Multioctave supercontinua and subcycle lightwave electronics [Invited]

Multioctave supercontinua provide a unique resource for ultrafast optical science, offering advanced tools for time-resolved spectroscopy, frequency comb technologies, nonlinear microscopy, and lightwave engineering. The physical scenarios that enable the generation of such ultrabroadband wave packets are not always easy to describe in terms of standard models of ultrafast nonlinear optics; their properties are often unusual, and their nonlinear dynamics are much more than meets the eye. To adequately understand these new electrodynamics and to identify scenarios whereby multioctave supercontinua can coherently add up yielding subcycle field waveforms, some basic concepts and models of ultrafast nonlinear optics have to be revisited. Originally intended to refer to a rapid buildup of the spectral bandwidth of ultrashort laser pulses propagating, as waveguide modes or as free beams, in media with a third-order optical nonlinearity, within the past decade, the term “supercontinuum generation” has been seamlessly extended, thanks to its all-embracing character, to include very-high-order and nonperturbative nonlinear optical processes and now applies to ultrabroadband field waveform generation in the ultraviolet and x-ray ranges, as well as high-harmonic attosecond and zeptosecond supercontinua. This paper offers a brief overview of this rapidly growing field of research.