In the ERC project MEGA-XUV, we developed a new approach for coherent XUV sources operating at megahertz repetition rates. We developed a compact XUV source that generates high harmonics directly inside the cavity of an ultrafast thin-disk laser oscillator, a laser concept that is power-scalable and that has been achieving the highest power levels from any femtosecond oscillator technology since its invention in the year 2000. Instead of amplifying a laser beam to high power levels and dumping it after the HHG interaction, the generation of high harmonics is placed directly inside the intra-cavity beam of the high power femtosecond laser. Thus, the unconverted light is “recycled”, and the laser medium only needs to compensate for the low losses of the resonator. In contrast to passive enhancement cavities, no complex input coupling of femtosecond pulses is required.
During the project, we strongly improved the ultrafast thin-disk laser technology, achieving new records in average output power, pulse energy, and pulse duration. We also proved that ultrafast thin disk lasers are well suited for ultrastable operation and the generation of optical frequency combs. The invention of optical frequency combs revolutionized numerous fields in metrology and was honored by the 2005 Nobel Prize in Physics for T.W. Hänsch and J.L. Hall. The technological potential of this invention is enormous, including areas such as metrology, optical clocks, synchronization and timing, and sensing for process control or bio-medical systems.
Optical frequency combs are based on femtosecond laser technologies and require the stabilization of the carrier-envelope offset (CEO) frequency. Our team recently invented a new method for CEO stabilization via opto-optical modulation (OOM) of a semiconductor saturable absorber, which overcomes limitations imposed by the gain life time. Moreover this method exhibits extremely high damage thresholds and low additional dispersion and optical nonlinearities, which makes it ideally suitable to high power oscillators such as ultrafast thin disk lasers. We patented our idea, the European Patent was granted on 25.05.2017 patent EP 3 053 226 B1. In this PoC proposal, we developed several technical demonstrators and design studies, which bring this invention closer to the market. In addition, we evaluated several commercialization plans.
