Researchers at the Fraunhofer Institute for Laser Technology (ILT) have developed an amplification concept for femtosecond (fs) lasers. As a result, they have been able to achieve mean power in the kilowatt range for the first time. Resonator of the yb:INNOSLAB femtosecond amplifier. (Image: Fraunhofer ILT) The short pulses of the fs lasers enable ultraprecise material processing. Thanks to the high mean power, the throughput in production can be increased significantly. While lasers with continuous radiation are often used to cut and weld, pulsed lasers are mostly used to ablate. For the latter, following generally applies — the shorter the pulse, the smaller the heat penetration depth, the higher the temperature at the material surface, and the higher the precision of the material processing. Material ablation mainly occurs via vaporization. The shorter pulses of the fs laser enable greater precision when ablating. In addition, materials can be processed that can only be poorly processed with lasers, or not at all. The fs laser has not yet become established in industrial production. This could soon change when fs lasers with higher mean power become commercially available, thus making great throughput, lower maintenance costs and easier usability possible. Researchers from the Fraunhofer ILT have finally succeeded achieving power in the kilowatt range with an fs laser — a first step in expanding the industrial use of fs lasers decidedly. Advanced Amplifier Design The amplifier design is based on the Innoslab technology. This in-house development of the Fraunhofer ILT is characterized by an especially simple, robust and compact construction. The researchers from Aachen have extended the amplifier design by using yb-doped YAG as active medium, which enables the amplification of ultrashort pulses due to its large bandwidth. 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 enables, in addition, more flexibility with respect to the repetition rate and the pulse duration, since to generate the pulse a variety of commercial fs oscillators are available based on fiber and solid-state lasers with about two watts of mean laser power. Dr. Peter Russbüldt, project leader at the Fraunhofer ILT, has cascaded two Innoslab amplifiers. In this way, the amplifier chain was able to generate a mean power of 1.1 kW at a peak pulse power of 80 MW and a pulse duration of 600 femtoseconds. The Aachen researchers have thus reached 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 fs laser slowly departs from its image as a scientifically complicated toy,” said 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 fs laser can now be applied in fields in which its throughput did not suffice in the past.” Typical applications of the fs laser in the macro sector are manufacturing processes for fiber-composite lightweight components. An fs laser can process the most varying of materials irrespective of their characteristics. In the micro sector the applications of this new beam source range from drilling of nozzles to tool engineering, solar cell engineering all the way to printing technology. The Fraunhofer ILT will hold a workshop on this topic on April 13 and 14, 2011 in Aachen. Experts from research and industry will provide information about the foundations and laser beam sources of ultrashort pulse lasers (USP) and discuss relevant applications for material processing jointly with participants. Technological developments and their market potential will be illuminated in this USP workshop. At SPIE Photonics West (San Francisco, Jan. 25 -27, 2011), the Fraunhofer ILT will be showing high precision assembly technology for optical components in the German Pavilion North Hall at Stand 4601 and presenting further developments of heat sinks for high power diode lasers. In the accompanying conference (LASE, Jan. 22 - 27, 2011), the Aachen experts will be presenting the new high power lasers. For more information, visit: www.ilt.fraunhofer.de