Abstract:The relative timing jitter of a multi-mJ sub-cycle 3-channel parametric waveform synthesizer pumped by an 18-mJ cryogenically cooled Ti:sapphire laser is studied. The system aims towards multi-mJ, 2-fs, phase-stable pulses covering the 0.52.4 µm range. High-energy sub-cycle optical waveforms have numerous intriguing applications in attoscience and strong-field physics, e.g., in the generation of intense isolated attosecond XUV pulses [1], relativistic laser-plasma interactions and laser-driven electron acceleration [2], valence-electron wavepacket dynamics in atoms and molecules [3], and the control of sub-cycle electron transport in solids [4].Shaping the electric field on a sub-cycle time scale requires an optical bandwidth of at least two octaves and precise control of the spectral phase over this bandwidth [5]. Supercontinuum generation in gas-filled hollow-core fiber compressors represents a rather mature technology for this purpose [3,6]. However, the scalability of gas-phase broadening schemes in terms of pulse energy and repetition rate seems to be limited by ionization losses, detrimental nonlinearities, heating-related problems and damage of materials. In contrast, parametric waveform synthesizers offer much better prospects for simultaneously scaling up both the pulse energy to the multi-mJ range and the repetition rate to tens or hundreds of kHz, which makes them very attractive for next-generation light sources such as SLAC, SACLA, FERMI and ELI-ALPS, targeting such operation parameter ranges.In earlier works, we already demonstrated coherent waveform synthesis between ultrabroadband 870-nm and 2.15-µm pulses based on optical parametric chirped-pulse amplification (OPCPA), resulting in a 15-µJ sub-cycle waveform [7], and also between two optical parametric amplifiers (OPAs) with 1-2 µJ energy each [8]. More recently, we have been developing a prototype multi-mJ 3-channel parametric synthesizer for generating 2-octavewide spectra with ~1.9-fs transform-limited pulse duration [9]. In this work, we investigate and demonstrate the feasibility to perform the final synthesis step in this parallel scheme at the multi-mJ level for the first time, with important implications for the above-mentioned next-generation light sources.In 2013, we proposed and reported first amplification results for our synthesizer pumped by a cryogenically cooled Ti:sapphire chirped-pulse amplifier (150 fs, 18 mJ, 1 kHz) [9]. We generate a common CEP-stable seed continuum (0.5-2.5 µm) [10] by white-light generation in a YAG crystal pumped by the second harmonic (1.06 µm) of the CEP-stable idler of a NIR OPA. The resulting continuum is then split with dichroic beam splitters [11] and seeds three OPA channels employing type-I BBO crystals, a VIS non-collinear OPA (NOPA), a NIR and an IR degenerate OPA (DOPA) channel, pumped by the fundamental wavelength pulses at 0.8 µm (IR DOPA) and by its second harmonic at 0.4 µm (VIS NOPA, NIR DOPA). Figure 1 shows the output spectra and pulse energies of the 3 channels obtained after ...