Plasma lens for focusing attosecond pulses

Broadband optical pulses with attosecond to femtosecond durations provide unique opportunities for studies of time-resolved electron dynamics. However, focusing these pulses—typically ranging from the vacuum ultraviolet to the soft-X-ray region—remains challenging. Conventional refractive lenses are not suitable owing to large dispersion and strong absorption, whereas reflective optics do not suffer from these issues but have high losses. Here we demonstrate a tunable hydrogen plasma lens to focus broadband extreme-ultraviolet attosecond pulses with energies of around 20 eV and 80 eV. Simulation results suggest that the stretching of attosecond pulses is negligible, and temporal compression is possible when atto-chirp is included. A key advantage of the plasma lens is its compatibility with nonlinear frequency conversion processes like high-harmonic generation. The different focusing properties of the fundamental and harmonic frequencies allow for an efficient separation of these components. Consequently, the transmission of high-harmonic generation beamlines can be increased to more than 80% and this approach can be suitable for applications requiring high photon flux.