Sub-optical-cycle parametric synthesizer controlling directly isolated attosecond pulses

Femtosecond and attosecond pulses have triggered in the last decades several scientific achievements in physics, chemistry, biology, technology. In recent years, the generation of optical pulses with sub-cycle duration, high energy and high average power has been a hot trend of research. Besides the mere scientific interest of sub-cycle pulses as optical sources, what attracts the scientific community is their applicability to several fields of physics, like strong field physics and biology. Their spectra can cover the ultraviolet, visible and infrared spectral ranges. If combined with high harmonic generation, they can also produce extreme ultraviolet radiation. They can be generated in different ways, like hollow core fiber compression and serial or parallel synthesis of parametric amplifiers. After several years of development, we recently produced mJ-level near-infrared pulses with full-width at half maximum duration down to 2.8 fs, that is 60% of the period of the 1.4-um central wavelength, and stable carrier envelope phase. The technique used is the parallel synthesis of two infrared optical parametric amplifiers, which in total span the 650-2200 nm wavelength range. With them, we generated isolated attosecond pulses via high harmonic generation without need for any additional gating technique. Despite the complex setup and high number of nonlinear optical stages, the pristine stability of the attosecond pulses is confirmed by the reproducibility of the streaking measurements. By controlling the pulse carrier envelope phase and the relative phase between the two individual pulses composing the synthesizer, we generated highly tunable attosecond pulses between 30 and 200 eV