Towards active multipass Kerr-lens mode-locked Yb:YAG thin-disk oscillators

Summary form only given. Yb:YAG thin-disk (TD) oscillators are able to deliver energetic femtosecond pulses without external amplification at hundreds of watts average power and MHz repetition rates [1, 2]. Such compact, high-power, low-noise sources are beneficial for scientific experiments and industrial micromachining. They also serve as a great starting point for spectral broadening, which allows transferring their power performance into the sub 20 fs region [3] and to other spectral domains like MIR [3] or XUV [4].In this work, we evaluated the applicability of multi-passing to KLM oscillators. A potential challenge is that high-peak power KLM operation requires the oscillator to run in a narrow region close to its resonatorinstability. However, more passes increase the influence of the thermal lens variation in the TD and, thus, shift the oscillator out of this KLM-region. To test if this prevents useful mode-locked operation a double pass TD oscillator was first built and characterized. This oscillator was then modified to exhibit three folded passes over the TD (Fig. 1). For better comparison with the previous configuration, the repetition rate was kept the same.