Beat Neuenschwander

Bern University of Applied Sciences | BFH · Department of Engineering and Information Technology

We study the properties of laser-induced periodic surface structures (LIPSS) formed on titanium-doped diamond-like nanocomposite (DLN) a-C:H:Si:O films during ablation processing with linearly-polarized beams of a visible femtosecond laser (wavelength 515 nm, pulse duration 320 fs, pulse repetition rates 100 kHz-2 MHz, scanning beam velocity 0.05–1...

We study the formation of laser-induced periodic surface structures (LIPSS) on diamond-like nanocomposite (DLN) a-C:H:Si:O films and titanium-doped DLN films during femtosecond (fs) laser ablation processing with linearly-polarized beams of IR and visible fs-lasers (wavelengths 1030 nm and 515 nm, pulse duration 320 fs, pulse repetition rates 100 k...

Preclinical studies often require animal models for in vivo experiments. Particularly in dental research, pig species are extensively used due to their anatomical similarity to humans. However, there is a considerable knowledge gap on the multiscale morphological and mechanical properties of the miniature pigs' jawbones, which is crucial for implan...

In the paper, we study the formation of laser-induced periodic surface structures (LIPSS) on diamond-like nanocomposite (DLN) a-C:H:Si:O films during nanoscale ablation processing at low fluences-below the single-pulse graphitization and spallation thresholds-using an IR fs-laser (wavelength 1030 nm, pulse duration 320 fs, pulse repetition rate 100...

(100) oriented silicon and germanium wafers, machined with 10 ps pulses in the NIR (1064 nm), clearly show two ablation regimes when the peak fluence is raised from the threshold to several J/cm ² . In the first regime the roughness increases with the fluence due to strong cavity formation whereas the second regime is dominated by the formation of...

The combination of diffractive optical elements or spatial light modulators with fully synchronized galvo scanners offers a possibility to scale up machining processes with ultra-short pulses to several 100 W of average power with minimal thermal impact. This will be demonstrated with the high-rate applications multi-pulse drilling on the fly and m...

Diamond-like nanocomposite (DLN) films (a-C:H:Si:O films) are characterized by their unique structure and remarkable tribological properties to be pronounced under various environmental and surface modification conditions. In this paper, we investigated the effects of environments (humid air, water and oil lubrication, elevated temperatures) and la...

Laser processing with ultra-short double pulses has gained attraction since the beginning of the 2000s. In the last decade, pulse bursts consisting of multiple pulses with a delay of several 10 ns and less found their way into the area of micromachining of metals, opening up completely new process regimes and allowing an increase in the structuring...

Ultrafast lasers are frequently used to machine rotational symmetric workpieces either with tangential processing for tools or with a helical gravure approach for structuring cylinders for printing and embossing applications. The highest precision and repeatability for seamless multilayer processing on the surface of a rotational symmetric workpiec...

(100), (110) and (111) oriented silicon shows different behavior when it is machined with 10 ps pulses in the NIR. For the (100) orientation the roughness increases to 2.8 µm when the peak fluence is raised to 1.6 J/cm ² then drops down to a value below 200 nm due to melting effects for a fluence of 2 J/cm ² and stays below 300 nm for fluences up t...

fs-GHz-burst experiments with up to 25 pulses per burst show strong melting effects and a tremendous decrease of the removal rate. The latter follows the tendency obtained for single pulses of corresponding pulse duration.

The up-scaling of laser micromachining processes with ultrashort pulses is limited due to heat accumulation and shielding effects. Multi beam scanning represents one of the strategies to overcome this drawback. It is in general realized by combining a diffractive beam splitter with a galvanometer scanner. A full synchronization with the laser repet...

GHz-bursts were reported to be highly efficient for ultra-short pulse laser ablation compared to single pulses. However, most comparisons were made for a drilling process or the machining of dimples. We investigated GHz-bursts (5.4 GHz) on copper, brass, stainless steel, silicon, zirconium oxide, soda-lime glass and sapphire for surface structuring...

Femtosecond laser ablation processing is applied for surface modification and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films). Using a visible femtosecond laser (wavelength 515 nm, pulse duration 320 fs), microgroove patterns have been fabricated on the DLN films, aimed at further studies of their properties. The studie...

In this paper, we have investigated the burst mode (BM) ablation and surface structuring of diamondlike nanocomposite (DLN) a-C:H:Si:O films with femtosecond laser pulses (wavelength λ = 515 nm, pulse duration τ = 320 fs, and pulse repetition rate f = 100 kHz) under different scanning conditions (single spots and linear structures). The pulse separ...

For most applications, the benefit of the burst mode can easily be explained: the energy of each pulse in an n-pulse burst is n times smaller compared to single pulses with identical average power and repetition rate. Thus, the peak fluence of each pulse is nearer the optimum value and the removal rate is therefore increased. It is generally not as...

For silicon machined with 10 ps pulses at 1064nm it was found that the specific removal rate increases by a factor of about 2.5 when an 8-pulse burst is used instead of single pulses [1]. This increase in the specific removal rate directly scales with a higher surface roughness. For copper and a 3-pulse burst the absorptance of a machined surface i...

We report on femtosecond laser ablation and surface micropatterning (texturing) of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films), aimed to improve tribological properties of laser-patterned films under lubricated sliding conditions. Femtosecond laser system generating pulses of 320-fs duration at the wavelength 515 nm is applied. Femtos...

The combination of diffractive optical elements (DOE) or spatial light modulators (SLM) with conventional beam guiding technologies as galvo scanning offers the possibility to deal with multi 100 W average power ultra-short pulsed laser systems.

Contact-mode atomic force microscopy (AFM) techniques (lateral force microscopy, force-distance curves) are applied to study the effects of femtosecond-laser ablation and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films) on the friction behavior at the nano and microscale. A femtosecond laser (wavelength 515 nm, pulse dur...

Ultra-short laser radiation is used in manifold industrial applications today. Although state-of-the-art laser sources are providing an average power of 10–100 W with repetition rates of up to several megahertz, most applications do not benefit from it. On the one hand, the processing speed is limited to some hundred millimeters per second by the d...

The usage of pulse bursts allows increasing the throughput, which still represents a key factor for machining with ultra-short pulsed lasers. The influence of the number of pulses within a burst on the specific removal rate is investigated for copper and stainless steel. Furthermore, calorimetric measurements were performed to estimate the residual...

The today available ultra-short pulsed laser systems offer average power in the range of 100 W or even more resulting in high pulse energies. In contrast to treat metals only moderate peak fluences are required to work at the well-known optimum point, where the ablation process is most energy efficient. In a standard setup the laser beam is deflect...

In certain cases the burst mode can lead to a higher efficient ablation process resulting in an increased specific removal rate as observed for different metals and also for silicon. Calorimetric measurements of the residual heat and the absorptance on copper indicate that the increased absorptance of a surface machined with a burst is responsible...

The influence of pulse-bursts is investigated using different spot sizes and different wavelengths as well. The specific removal is calculated and compared as a function the peak fluence of the single pulses (not total fluence of the burst package). A drop in the specific removal for copper and alumi-num is observed for a 2 pulse-burst, whereas for...

Especially for metals it was shown that the material removal process with ultra-short laser pulses shows an optimum point with highest efficiency i.e. with maximum specific removal rate. A scale-up process should therefore be realized by keeping the applied fluence near this optimum value i.e. by linearly increasing the repetition rate with the ave...

Laser surface micropatterning (texturing) of hard materials and coatings is an effective technique to improve tribological systems. In the paper, we have investigated the laser-induced surface modifications and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H,Si:O) using IR and visible femtosecond (fs) lasers, focusing on the improv...

The influence of the burst mode is investigated for steel, copper, silver and gold. It is shown that the gain in the removal rate, reported in literature, is generally caused by the lower fluence of the single pulses in the burst which is nearer the optimum value showing higher efficiency. Therefore, identical or even better results are obtained wi...

Hollow core and kagome photonic crystal fibers offer the possibility to guide ultrashort laser pulses of high energy and average power. They could represent a valuable tool for the power transport from the laser source to the processing unit and would therefore facilitate the integration of ultrashort pulsed laser systems. Many works dealt with the...

Previously the influence of picosecond laser spot size on ablation depth and threshold fluence on copper has been experimentally investigated. In order to have a comprehensive understanding of the corresponding mechanisms for high laser fluence cases, in which the laser fluence is several folds larger than the optimal ablation fluence, an axisymmet...

We report on femtosecond laser surface modification and microstructuring of diamond-like nanocomposite (DLN) films (a-C:H,Si:O), and investigation of the frictional properties of laser-micropatterned DLN films on the nano, micro and macroscale. DLN films of 2–3 μm thickness were irradiated using a femtosecond laser (wavelength 1030 nm, pulse durati...

Compared to single pulses the utilization of pulse bursts on steel samples was reported to be more efficient. But with regards to the specific removal rate it can be shown that a maximum value is achieved when the applied peak fluence equals exp(2) times the threshold fluence. The higher reported efficiency is caused by the reduced energy of the si...

Laser surface texturing using ultra short pulsed lasers in combination with galvo scanners is limited to the scan field of the galvo scanner which is typically 65x65 mm using a 160 mm objective. By combine the galvo scanner with an additional high precision linear axis, it is possible to enhance the working field. Increased surface roughness and vi...

Especially for surface structuring the machining quality often represents a crucial factor and fosters the application of ultra-short pulsed laser systems. In literature the machining quality is often discussed with respect to pulse duration, machining strategy, pulse energy and/or average power. But also the initial surface finish may have a stron...

High throughput still represents a key factor for industrial use of ultrashort pulses in the field of surfacestructuring. Reliable systems with average powers up to 100 W are today available. It has already been proved that metals, especially steel having a low threshold fluence, can be machined with excellent surface quality at average powers of m...

High accuracy, quality and throughput are key factors in laser micro machining. To obtain these goals the ablation process, the machining strategy and the scanning device have to be optimized. The precision is influenced by the accuracy of the galvo scanner and can further be enhanced by synchronizing the movement of the mirrors with the laser puls...

We report on the enhancement of nitrogen-vacancy (NV) luminescence induced by the bulk structure modification of a type IIa single-crystal diamond with a visible picosecond laser. Using online monitoring of picosecondlaser-induced photoluminescence (PL) in the bulk regions we found that the integrated intensity of the NV PL is significantly increas...

Picosecond laser systems have been widely used in industrial microprocessing applications since they are a cost-effective tool to achieve high throughput. To better understand the ablation process, firstly the dependence of the ablation depth and the threshold fluence on the laser spot size were determined experimentally by performing ablation with...

Ultra short laser pulses often are the tool of choice when high requirements concerning machining quality are demanded. But for industrial use the process has also to be efficient, meaning that the removal rate (ablated volume per time and average power) should be as high as possible. Many publications deal with the threshold fluence and the remova...

Multicrystalline Silicon was textured with picosecond laser. Different laser wavelengths (λ = 1064, 532, 355 nm) where compared regarding laser-induced damage. We found that λ = 355 nm picosecond radiation resulted in shallower defect-reach region

The burst mode for ps and fs pulses for steel and copper is investigated. It is found that the reduction of the energy in a single pulse (in the burst) represents the main factor for the often reported gain in the removal rate using the burst mode e.g. for steel no investigated burst sequence lead to a higher removal rate compared to single pulses...

In earlier work the capabilities of synchronizing a galvo scanner or a polygon line scanner with a picosecond laser system in MOPA arrangement were presented. However these systems only enabled precise positioning of laser pulses on the target relatively to each other. Since then a novel approach to increase the absolute precision in positioning ha...

Glass-ceramic materials are increasingly becoming the material of choice in the field of dental prosthetics, as they can feature both high strength and very good aesthetics. It is believed that their color, microstructure and mechanical properties can be tuned such as to achieve an optimal lifelike performance. In order to reach that ultimate perfe...

When high requirements concerning machining quality are demanded, ultra short pulsed lasers with pulse durations from a few 100fs to 10ps may be the tool of choice. For these pulses it is known that the removal rate and machining quality slightly increases with shorter pulse duration. But as cost-effectiveness is also a key factor for a successful...

The interest using ultra-short pulsed laser systems for industrial applications increased remarkably as reliable high power systems with average power exceeding several 10W became available, facilitating the development of high throughput processes. Exhausting the potential of these systems demands an optimized process and an adapted process strate...

High throughput is a key aspect in laser micro machining. Using the full power range of new industrial ps-laser and keeping the process at the point with maximum material removal rate per average power demands high repetition rates in the MHz regime. For high quality the scan speed has to be linearly increased with the repetition rate up to several...

Optimized ps laser processing improves direct laser engraving of embossing rollers and high power fiber laser combined with ultrafast modulation and scanning techniques enable for digital print applications based on laser induced forward transfer (LIFT).

Keeping the high efficiency and machining quality with today high average power ultrafast lasers demands new and fast beam deflecting systems. We will report on our latest results obtained with a fast polygon line scanner synchronized with a picosecond and femtosecond laser.

In this paper, we report on the bulk modifications of type IIa single-crystal diamond with visible 10-ps pulses (at λ = 532 nm) and microstructural changes characterized by the appearance of several ‘unidentifiable’ vibrational modes in the frequency range of 1000–1400 cm−1 in the Raman spectra of laser-modified diamond. It is found that the new Ra...

Bulk modification and micro-structuring of diamonds using ultra-short laser pulses is of great interest due to its potential in photonic applications, radiation detectors and diamond gem marking. We report on bulk micro-structuring and stimulated Raman scattering (SRS) in type IIa single crystal diamond with multi pulse irradiation by picosecond-la...

To be competitive in laser micro machining, high throughput is an important aspect. One possibility to increase productivity is scaling up the ablation process i.e. linearly increasing the laser repetition rate together with the average power and the scan speed. In the MHz-regime high scan speeds are required which cannot be provided by commerciall...

Optimized ps laser processing is used to improve laser engraving of embossing rollers. The optimized ablation process is characterized by the condition that the ablation depth of a single pulse is just as deep as the effective penetration depth of the energy. In this case the fluence F of the pulse is only a little above the threshold fluence e.g....

High throughput is a key aspect in laser micro machining. In order to achieve excellent processing quality with high power, high repetition rate ultrafast lasers new and fast beam deflecting systems as e.g. polygon line scanners with marking speeds up to 100 m/s and more or – alternatively – fast rotating cylindrical work pieces are useful. These d...

High precision laser micromachining requires an exact synchronization of the laser pulse train with the mechanical axes of the motion system to ensure for each single pulse a precise control of the laser spot position - on the target. For ultra short pulsed laser systems this was already demonstrated with a conventional two-axis galvanometer scanne...

When high requirements concerning machining quality are demanded, ultra short laser pulses from a few 100fs to 10ps may be the tool of choice. For these pulses it is known that the removal rate and machining quality slightly increases with shorter pulse duration. But as cost-effectiveness is also a key factor for a successful transfer of a technolo...