  The generation of coherent light pulses in the extreme ultraviolet (XUV)
spectral region with attosecond pulse durations constitutes the foundation of
the field of attosecond science. Twenty years after the first demonstration of
isolated attosecond pulses, they continue to be a unique tool enabling the
observation and control of electron dynamics in atoms, molecules and solids. It
has long been identified that an increase in the repetition rate of attosecond
light sources is necessary for many applications in atomic and molecular
physics, surface science, and imaging. Although high harmonic generation (HHG)
at repetition rates exceeding 100 kHz, showing a continuum in the cut-off
region of the XUV spectrum was already demonstrated in 2013, the number of
photons per pulse was insufficient to perform pulse characterisation via
attosecond streaking, let alone to perform a pump-probe experiment. Here we
report on the generation and full characterisation of XUV attosecond pulses via
HHG driven by near-single-cycle pulses at a repetition rate of 100 kHz. The
high number of 10^6 XUV photons per pulse on target enables attosecond electron
streaking experiments through which the XUV pulses are determined to consist of
a dominant single attosecond pulse. These results open the door for attosecond
pump-probe spectroscopy studies at a repetition rate one or two orders of
magnitude above current implementations.
