The adjustment of the relative phase or amplitude of quasi-monochromatic modes extending over superoctave spectrally allowed a sub-cycle sculpting of these waveforms but the overall picosecond to nanosecond confinement of these pulses considerably inhibits application in attosecond metrology and control.
Remarkably though a nearly 5-fold increase of the spectral width with respect to that achieved in the inaugural experiments of this technique is essential to achieving superoctave pulses that fulfill the requirements for sub-cycle field synthesis.
Whereas the number of subdivisions of a given superoctave bandwidth may appear at a first glance essential it is only the total spectral width that determines the attainable temporal resolution.
Whereas conventional pulse metrology [57, 58] is appropriate to capture the characteristics of the pulses in each of the constituent channels it fails to offer a reliable, instantaneous-field sensitive characterization required for field-controlled superoctave waveforms.