"At the heart of strong-field phenomena such as high harmonic generation (HHG) lie electron trajectories starting with tunnel ionization and ending ~1 fs later with recollision of the continuum electron with the parent ion. Demonstration of a ground-breaking level of control over these trajectories via the driving laser waveform is the goal of this project.We propose to develop a multi-color waveform synthesizer, sufficiently intense to drive high harmonic generation (HHG). To this end, an actively carrier-envelope phase (CEP) stabilized, <200-fs laser with >5 mJ pulse energy@1-kHz will be developed based on the Yb,Na:CaF2 amplifier crystal already well proven in Vienna. This 1µm-laser will pump a white-light seeded Optical Parametric Amplifier (OPA), generating 1.5-µm-signal and 3-µm-idler pulses phase-locked to the pump laser. With these 3 absolute-phase locked color components, light waveform synthesis becomes possible.We will demonstrate the enabling nature of the light waveform synthesizer by realizing “the perfect wave”: an appropriately designed waveform driving HHG with higher photon energies and far superior efficiency as compared to the benchmark set by a single-color pulse driving HHG in the saturated regime. The principles of such a waveform have recently been laid out by the group of J. Marangos (Imperial College London), with whom we will collaborate. Our goal is efficient generation of 200-eV photons by HHG.This demonstration will prove the potential of electron trajectory engineering, e.g. for generating intense femtosecond or attosecond x-ray pulses in the “water-window”or for probing attosecond dynamics in molecules with an engineered recolliding electron wave packet.The fellow is an expert of HHG and attosecond physics, and in particular the molecular imaging aspect of it. He will gain competencies in laser and OPA development and build and validate a source with fantastic potential for molecular imaging by HHG and many other fields."