Laser assisted electron scattering in strong field ionization of dense water vapor by few cycle laser pulses

We report on strong field ionization of dense water gas in a short laser pulse of a few optical cycles. By employing a unique combination of photoelectron spectroscopy with a liquid micro jet technique, we observe how the character of electron emission at high kinetic energies changes with the increase of the gas density. This change is associated with the process of laser assisted electron scattering LAES on neighboring particles, which becomes a dominant mechanism of hot electron emission at higher medium densities. The manifestation of this mechanism is found to require densities which are orders of magnitude lower than those considered for heating of laser generated plasmas via the LAES process. The experimental results are supported by simulations of the LAES yield with the use of the Kroll Watson theor