Abstract-Waveform nonlinear optics aims to study and control the nonlinear interactions of matter with extremely short optical waveforms custom-tailored within a single cycle of light. Different technological routes to generate such multimillijoule sub-opticalcycle waveforms are currently pursued, opening up unprecedented opportunities in attoscience and strong-field physics. Here, we discuss the experimental schemes, introduce the technological challenges, and present our experimental results on high-energy sub-cycle optical waveform synthesis based on (1) parametric amplification and (2) induced-phase modulation in a two-color-driven gas-filled hollow-core fiber compressor. More specifically, for (1), we demonstrate a carrier-envelope-phase (CEP)-stable, multimillijoule three-channel parametric waveform synthesizer generating a >2-octave-wide spectrum (0.52-2.4 μm). After two amplification stages, the combined 125-μJ output supports 1.9-fs FWHM waveforms; energy scaling to >2 mJ is achieved after three amplification stages. FROG pulse characterization of all three second-stage outputs demonstrates the feasibility to recompress all three channels simultaneously close to the Fourier limit and shows the flexibility of our intricate dispersion management scheme for different Manuscript received January 23, 2015; revised April 16, 2015; accepted April 21, 2015. This work was supported by the Center for Free-Electron Laser Science at DESY, the excellence cluster "The Hamburg Centre for Ultrafast Imaging-Structure, Dynamics and Control of Matter at the Atomic Scale" of the Deutsche Forschungsgemeinschaft, the ERC-Synergy grant AXSIS under Grant 609920, and by JRA-INREX from LASERLAB-EUROPE under Grant 284464, ECS Seventh Framework Programme. The work of C. Manzoni was supported by MIUR FIRB under Grant RBFR12SW0J. experimental situations. For (2), we generate CEP-stable 1.7-mJ waveforms covering 365-930 nm (measured at 1% of the peak intensity) obtained from induced-phase modulation in a two-colordriven gas-filled hollow-core fiber. Using custom-designed doublechirped mirrors and a UV spatial light modulator will permit compression close to the 0.9-fs FWHM transform limit. These novel sources will become versatile tools for controlling strong-field interactions in matter and for attosecond pump-probe spectroscopy using VIS/IR and XUV/soft-X-ray pulses.Index Terms-Ultrabroadband sources, parametric oscillators and amplifiers, gas-filled hollow-core fiber pulse compression, pulse synthesis, waveform nonlinear optics.

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