The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 1020 W/cm2 with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-field-driven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources.

We report on a novel 18-TW peak power light source delivering pulses with 80-mJ energy and 4.5-fs duration. The system is based on optical parametric synthesizer principle involving multi-color optical parametric chirped pulse amplification stages.

The endeavour of generating shorter and shorter light pulses lead to the optical parametric chirped pulse amplification (OPCPA) technique, which provides considerable broader gain bandwidth corresponding to a pulse duration of one to three optical cycles. Systems with such a short duration and multi-terawatt to petawatt power levels provide a unique tool for attosecond [1] and laser-plasma physics [2]. This way the generation of single attosecond pulses with unprecedented energy opens up the route to nonlinear X-ray science.

We report on the first laser-driven electron acceleration experiment with a sub-2-cycle multi-10-TW laser. About 10 MeV energy, few pC charge dark-current-free mono-energetic electron bunches together with indication of carrier-envelope-phase dependence were observed.

We report on the development and relevant characteristics of an optical parametric synthesizer light source delivering sub-5-fs pulses with 80 mJ energy. The first applications of the system are attosecond and relativistic laser-plasma physics.

We demonstrate the control of electron tunneling in the high-order harmonic generation process and subsequent positive-energy wavepacket propagation until recollision with the unprecedented precision of about 10 attoseconds. This is accomplished with waveforms synthesized from a few-cycle near-infrared pulse and its second harmonic. The presented attosecond control of few-cycle-driven high harmonics permits the generation of tunable isolated attosecond pulses, opening the prospects for a new class of attosecond pump–probe experiments.

Full characterization of single ultrashort laser pulses, as needed for attosecond metrology and spectroscopy, requires precise measurement of the offset between the electric field and pulse envelope, or carrier–envelope phase (CEP). Until now, all CEP measurements have been made by averaging over a large number of phase-stabilized laser pulses. Here, we demonstrate the first single-shot CEP measurement of intense few-cycle laser pulses. We focus a laser pulse on a gas target and detect photoelectrons emitted in opposing directions (‘left–right’) parallel to the polarization of the laser. By comparing the left–right asymmetries of photoelectrons at different energies, we mapped the CEP of consecutive non-phase-stabilized pulses on a parametric plot. This new evaluation method enables us to determine the CEP without phase ambiguity at unprecedented measurement precision. Future investigation of phase-dependent phenomena with CEP tagging at a much lower phase jitter than accessible at present with phase-stabilized lasers is now possible.

A method for complete characterization of the waveform of individual few-cycle laser pulses is presented. By analyzing the ``left'' and ``right'' asymmetries of high-energy photoelectrons along the polarization axis using the recently developed quantitative rescattering theory, we show that the carrier-envelope phase (CEP), pulse duration, and peak intensity of each single-shot pulse can be readily retrieved. By CEP tagging each laser shot, the method permits the study of waveform-dependent processes be extended to relativistic beams and to wavelengths, where CEP stabilization is not yet possible.