Progress on table-top isolated attosecond light sources

Research on isolated attosecond pulses (IAPs) based on high-order harmonic generation changed substantially around 2010. Before then, the Ti:sapphire laser was the de facto standard as the driving light source, so the cutoff energy was limited to similar to 100 eV. After 2010, the mid-infrared optical parametric amplifier became the mainstream driving source. The shortest pulse width of an IAP has reached similar to 50 as, an intensity over a gigawatt has been achieved, and the photon energy has been extended to 500 eV. However, owing to the low flux of IAPs, the use of IAPs is still limited in terms of applications. Here we focus on the vigorous efforts in the past decade to extend the performance of IAPs.