Pulse dynamics control in passively mode-locked high energy solid state laser oscillators

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Mode-locked laser oscillators emitting femtosecond pulses with high repetition rates become more and more powerful. Employing state-of-the-art techniques such as thin-disk or slab based schemes, pulse energies in the 10 µJ range have been generated directly from the laser oscillator. At the same time during this development, people realized a substantial increase of pulse duration well beyond the gain bandwidth limitations which at least partially counteracts the high energy again; we refer it here the scaling problem. From the solitary mode-locked laser oscillator employing a semiconductor saturable absorber - which is the most common type - it is well known that two-photon absorption processes in the absorber mirror form the main limiting process. Nevertheless, a convincing concept for overcoming this limitation was not yet demonstrated. This shall be the subject of this proposal: On the base of a concise analysis of the pulse shaping mechanisms an FPGA control concept is investigated and implemented leading to much shorter pulses from high energy oscillators. Surprisingly enough, the scaling problem is also known from chirped-pulse oscillators (CPO) with net positive dispersion where the pulses are chirped all the time during the oscillator roundtrip. Due to the chirp the model of excessive nonlinearity in the absorber cannot be simply adapted to this case. The scaling problem in this parameter range is not yet explored systematically which shall be subject of this project as well. At the end we will gain new fundamental insight into the nonlinear pulse propagation in high energy solid-state laser oscillators, into their limitations, and into the external control of laser dynamics. We will explore concepts to overcome the scaling problem and to generate high-energy pulses much shorter than now which in turn will be of relevance for many applications in physics and beyond.