M. Zimmermann

Ultra-high-precision surface structuring by synchronizing a galvo scanner with an ultra-short-pulsed laser system in MOPA arrangement

For surface and 3D structuring the ultra short pulsed laser systems are mostly used in combination with galvo scanners. This work reports on the synchronization of the scanner mirror motion with the clock of the laser pulses, which is usually in the range of 100 kHz and higher, by a modification of the electronic scanner control. This synchronization facilitates the placement of the small ablation craters from single pulses with the precision of about 1 μm relative to each other. The precise control of the crater positions offers the possibility to test and optimize new structuring strategies. Results of this optimization process with respect to minimum surface roughness, steepness of wall, accuracy to shape and efficiency will be presented.

High Throughput and High Precision Laser Micromachining with ps-Pulses in Synchronized Mode with a fast Polygon Line Scanner

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 commercially available galvo scanners. In this work we will report on the results by using a polygon line scanner having a maximum scan speed of 100 m/s and a 50 W ps-laser system, synchronized via the SuperSync™ technology. We will show the results concerning the removal rate and the surface quality for working at the optimum point i.e. most efficient point at repetition rates up to 8.2 MHz.

High throughput laser micro machining on a rotating cylinder with ultra short pulses at highest precision

For surface and 3D structuring ultra-short pulsed laser systems are used in combination with mechanical axes, whereas the mechanical axes can include electrical motor as well as beam deflecting systems like a galvo scanner. The motion of the axes is synchronized with the clock of the laser pulses, which is usually in the range of 100 kHz and above, by a modification of the electronic axes control. This work shows the scalability of the ablation process up to MHz-regime in relation to surface quality and ablation efficiency. Furthermore the transfer of the machining strategy from a synchronized galvo scanner to a rotating cylinder setup is shown.

High throughput surface structuring with ultrashort pulses in synchronized mode with fast polygon line scanner

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 scanner. But this solution is limited by the scanner architecture to a marking speed of about 10m/s with a maximum scan line length of about 100mm. It is therefore not suited for average powers far beyond 10W when working at the optimum point with highest removal rate and machining quality is desired. A way to overcome this limitation is offered by polygon line scanners which are able to realize much higher lateral speeds at large scan line lengths.In this work we will report on the results with a polygon line scanner having a maximum moving spot velocity of 100m/s, a scan line length of 170mm, spot diameters of 45µm (1064nm) and 22µm (532nm) together with a 50W, 10-ps laser system. The precise control of the laser spot position i.e. the synchronization is realized via the new SuperSyncTM technology. Decoating, perforation and 3D patterning will act as benchmark processes to evaluate this scanning technology.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 scanner. But this solution is limited by the scanner architecture to a marking speed of about 10m/s with a maximum scan line length of about 100mm. It is therefore not suited for average powers far beyond 10W when working at the optimum point with highest removal rate and machining quality is desired. A way to overcome this limitation is offered by polygon line scanners which are able to realize much higher lateral speeds at large scan line lengths.In this work we will report on the results with a polygon line scanner having a maximum moving spot velocity of 100m/s, a scan line length of 170mm, spot diameters of 45µm (1064nm) and 22µm (532nm) together with a 50W, 10-p...

High precision and high throughput surface structuring by synchronizing mechanical axes with an ultra short pulsed laser system in MOPA arrangement

For surface and 3D structuring ultra short pulsed laser systems are mostly used in combination with galvo scanners. This work reports on the synchronization of the scanner mirror motion with the clock of the laser pulses, which is usually in the range of 100 kHz up to several MH, by a modification of the electronic scanner control. This synchronization facilitates the placement of the small ablation craters from single pulses during the mirror motion with the precision of about 1 µm relative to each other. The precise control of the crater positions offers the possibility to test and optimize new structuring strategies. Results of this optimization process with respect to minimum surface roughness, steepness of wall, accuracy to shape and efficiency will be presented.For surface and 3D structuring ultra short pulsed laser systems are mostly used in combination with galvo scanners. This work reports on the synchronization of the scanner mirror motion with the clock of the laser pulses, which is usually in the range of 100 kHz up to several MH, by a modification of the electronic scanner control. This synchronization facilitates the placement of the small ablation craters from single pulses during the mirror motion with the precision of about 1 µm relative to each other. The precise control of the crater positions offers the possibility to test and optimize new structuring strategies. Results of this optimization process with respect to minimum surface roughness, steepness of wall, accuracy to shape and efficiency will be presented.

Influence of particle shielding and heat accumulation effects onto the removal rate for laser micromachining with ultra-short pulses at high repetition rates

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 devices facilitate to work at high repetition rates in the MHz-regime and it has to be clarified if particle shielding and heat accumulation effects may become evident in this regime of repetition rates.Experiments up to 43 W of average power at 6.8 MHz repetition rate and a pulse to pulse distance of one half of a spot radius have been performed on five different steel grades and on copper. Hints for a particle shielding effect were only found for steel 1.4301, but the effect is weak and, if it really exists, only in the range of 10%. For all other steel grades and copper no shielding or heat accumulation effects were observed up the maximum power of 43 W of the laser system.Experiments with a galvo scanner and reduced pitches showed an oxidation effect which is not caused by the heat accumulation during the marking of a single line but eventually by the short time interval between marked lines which may lead to a long time heat accumulation.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 devices facilitate to work at high repetition rates in the MHz-regime and it has to be clarified if particle shielding and heat accumulation effects may become evident in this regime of repetition rates.Experiments up to 43 W of average power at 6.8 MHz repetition rate and a pulse to pulse distance of one half of a spot radius have been performed on five different steel grades and on copper. Hints for a particle shielding effect were only found for steel 1.4301, but the effect is weak and, if it really exists, only in the range of 10%. For all other steel grades and copper no shielding or heat accumulation effects were observed up the maximum power of 43 W of the...

Time-optimized laser micro machining by using a new high dynamic and high precision galvo scanner

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 pulse train. To maintain a high machining quality i.e. minimum surface roughness, the pulse-to-pulse distance has also to be optimized. Highest ablation efficiency is obtained by choosing the proper laser peak fluence together with highest specific removal rate. The throughput can now be enhanced by simultaneously increasing the average power, the repetition rate as well as the scanning speed to preserve the fluence and the pulse-to-pulse distance. Therefore a high scanning speed is of essential importance. To guarantee the required excellent accuracy even at high scanning speeds a new interferometry based encoder technology was used, that provides a high quality signal for closed-loop control of the galvo scanner position. Low inertia encoder design enables a very dynamic scanner system, which can be driven to very high line speeds by a specially adapted control solution. We will present results with marking speeds up to 25 m/s using a f = 100 mm objective obtained with a new scanning system and scanner tuning maintaining a precision of about 5 μm. Further it will be shown that, especially for short line lengths, the machining time can be minimized by choosing the proper speed which has not to be the maximum one.

Improvements in ultra-high precision surface structuring using synchronized galvo or polygon scanner with a laser system in MOPA arrangement

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 has been developed. This improvement enables new and more efficient process strategies such as bidirectional processing or high precision structuring of large areas in combination with additional mechanical axes. These improvements represent a major step towards large scale industrial applications in laser based micromachining.