Powerful light wave synthesis at MHz repetition rates

Until recently, the pulse energies delivered directly by femtosecond laser oscillators did not suffice for efficient nonlinear frequency conversion. To this end, pulses first had to be picked from the MHz train and amplified at a strongly-reduced repetition rate. Two recent advances, pioneered and co-pioneered by MAP scientists, changed the situation. The nanojoule energy of pulses delivered by a standard fs oscillator was boosted by several orders of magnitude inside a passive “build-up” (slave) cavity)¹⁾ and used — inside the slave — for generating high-order harmonics for the first time at the full — MHz — repetition rate of an oscillator^{2, 3)}. Independently, implementation of the concept of chirped-pulse oscillators (CPO)⁴⁾ permitted the generation of sub-microjoule, sub-50-fs pulses directly from the oscillator⁵⁾. Here we propose to combine these two novel concepts, the master-slave and CPO concepts, for scaling 10-fs-scale femtosecond oscillator technology dramatically in terms of both average and peak power (Fig. A.1.1).

The sub-microjoule output from a CPO will be launched into a resonant build-up cavity (slave). By incorporating both in the master and in the slave cavity a laser amplifier, we will pursue, as the central long-term goal of this project, the scaling of femtosecond oscillator technology towards the kilowatt and gigawatt frontiers in terms of average and peak powers, respectively. Achieving these goals will rely on the development of broad-band chirped mirrors with low loss and smooth dispersion (A.1.4). Difference-frequency and high-harmonic generation in the slave will result in coherent IR/XUV/SXR sources with unprecedented characteristics for a wide range of applications. These developments will push the frontiers of precision spectroscopy (B.2.1) and infrared bioimaging (C.3.5) and will allow the development of an electron gun for femto-/attosecond electron diffraction (A.2.1), the efficient generation of multi-photon entanglement (B.2.5) and attosecond coincidence spectroscopy (C.1.2).