key requirement for e-textiles is the development of conductive patterns with high design flexibility, high electrical conductivity, and strong adhesion to the textile substrates. In this study, a simple approach combining laser-induced forward transfer (LIFT) and electroless copper (Cu) deposition to create high-resolution, highly conductive patterns on textiles is presented. LIFT is used to deposit microsized silver (Ag) seeds onto textiles, offering significant design flexibility for conductive patterns due to the precise control provided by the automated laser system. The silver seeds act as catalysts for subsequent electroless Cu deposition, leading to localized continuous copper tracks with high conductivity. An appropriate spatial distribution of the Ag particles is essential for achieving uniform copper deposition. This was attained through an appropriate design of the donor for the LIFT process. To enhance the adhesion of the Cu coating to the textile, a siloxane-based intermediate layer was introduced between the textile and silver seeds, which significantly improved the adhesion of the copper deposits. As a proof of concept, the methodology was employed for the preparation of inductive antennas on textiles. The combination of LIFT and electroless deposition demonstrates an effective approach for the production of e-textiles.

This study investigates the correlation between sample surface roughness and surface acoustic waves visibility in pump-probe microscopy using hard biological samples, like dentin and enamel. Further adjustments are presented to improve the excitation of SAWs. (c) 2025 The Author(s)

The utilization of lasers in dentistry expands greatly in recent years. For instance, fs-lasers are effective for both drilling and caries prevention, while cw-lasers are useful for adhesive hardening. A cutting-edge application of lasers in dentistry is the debonding of veneers. While there are pre-existing tools for this purpose, there is still potential for improvement. Initial efforts to investigate laser assisted debonding mechanisms with measurements of the optical and mechanical properties of teeth and prosthetic ceramics are presented. Preliminary tests conducted with a laser system used for debonding that is commercially available showed differences in the output power set at the systems console to that at specified distances from the handpiece. Furthermore, the optical properties of the samples (human teeth and ceramics) were characterised. The optical properties of the ceramics should closely resemble those of teeth in terms of look and feel, but they also influence the laser assisted debonding technique and thus must be taken into account. In addition first attempts were performed to investigate the mechanical properties of the samples by means of pump-probe-elastography under a microscope. By analyzing the sample surface up to 20 ns after a fs-laser pulse impact, pressure and shock waves could be detected, which can be utilized to determine the elastic constants of specific materials. Together such investigations are needed to shape the basis for a purely optical approach of debonding of veneers utilizing acoustic waves.

This study reports an imaging method for gigahertz surface acoustic waves in transparent layers using infrared subpicosecond laser pulses in the ablation regime and an optical pump-probe technique. The reflectivity modulations due to the photoelastic effect of generated multimodal surface acoustic waves were imaged by an sCMOS camera illuminated by the time-delayed, frequency-doubled probe pulses. Moving the delay time between 6.0nsto11.5ns, image stacks of wave field propagation were created.Two representative samples were investigated: wafers of isotropic fused silica and anisotropic x-cut quartz. Rayleigh (SAW) and longitudinal dominant high-velocity pseudo-surface acoustic wave (HVPSAW) modes could be observed and tracked along a circular grid around the excitation center, allowing the extraction of angular profiles of the propagation velocity. In quartz, the folding of a PSAW was observed. A finite element simulation was developed to predict the measurement results. The simulation and measurement were in good agreement with a relative error of 2% to 5%.These results show the potential for fast and full-field imaging of laser-generated ultrasonic surface wave modes, which can be utilized for the characterization of thin transparent samples such as semiconductor wafers or optical crystals in the gigahertz frequency range.

Existing optical tissue phantoms are usually designed for wide field imaging systems and not readily usable for microscopic or endoscopic systems, especially such without any z-stage. Therefore a fs-laser microstructured artificial tissue phantom with adaptable geometric, tissue-optical and localized fluorescence properties enabling comparison and testing of different microscopic/endoscopic systems was designed, characterized and tested.

Synthetic polymers, such as polyamide (PA), inherently possess a moderate number of surface functionalities compared to natural polymers, which negatively impacts the uniformity of metallic coatings obtained through wet-chemical methods like electroless plating. The paper presents the use of a siloxane interlayer formed from the condensation of the hydrolyzed 3-triethoxysilylpropyl succinic anhydride (TESPSA) precursor as a strategy to modify the surface properties of polyamide 6.6 (PA66) fabrics and improve the uniformity of the copper surface coating. The application of the siloxane intermediate coating demonstrates a significant improvement in electrical conductivity, up to 20 times higher than fabrics without the interlayer. The morphology of the coatings was investigated using scanning electron (SEM) and laser confocal scanning microscopy (LSM). In addition, dye adsorption, flexural rigidity, air permeability and contact angle measurements were conducted to monitor the change in the PA66 properties after the siloxane functionalization.

In recent years much research focused on using laser-induced forward transfer (LIFT) for direct writing of electric circuits. However, the generation of conductive paths is extremely challenging. Laser irradiation typically causes donors of thin metallic films to separate into nano and micro particles. Thus, metallic pastes have become the donor material of choice for LIFT. Due to the flexibility of the pastes, it is also a promising fabrication technique for generating circuits for smart or e-textiles. However, it is extremely challenging to maintain the conductivity on stretchable fabrics. To overcome this problem, techniques surrounding the fibres with metal, such as electroless metal deposition, are advantageous. To generate circuits, this technique requires the printing of seed paths consisting e.g. of silver nano particles. This is the point where the original LIFT of thin metallic films, which enables direct writing of paths of nano and micro particles, finds a novel and promising application field. In the present paper we present a parametric study to optimise particle formation and present initial results of conductive paths generated utilizing LIFT to form Ag seed paths for electroless copper deposition.

Pump-probe microscopy can be utilized to image laser-induced acoustic waves, which carry information about elastic properties. This paper shows how the pulse number and energy affects the imaging quality of waves in water and glass.

In recent years pump-probe microscopy has been used in several studies to investigate laser-material interaction processes. Thereby, acoustic waves could be imaged that were released into the vicinity of the irradiated spot. Since these waves carry information about the elastic properties of the material, the question arose how pump-probe microscopy could be utilized for elastography of biological materials. Therefore, the influence of the pump-pulse energy on the radius and thus on the speed of acoustic waves in solid and fluid media was investigated in this study.

The influence of inhomogeneities in the emission characteristics of optical fiber diffusers on the light distribution within biological tissue was evaluated by Monte Carlo (MC) simulations and by experiments on optical phantoms. Due to the strong scattering of light within biological tissue, inhomogeneities in the emission profile become blurred within a short light propagation distance, so that the light distribution within the tissue approaches that of a homogeneous diffuser. The degree of feature vanishing in the light distribution is mainly determined by the width of the inhomogeneities. It was shown that the influence of local inhomogeneities on top of a homogeneous light distribution fades away very effectively within 1 mm of tissue depth, which results in a light distribution very close to that for a homogeneously emitting diffuser. Emission profiles composed of multiple narrow peaks distributed over the full diffuser length with a peak-to-peak distance of less than 2 mm result in an almost homogeneous light distribution after approximately 1 mm of tissue depth. While this article is focused on the impact of diffuser inhomogeneities on the light distribution within the tissue, the importance of further investigations on the related thermal effects is also discussed.

By internally structuring optical fibers, using an ultrafast laser, diffusers for selective illumination of tissue regions can be obtained, while maintaining decoupling efficiencies of up to 83% and mechanical stabilities comparable to non-machined optical fibers.

In recent years, the burst-mode caught a lot of attention in the field of ultrashort-pulse laser micro machining. One of the major issues is the influence of the burst pulse number and frequency on ablation efficiency and quality. A recent publication reported of a significant increase in ablation efficiency when processing with >= 25 burst pulses at >= 100 MHz burst frequencies. This raises the question of whether processing with such high pulse densities can be attributed to non-thermal ablation, or whether a quasi-nanosecond laser ablation behavior is achieved. To answer this question, we determined ablation efficiencies as function of fluence for silicon, stainless steel, and copper and compared the ablation quality at the optimal fluence using the following laser systems: femtosecond laser operated in single-pulse mode, fs laser operated in 28-pulse-burst mode with a burst pulse frequency of 148 MHz, and a nanosecond laser with a pulse duration of 175 ns, which is identical with the temporal length of the burst pulse train. The comparison showed that the burst mode used produces similar surface morphologies and melt burrs as the nanosecond laser, but at about 2/3 of its efficiency.

Background and ObjectivesLight delivery is an essential part of therapy forms like photodynamic therapy (PDT), laser‐induced thermotherapy, and endovenous laser therapy. While there are approaches to the light application for all three therapies, there is no diffuser that can be used for all three approaches. This diffuser must meet the following criteria: Homogeneous radiation profile over a length of 40 mm, efficient light extraction in the diffuser area, mechanical breakage resistance as well as thermal stability when applying high power.Study Design/Materials and MethodsAn ultrashort pulse laser was used to inscribe inhomogeneities into the core of a fused‐silica fiber core while scanning the laser focus within a linear arrangement of cuboids centered around the fiber axis. The manufactured diffuser was optically and mechanically characterized and examined to determine the maximum power that can be applied in a tissue environment.ResultsBased on the analysis of all examined diffusers, the manufactured diffuser exhibits an emission efficiency ε = (81.5 ± 5.9)%, an intensity variability of (19 ± 5)% between distal and proximal diffuser end, and a minimum bending radius Rb = (15.4 ± 1.5) mm. It was taken advantage of the fact that the outer areas of the fiber core do not undergo any structural changes due to the machining and therefore do not suffer a major loss of stability. Tissue experiments revealed that a maximal power of 15 W was deliverable from the diffuser without harming the diffuser itself.ConclusionsIt could be shown that a diffuser manufactured by ultrafast‐laser processing can be used for low power applications as well as for high power applications. Further tests have to show whether the mechanical stability is still maintained after the application of high power in a tissue environment. Lasers Surg. Med. © 2020 Wiley Periodicals LLC

In recent years, the burst-mode caused a lot of attention and confusion in the field of micro machining with ultrashort-pulsed lasers. There is an ongoing debate about the laser-matter interaction and the impact on ablation efficiency and quality of applying burst trains with two to hundreds of pulses at MHz to GHz frequencies. Our results reveal that the ablation behaviour achieved with bursts of 28 pulses at 154 MHz is rather similar to the ablation with a ns-laser with a pulse duration equal to the temporal burst train length of 175 ns than to a fs-laser operated in single-pulse mode.

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Photodynamic therapy is a promising method to selectively treat cancer with light. Therefore, the tumour cells have to be illuminated homogeneously by distributing optical fibers with diffuser tips within the tumour tissue. The challenge is to measure and thereby, tailor the irradiation of the diffusers. In this paper, a novel non-imaging, camera-based method to measure the radiation profile is introduced and compared to an established imaging-based method. The radiation profile of a commercial polymer diffuser with radial homogeneous emittance and the profile of an ultrafast-laser surface structured fiber with radially asymmetric emission was evaluated. For the novel method, the diffuser was positioned in close contact to the image sensor. After coupling a LED to the diffuser, images were recorded for various radial positions. The irradiation profiles of the diffusers were also determined using an imaging camera system. The radiation profiles measured with the novel approach stand in good agreement with the existing imaging method using radial homogeneously emitting diffusers. However, the comparison revealed that the novel approach is advantageous, if the radiation profile is radially asymmetric and if the near-field is of special interest. In this case, several details, such as double peaks, were resolved, which were invisible using other methods. The novel approach is of special interest for the development of simulation models to gain further knowledge about the laser-tissue interaction in the near-field of the fiber. Thereby, irradiation profiles of diffusers could be predicted and tailored towards an application specific irradiation.

Interstitial Photodymanic Therapy (iPDT) selectively treats malignant brain cancer. A photoactive drug, which accumulates specifically in tumour cells, is delivered to the patient. By irradiation of the targeted brain region with low power laser light, radical oxygen is generated, leading to apoptosis or necrosis. For the illumination, glass fibers are connected to a laser source and inserted through boreholes into the human skull. At the distal fiber end, light is decoupled from the fiber and spread into the surrounding tissue. Various approaches target the decoupling process from the fiber core to the surrounding tissue including the use of polymer diffusers, surface roughening or internal glass modification using ultrafast laser sources. While the manufacturing process is a widely debated topic, the measurement of the radiation profile of the fibers is rarely discussed. Therefore, this study targets the introduction of a novel method, using a plain camera sensor, which was brought in close contact to the fibre diffuser surface. Thereby, an angle-resolved profile should be accessible. The gained profiles were afterwards compared to the state-of-the-art method, a camera setup recording an image of the diffuser surface through an optical lens, as well as to an integrating sphere, collecting all emitted rays along the diffuser length. The results showed that the main characteristics are similar in between all three methods, however its development strongly differs. This could be explained by the limitations of the camera setup, which is limited by the acceptance angle of the used camera lens. Rays emitted under a flat angle from the fibre surface miss the lens aperture and won't be detected. For the camera sensor and the integrating sphere setup, those rays are detected. The results show a dependency of the radiation profile on the selected method. The novel camera sensor method allows an angle-resolved measurement detecting almost the full radiation profile. Furthermore, a simulation model can be easily established, which could be used to predetermine the radiation profile of manufactured diffusers.

Photodynamic Therapy (PDT) is a gentle method to treat cancer through irradiation by light. To guarantee a positive result from the treatment, a complete illumination of the treated malignant volume has to be reached. The technical challenge is to specifically decouple light from a wave guide, inserted into malignant regions. The aim of this study was to measure and simulate the radiation profile of radially emitting diffusers. An ultrafast laser system combined with a rotational axis was used to machine the distal end of optical fibers. Cylindrical and tapered shaped diffusers were produced. A low power diode laser (lambda = 670 nm) was coupled into the fiber to determine the emission profile, which was measured via a camera setup. The measured emission profiles were simulated using a 2D-Matlab model and a 3D-LightTools model. The simulated and measured intensity profile along the cylindrical and the tapered fiber tip is characterized by an intensity maximum at the beginning, constant intensity in the middle, and exponentially decreasing intensity at the end. The studies indicate that fiber diffusers with tailored 3D radiation profile can be manufactured using ultrafast lasers. Further investigations have to be performed to adapt the simulations to the measured data.