Abstract
Laser high-order harmonics in the extreme ultraviolet (EUV) and soft X-ray region serve as a unique
tool to study ultrafast molecular dynamics associated with valence or inner-shell electron excitations.
The harmonics are often obtained as a train of pulses, which result in a spectrum with a comb consisting
of the odd harmonic orders. However, it is often the case that isolated pulses rather than pulse trains are
preferred in the conventional pump-probe spectroscopy, to avoid signal overlaps associated with different
harmonic orders. Here we review our approach for the single-order harmonics generation in EUV by
using dielectric multilayer mirrors and metal foils, and the application to photoelectron spectroscopy on
wavepacket dynamics of simple molecules such as Br2, I2 and N2.
