Researchers at the Fraunhofer Institute for Laser Technology (ILT) have developed a novel amplification concept for femtosecond lasers allowing mean power outputs in the kilowatt range. Femtosecond lasers are used for highly precise material processing applications, where the high mean power of the new device is expected to increase production significantly.
Pulsed lasers are most often used to ablate material, and in these applications a shorter pulse duration is associated with a the shallower heat penetration depth, a higher temperature at the material's surface, and a higher precision material processing outcome. Despite numerous advantages over longer-pulse length and continuous wave lasers, femtosecond technology has not yet become established in industrial production. According to the Fraunhofer researchers, the availability of a femtosecond laser source with higher mean power could change this.
The amplifier design is based on the Innoslab technology developed by the Fraunhofer ILT and characterised by a simple, robust and compact construction. The researchers have extended the amplifier design by using Yb:YAG as the active medium - a large bandwidth material well-suited to ultrashort pulses. Since ytterbium-doped crystals place great demands upon the pump beam source, the availability of brilliant pump diodes has made this step first possible. The oscillator-amplifier system also allows greater flexibility with respect to the repetition rate and the pulse duration than existing technologies, since a range of commercial femtosecond oscillators are available based on fibre and solid-state lasers with power outputs in the 2W range.
Dr Peter Rußbüldt, project leader at the Fraunhofer ILT, cascaded two Innoslab amplifiers in order to generate a mean power of 1.1 kW at a peak pulse power of 80MW and a pulse duration of 600 femtoseconds - a level that the team claims is a new record.
The original purpose of the joint project with the Max Planck Institute for Quantum Optics, funded by the BMBF (the German Federal Ministry of Education and Research), was a scientific application: the generation of coherent EUV radiation. During the project, researchers continued to develop the laser at the Fraunhofer ILT. 'Thanks to this new power output, the femtosecond laser slowly departs from its image as a scientifically complicated toy,' says Dr Rußbüldt. 'The higher power means the throughput also increases in production, which, in turn, means an enormous time and cost-based advantage for manufacturers. Therefore, the femtosecond laser can now be applied in fields in which its throughput did not suffice in the past.'
Typical applications of the femtosecond laser in the macro sector are manufacturing processes for fibre-composite lightweight components, where a femtosecond laser can process varying materials irrespective of their characteristics. In the micro sector potential applications for this new beam source include the drilling of nozzles, tool engineering, solar cell engineering, and even printing technology.