A unique property of ultrafast lasers is that they enable high precision micro-processing of almost any material. They can precisely ablate target area without causing any damage to the surroundings. Unfortunately, material processing based on this kind of lasers is relatively slow and cannot meet the requirements of current advanced industrial processing (industry 4.0) that usually needs very high throughput and at the same time allows for the customization of the process.
To meet these needs, laser-processing system requires high average power ultrashort lasers (kW range) and an output beam splitting solution to parallelize the processing. Further, such lasers should exhibit high reliability in order to operate in the real industrial environment (24/7 operation) and offer some degree of flexibility and adaptability to the processing unit. The fiber laser technology intrinsically offers not only high reliability, but also high beam quality, extremely high-energy efficiency and maintenance free operation. These advantages have been already demonstrated in the area of continuous wave (CW) fiber lasers where lasers with output power of 1 kW and beyond have been introduced in several modern industrial systems. Unfortunately, the same fiber solutions cannot be directly used for the high-power ultrashort pulse laser due to two main restriction. The first are the nonlinear effects (SPM ,SRS,…) that appear within the optical fiber, limiting the peak power of the ultrashort laser pulses and consequently the pulse energy. The second restriction are the transverse mode instabilities (TMI) that limit average power. These restrictions could be circumvented by new approaches in fiber laser design that are proposed in this project.
The problem of efficient high speed processing with ultrashort pulses is currently being addressed in the two key EU Horizon 2020 projects (MultiFlex and Multipoint). Both predict development of a high power ultrashort laser with kW output and mJ level energy based on solid state technology to avoid the nonlinear effects and a complex beam splitting unit that enables parallel processing (several 10s of parallel beams) with the optimal energy for the process. This kind of beam splitting requires additional highly sophisticated unit, based on free space optics and control electronics that is precisely synchronized with the laser source. Overall, the result will be a very high performance system, but also an extremely complex one.
Within this project proposal, we suggest a completely different solution to the original problem of efficient high speed processing using laser system based on fiber technology. The key difference is where to split the laser beam. In contrast to the above mentioned project we propose to split the beam within the ultrashort laser itself, therefore to develop a multi‑channel laser with several output stages. The main advantage is that in this case there is no need to amplify the laser pulses to high energies that are the key source of problems (due to nonlinear effects). Furthermore, the pulse energy is directly tailored to the material that is processed without the need of high energy pulses being attenuated by splitting.
The main advantages of this proposed approach are:
- There is only one unit that directly generates several output laser beams that are required for multi-beam processing.
- Multichannel approach results in a relatively low pulse energy as well as average power per channel - consequently fiber laser technology can be used that enables all the advantages related to this approach.
- Control of each channel (average power and especially pulse on demand) can be realized more efficiently, because it can be done at relatively low average power (for example at the input of the each output amplifier) - low power high speed modulator can be used.
- Individual channels can be controlled independently to a high degree of freedom.
