We report on TRUMPF´s ultrafast laser systems equipped with industrialized hollow core fiber laser light cables. Beam guidance in general by means of optical fibers, e.g. for multi kilowatt cw laser systems, has become an integral part of laser-based material processing. One advantage of fiber delivery, among others, is the mechanical separation between laser and processing head. An equally important benefit is given by the fact that the fiber end acts as an opto-mechanical fix-point close to successive optical elements in the processing head. Components like lenses, diffractive optical elements etc. can thus be designed towards higher efficiency which results in better material processing. These aspects gain increasing significance when the laser system operates in fundamental mode which is usually the case for ultrafast lasers. Through the last years beam guidance of ultrafast laser pulses by means of hollow core fiber technology established very rapidly. The combination of TRUMPF´s long-term stable ultrafast laser sources, passive fiber coupling, connector and packaging forms a flexible and powerful system for laser based material processing well suited for an industrial environment. In this article we demonstrate common material processing applications with ultrafast lasers realized with TRUMPF´s hollow core fiber delivery. The experimental results are contrasted and evaluated against conventional free space propagation in order to illustrate the performance of flexible ultrafast beam delivery.
The present work investigates the influence of the pulse duration and the temporal spacing between pulses on the ablation of aluminosilicate glass by comparing the results obtained with pulse durations of 0.4 ps and 6 ps. We found that surface modifications occur already at fluences below the single pulse ablation threshold and that laser-induced periodic surface structures (LIPSS) emerge as a result of those surface modifications. For 0.4 ps the ablation threshold fluences is lower than for 6 ps. Scanning electron micrographs of LIPSS generated with 0.4 ps exhibit a more periodic and less coarse structure as compared to structures generated with 6 ps. Furthermore we report on the influence of temporal spacing between the pulses on the occurrence of LIPSS and the impact on the quality of the cutting edge. Keywords: LIPSS,
The unique properties of ultrafast laser pulses pave the way to numerous novel applications. Particularly lasers in the sub-pico second regime, i.e. femtosecond lasers, in the last decade arrived at a level of reliability suitable for the industrial environment and now gain an increasing recognition since these pulse durations combine the advantages of precise ablation with higher efficiency especially in the case of processing metallic materials. However, for some micro processing applications the infrared wavelength of these lasers is still a limiting factor. Thus, to further broaden the range of possible applications, industrial femtosecond lasers should combine the advantages of femtosecond pulses and shorter wavelengths. To that extend, we present results obtained with a frequency doubled TruMicro 5000 FemtoEdition. We show that depending on the processed material, the higher photon energy as well as tighter focusing options of the shorter wavelength can open up a new regime of processing parameters. This regime is not accessible by infrared light, leading to a wider range of possible applications.
We investigate cutting of transparent materials using ultra short laser pulses with pulse durations in the sub to a few ps
regime. All compared methods base on nonlinear absorption including ablation cutting and cleaving or selective etching
supported by laser induced modification inside the bulk material. For most of the experiments samples of hardened glass
(Corning Gorilla®) with thickness up to 700 μm were used, ablation cutting of sapphire is presented additionally.
Absorption and modification inside the volume is analyzed in detail, aiming for tailored modifications. Besides optical
microscopy a pump probe setup was used. We show results of time resolved absorption measurements of 6 ps pulses
focused into the volume. We observe shielding due to the interaction region and accumulation effects influencing the
modifications. First results on inscribing and cutting by using beam shaping indicate the importance of tailoring the
shape and arrangement of the pulses temporally and spatially. The results presented for the different cutting methods
supports an assessment of the individual potential and a selection of the applicable method based on the requirements.
Ultrashort pulses are capable of processing practically any material with negligible heat affected zone. Typical pulse durations for industrial applications are situated in the low picosecond-regime. Pulse durations of 5 ps or below are a well established compromise between the electron-phonon interaction time of most materials and the need for pulses long enough to suppress detrimental effects such as nonlinear interaction with the ablated plasma plume. However, sub-picosecond pulses can further increase the ablation efficiency for certain materials, depending on the available average power, pulse energy and peak fluence. Based on the well established TruMicro 5000 platform (first release in 2007, third generation in 2011) an Yb:YAG disk amplifier in combination with a broadband seed laser was used to scale the output power for industrial femtosecond-light sources: We report on a subpicosecond amplifier that delivers a maximum of 160 W of average output power at pulse durations of 750 fs. Optimizing the system for maximum peak power allowed for pulse energies of 850 μJ at pulse durations of 650 fs. Based on this study and the approved design of the TruMicro 5000 product-series, industrygrade, high average power femtosecond-light sources are now available for 24/7 operation. Since their release in May 2013 we were able to increase the average output power of the TruMicro 5000 FemtoEdition from 40 W to 80 W while maintaining pulse durations around 800 fs. First studies on metals reveal a drastic increase of processing speed for some micro processing applications.
Processing of thin and ultra-thin glass displays is becoming more important in the fast increasing market of display manufacturing. As conventional technologies such as mechanical scribing followed by manual breaking mostly lead to bad edge quality and thus to a huge amount of reject, other processes like ablation processes  with picosecond lasers are getting more and more interesting. However processing with ultrashort pulsed lasers partially leads to unwanted effects which should be understood in a better way by means of intensive basic research. Therefore the ablation mechanism of ultrashort pulses on transparent materials was investigated in this research project. On the one hand the ablation mechanism was analyzed in a simulative way by means of rate equations on the other hand by laboratory experiments.
Thin glass sheets (thickness <1 mm) have a great potential in OLED and LCD displays. While the conventional
manufacturing methods, such as mechanical scribing and breaking, result in poor edge strength, ultra-short-pulsed laser
processing could be a promising solution, offering high-quality cutting edges. However laser precision glass cutting
suffers from unwanted material modification and even severe damage (e.g. cracks and chipping). Therefore it is essential
to have a deep understanding of the ultra-short-pulsed laser ablation mechanism of transparent dielectrics in order to
remedy those drawbacks.
In this work, the ablation mechanism of transparent dielectrics irradiated by picosecond laser pulses has been studied.
Ultrafast dynamics of free-electrons is analyzed using a rate equation for free-electron density including multi-photon
ionization, avalanche ionization and loss terms. Two maps of free-electron density in parameter space are given to
discuss the dependence of ablation threshold intensity/fluence on pulse duration. The laser ablation model describing
laser beam propagation and energy deposition in transparent dielectrics is presented. Based on our model, simulations
and experiments have been performed to study the ablation dynamics. Both simulation and experimental results show
good agreement, offering great potential for optimization of laser processing in transparent dielectrics. The effects of
recombination coefficient and electron-collision time on our model are investigated.