Recent strong-field experiments [1,2] have used few-cycle mid-infrared (MIR) laser pulses to generate soft X-ray supercontinua able to support isolated attosecond pulses (IAPs) with durations close to the atomic unit of time (24 as). Efforts have been focused on improving the disadvantageous low efficiency of high harmonic generation (HHG)  from long-wavelength driver fields, as well as on generating shorter and chirp-free IAPs . Tailoring waveforms by the superposition of controlled electric fields has shown the potential to overcome such limitations of single-color-driven HHG . Here, we present the spatial characterization and spatiotemporal overlap  between near-(NIR) and mid-(MIR) infrared beams from a two-channel, optical paramemtric amplifier (OPA)-based waveform synthesizer. This, together with the demonstrated temporal  and beam pointing stabilization, will allow us to achieve full 3D, long-term stable synthesis.
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