  High-brightness sources of coherent and few-cycle-duration light waveforms
with spectral coverage from the UV to the THz would offer unprecedented
versatility and opportunities for a spectacular range of applications from
bio-chemical sensing, to time-resolved and nonlinear spectroscopy, to
attosecond light-wave electronics. Combinations of various sources with
frequency conversion and supercontinuum generation can provide relatively large
spectral coverage, but many applications require much broader spectral range
and low-jitter synchronization for time-domain measurements. Here, we present a
carrier-envelope-phase stable light source, seeded by a mid-IR frequency comb,
with simultaneous spectral coverage across 7 optical octaves, from the UV (340
nm) into the THz (40,000 nm). Combining soliton self-compression and dispersive
wave generation in an anti-resonant-reflection photonic crystal fibre with
intra-pulse difference frequency generation in BaGa2GeSe6, the spectral
brightness is 2-5 orders of magnitude above synchrotron sources. This enables
high-dynamic-range spectroscopies and provides enticing prospects for
attosecond physics and material sciences.
