Strong-field photoelectron momentum imaging of OCS at finely resolved incident intensities

Joss Wiese,Sebastian Trippel,Jean-François Olivieri,Andrea Trabattoni,Jochen Küpper

doi:10.1088/1367-2630/ab34e8

Abstract

Photoelectron momentum distributions from strong-field ionization of carbonyl sulfide with 800 nm central-wavelength laser pulses at various peak intensities from 4.6 to 13 × 1013 W cm−2 were recorded and analyzed regarding resonant Rydberg states and photoelectron orbital angular momentum. The evaluation of the differentials of the momentum distributions with respect to the peak intensity highly suppressed the impact of focal volume averaging and allowed for the unambiguous recognition of Freeman resonances. As a result, previously made assignments of photoelectron lines could be reassigned. An earlier reported empirical rule, which relates the initial state's orbital momentum and the minimum photon expense to ionize an ac Stark shifted atomic system to the observable dominant photoelectron orbital momentum, was confirmed for the molecular target.

Highlights

Studies in strong-field physics aim at the understanding and control of the electron wave packet emitted by an atomic or molecular target following the exposure to intense radiation
Peak intensities as determined by a combination of beam-profiling, auto-correlation, and measurement of the pulse energy were found to be too low by 20% compared to the intensity-dependent kinetic energy shift of distinct above-threshold ionization (ATI) peaks, see (8)
Using the microchannel plate (MCP) open area ratio of 0.64 as instrument sensitivity α, a transverse focal standard deviation of σr = 22 μm and a molecular beam diameter of D = 2.2 mm resulted in a sample density of ñ = 1 × 108 W cm−3

Summary

Introduction

Studies in strong-field physics aim at the understanding and control of the electron wave packet emitted by an atomic or molecular target following the exposure to intense radiation. In general for strong-field ionization, the electron wave packets initial distribution in phase space—and thereby its subsequent dynamics in the field—is strongly shaped by the intensity of the electric field [11]. Within the framework of multi-photon ionization the intensity-dependent ac Stark shift alters the energies of initial and final target states as well as of any intermediate state that is resonantly passed through. The continuum the electron is born into is raised by the intensity-dependent ponderomotive energy. The outgoing electron wave packet is substantially dependent on the target system, and on the intensity of the driving field

Methods

Results

Conclusion