Power scaling of ultrashort pulses by spatial and temporal coherent combining
Ytterbium-doped solid-state lasers are versatile tools for the generation of intense ultrashort pulses, which are the key for many industrial and scientific applications. High pulse-peak powers and high average powers are desired at the same time, e.g. to initiate a physical process of interest while providing fast data-acquisition times. Although sophisticated state-of-the-art laser concepts have already demonstrated remarkable performance figures, their working principles hamper the simultaneous delivery of both high peak power and high average power. Coherent combination of pulses provided by an amplifier array constitutes a novel concept for scaling both the average power and the peak power. Although this technique is applicable to any laser concept, it is especially well suited for fibers due to their high single-pass gain and their reproducible, excellent beam quality. As the number of amplifier channels may become too large for the ambitious energy levels being targeted, divided-pulse amplification (DPA) the coherent combination of a pulse burst into a single pulse can be applied as another energy-scaling approach, which is the focus of this thesis. In this regard, the energy-scalability of DPA implementations as an extension to well established chirped-pulse amplification (CPA) is analyzed and actively-controlled DPA is demonstrated. Moreover, the potential of merging spatial and temporal coherent combining concepts in a power- and energy-scalable architecture has been demonstrated. Based on the findings, a state-of-the-art high-power fiber-CPA system is extended by eight parallel main-amplifier channels, in which bursts of up to four pulse replicas are amplified that are eventually stacked into a single pulse. With this technique < 300 fs pulses of 12 mJ pulse energy at 700 W average power have been achieved, which is an order of magnitude improvement in both energy and average power compared to the state-of-the-art at the beginning of this work.