Machining of stainless steel with ultrashort laser pulses is often a challenging task due to heat accumulation problems leading to bumpy surfaces or due to the formation of cavities or cone-like protrusions (CLP) at high pulse energies. With a specific diffractive optical element (DOE) leading to a special beam shape and synchronized scanning a removal rate of 16 mm3/min was achieved on steel AISI 304 with an average power of 180 W and a repetition rate of 1 MHz. Flat and shiny surfaces without CLP's and bumps having a surface roughness of sa < 500 nm were achieved. In case of copper the maximum removal rate amounted 17 mm3/min with a surface roughness of sa < 400 nm at a repetition rate of 400 kHz and an average power of about 150 W. The experiments clearly show, that with beam forming high average powers can be used for high quality laser micromachining with ultrashort laser pulses and single beams at average powers exceeding 100 W.
For most micromachining applications, the laser focus has to be moved across the workpiece, either by steering the beam or by moving the workpiece. To maximize throughput, this movement should be as fast as possible. However, the required positioning accuracy often limits the obtainable speed. Especially the machining of small and complex features with high precision is constrained by the motion-system’s maximum acceleration, limiting the obtainable moving spot velocity to very low values. In general, processing speed can vary widely within the same processing job. To obtain optimum quality at maximum throughput, ideally the pulse energy and the pulse-to-pulse pitch on the workpiece are kept constant. This is only possible if laser-pulses can be randomly triggered, synchronized to the current spot velocity. For ultrafast lasers this is not easily possible, as by design they are usually operated at a fixed pulse repetition rate. The pulse frequency can only be changed by dividing down with integer numbers which leads to a rather coarse frequency grid, especially when applied close to the maximum used operating frequency.
This work reports on a new technique allowing random triggering of an ultrafast laser. The resulting timing uncertainty is less than ±25ns, which is negligible for real-world applications, energy stability is <2% rms.
The technique allows using acceleration-ramps of the implemented motion system instead of applying additional override moves or skywriting techniques. This can reduce the processing time by up to 40%.
Results of applying this technique to different processing geometries and strategies will be presented.
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.
In this work, we discuss mode-locking results obtained with low-loss, ion-exchanged waveguide lasers. With Yb3+-doped phosphate glass waveguide lasers, a repetition rate of up to 15.2 GHz was achieved at a wavelength of 1047 nm with an average power of 27 mW and pulse duration of 811 fs. The gap between the waveguide and the SESAM introduced negative group velocity dispersion via the Gires Tournois Interferometer (GTI) effect which allowed the soliton mode-locking of the device. A novel quantum dot SESAM was used to mode-lock Er3+, Yb3+-doped phosphate glass waveguide lasers around 1500 nm. Picosecond pulses were achieved at a maximum repetition rate of 6.8 GHz and an average output power of 30 mW. The repetition rate was tuned by more than 1 MHz by varying the pump power.
We present timing jitter measurements of a free-running SESAM modelocked VECSEL generating 8-ps pulses with
1.88-GHz repetition rate and 80-mW average output power. We observed very good performance comparable with iondoped
solid-state-lasers which typically show excellent stability. We measured the two-sided noise power spectral
density at the 10th harmonic of the laser output with the von der Linde method. The rms timing jitter integrated over an
offset frequency range from 100 Hz to 100 kHz gives a free-running timing jitter of ≈400 fs which is an upper limit
because the measurement was already system noise limited above 10 kHz.
Conference Committee Involvement (4)
Laser-based Micro- and Nanoprocessing XII
30 January 2018 | San Francisco, California, United States
Laser-based Micro- and Nanoprocessing XI
31 January 2017 | San Francisco, California, United States
Laser-based Micro- and Nanoprocessing X
16 February 2016 | San Francisco, California, United States
Laser-based Micro- and Nanoprocessing IX
10 February 2015 | San Francisco, California, United States
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