Final Report Summary - ACOPS (Advanced Coherent Ultrafast Laser Pulse Stacking)
The goal of the ACOPS project was to develop a compact, efficient, scalable, and cost-effective high-average and high-peak power ultra-short pulse laser concept. The core idea was to coherently superimpose temporally and spatially multiplexed laser pulses, either in optical delay lines or in an enhancement cavity (EC) followed by cavity dumping, a process referred to as stack-and-dump (SnD).
We demonstrated the ‘stack-and-dump’ scheme in a 30-m long EC, corresponding to a length increase of a factor of 10 over the state of the art. Towards tapping the full potential of ECs as stacking devices for ultrashort pulses, this constitutes a crucial design criterion relaxing the thermal stress in the switch and in the cavity optics and allowing for longer times between successive pulses. Possible limitations caused by phase fluctuations or thermal issues have been investigated and suitable solutions were found. The EC supported a steady-state power enhancement factor exceeding 200 when seeded with a 10-MHz repetition-rate train of 3-µJ pulses. This way, pulses with the accumulated energy of up to 65 input pulses, i.e. 0.2 mJ, were extracted at 30 kHz by an acousto-optic modulator. These pulses were recompressed to the initial duration of 800 fs, demonstrating the feasibility of SND with strongly stretched pulses and energies surpassing previous results by three orders of magnitude. These results, even if not stating new laser parameter records on their own, constitute a milestone towards a power-scalable device and, thus, are a necessary step towards the first stack-and-dump system providing truly unprecedented laser parameters.
Additionally, the fiber development necessary in order to scale the available input power to achieve the project goals was successfully driven forward. The reason for the onset of mode instabilities is the thermal heat load in the amplifier. It has been revealed that two effects can lead to heat development in a doped fiber. Firstly: the quantum defect and secondly photo-darkening. We found out, that the impact of photodarkening is equally large and can therefore not be neglected as it was done before. Hence, using longer, less doped fibers is a possibility to reduce the heat load per meter and allow for much higher output powers. In addition, novel techniques to suppress such mode instabilities have been successfully investigated.
Based on the concepts pursued within ACOPS two highlights have been achieved, namely a record high pulse energy and a record high average power from an ultrafast fiber lasers system, during the final period of the project: 3.5kW of average power and 27mJ pulse energy from fiber-based femtosecond systems constitute remarkable achievements.
Overall, the findings of ACOPS pave the way to a new realm of laser parameters allowing to address a number of future applications.
We demonstrated the ‘stack-and-dump’ scheme in a 30-m long EC, corresponding to a length increase of a factor of 10 over the state of the art. Towards tapping the full potential of ECs as stacking devices for ultrashort pulses, this constitutes a crucial design criterion relaxing the thermal stress in the switch and in the cavity optics and allowing for longer times between successive pulses. Possible limitations caused by phase fluctuations or thermal issues have been investigated and suitable solutions were found. The EC supported a steady-state power enhancement factor exceeding 200 when seeded with a 10-MHz repetition-rate train of 3-µJ pulses. This way, pulses with the accumulated energy of up to 65 input pulses, i.e. 0.2 mJ, were extracted at 30 kHz by an acousto-optic modulator. These pulses were recompressed to the initial duration of 800 fs, demonstrating the feasibility of SND with strongly stretched pulses and energies surpassing previous results by three orders of magnitude. These results, even if not stating new laser parameter records on their own, constitute a milestone towards a power-scalable device and, thus, are a necessary step towards the first stack-and-dump system providing truly unprecedented laser parameters.
Additionally, the fiber development necessary in order to scale the available input power to achieve the project goals was successfully driven forward. The reason for the onset of mode instabilities is the thermal heat load in the amplifier. It has been revealed that two effects can lead to heat development in a doped fiber. Firstly: the quantum defect and secondly photo-darkening. We found out, that the impact of photodarkening is equally large and can therefore not be neglected as it was done before. Hence, using longer, less doped fibers is a possibility to reduce the heat load per meter and allow for much higher output powers. In addition, novel techniques to suppress such mode instabilities have been successfully investigated.
Based on the concepts pursued within ACOPS two highlights have been achieved, namely a record high pulse energy and a record high average power from an ultrafast fiber lasers system, during the final period of the project: 3.5kW of average power and 27mJ pulse energy from fiber-based femtosecond systems constitute remarkable achievements.
Overall, the findings of ACOPS pave the way to a new realm of laser parameters allowing to address a number of future applications.