Observation of recollision-based high-harmonic generation in liquid isopropanol and the role of electron scattering

We report extreme-ultraviolet high-harmonic generation (HHG) from liquid isopropanol, extending up to 50 eV, when using 1800-nm carrier envelope phase stable pulses of 1.8 cycles with intensities below the laser breakdown threshold. We study the mechanism of the harmonic emission through its dependence on the driving field and find it to be consistent with a strong-field recombination mechanism. We explore the role of scattering from neighboring molecules in simulations using empirical cross-section data. We find that these simulations, within a full propagation calculation, provide good quantitative agreement with the measured intensity-dependent harmonic cutoffs and demonstrate that HHG emission in the liquid phase can be used to corroborate ultrafast electron-scattering processes.