Relativistic-intensity near-single-cycle light waveforms at kHz repetition rate.

Relativistic optics: High intensity ultra-short fast-repeating light pulses A pioneering laser source combines extremely high intensity and fast-repeating pulses with ultra-short pulse duration, opening new opportunities in the field of research and technology called relativistic optics. This requires lasers that are sufficiently intense to accelerate particles such as electrons to close to light speed, when effects of relativity theory become increasingly significant. Marie Ouille and colleagues at the CNRS Laboratoire d'Optique Appliquee in France, with co-workers in Germany, combined laser sources with light compression and manipulation methods to generate relativistic intensity pulses almost as short as a single cycle of the light wave. They say their system is currently the only light source capable of achieving pulses shorter than four femtoseconds combined with peak powers up to 1 terawatt. The researchers also demonstrated precise control over the fine structure of the light pulses. The development of ultra-intense and ultra-short light sources is currently a subject of intense research driven by the discovery of novel phenomena in the realm of relativistic optics, such as the production of ultrafast energetic particle and radiation beams for applications. It has been a long-standing challenge to unite two hitherto distinct classes of light sources: those achieving relativistic intensity and those with pulse durations approaching a single light cycle. While the former class traditionally involves large-scale amplification chains, the latter class places high demand on the spatiotemporal control of the electromagnetic laser field. Here, we present a light source producing waveform-controlled 1.5-cycle pulses with a 719 nm central wavelength that can be focused to relativistic intensity at a 1 kHz repetition rate based on nonlinear post-compression in a long hollow-core fiber. The unique capabilities of this source allow us to observe the first experimental indications of light waveform effects in laser wakefield acceleration of relativistic energy electrons.