Near-keV coherent X-ray generation with sub-10-fs lasers

Recent advances in solid-state laser technology and ultrafast optics have led to the generation of optical pulses as short as 5 fs with peak powers up to 0.1 TW from a compact kilohertz-repetition-rate all-solid-state laser. This source significantly pushes the frontiers of nonlinear optics. Intriguing possibilities include the development of a compact laser-driven coherent soft-X-ray source at photon energies near 1 keV, and the generation of autosecond XUV pulses. This paper analyzes strong-field ionization and high-harmonic generation in the few-cycle regime, and reviews the first experimental realization of high-harmonic generation with 5-fs pulses. These experiments have resulted in the emission of coherent X-rays at photon energies greater than 0.5 keV (λ<2.5 nm), representing the highest photon energies achieved with a laser-driven coherent source so far. The generated XUV beam is well collimated and predicted to be delivered, after suitable spectral filtering, in a single burst of autosecond duration