Ultrafast laser oscillators are indispensable tools for diverse applications in scientific research and industry. When the phases of the longitudinal laser cavity modes are locked, pulses as short as a few femtoseconds can be generated. As most high-power oscillators are based on narrow-bandwidth materials, the achievable duration for high-power output is usually limited. Here, the attoworld-team presents a distributed Kerr-lens mode locked Yb:YAG thin-disk oscillator which generates sub-50 fs pulses with spectral widths far broader than the emission bandwidth of the gain medium at full-width-at-half-maximum. Simulations were also carried out, indicating good qualitative agreement with the experimental results. The proof-of-concept study shows that this new mode-locking technique is pulse-energy and average-power scalable and applicable to other types of gain media, which may lead to new records in the generation of ultrashort pulses.