Laser-assisted electron scattering in strong-field ionization of dense water vapor by ultrashort laser pulses

M Wilke,N Engel,E F Aziz,R Al-Obaidi,A Moguilevski,J Metje,A Kothe,I Yu Kiyan

doi:10.1088/1367-2630/16/8/083032

Abstract

We report on strong-field ionization of dense water gas in a short infrared laser pulse. 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 medium 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 that are orders of magnitude lower than those considered for heating the 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 theory.

Highlights

The strong-field light–matter interaction has received great attention during the past few decades
We report on strong-field ionization of dense water gas in a short infrared laser pulse
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 medium 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

Summary

Introduction

The strong-field light–matter interaction has received great attention during the past few decades. Ionization is one of the fundamental processes which has been studied in detail at the elementary level of the field interaction with isolated atoms or molecules [1, 2]. Generation of hot electrons represents a characteristic feature of this process at high laser intensities. It is well known that the spectrum of electrons emitted directly to the continuum in the process of above-threshold ionization (ATI) extends up to kinetic energies of 2Up. The high-order ATI occurs due to rescattering of the direct electron on the parent core in the presence of the laser field. Its spectrum has a cutoff energy of approximately 10Up [1, 2]. For a laser intensity of 1015 W cm−2 and a photon energy of 1 eV this cutoff lies at 1.4 keV

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Conclusion