Attosecond pulses are indispensable tools for time-resolved studies of electron dynamics on their natural time scale (1 attosecond = 10-18 seconds). Such studies include coincidence spectroscopy and experiments with high demands on statistics or signal-to-noise ratio, especially in the case of solid and molecular samples in chemistry and biology, all with an exponentially growing interest. For these cutting-edge research topics, scientists need to increase the number of attosecond pulses in a certain unit of time, which can only be achieved by increasing the repetition rate of the attosecond source. To do so, a laser source of high average power and high repetition rate is necessary. However, the high average power of the driving laser source presents a difficulty when compared to conventional attosecond beamlines using lower power drivers: it is not easy to separate the attosecond pulses from the high-average-power laser beam after generation. To overcome this issue, scientists of the Extreme Light Infrastructure Attosecond Pulse Light Source (ELI ALPS) shaped the laser beam to an annular shape: Combining this approach with the proper experimental configuration, they achieved the highest attosecond-pulse-train energy per shot produced by a system with a repetition rate above 10 kHz.
